Reciprocating Engine

224 C H A P T E R 6 RECIPROCATING INTERNAL COMBUSTION ENGINES 6. 1 Introduction Perhaps the best-known engine in the world is the reciprocating internal combustion (IC) engine. Virtually every person who has driven an automobile or pushed a power lawnmower has used one. By far the most widely used IC engine is the spark-ignition gasoline engine, which takes us to school and work and on pleasure jaunts. Although others had made significant contributions, Niklaus Otto is generally credited with the invention of the engine and with the statement of its theoretical cycle.Another important engine is the reciprocating engine that made the name of Rudolf Diesel famous. The Diesel engine, the workhorse of the heavy truck industry, is widely used in industrial power and marine applications. It replaced the reciprocating steam engine in railroad locomotives about fifty years ago and remains dominant in that role today. The piston, cylinder, crank, and connecting rod provide the geometric basis of the reciprocating engine. While two-stroke-cycle engines are in use and of continuing interest, the discussion here will emphasize the more widely applied four-stroke-cycle engine.In this engine the piston undergoes two mechanical cycles for each thermodynamic cycle. The intake and compression processes occur in the first two strokes, and the power and exhaust processes in the last two. These processes are made possible by the crank-slider mechanism, discussed next. 6. 2 The Crank-Slider Mechanism Common to most reciprocating engines is a linkage known as a crank-slider mechanism. Diagramed in Figure 6. 1, this mechanism is one of several capable of producing the straight-line, backward-and-forward motion known as reciprocating.Fundamentally, the crank-slider converts rotational motion into linear motion, or vice-versa. With a piston as the slider moving inside a fixed cylinder, the mechanism provides the vital capability of a gas engine: the ability to compress and expand a gas . Before delving into this aspect of the engine, however, let us examine the crank-slider mechanism more closely. 225 It is evident from Figure 6. 2 that, while the crank arm rotates through 180Â °, the piston moves from the position known as top-center (TC) to the other extreme, called bottom-center (BC).During this period the piston travels a distance, S, called the stroke, that is twice the length of the crank. For an angular velocity of the crank,
, the crank pin A has a tangential velocity component
S/2. It is evident that, at TC and at BC, the crank pin velocity component in the piston direction, and hence the piston velocity, is zero. At these points, corresponding to crank angle  = 0Â ° and 180Â °, the piston reverses direction. Thus as  varies from 0Â ° to 180Â °, the piston velocity accelerates from 0 to a maximum and then returns to 0.A similar behavior exists between 180Â ° and 360Â °. The connecting rod is a two-force member; hence it is evident that there ar e both axial and lateral forces on the piston at crank angles other than 0Â ° and 180Â °. These lateral forces are, of course, opposed by the cylinder walls. The resulting lateral force component normal to the cylinder wall gives rise to frictional forces between the piston rings and cylinder. It is evident that the normal force, and thus the frictional force, alternates from one side of the piston to the other during each cycle.Thus the piston motion presents a challenging lubrication problem for the control and reduction of both wear and energy loss. The position of the piston with respect to the crank centerline is given by x = (S/2)cos + Lcos [ft | m] (6. 1) where yA = (S/2)sin = Lsin can be used to eliminate  to obtain x/L = (S/2L)cos + [1? (S/2L)2 sin2  ]? [dl] (6. 2) Thus, while the axial component of the motion of the crank pin is simple harmonic, xA = (S/2)cos, the motion of the piston and piston pin is more complex. It may be 226 seen from Equation (6. ), however , that as S/L becomes small, the piston motion approaches simple harmonic. This becomes physically evident when it is recognized that, in this limit, the connecting rod angle,  , approaches 0 and the piston motion approaches the axial motion of the crank pin. Equations (6. 1) and (6. 2) may be used to predict component velocities, accelerations, and forces in the engine. The volume swept by the piston as it passes from TC to BC is called the piston displacement, disp. Engine displacement, DISP, is then the product of the piston displacement and the number of cylinders, DISP = (n)(disp).The piston displacement is the product of the piston cross-sectional area and the stroke. The cylinder inside diameter (and, approximately, also the piston diameter) is called its bore. Cylinder bore, stroke, and number of cylinders are usually quoted in engine specifications along with or instead of engine displacement. It will be seen later that the power output of a reciprocating engine is proport ional to its displacement. An engine of historical interest that also used the crank-slider mechanism is discussed in the next section. 6. 3 The Lenoir CycleAn early form of the reciprocating internal combustion engine is credited to Etienne Lenoir. His engine, introduced in 1860, used a crank-slider-piston-cylinder arrangement 227 in which a combustible mixture confined between the piston and cylinder is ignited after TC. The resulting combustion gas pressure forces acting on the piston deliver work by way of the connecting rod to the rotating crank. When the piston is at BC, combustion gases are allowed to escape. The rotational momentum of the crank system drives the piston toward TC, expelling additional gases as it goes.A fresh combustible mixture is again admitted to the combustion chamber (cylinder) and the cycle is repeated. The theoretical Lenoir cycle, shown in Figure 6. 3 on a pressure-volume diagram, consists of the intake of the working fluid (a combustible mixture) fro m state 0 to state 1, a constant-volume temperature and pressure rise from state 1 to state 2, approximating the combustion process, an isentropic expansion of the combustion gases to state 3, and a constant-pressure expulsion of residual gases back to state 0.Note that a portion of the piston displacement, from state 0 to state 1, is used to take in the combustible mixture and does not participate in the power stroke from state 2 to state 3. The engine has been called an explosion engine because the power delivered is due only to the extremely rapid combustion pressure rise or explosion of the mixture in the confined space of the cylinder. Hundreds of Lenoir engines were used in the nineteenth century, but the engine is quite inefficient by todays standards. In 1862, Beau de Rochas pointed out that the 228 fficiency of internal combustion could be markedly improved in reciprocating engines by compression of the air-fuel mixture prior to combustion. In 1876 Niklaus Otto (who is thou ght to have been unaware of Rochas? suggestion) demonstrated an engine that incorporated this important feature, as described next. 6. 4 The Otto Cycle The Otto cycle is the theoretical cycle commonly used to represent the processes in the spark ignition (SI) internal combustion engine. It is assumed that a fixed mass of working fluid is confined in the cylinder by a piston that moves from BC to TC and back, as shown in Figure 6. . The cycle consists of isentropic compression of an air-fuel mixture from state 1 to state 2, constant-volume combustion to state 3, isentropic expansion of the combustion gases to state 4, and a constant-volume heat rejection back to state 1. The constant-volume heat rejection is a simple expedient to close the cycle. It obviates the need to represent the complex expansion and outflow of 229 combustion gases from the cylinder at the end of the cycle. Note that the Otto cycle is not concerned with the induction of the air-fuel mixture or with the expulsion of residual combustion gases.Thus only two mechanical strokes of the crank-slider are needed in the Otto cycle, even when it is used to represent an ideal four-stroke-cycle Otto engine. In this case the remaining strokes are used to execute the necessary intake and exhaust functions. Because it involves only two strokes, the Otto cycle may also represent a two-stroke-cycle engine. The two-stroke-cycle engine is in principle capable of as much work in one rotation of the crank as the four-stroke engine is in two. However, it is difficult to implement because of the necessity of making the intake and exhaust functions a part of those wo strokes. It is therefore not as highly developed or widely used as the four-stroke-cycle engine. We will focus on the fourstroke- cycle here. The simplest analysis of the Otto cycle assumes calorically perfect air as the working fluid in what is called the Air Standard cycle analysis. Following the notation of Figure 6. 4, the compression process can be represented by the isentropic relation for a calorically perfect gas, Equation (1. 21), as p2/p1 = (V1/V2)k [dl] (6. 3) where the compression ratio, CR = V1/V2, is a fundamental parameter of all reciprocating engines.The diagram shows that the expansion ratio for the engine, V4 /V3, has the same value, V1/V2. The clearance volume, V2, is the volume enclosed between the cylinder head and the piston at TC. Thus the compression ratio may be expressed as the ratio of the sum of the clearance and displacement volumes to the clearance volume: CR = [V2 + (V1 ? V2)]/V2 Thus, for a given displacement, the compression ratio may be increased by reducing the clearance volume. The efficiency of the cycle can be most easily determined by considering constantvolume- process heat transfers and the First Law cyclic integral relation, Equation (1. ). The heat transferred in the processes 2
3 and 4
1 are q2
3 = cv (T3 ? T2) [Btu/lbm | kj/kg] (6. 4) and q4
1 = cv (T1 ? T4) [Btu/lbm | kJ/kg] (6. 5) B oth the expansion process, 3
4, and the compression process, 1
2, are assumed to be isentropic. Thus, by definition, they are both adiabatic. From the cyclic integral, the net work per unit mass is then: w = q2
3 + q4
1 = cv (T3 ? T2 + T1 ? T4) [Btu/lbm | kJ/kg] (6. 6) 230 As before, the cycle thermal efficiency is the ratio of the net work to the external heat supplied: Otto = w/q2
3 = cv (T3 ? T2 + T1 ?T4) / [cv (T3 ? T2)] = 1 + (T1 ? T4) / (T3 ? T2) = 1 ? T1/T2 = 1 ? 1 / CR k-1 [dl] (6. 7) where Equation (1. 20) has been used to eliminate the temperatures. Equation (6. 7) shows that increasing compression ratio increases the cycle thermal efficiency. This is true for real engines as well as for the idealized Otto engine. The ways in which real spark ignition engine cycles deviate from the theoretical Otto cycle are discussed later. EXAMPLE 6. 1 An Otto engine takes in an air-fuel mixture at 80Â °F and standard atmosphere presssure. It has a compression ratio of 8.Using Air Stan dard cycle analysis, a heating value of 20,425 Btu/lbm, and A/F = 15, determine: (a) The temperature and pressure at the end of compression, after combustion, and at the end of the power stroke. (b) The net work per pound of working fluid. (c) The thermal efficiency. Solution We use the notation of Figure 6. 4: (a) p2 = p1(V1/V2)k = 1(8)1. 4 = 18. 38 atm T2 = T1(V1/V2)k ? 1 = (540)(8)0. 4 = 1240. 6Â °R T3 = T2 + qa /cv = T2 + (F/A)(HV)k/cp = 1240. 6 + 1. 420,425/150. 24 = 9184Â °R p3 = p2T3 /T2 = 18. 38(9184/1240. 6) = 136. 1 atm T4 = T3 /CRk? 1 = 9184/ 80. 4 = 3997. Â °R p4 = p3 /CRk = 136. 1/81. 4 = 7. 4 atm (b) The constant-volume heat addition is governed by the fuel-air ratio and the fuel heating value: qa = HV(F/A) = 20,425/15 = 1361. 7 Btu/lbm of air 231 qr = cv (T1 ? T4) = (0. 24/1. 4)( 540 ? 3997. 4) = ? 592. 7 Btu/lbm w = qa + qr = 1361. 7 + ( ? 592. 7) = 769 Btu/lbm (c) The cycle termal efficiency may then be determined from the definition of the heat engine thermal efficiency or Equation (6. 7): th = w/qa = 769/1361. 7 = 0. 565 th = 1 ? 1/80. 4 = 0. 565 _____________________________________________________________________ In view f the discussion of gas properties and dissociation in Chapter 3, the values of T3 and T4 in Example 6. 1 are unrealistically high. Much of the energy released by the fuel would go into vibration and dissociation of the gas molecules rather than into the translational and rotational degrees of freedom represented by the temperature. As a result, significantly lower temperatures would be obtained. Thus, while the analysis is formally correct, the use of constant-low-temperature heat capacities in the Air Standard cycle makes it a poor model for predicting temperature extremes when high energy releases occur.Some improvement is achieved by using constant-hightemperature heat capacities, but the best results would be achieved by the use of real gas properties, as discussed in several of the references. 6. 5 Combustion in a Reciprocating Engine The constant-volume heat transfer process at TC in the Otto cycle is an artifice to avoid the difficulties of modeling the complex processes that take place in the combustion chamber of the SI engine. These processes, in reality, take place over a crank angle span of 30Â ° or more around TC.Let us consider aspects of these processes and their implementation in more detail. Normally, the mixture in the combustion chamber must have an air-fuel ratio in the neighborhood of the stoichiometric value for satisfactory combustion. A more or less homogeneous mixture may be produced outside the cylinder in a carburetor, by injection into the intake manifold, or by throttle-body injection into a header serving several intake manifolds. In the case of the carburetor, fuel is drawn into the engine from the carburetor by the low pressure created in a venturi through which the combustion air flows.As a result, increased air flow causes lower venturi pressure and hence in creased fuel flow. The fuel system thus serves to provide an air-fuel mixture that remains close to the stoichiometric ratio for a range of air flow rates. Various devices designed into the carburetor further adjust the fuel flow for the special operating conditions encountered, such as idling and rapid acceleration. Maximum fuel economy is usually attained with excess air to ensure that all of the fuel is burned. A mixture with excess air is called a lean mixture.The carburetor 232 usually produces this condition in automobiles during normal constant-speed driving. On the other hand, maximum power is achieved with excess fuel to assure that all of the oxygen in the air in the combustion chamber is reacted. It is a matter of exploiting the full power-producing capability of the displacement volume. A mixture with excess fuel is called a rich mixture. The automotive carburetor produces a rich mixture during acceleration by supplying extra fuel to the air entering the intake manifold. The equivalence ratio is sometimes used to characterize the mixture ratio, whether rich or lean. The equivalence ratio,
, is defined as the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio. Thus
> 1 represents a rich mixture and
< 1 represents a lean mixture. In terms of air-fuel ratio,
= (A/F)stoich /(A/F). Homogeneous air-fuel mixtures close to stoichiometric may ignite spontaneously (that is, without a spark or other local energy source) if the mixture temperature exceeds a temperature called the autoignition temperature.If the mixture is brought to and held at a temperature higher than the autoignition temperature, there is a period of delay before spontaneous ignition or autoignition This time interval is called the ignition delay, or ignition lag. The ignition delay depends on the characteristics of the fuel and the equivalence ratio and usually decreases with increasing temperature. In spark-ignition engines, compression ratios and therefore the temperatures at the end of compression are low enough that the air-fuel mixture is ignited by the spark plug before spontaneous ignition can occur.SI engines are designed so that a flame front will propagate smoothly from the spark plug into the unburned mixture until all of the mixture has been ignitied. However, as the flame front progresses, the temperature and pressure of the combustion gases behind it rise due to the release of the chemical energy of the fuel. As the front propagates, it compresses and heats the unburned mixture, sometimes termed the end-gas. Combustion is completed as planned when the front smoothly passes completely through the end-gas without autoignition. However, if the end-gas autoignites, a pinging or low-pitched sound called knock is heard.The avoidance of knock due to autoignition of the end-gas is a major constraint on the design compression ratio of an SI engine. If hot spots or thermally induced compression of the end-gas ignite it before the flame front does, there is a more rapid release of chemical energy from the end-gas than during normal combustion. Knock is sometimes thought of as an explosion of the end gas that creates an abrupt pulse and pressure waves that race back and forth across the cylinder at high speed, producing the familiar pinging or low-pitched sound associated with knock.Knock not only reduces engine performance but produces rapid wear and objectionable noise in the engine. Thus it is important for a SI engine fuel to have a high autoignition temperature. It is therefore important for SI engine fuel to have a high autoignition temperature. Thus the knock characteristics of commercially available fuels limit the maximum allowable design compression ratio for SI engines and hence limit their best efficiency. The octane number is a measure of a gasoline’s ability to avoid knock. Additives such as tetraethyl lead have been used in the past to suppress engine knock.However, the accumulation of lead in the environment and its penetration into the food cycle has 233 resulted in the phaseout of lead additives. Instead refineries now use appropriate blends of hydrocarbons as a substitute for lead additives in unleaded fuels. The octane number of a fuel is measured in a special variable-compression-ratio engine called a CFR (Cooperative Fuels Research) engine. The octane rating of a fuel is determined by comparison of its knocking characteristics with those of different mixtures of isooctane, C8H18, and n-heptane, C7H16.One hundred percent isooctane is defined as having an octane number of 100 because it had the highest resistance to knock at the time the rating system was devised. On the other hand, n-heptane is assigned a value of 0 on the octane number scale because of its very poor knock resistance. If a gasoline tested in the CFR engine has the same knock threshold as a blend of 90% isooctane and 10% n-heptane, the fuel is assigned an octane rating of 90. In combustion chamber de sign, the designer attempts to balance many factors to achieve good performance.Design considerations include locating intake valves away from and exhaust valves near spark plugs, to keep end-gas in a relatively cool area of the combustion chamber and thereby suppress hot-surface-induced autoignition tendencies. Valves are, of course, designed as large as possible to reduce induction and exhaust flow restrictions. More than one intake and one exhaust valve per cylinder are now used in some engines to improve ? engine breathing.? In some engines, four valves in a single cylinder are employed for this purpose.The valves are also designed to induce swirl and turbulence to promote mixing of fuel and air and to improve combustion stability and burning rate. Pollution and fuel economy considerations have in recent years profoundly influenced overall engine and combustion chamber design. Stratified-charge engines, for example, attempt to provide a locally rich combustion region to control peak temperatures and thus suppress NOx formation. The resulting combustion gases containing unburned fuel then mix with surrounding lean mixture to complete the combustion process, thus eliminating CO and unburned hydrocarbons from the exhaust.These processes occur at lower temperatures than in conventional combustion chamber designs and therefore prevent significant nitrogen reactions. 6. 6 Representing Reciprocating Engine Perfomance In an earlier section, the theoretical work per unit mass of working fluid of the Otto engine was evaluated for a single cycle of the engine, using the cyclic integral of the First Law of Thermodynamics. The work done by pressure forces acting on a piston can also be evaluated as the integral of pdV. It is evident therefore that the work done during a single engine cycle is the area enclosed by the cycle process curves on the pressure-volume diagram.Thus, instead of using the cyclic integral or evaluating pdV for each process of the cycle, the work o f a reciprocating engine can be found by drawing the theoretical process curves on the p? V diagram and graphically integrating them. Such a plot of pressure versus volume for any reciprocating engine, real or theoretical, is called an indicator diagram. 234 In the nineteenth and early twentieth centuries a mechanical device known as an engine indicator was used to produce indicator cards or diagrams to determine the work per cycle for slow-running steam and gas reciprocating ngines. The indicator card was attached to a cylinder that rotated back and forth on its axis as the piston oscillated, thus generating a piston position (volume) coordinate. At the same time a pen driven by a pressure signal from the engine cylinder moved parallel to the cylinder axis, scribing the p-V diagram over and over on the card. The work of high speed engines is still evaluated from traces of pressure obtained with electronic sensors and displayed on electronic monitors and through digital techniques.T he work done per cycle (from an indicator card, for instance) can be represented as an average pressure times a volume. Because the displacement volumes of engines are usually known, an engine performance parameter known as the mean effective pressure, MEP, is defined in terms of the piston displacement. The mean effective pressure is defined as the value of the pressure obtained by dividing the net work per cylinder per cycle at a given operating condition by the piston displacement volume: MEP = W/disp [lbf/ft2 | kPa] (6. 8)Thus the MEP is a measure of the effectiveness of a given displacement volume in producing net work. The power output of an engine with identical cylinders may be represented as the product of the work per cycle and the number of cycles executed per unit time by the engine. Thus if the engine has n cylinders, each executing N identical thermodynamic cycles per unit time, and delivering W work units per cylinder, with a piston displacement, disp, the power outpu t is given by P = n
N
W = n
N MEP  disp [ft-lbf /min | kW] (6. 9)Expressed for the entire engine, the engine displacement is DISP = ndisp and the engine work is MEP DISP. Hence the engine power is: P = N MEPDISP [ft-lbf /min | kW] (6. 10) where N, the number of thermodynamic cycles of a cylinder per unit time, is the number of crank-shaft revolutions per unit time for a two-stroke-cycle engine and one-half of the revolutions per unit time for a four-stroke-cycle engine. The factor of ? for the four-stroke-cycle engine arises because one thermodynamic cycle is executed each time the crank rotates through two revolutions. EXAMPLE 6. 2What is the displacement of an engine that develops 60 horsepower at 2500 rpm in a four-stroke-cycle engine having an MEP of 120 psi? 235 Solution From Equation (6. 10), the displacement of the engine is DISP = P/(N MEP) = (60)(33,000)(12)/[(2500/2)(120)] = 158. 4 in3 Checking units: (HP)(ft-lbf/HP-min)(in/ft)/[(cycles/min)(lbf/in2)] = in3 ________ _____________________________________________________________ If the work is evaluated from an indicator diagram the work is called indicated work; the MEP is called the indicated mean effective pressure, IMEP; and the power is indicated power, IP.Note that the indicated work and power, being associated with the work done by the combustion chamber gases on the piston, do not account for frictional or mechanical losses in the engine, such as piston-cylinder friction or the drag of moving parts (like connecting rods) as they move through air or lubricating oil. Brake Performance Parameters Another way of evaluating engine performance is to attach the engine output shaft to a device known as a dynamometer, or brake. The dynamometer measures the torque, T, applied by the engine at a given rotational speed.The power is then calculated from the relation P = 2rpm T [ft-lbf /min | N-m/min] (6. 11) A simple device called a prony brake, which was used in the past, demonstrates the concept for the measurement of the shaft torque of engines. Figure 6. 5 shows the prony brake configuration in which a stationary metal band wrapped around the rotating flywheel of the engine resists the torque transmitted to it by friction. The product of the force measured by a spring scale, w, and the moment arm, d , gives the resisting torque. The power dissipated is then given by 2(rpm)w d.Modern devices such as water brakes and electrical dynamometers long ago replaced the prony brake. The water brake is like a centrifugal water pump with no outflow, mounted on low-friction bearings, and driven by the test engine. As with the prony brake, the force required to resist turning of the brake (pump) housing provides the torque data. This, together with speed measurement, yields the power output from Equation (6. 11). The power dissipated appears as increased temperature of the water in the brake and heat transfer from the brake. Cool water is circulated slowly through the brake to mainta in a steady operating condition.The torque measured in this way is called the brake torque, BT, and the resulting power is called the brake power, BP. To summarize: while indicated parameters relate to gas forces in the cylinder, brake parameters deal with output shaft forces. Thus the brake power differs from the indicated power in that it accounts for the effect of all of the energy losses in the engine. The difference between the two is referred to as the friction power, FP. Thus FP = IP ? BP. 236 Friction power varies with engine speed and is difficult to measure directly.An engine is sometimes driven without fuel by a motor-dynamometer to evaluate friction power. An alternative to using friction power to relate brake and indicated power is through the engine mechanical efficiency, m: m = BP/IP [dl] (6. 12) Because of friction, the brake power of an engine is always less than the indicated power; hence the engine mechanical efficiency must be less than 1. Clearly, mechanical e fficiencies as close to 1 as possible are desired. The engine indicated power can also be expressed in terms of torque, through Equation (6. 11). Thus an indicated torque, IT, can be defined.Similarly, a brake mean effective pressure, BMEP, may be defined that, when multiplied by the engine displacement and speed, yields the brake power, analogous to Equation (6. 10). Table 6. 1 summarizes these and other performance parameters and relations. The thermal efficiency, as for other engines, is a measure of the fuel economy of a reciprocating engine. It tells the amount of power output that can be achieved for a given rate of heat release from the fuel. The rate of energy release is, in turn, the product of the rate of fuel flow and the fuel heating value.Thus, for a given thermal efficiency, power output can be increased by employing a high fuel flow rate and/or selecting a fuel with a high heat of combustion. If the thermal efficiency is evaluated using the brake power, it is called t he brake thermal efficiency, BTE. If the evaluation uses the indicated power, it is called the indicated thermal efficiency, ITE. 237 It is common practice in the reciprocating engine field to report engine fuel economy in terms of a parameter called the specific fuel consumption, SFC, analogous to the thrust specific fuel consumption used to describe jet engine performance.The specific fuel consumption is defined as the ratio of the fuel-mass flow rate to the power output. Typical units are pounds per horsepower-hour or kilograms per kilowatt-hour. Obviously, good fuel economy is indicated by low values of SFC. The SFC is called brake specific fuel consumption, BSFC, if it is defined using brake power or indicated specific fuel consumption, ISFC, when based on indicated power. The SFC for a reciprocating engine is analogous to the heat rate for a steam power plant in that both are measures of the rate of energy supplied per unit of power output, and in that low values of both are d esirable.Volumetric Efficiency The theoretical energy released during the combustion process is the product of the mass of fuel contained in the combustion chamber and its heating value if the fuel is completely reacted. The more air that can be packed into the combustion chamber, the Table 6. 1 Engine Performance Parameters Indicated Brake Friction Mean effective pressure IMEP BMEP FMEP = IMEP – BMEP
m = BMEP / IMEP Power IP BP FP = IP – BP
m = BHP / IHP Torque IT BT FT = IT – BT
m = BT / IT Thermal efficiency ITE BTE
m = BTE / ITE Specific fuel consumption ISFC BSFC
m = ISFC / BSFC more fuel that can be burned with it.Thus a measure of the efficiency of the induction system is of great importance. The volumetric efficiency, v, is the ratio of the actual mass of mixture in the combustion chamber to the mass of mixture that the displacement volume could hold if the mixture were at ambient (free-air) density. Thus the average mass-flow rate of air through a cylinder is v (disp) aN. Pressure losses across intake and exhaust valves, combustion-chamber clearance volume, the influence of hot cylinder walls on mixture density, valve timing, and gas inertia effects all influence the volumetric efficiency.EXAMPLE 6. 3 A six-cylinder, four-stroke-cycle SI engine operates at 3000 rpm with an indicated mean effective pressure of five atmospheres using octane fuel with an equivalence ratio 238 of 0. 9. The brake torque at this condition is 250 lbf? ft. , and the volumetric efficiency is 85%. Each cylinder has a five inch bore and 6 inch stroke. Ambient conditions are 14. 7 psia and 40Â °F. What is the indicated horsepower, brake horsepower, and friction horsepower; the mechanical efficiency; the fuel flow rate; and the BSFC? Solution The six cylinders have a total displacement ofDISP = 6? 52? 6/4 = 706. 86 in3 Then the indicated horsepower is IP = MEP? DISP? N /[12? 33,000] [lbf /in2][in3][cycles/min]/[in/ft][ft-lbf /HP-min] = (5)(14. 7)(706 . 86)(3000/2)/[12? 33,000] = 196. 8 horsepower The brake horsepower, from Equation (6. 11), is: BP = 2 ? 3000 ? 250 / 33,000 = 142. 8 horsepower Then the friction power is the difference between the indicated and brake power: FP = 196. 8 ? 142. 8 = 54 horsepower and the mechanical efficiency is m = 142. 8/196. 8 = 0. 726 The ambient density is a = 14. 7 ? 144/ [53. 3 ? 500] = 0. 0794 lbm /ft3 nd the mass flow rate of air to the engine is ma = 0. 85? 0. 0794? 706. 86? (3000/2)/1728 = 41. 4 lbm /min For octane the stoichiometric reaction equation is C8H18 + 12. 5O2 + (12. 5? 3. 76)N2
8CO2 + 9H2O + (12. 5? 3. 76)N2 The fuel-air ratio is then F/A = 0. 9? [(8? 12) + (18? 1)]/[12. 5(32 + 3. 76? 28)] = 0. 0598 lbm-fuel /lbm-air 239 The fuel flow rate is mf = ma (F/A) = 41. 4 ? 0. 0598 = 2. 474 lbm /min The brake specific fuel consumption is BSFC = 60 mf /BHP = 60? 2. 474/142. 8 = 1. 04 lbm /BHP-hr ____________________________________________________________________ 6. Spark-Ignition E ngine Performance A typical indicator diagram showing intake and exhaust processes, valve actuation, and spark timing for a four-stroke-cycle SI engine is shown in Figure 6. 6. It is assumed that an appropriate air-fuel mixture is supplied from a carburetor through an intake manifold to an intake valve, IV, and that the combustion gas is discharged through an exhaust valve, EV, into an exhaust manifold. The induction of the air-fuel mixture starts with the opening of the intake valve at point A just before TC.As the piston sweeps to the right, the mixture is drawn into the cylinder through the IV. The pressure in the cylinder is somewhat below that in the intake manifold due to the pressure losses across the intake valve. In order to use the momentum of the mixture inflow through the valve at the end of the intake stroke to improve the volumetric efficiency, intake valve closure is delayed to shortly after BC at point B. Power supplied from inertia of a flywheel (and the other rotat ing masses in the engine) drives the piston to the left, compressing and raising the temperature of the trapped mixture.The combustion process in a properly operating SI engine is progressive in that the reaction starts at the spark plug and progresses into the unburned mixture at a finite speed. Thus the combustion process takes time and cannot be executed instantaneously as implied by the theoretical cycle. In order for the process to take place as near to TC as possible, the spark plug is fired at point S. The number of degrees of crank rotation before TC at which the spark occurs is called the ignition advance. Advances of 10Â ° to 30Â ° are common, depending on speed and load.The spark advance may be controlled by devices that sense engine speed and intake manifold pressure. Microprocessors are now used to control spark advance and other functions, based on almost instantaneous engine performance measurements. Recalling the slider-crank analysis, we observ that the piston vel ocity at top center is momentarily zero as the piston changes direction. Therefore no work can be done at this point, regardless of the magnitude of the pressure force. Thus, to maximize the work output, it is desired to have the maximum cylinder pressure occur at about 20Â ° after TC.Adjustment of the spark advance (in degrees before TC) allows some control of the combustion process and the timing of peak pressure. For a fixed combustion duration, the combustion crank-angle interval must increase with engine speed. As a consequence, the ignition advance must increase with increasing engine speed to 240 maintain optimum timing of the peak pressure. Following combustion, the piston continues toward bottom center as the high pressure gases expand and do work on the piston during the power stroke. As the piston approaches BC, the gases do little work on the piston as its velocity again approaches zero.As a result, not much work is lost by early opening of the exhaust valve before BC ( at point E) to start the blowdown portion of the exhaust process. It is expedient to sacrifice a little work during the end of the power stroke in order to reduce the work needed to overcome an otherwise-high exhaust stroke cylinder pressure. Inertia of the gas in the cylinder and resistance to flow through the exhaust valve opening slow the drop of gas pressure in the cylinder after the valve opens. Thus the gases at point E are at a pressure above the exhaust manifold pressure and, during blowdown, rush out through the EV at high speed.Following blowdown, gases remaining in the cylinder are then expelled as the piston returns to TC. They remain above exhaust manifold pressure until reaching TC because of the flow resistance of the exhaust valve. The EV closes shortly after TC at point C, terminating the exhaust process. The period of overlap at TC between the intake valve opening at point A and exhaust valve closing at point C in Figure 6. 6 allows more time for the intake and exh aust processes at high engine speeds, when about 10 milliseconds may be available for these processes.At low engine speed and at idling there may be some mixture loss through the exhaust valve and discharge into the intake manifold during this valve overlap period. The combined exhaust and induction processes are seen to form a ? pumping loop? that traverses the p-V diagram in a counterclockwise direction and therefore 241 represents work input rather than work production. The higher the exhaust stroke pressure and the lower the intake stroke pressure, the greater the area of the pumping loop and hence the greater the work that must be supplied by the power loop (clockwise) to compensate.Great attention is therefore paid to valve design and other engine characteristics that influence the exhaust and induction processes. Volumetric efficiency is a major parameter that indicates the degree of success of these efforts. Performance Characteristics A given ideal Otto-cycle engine produce s a certain amount of work per cycle. For such a cycle, MEP = W/disp is a constant. Equating the power equations (6. 9) and (6. 11) shows that the average torque is proportional to MEP and independent of engine engine speed.Therefore power output for the ideal engine is directly proportional to the number of cycles executed per unit time, or to engine speed. Thus an Otto engine has ideal torque and power characteristics, as shown by the solid lines in Figure 6. 7. The characteristics of real engines (represented by the dashed lines) tend to be similar in nature to the ideal characteristics but suffer from speed-sensitive effects, particularly at low or high speeds. Torque and power characteristics for a 3. 1 liter V6 engine (ref. 9) are shown by the solid lines in Figure 6. 8.Note the flatness of the torque-speed curve and the expected peaking of the power curve at higher speed than the torque curve. Rather than present graphical characteristics such as this in their 242 brochures, automobile manufacturers usually present only values for the maximum power and torque and the speeds at which they occur. Engine characteristics such as those shown in the figure are invaluable to application engineers seeking a suitable engine for use in a product. 6. 8 The Compression-Ignition or Diesel Cycle The ideal Diesel cycle differs from the Otto cycle in that combustion is at constant pressure rather than constant volume.The ideal cycle, shown in Figure 6. 9, is commonly implemented in a reciprocating engine in which air is compressed without fuel from state 1 to state 2. With a typically high compression ratio, state 2 is at a temperature high enough that fuel will ignite spontaneously when sprayed directly into the air in the combustion chamber from a high-pressure fuel injection system. By controlling the fuel injection rate and thus the rate of chemical energy release in relation to the rate of expansion of the combustion gases after state 2, a constant243 pressure pro cess or other energy release pattern may be achieved as in Figure 6. . For example, if the energy release rate is high, then pressure may rise, as from 2 to 3’, and if low may fall to 3’’. Thus constant-pressure combustion made possible by controlling the rate of fuel injection into the cyclinder implies the use of a precision fuel injection system. Instead of injecting fuel into the high-temperature compressed air, the cycle might be executed by compression of an air-fuel mixture, with ignition occurring either spontaneously or at a hot spot in the cylinder near the end of the compression process.Inconsistency and unpredictability of the start of combustion in this approach, due to variations in fuel and operating conditions, and to lack of control of the rate of heat release with the possibility of severe knock, makes the operation of such an engine unreliable, at the least, and also limits the maximum compression ratio. The Diesel engine therefore usually emp loys fuel injection into compressed air rather than carbureted mixture formation. In the Air Standard cycle analysis of the Diesel cycle, the heat addition process is at constant pressure: q2
3 = cp(T3 ? T2) [Btu/lbm | kJ/kg] (6. 13) nd, as with the Otto cycle, the closing process is at constant volume: q4
1 = cv(T1 ? T4) [Btu/lbm | kJ/kg] (6. 14) 244 The net work and thermal efficiency are then: w = q2
3 + q4
1 = cp(T3 ? T2) + cv(T1 ? T4) = cvT1[k(T3/T1 ? T2/T1) + 1 ? T4/T1] [Btu/lbm | kJ/kg] (6. 15) Diesel = w/q2
3 = 1 + q4-
1/q2
3 = 1 + (cv/cp)(T1 ? T4)/(T3 ? T2) = 1 ? (1/k)(T1/T2)(T4/T1 ? 1)/(T3/T2 ? 1) [dl] (6. 16) The expressions for the net work and cycle efficiency may be expressed in terms two parameters, the compression ratio, CR = V1/V2 (as defined earlier in treating the Otto cycle) and the cutoff ratio, COR = V3/V2.The temperature ratios in Equations (6. 15) and (6. 16) may be replaced by these parameters using, for the constant-pressure process, COR = V3/V2 = T3/T2 an d by expanding the following identity: T4 /T1 = (T4/T3)(T3/T2)(T2 /T1) = (V3 /V4)k-1(V3/V2)(V1/V2)k-1 = [(V3/V4)(V1/V2)]k-1COR = (COR)k-1COR = CORk where the product of the volume ratios was simplified by recognizing that V4 = V1. Thus the nondimensionalized net work and Diesel-cycle thermal efficiency are given by w /cvT1 = kCRk-1(COR ? 1) + (1 ? CORk) [dl] (6. 17) and Diesel = 1 ? (1/k)[(CORk ? 1)/(COR ? 1)]/CRk-1 [dl] (6. 8) where the cutoff ratio, COR, is the ratio of the volume at the end of combustion, V3, to that at the start of combustion, V2. Thus the cutoff ratio may be thought of as a measure of the duration of fuel injection, with higher cutoff ratios corresponding to longer combustion durations. 245 Diesel-cycle net work increases with both compression ratio and cutoff ratio. This is readily seen graphically from Figure 6. 9 in terms of p-V diagram area. As with the Otto cycle, increasing compression ratio increases the Diesel-cycle thermal efficiency. Increasing cutof f ratio, however, decreases thermal efficiency.This may be rationalized by observing from the p-V diagram that much of the additional heat supplied when injection is continued is rejected at increasingly higher temperatures. Another view is that heat added late in the expansion process can produce work only over the remaining part of the stroke and thus adds less to net work than to heat rejection. EXAMPLE 6. 4 A Diesel engine has a compression ratio of 20 and a peak temperature of 3000K. Using an Air Standard cycle analysis, estimate the work per unit mass of air, the thermal efficiency, the combustion pressure, and the cutoff ratio.Solution Assuming an ambient temperature and pressure of 300K and 1 atmosphere, the temperature at the end of the compression stroke is T2 = (300)(20)1. 4 ? 1 = 994. 3K and the combustion pressure is p2 = (1)(20)1. 4 = 66. 3 atm Then the cutoff ratio is V3/V2 = T3/T2 = 3000/994. 3 = 3. 02 The expansion ratio is calculated as follows: V4 /V3 = (V1/V2)/(V 3 /V2) = 20/3. 02 = 6. 62 T4 = T3 (V3 /V4)1. 4 ? 1 = 3000/6. 620. 4 = 1409K w = 1. 005(3000 ? 994. 3) + (1. 005/1. 4)(300 ? 1409) = 1219. 6 kJ/kg qa = 1. 005(3000 ? 994. 3) = 2015. 7 kJ/kg th = w/qa = 1219. /2015. 6 = 0. 605, or 60. 5% _____________________________________________________________________ 246 6. 9 Comparing Otto-Cycle and Diesel-Cycle Efficiencies A reasonable question at this point is: Which cycle is more efficient, the Otto cycle or the Diesel cycle? Figure 6. 10 assists in examining this question. In general notation, the cycle efficiency may be written as th = wnet /qin = wnet /(wnet + |qout|) = 1 /(1 + |qout| /wnet) [dl] (6. 19) Comparing the Otto cycle 1? 2? 3? 4 and the Diesel cycle with the same compression ratio 1? 2? 3’? , we see that both have the same heat rejection but that the Otto cycle has the higher net work. Equation (6. 19) then shows that, for the same compression ratio, the Otto cycle has the higher efficiency. It has been observed that Diesel-cycle efficiency decreases with increasing cutoff ratio for a given compression ratio. Let us examine the limit of the Diesel-cycle efficiency for constant CR as COR approaches its minimum value, 1. We may write Equation (6. 18) as Diesel = 1 ? 1 /(kCRk-1) f (COR) where f(COR) = (CORk ? 1)/(COR ? 1). Applying L’Hospital’s rule, with primes 247 esignating differentiation with respect to COR, to the limit of f(COR) as COR
1, yields lim f(COR) = lim (CORk ? 1)’/ Lim (COR? 1)’ = lim kCORk ? 1 = k COR
1 COR
1 COR
1 and limDiesel = 1 ? 1 /CRk ? 1 COR
1 = Otto Thus the limit of the Diesel-cycle efficiency as COR approaches 1 is the Otto cycle efficiency. Hence Equation (6. 18) shows that the efficiency of the Diesel cycle must be less than or equal to the Otto-cycle efficiency if both engines have the same compression ratio, the same conclusion we reached by examination of the p-V diagram.Suppose, however, that the compression ratios are not the same. Compare the Otto cycle 1? 2’? 3’? 4 with the Diesel cycle 1? 2? 3’? 4 having the same maximum temperature in Figure 6. 10. The Otto cycle has a smaller area, and therefore less work, than the Diesel cycle, but the same heat rejection. Equation (6. 19) demonstrates that the Otto cycle has a lower thermal efficiency than the Diesel cycle with the same maximum temperature. The conclusion that must be drawn from the above comparisons is quite clear. As in most comparative engineering studies, the result depends on the ground ules which were adopted at the start of the study. The Otto cycle is more efficient if the compression ratio is the same or greater than that of the competing Diesel cycle. But knock in spark-ignition (Otto) engines limits their compression ratios to about 12, while Diesel-engine compression ratios may exceed 20. Thus, with these higher compression ratios, the Air Standard Diesel-cycle efficiency can exceed that of the Otto cycle. In practice, Diesel engines tend to have higher efficiencies than SI engines because of higher compression ratios. 6. 0 Diesel-Engine Performance In 1897, five years after Rudolph Diesel’s first patents and twenty-one years after Otto’s introduction of the spark-ignition engine, Diesel’s compression-ignition engine was proven to develop 13. 1 kilowatts of power with an unprecedented brake thermal efficiency of 26. 2% (ref. 7). At that time, most steam engines operated at thermal efficiencies below 10 %; and the best gas engines did not perform much better than the steam machines. Diesel claimed (and was widely believed) to have developed his engine from the principles expounded by Carnot.He had developed â€Å"the rational engine. † Whether his claims were exaggerated or not, Diesel’s acclaim was well deserved. He had developed an engine that operated at unprecedented temperatures and pressures, had proven his concept of ignition of fuel by injection into the c ompressed high-temperature air, and had overcome the formidable problems of injecting a variety of fuels in appropriate 248 amounts with the precise timing required for satisfactory combustion. His is a fascinating story of a brilliant and dedicated engineer (refs. 7, 8).In the Diesel engine, the high air temperatures and pressures prior to combustion are attributable to the compression of air alone rather than an air-fuel mixture. Compression of air alone eliminates the possibility of autiognition during compression and makes high compression ratios possible. However, because of the high pressures and temperatures, Diesel engines must be designed to be structurally more rugged. Therefore, they tend to be heavier than SI engines with the same brake power. The energy release process in the Diesel engine is controlled by the rate of injection of fuel.After a brief ignition lag, the first fuel injected into the combustion chamber autoignites and the resulting high gas temperature susta ins the combustion of the remainder of the fuel stream as it enters the combustion chamber. Thus it is evident that the favorable fuel characteristic of high autoignition temperature for an SI engine is an unfavorable characteristic for a Diesel engine. In the Diesel engine, a low autoignition temperature and a short ignition delay are desirable. Knock is possible in the Diesel engine, but it is due to an entirely different cause than knock in a spark-ignition engine.If fuel is ignited and burns as rapidly as it is injected, then smooth, knock-free combustion occurs. If, on the other hand, fuel accumulates in the cylinder before ignition due to a long ignition lag, an explosion or detonation occurs, producing a loud Diesel knock. The cetane number is the parameter that identifies the ignition lag characteristic of a fuel. The cetane number, like the octane number, is determined by testing in a CFR engine. The ignition lag of the test fuel is compared with that of a mixture of n-ceta ne, C16H34, and heptamethylnonane, HMN (ref. 0). Cetane, which has good ignition qualities, is assigned a value of 100; and HMN, which has poor knock behavior, a value of 15. The cetane number is then given by the sum of the percentage of n-cetane and 0. 15 times the percentage of HMN in the knock-comparison mixture. A cetane number of 40 is the minimum allowed for a Diesel fuel. 6. 11 Superchargers and Turbochargers The importance of the volumetric efficiency, representing the efficiency of induction of the air-fuel mixture into the reciprocating-engine cylinders, was discussed earlier.Clearly, the more mixture mass in the displacement volume, the more chemical energy can be released and the more power will be delivered from that volume. During the Second World War, the mechanical supercharger was sometimes used with SI aircraft engines to increase the power and operational ceiling of American airplanes. Today supercharging is used with both Diesel engines and SI engines. The super charger is a compressor that supplies air to the cylinder at high pressure so that the as density in the cylinder at the start of compression is well above the free-air density. The piston exhaust gases are allowed to expand freely to the atmosphere through the exhaust manifold and tailpipe. The supercharger is usually driven by a belt or gear train from the engine crank shaft. 249 Figure 6. 11 shows a modification of the theoretical Otto cycle to accommodate mechanical supercharging. The supercharger supplies air to the engine cyclinders at pressure p7 in the intake process 7
1. The processes 4
5
6 purge most of the combustion gas from the cylinder.The most striking change in the cycle is that the induction-exhaust loop is now traversed counterclockwise, indicating that the cylinder is delivering net work during these processes as well as during the compressionexpansion loop. It should be remembered, however, that part of the cycle indicated power must be used to drive the ex ternal supercharger. The turbosupercharger or turbocharger, for short, is a supercharger driven by a turbine using the exhaust gas of the reciprocating engine, as shown schematically in Figure 6. 12. A cutaway view of a turbocharger is shown in Figure 6. 3(a). Figure 6. 13(b) presents a diagram for the turbocharger. Compact turbochargers commonly increase the brake power of an engine by 30% or more, as shown in Figure 6. 8, where the performance of an engine with and without turbocharging is compared. There, a substantial increase in peak torque and flattening of the torque-speed curve due to turbocharging is evident. For a supercharged engine, the brake power, BP, is the indicated power (as in Figure 6. 11) less the engine friction power and the supercharger shaft power: BP = DISP  IMEP  N ? Pm ?FP [ft-lbf /min | kJ/s] (6. 15) 250 where Pm is the supercharger-shaft mechanical power supplied by the engine (0 for a turbocharger). The IMEP includes the positive work contribution of the exhaust loop. The exhaust back pressure of the reciprocating engine is higher with a turbocharger than for a naturally aspirated or mechanically supercharged engine because of the drop in exhaust gas pressure through the turbine. The engine brake power increases primarily because of a higher IMEP due to the added mass of fuel and air in the cylinder during combustion.Intercooling between the compressor and the intake manifold may be used to further increase the cylinder charge density. Turbocharging may increase engine efficiency, but its primary benefit is a substantial increase in brake power. In a turbocharged engine, a wastegate may be required to bypass engine exhaust gas around the turbine at high engine speeds. This becomes necessary when the compressor raises the intake manifold pressure to excessively high levels, causing engine knock or threatening component damage. Thirty to forty percent of the exhaust flow may be bypassed around the turbine at maximum speed and load (ref. ). 251 252 6. 12 The Automobile Engine and Air Pollution Since the Second World War, concern for environmental pollution has grown from acceptance of the status quo to recognition and militance of national and international scope. Among other sources, causes of the well-known Los Angeles smog problem were identified as hydrocarbons (HC) and oxides of nitrogen (NOx) in exhaust emissions from motor vehicle reciprocating engines. As a result, national and California automobile air pollution limits for automobiles have been established and toughened.Prior to the Clean Air Act of 1990, the U. S. federal exhaust-gas emissions standards limited unburned hydrocarbons, carbon monoxide, and oxides of nitrogen to 0. 41, 3. 4, and 1. 0 g/mile, respectively. According to reference 12, today it takes 25 autos to emit as much CO and unburned hydrocarbons and 4 to emit as much NOx as a single car in 1960. The reference anticipated that, led by existing California law and other factors, futur e engine designs should be targeted toward satisfying a tailpipe standard of 0. 5, 3. 4, 0. 4 g/mile. Indeed, the 1990 Clean Air Act (refs. 15,16) specified these limits for the first 50,000 miles or five years of operation for all passenger cars manufactured after 1995. In addition to the regulations on gaseous emissions, the Clean Air Act of 1990 adopted the California standard for particulate matter of 0. 08 g/mile for passenger cars. The standards on particulates are particularly difficult for the Diesel engine, because of its of soot-producing tendency.The automobile air pollution problem arises in part because the reactions in the exhaust system are not in chemical equilibrium as the gas temperature drops. Oxides of nitrogen, once formed in the cylinder at high temperature, do not return to equilibrium concentrations of nitrogen and oxygen in the cooling exhaust products. Likewise, CO formed with rich mixtures or by dissociation of CO2 in the cylinder at high temperature does not respond rapidly to an infusion of air as its temperature drops in the exhaust system. Their concentrations may be thought of as constant or frozen.Unburned hydrocarbons are produced not only by rich combustion but also by unburned mixture lurking in crevices (such as between piston and cylinder above the top piston ring), by lubricating oil on cylinder walls and the cylinder head that absorbs and desorbs hydrocarbons before and after combustion, and by transient operating conditions. Starting in 1963, positive crankcase ventilation was used in all new cars to duct fuel-rich crankcase gas previously vented to the atmosphere back into the engine intake system. Later in the ? 0s, various fixes were adopted to comply with regulation of tailpipe unburned hydrocarbons and CO, including lowering compression ratios. In 1973, NOx became federally regulated, and exhaust gas recirculation (EGR) was employed to reduce NOx formation through reduced combustion temperatures. At the same time, HC and CO standards were reduced further, leading to the use of the oxidizing catalytic converter. Introduction of air pumped into the tailpipe provided additional oxygen to assist in completion of the oxidation reactions.In 1981, a reducing catalytic converter came into use to reduce NOx further. This device does not perform well in an oxidizing atmosphere. As a result, two-stage catalytic converters were applied, with the first stage reducing NOx in a near-stoichiometric mixture and the 253 second oxidizing the combustibles remaining in the exhaust with the help of air introduced between the stages. This fresh air does not the increase NOx significantly, because of the relatively low temperature of the exhaust.The three-way catalytic converter using several exotic metal catalysts to reduce all three of the gaseous pollutants was also introduced. The use of catalytic converters to deal with all three pollutants brought about significant simultaneous reductions in the three major ga seous pollutants from automobiles. This allowed fuel-economy-reducing modifications that had been introduced earlier to satisfy emission reduction demands to be eliminated or relaxed, leading to further improvements in fuel economy.Catalytic converters, however, require precise control of exhaust gas oxygen to near-stoichiometric mixtures. The on-board computer has made possible control of mixture ratio and spark timing in response to censor outputs of intake manifold pressure, exhaust gas oxygen, engine speed, air flow, and incipient knock. The oxygen, or lambda, censor located in the exhaust pipe upstream of the three-way converter or between the two-stage converters is very sensitive to transition from rich to lean exhaust and allows close computer control of the mixture ratio to ensure proper operation of the catalytic converter.Computer control of carburetors or fuel injection as well as other engine functions has allowed simultaneous improvement in fuel economy and emissions i n recent years. Thus, while emissions have been drastically reduced since 1974, according to reference 11 the EPA composite fuel economy of the average U. S. passenger car has nearly doubled; although this improvement has not come from the engine alone. Despite the hard-won gains in emissions control and fuel economy, further progress may be expected. EXAMPLE 6. 5 The 1990 NOx emissions standard is 0. grams per mile. For an automobile burning stoichiometric octane with a fuel mileage of 30 mpg, what is the maximum tailpipe concentration of NOx in parts per million? Assume that NOx is represented by NO2 and that the fuel density is 692 kilograms per cubic meter. Solution For the stoichiometric combustion of octane, C8H18, the air-fuel ratio is 15. 05 and the molecular weight of combustion products is 28. 6. The consumption of octane is mf = (692)(1000)(3. 79? 10-3)/ 30 = 87. 4 g/mile [Note: (kg/m3)(g/kg)(m3/gal)/(mile/gal) = g/mile. The concentration of NOx is the ratio of the number of moles of NOx to moles of combustion gas products: mole Nox /mole cg = (mNOx /mf)(mf / mcg)(Mcg /MNOx) = (0. 4/87. 4)(28. 6/46)/ (15. 05 + 1) = 0. 0001773 254 or 177. 3 parts per million (ppm). _____________________________________________________________________ Bibliography and References 1. Heywood, John B. , Internal Combustion Engine Fundamentals. New York: McGraw-Hill, 1988. 2. Ferguson, Colin R. , Internal Combustion Engines. New York: Wiley, 1986. 3. Adler, U. , et al. , Automotive Handbook, 2nd ed. Warrendale, Pa. Society of Automotive Engineers. , 1986. 4. Lichty, Lester C. , Internal Combustion Engines. New York: McGraw Hill, 1951. 5. Crouse, William H. , Automotive Engine Design. New York: McGraw-Hill, 1970. 6. Obert, Edward, Internal Combustion Engines, Analysis and Practice. Scranton, Pa. : International Textbook Co. , 1944. 7. Grosser, Morton, Diesel: The Man and the Engine. New York: Atheneum, 1978. 8. Nitske, W. Robert, and Wilson, Charles Morrow, Rudolph Diesel: Pioneer of the Age of Power. Norman, Okla. : University of Oklahoma Press, 1965. 9. Demmler, Albert W. Jr. , et al. , ? 989 Technical Highlights of Big-three U. S. Manufacturers,? Automotive Engineering. Vol. 96, No. 10, October 1988, p. 81. 10. Anon. , ? Ignition Quality of Diesel Fuels by the Cetane Method,? ASTM D 613-84, 1985 Annual Book of ASTM Standards, Section 5. 11. Amann, Charles A. , ? The Automotive Spark Ignition Engine-A Historical Perspective,? American Society of Mechanical Engineers, ICE-Vol. 8, Book No. 100294, 1989. 12. Amann, Charles A. , ? The Automotive Spark-Ignition Engine-A Future Perspective,? Society of Automotive Engineers Paper 891666, 1989. 13. Amann, Charles A. , ?The Passenger Car and the Greenhouse Effect,? Society of Automotive Engineers Paper, 1990. 14. Taylor, Charles Fayette, The Internal Combustion Engine in Theory and Practice, 2nd ed. , revised. Cambridge, Mass. : MIT Press, 1985. 255 15. Public Law 101-549, ? An Act to Amend the Clean Air Ac t to Provide for Attainment and Maintenance of Health, Protection, National Air Quality Standards, and Other Purposes,? November 15, 1990. 16. Anon. , ? Provisions? Clean Air Amendments,? Congressional Quarterly, November 24, 1990. 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. 6. 4 Derive an equation for the Otto-engine net work by integration of pdV for the Air Standard cycle.Compare with Equation (6. 6). 6. 5* Use a spreadsheet to calculate and plot cycle ef ficiency as a function of compression ratio for the Diesel cycle for cutoff ratios of 1, 2, and 3. Indentify the Otto-cycle efficiency on the plot. Explain and show graphically from the plot how a Diesel engine can be more efficient than an Otto engine. 6. 6 A single-cylinder Air Standard Otto engine has a compression ratio of 8. 5 and a peak temperature of 3500Â °F at ambient conditions of 80Â °F and one atmosphere. Determine the cycle efficiency, maximum cylinder pressure, and mean effective pressure. 6. A six-cylinder engine with a compression ratio of 11 runs at 2800 rpm at 80Â °F and 14. 7 psia. Each cylinder has a bore and stroke of three inches and a volumetric efficiency of 0. 82. Assume an Air Standard, four-stroke Otto cycle _______________________ * Exercise numbers with an asterisk indic

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due to the possibility of a decrease in response to the treatments that followed. This is accurate for sequential endocrine, anti-HER2 or chemotherapy-based programs. At each stage of the disease, a thorough assessment of benefits versus damage is required using treatments for each patient. Knowing the side effects of each treatment and toxicity is a key factor in the evaluations. Some of the factors that used in chemotherapy for breast cancer include: -Taxanes: The max active and greatly popular used chemotherapy agents to treat breast cancer at an early stage. -Anthracyclines: Used in treatments for an early stage of breast cancer for many years, although concerns about associated cardiotoxicity or leukemogenesis may remain. -Tamoxifen:†¦show more content†¦Ultrasound is used for helping guide biopsy needle in an area of changes. Therefore, cells can be removed and examined for cancer. It possibly utilised to search for and guide the biopsy needle in the swollen lymph nodes under the arm. (Cancer.org, 2017) MRI According to (Morris and Liberman, 2005), MRI is principles technique which has a different physical from mammography and ultrasound. It indicates the protons water density in tissues including its magnetic interactions with molecules in its local surroundings. Magnetic interactions affect on MRI signal, that influences how fast the water protons can get back to equilibrium after receiving the radio-frequency energy from RF coil. MRI Parameters system can adapt to switch of T1 and T2 weighting that is providing image contrast to be formed. MRI is carried out by utilising a weighted T1 parameter that is reasonable for collecting Gadolinium contrast factors which the performance of T1 shortens and high signal intensity. Therefore, a significant increase in the signal from the breast tissue area shows higher density plus greater leakage of the microfilms, leading to re-purification of the vascular lesion. Although larger mammalian breast tumours provide enhanced signal, not all signal improvements describe cancer, causing a high sensitivity, despite low to moderate specific breast magnetic resonance imaging. MRI has two key features forShow MoreRelatedThe Death Of Breast Cancer1386 Words   |  6 PagesBreast cancer isn’t a death sentence as it was before. Women used to fear being diagnosed with this disease because there was no cure for it. Breast cancer has been around for centuries, but the advancement of medicine has increased the chances of survival, and in the future the improvements will be even greater. The first mention of breast cancer was documented in Egypt in 1600 B.C. It was considered a mysterious disease with no cure to it. In The Edwin Smith Papyrus, there are eight cases of tumorsRead MoreRadiation versus Chemotherapy in the Elderly with Breast Cancer1113 Words   |  5 Pagesversus Chemotherapy in the Elderly with Breast Cancer In clinical practice today the population is increasing in the number of elderly patients, as is the occurrence of breast cancer in women 60 years of age and older. According to Tang et al. (2011) the occurrence of breast cancer in women 65 years old and older is greater than â€Å"400 cases per 100, 000 women† (p. 3). The appropriate treatment options for the elderly are not as standard as those for a younger generation related to the effects theRead MoreCauses And Risk Of Breast Cancer1026 Words   |  5 PagesCauses risk of breast cancer Breast cancer is a disorder that mostly happens to women, as for men it is very rare. BRCA1 and BRCA2 work as DNA but when they are not replaced correctly it can lead to cancer. 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Two systemic hormonal therapies useful in women with ER-positive breast cancer are tamoxifen and aromatase-inhibitorsRead MoreThe Effects Of Herceptin On Cancer Models And Patients With Her2 + Breast Cancer1735 Words   |  7 Pagesepidermal growth factor 2) receptors found on breast cells( Tan, 2010) . HER2 is a receptor protein that is a member of the epidermal growth factor receptor family and is over expressed in approximately 10-20% of breast cancers that have amplification of the HER2 gene (Jatoi, et al., 2010). Herceptin has been found to selectively apply anti-tumor effects in cancer models and patients with HER2+ breast cancer (Gajria Chandarlapaty, n.d.). Although all normal breast cells present HER2 receptors on their

Legos Essay example - 966 Words

Legos are the multi-colored blocks we used as children to build creations that were only limited by our imaginations. I remember adding to my multi-colored plastic sculptor, each block putting me one step closer to the final product. The process would always entail first setting up a strong foundation, and then creating structural support, while always having a plan in the back of my mind. The outcome of which, would tower above me; to think it all began with a single block. In many ways people are similar to Legos. We are the combination of our experiences, each adding to our personas, and shaping how we view the world. Also like Legos, to have a stable and functioning final product it must have a foundation, support and a plan. I was†¦show more content†¦However, one thing that I did love at Rochester was the extra-curricular activities. I found myself enjoying the organizations more than my academics. Grades became secondary to activities; it was an occasion in my life w hen I unable to prioritize and balance my time correctly. I was not doing as well as I wanted too at Rochester, however it is was where I gained an eternal support system. The shy, quiet and self-doubting kid I once was shattered, revealing a self - confident adult who was ready to take on the world. It was as if I could feel the sun for the first time, but unbeknownst to me a storm was on the horizon. On January 5, 2009 my father pasted away. He and I did not have the typical father-son relationship; we did not have a relationship at all. I presumed that it would have a little if any affect on me. However, as the semester continued, it seemed to get worse. Besides my father’s passing, several weeks later my grandmother was diagnosed with dementia. It was difficult for me to deal with, but it was more difficult for my mother to handle. It was then I decided that I should leave school and take care of things at home. This was the most difficult decision I have ever made. So I resigned from the position as president of my fraternity, and left with only three weeks left, thereby missing my senior year. Returning home, I felt like the prodigal’s son, embarrassed and depressed becauseShow MoreRelatedLego Of The Lego Group1723 Words   |  7 PagesBackground The Lego group was established in 1932 by Ole Kirk Christiansen in Billund, Denmark. Lego today is one of the most recognizable brands in the world. However, that does not mean that they haven’t had to make some changes along the way to reach and stay at that position. Lego needed to change because of increased expansion of their product line which lead Lego to the brink of going bankrupt. In the year 2000, the Lego group had a huge sales growth. By 2004, they were projected to lose somewhereRead MoreLego : A Case Study Of Lego921 Words   |  4 PagesLEGO Case Study Introduction Lego is founded in 1932. It is privately-held and it is still owned by the family of the founder, Ole Kirk Kristiansen. Lego is an abbreviation of two Danish words, leg godt meaning play well†. Lego discovered its specialty in 1932 when the main wooden building pieces were made, from that minute the organization had discovered its motivation in making toys for kids. The company had forty-nine different designs for wooden toys, but in 1942 the company destroyedRead MoreLego Toys And The Lego Company2715 Words   |  11 PagesThe Lego company, it started as a small carpenter’s workshop and transformed into the modern, huge company it is today, creating some of the most known toys in the world. The Lego company created the Lego (brick). The Lego (brick) is the most well known toy in the world. 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Date : 03 March 2012 Programme : BTECH-MANAGEMENT IV Question 1 Explain how the development of strategy at the LEGO Group reflect the key characteristics of strategic management outlined in section 1.2 and in the model in Figure 1.4? â€Å"Strategy is the long-term direction of an organization† (Johnson, Whittington and Scholes, 2011, p.3). The LEGO Group started with the manufacture of stepladders,Read MoreLego Structure Of The Lego Company1448 Words   |  6 PagesLego is one of the most recognizable companies across the world. The Lego Group was founded in 1932 by Ole Kirk Kristiansen and has since been passed down from generation to generation, currently owned by Kjeld Kirk Kristiansen. The Lego Group has headquarters in Billund, Denmark and main offices in USA, UK, China, and Singapore. The Lego name originated from the abbreviation of two Danish words â€Å"leg godt† meaning â€Å"play well†. 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Business Report Developing Leadership

Question: Describe about the Business Report for Developing Leadership. Answer: 1, Bison should take the hands-off approach to business in his management role in order to realize the goals and objectives of the company. Developing leadership in an organization requires a good strategy because organizations that succeed in creating leadership among their employees give employees autonomy and space to do their work. Top management exercises little supervision of employees because they believe that it is through this processes that junior employees learn from their mistakes. To successfully implement a senior leadership change strategy, company management needs to have a leader who employs hands-off management approach (Beycioglu Pashiardis, 2015). The change of organizational behavior requires that organizational structure is changed from hierarchical to a more horizontal structure (Dalkir Liebowitz, 2011). The horizontal structure allows front-line and junior workers to play a more central role in management while at the same time they become more accountable for their actions (Beycioglu et al. 2015). Horizontal structure is only more effective if the top management employs the hands-off approach to business management. This strategy will allow top management to delegate most of the duties to front-line employees as opposed to hierarchical structure where the top management makes almost all the decisions (Chandler et al. 2007). When top management moves aside to create a vacuum, employees are given an opportunity to fill the vacuum. Employees tend to be motivated when they have a chance to lead and carry out some managerial functions. To achieve a growth target of one billion dollars by 2020 requires a lot of motivated employees. One of the ways to motivate employees is using of hands-off management approach where most of the tasks are delegated by the top management. Through delegation, employees feel appreciated and part of the organization rather than when all the main decisions and tasks are carried out by the top management. Therefore, it is logical that Bison employs hands-off approach management approach at MeatPack as a motivation for employees to take more responsibility and be accountable for their performance. MeatPack Company is undergoing cultural and performance changes and senior leadership change which require that all the departments and employees should be actively involved in the process. To bring all departments on board cannot be achieved by the efforts of the manager alone because the organization is large and complex. For this reason, Bison needs to employ hands-off management approach by forming teams headed by leaders and delegating some of the management duties to team leaders. By delegating some of the duties to team leaders and giving them targets to be achieved, Bison will have an easy time running the company. Hands-off management facilitates creativity, development and growth among employees. By giving team managers and employees more responsibility and an opportunity to be leaders in their departments, employees exploit their talents and abilities fully. Employees under such management reveal skills that top management never knew they possessed thus accomplishing greater things than anticipated by the management. Full potential of employees can never be realized when top management keeps interfering with the working of employees. Therefore, Bison will benefit from employees full capabilities by using the hands-off management approach. There are some things that Bison cannot do them by himself but when employees are left on their own to explore their skills, they will not do them the same way Bison would them but they might achieve tremendous results that the company never expected to achieve. Every employee has some hidden skills and talent which most leaders do not discover because of t he interference and regulations that management has over them (Haines, 2016). In such a case Biro should not be involved in the day to day details of work that employees do but rather He should play the role of a facilitator and orchestrator to show team leaders on how some tasks should be carried out. This approach will help Bison to exercise more effectively his leadership and management skills. This is because best managing leaders help people to reach their full potential by allowing them to do as much as they can in the best way possible. Reaching targets is virtually impossible if top management employs hands-on business management in the operations of the company (Haines, 2016). Hands-off approach will allow Bison to concentrate on larger projects and duties such as decision making at top level management. Subordinate roles, responsibilities and decision making at lower levels without having to consult with the top management. This strategy will save on time because Bison and his senior management team will focus on creating ties with other business partners and holding high-level consultative meetings with board management. Save on time will translate to saving on company's financial resources. Hands-off approach gives other junior employees some leadership responsibilities and accountability which forms the basis for future leadership of the enterprise (Tour et al. 2014). Any business growth and development comes with additional leadership responsibilities and the ability of a company to maintain its growing capacity depends on the preparedness of the management (Brulin Svensson, 2012). Preparedness includes but not limited to having good leadership in place to spearhead the organization to another level even after the current management is long gone. Therefore, hands-off management strategy by Bison will help the company groom future leaders to take over the companys leadership long after the current management is gone (Brulin et al. 2012). Without such leaders, even the growth that the company aims to achieve by 2020 will not be sustainable at all. Since Bison is on the way to implement senior management changes and performance changes, he needs efficiency in compartmentalization of roles. Hands-off approach provides effective allocation of roles amongst different teams because everyone knows the exact role and responsibility to play during the change implementation process (Tour et al. 2014). Bison will have easy time in managing change because most of the feedback about the progress will be given to him via reports by team leaders which will enable him to determine whether the company is making progress or not (The Globe and Mail, 2012). Such strategy will make sure that top management does not need to go through all these tussles of knowing everything about the progressive change which the organization undergoes. 2. By changing the structure within the organization, all members of the senior leadership play a major role in policy making (Anderson et al. 2010). This move also ensures that senior leadership focuses on some key projects and they make larger decisions while leaving other functions to be carried out by other employees. Therefore, the senior leadership of MeatPack has become more efficient in executing leadership roles. Senior leadership change has been able to make significant changes in the human resources' structure of the company to allow for transition. The company has succeeded in designing of the whole company leadership development program to lay a foundation in anticipation of the new major senior leadership changes to be made (Kirkpatrick, 2009). This is positive because wider organizational leadership is one of the most crucial tools that are necessary for organizational change. Since senior strategy team is in charge of setting long-term goals of the company and designing necessary strategy to achieve the goals, consultative coaching is very necessary for the team (Shani et al. 2014). Through consultative coaching, the team becomes more efficient in making important strategic decisions because they have fast hand knowledge about the market and future of the industry. Without consultative coaching, senior strategy team cannot make sound strategic decisions that propel the company forward towards its long term goals (Shani et al. 2014). The senior leadership change has been able to create a general positive dynamic amongst members of the senior strategy team (Beycioglu et al. 2015). This implies that before the changes, members of the senior strategy team did not coordinate well but since senior leadership changes were initiated, the mood and response among companys senior leadership changed (Palmer et al. 2009). Through senior leadership change, Bison has initiated open discussion and dialogue between him and other senior strategy team members. Through this dialogue, members are encouraged to give out their views in an open manner amongst themselves and to him during company meetings (Bremer, 2012). Through such open forums and one on one basis where other senior strategy team members are given an opportunity to openly discuss their pressings issues, Bison is able to get crucial information to assist in decision making process (Kirkpatrick, 2009). Bison together with his senior strategy team are able to hold important discussions about the mandate of the team, composition of the team and how the team can be effective in delivering its mandate (Burnes, 2009). Senior leadership change has been able to initiate major structural changes whereby some new Chief Executive Officers (CEOs) were recruited to carry out different roles within the company. These structural changes shifted the line of command and there were new roles created for the senior strategy team. Most of such structural changes come with a lot of benefits and one of the benefits is that they increase efficiency within the company (Palmer et al. 2009). 3. First, the structure has changed the method of communication between employees and management. Before the flatter structure was adopted, forms of communication were aggressive, abusive and staff was supposed to work as per the commands from the above. There was a long chain of communication from the top management to employees. Top management was only but obsessed with making things to happen without even understanding how tasks are carried out (Kru?Hler, 2012). However, when flatter organizational structure was introduced into the company, mode of communication changed because employees are supposed to report to few authorities in the company. Furthermore, there is more understanding amongst employees because management shifted its focus from making things happen to understanding how tasks are carried out. Communication has also shifted from top-down to become more collaborative where employees comfortably speak up their minds (Bremer, 2012). The structure has empowered managers and supervisors to be more responsible and accountable for their respective duties. For instance, line managers play a role in recruiting new personnel and carrying out performance appraisals for employees. By Bison giving more responsibility to managers and supervisors, culture of management is being eroded and replaced by the culture of leadership. This is because leadership comes with more responsibility and accountability rather than looking up to the top management to make decisions (Cummings et al. 2009). The culture is having different people to report to has changed because Bison advocates to have six to eight people for every report to make sure that supervisors and managers are clearly accountable. Flatter structure has made it necessary for Bison to invest heavily in team leader and management courses so as to have trained shift leaders that have been newly promoted. The company has also changed performance by shifting focus from top-down management approach to a line focus where front line employees are directly involved in the development of efficiency (Lawler et al. 2011). This move has made front-line employees feel appreciated and valued part of the company (Burnes, 2009). The structure has also allowed managers and employees to sit down and discuss various pertinent issues affecting the performance of employees. Managers are also authorized to take some time and relax while reflecting on how to solve some situations within their departments (Franz, 2012). Managers in the company are more open minded, fresh, young and close to employees more than before which acts as a motivation to junior employees. It is a motivation because employees can comfortably engage their managers on many different issues and managers listen to them attentively as opposed to top-down structure where managers were the ones issuing commands and directives to employees (Shani et al. 2011). Barriers to cultural change within the company Some top level and middle managers are opposed to changes being implemented on how tasks are carried out. For instance CFO and COO feel that the hands-off strategy being implemented by Bison is not appropriate and thus should be changed. They feel that Bison should be exemplary to managers and other employees rather than giving almost all the responsibilities of supervisors and managers within the company. Given that some employees have been with the company for as long as more than 15 years, there is a tendency of reluctance to embrace new cultural changes (Hoffmann, 2011). The employees are used to doing things in their own way and thus become a hard task for management to change these peoples culture (Reiss, 2012). Conclusion Organizational change is very critical for any organization because it defines the future where the organization is headed and determines whether the organization will attain its long-term strategic business objectives or not. In the case of MeatPack, Bison should employ hands-off approach because it is large company and given the strategic business objectives to achieved by 2020, delegating duties is the most effective way to manage (Reiss, 2012). Senior leadership change is effective because it has managed to change human resource structure, created positive dynamism and initiated open discussion forums. Lastly, flatter structure implemented by Bison has increased accountability among employees, simplified method of communication and initiated open-mindedness among managers. Recommendations for senior leadership Senior leadership should lead outside the lines. Senior leadership change takes place more efficiently in an organization if the top management involves everyone who has authority and influence over the operations of the company (Anderson et al. 2010). There are people of influence within a company that do not have formal positions but play a very central in the company either because of their network, their expertise or personal qualities. These kinds of people are called informal leaders, and they might include experienced employees, innovative project managers or some high-profile consultants. Research shows that most companies that succeed in implementing senior leadership change identify these informal leaders early enough and bring them on board when implementing change within their organization (Bilney Pillay, 2015). Senior leadership should continue to engage and consult widely amongst them and other partners whom they deem can provide important insights to spearhead top leadership change. Carter et al. (2005), says positive and sustainable change within an organization especially at the top management requires constant communication throughout the process of rolling out change and even after major plan elements have been put in place. By engaging different groups throughout the organization, senior management will get some important information about what other partners think of the change (Kru?Hler, 2012). This information gives senior leadership a blueprint on whether the change they are implementing is bound to succeed or fail. Senior leadership should carry out an assessment and adapt accordingly. For any company to succeed in implementing high leadership change, it must measure its success before embarking on the change process (Bilney Pillay, 2015). Senior leadership should take time to discover what is working and what is not working in their change strategy so as to effectively adjust their next steps in order for them to be aligned according to the prevailing conditions. Failure to regularly carry out an assessment and adapt denies the organization crucial information on how to support senior leadership change. Senior leadership should make both emotional and rational cases together. Top leadership should relate strategic business objectives and emotions because strategic business objectives alone cannot be achieved unless the emotional part of other leaders is engaged (Carter et al. 2005). Genuine commitment to change begins by top most leader reaching out emotionally to other leaders about the desired change within the organization. Human beings are created such that their hearts and minds respond calls to change when their emotions are engaged (Franz, 2012). This is the case because emotional involvement will make leaders feel they are part of change. Implementation It is the senior leadership within the company comprising of the CEO, operations manager and all the departmental managers. Implementation period should take a period of six months to one year. The estimated cost of implementing the senior leadership change is $250,000. References Anderson, D., Ackerman-Anderson, L. S. (2010). Beyond change management: how to achieve breakthrough results through conscious change leadership. San Francisso, Pfeiffer. https://www.books24x7.com/marc.asp?bookid=41035. Beycioglu, K., Pashiardis, P. (2015). Multidimensional perspectives on principal leadership effectiveness. https://search.ebscohost.com/login.aspx?direct=truescope=sitedb=nlebkdb=nlabkAN=937773.. Bilney, C., Pillay, S. (2015). Public sector organizations and cultural change. https://search.ebscohost.com/login.aspx?direct=truescope=sitedb=nlebkdb=nlabkAN=1091422.. Blazey, M. L. (2013). Insights to performance excellence, 2013-2014: understanding the integrated management system and the Baldridge criteria. Milwaukee, Asq Quality Press. Bremer, M. (2012). Organizational culture change: unleash your organizations potential in circles of 10. Zwolle, Kikker Groep. Brulin, G., Svensson, L. (2012). Managing sustainable development: a learning approach to change. Farnham, Gower. Burnes, B. (2009). Managing change. Harlow, Financial Times Prentice Hall. Carter, L., Ulrich, D., Goldsmith, M. (2005). Best practices in leadership development and organization change: how the best companies ensure meaningful change and sustainable leadership. San Francisco, Pfeiffer. https://public.eblib.com/choice/publicfullrecord.aspx?p=221275. Chandler, S., Black, D. (2007). The hands-off manager: how to mentor people and allow them to be successful. Franklin Lakes, NJ, Career Press. Cummings, T. G., Worley, C. G. (2009). Organization development change. Australia, South-Western/Cengage Learning.. Dalkir, K. and Liebowitz, J., 2011. Knowledge management in theory and practice. MIT press. Franz, T. M. (2012). Group dynamics and team interventions: understanding and improving team performance. Hoboken, John Wiley Sons. https://public.eblib.com/choice/publicfullrecord.aspx?p=875438. Haines, S., 2016. The systems thinking approach to strategic planning and management. CRC Press. Hoffmann, E. A. (2011). Co-operative workplace dispute resolution: organizational structure, ownership, and ideology. Farnham, Surrrey, England, Gower Pub. Kenny, G. (2005). Strategic planning and performance management: develop and measure winning strategy. Routledge. Kirkpatrick, D.L., 2009. Managing change effectively. Routledge.. Kru?Hler, M. (2012). Managing business portfolios effectively: on the explanatory power of the parenting advantage concept. Wiesbaden, Springer Gabler. https://public.eblib.com/choice/publicfullrecord.aspx?p=973984_0. Lawler, E. E., Worley, C. G., Creelman, D. (2011). Management reset organizing for sustainable effectiveness. San Francisco, Calif, Jossey-Bass. https://proxy2.hec.ca/login?url=https://library.books24x7.com/library.asp?B?bookid=41002. Palmer, I., Dunford, R. and Akin, G., 2009. Managing organizational change: A multiple perspectives approach. New York: McGraw-Hill Irwin. Reiss, M. (2012). Change management: a balanced and blended approach. Norderstedt, Books on Demand. Shani, A. B. R., Noumair, D. A. (2014). Research in Organizational Change and Development. Bradford, Emerald Group Publishing Limited. https://public.eblib.com/choice/publicfullrecord.aspx?p=1725934. Shani, A. B., Woodman, R. W., Pasmore, W. A. (2011). Research in organizational change and development. Bingley, UK, Emerald. Smallbusiness.chron.com. (2016). Benefits in a Flat Organizational Structure. [online] Available at: https://smallbusiness.chron.com/benefits-flat-organizational-structure-281.html [Accessed 8 Oct. 2016]. The Globe and Mail. (2012). The hands-off approach to leadership. [online] Available at: https://www.theglobeandmail.com/report-on-business/careers/the-hands-off-approach-to-leadership/article4480738/ [Accessed 8 Oct. 2016]. Tour, P., WorkZone?, W., Customers, O., Pricing, D. and Us, A. (2014). Hands-on Managers vs Hands-off Managers | WorkZone. [online] WorkZone. Available at: https://www.workzone.com/blog/hands-on-managers-vs-hands-off-managers/ [Accessed 8 Oct. 2016].

Social, Political and Economic Conditions of the 1950s

Table of Contents Introduction Social Aspect Political Economic Discussion Conclusion Works Cited Introduction The conclusion of the Second World War brought many changes to the world. In the United States, President Truman spearhead programs that would rehabilitate the society through economic policies that would help the citizens in the United States recover from the war. The trauma experienced by the Americans was unimaginable for their fear of bombs and war devices grew at the same time the government was also on constant alert by ideologies that differ from the Western version of democracy.Advertising We will write a custom essay sample on Social, Political and Economic Conditions of the 1950s specifically for you for only $16.05 $11/page Learn More The United States continued to support wars of other democratic nations against communists thus domestic policies suffered for budgets were mostly allocated to national security and funding of wars. The growing racism of the 1950s contributed to the birth of civil rights groups where white youths protest to equalize the system. As the United States government aggressively supports foreign wars against communism, a chunk of the federal budget is allocated to national defense and security programs. Domestic programs suffer thus the American population suffer for the number of poor people increased during the 1950s to 1960s. America’s intervention in the Vietnam War cost constrains where a civil war almost broke out. The citizens grew weary and angry of the government’s decisions and actions to aid the French in controlling communist Vietnam. People suspected that the United States government’s ulterior motive in financially supporting the French in the war is because the former wanted to colonize the country. American families lost allot of their family members in the Vietnam War. This paper aims to evaluate and analyze the social, political and economic cond itions of the 1950s in the United States. It aims to provide an explanation by discussing factors that lead to the social upheaval of the 1960s. Chosen events after the World War II will be the subject of the study in order to fully understand the development of the American society in the 1960s. Social Aspect After the Second World War, Americans experienced a tremendous personal fear which was a result of bombs during the war (Henriksen). Government social programs resulted in large –scale suburban housing resulted in the more suburban than urban American in the 1960s. The fairly new suburban architecture after the war necessitated new social relations with the emphasis on immediate family more than extended family. The American suburban life exaggerated the traditional male and female roles and relations. In the suburban identity there is a lack of traditional ethnic and religious diversity which are found in city life. In the 1950s femininity required conformity, passivit y and deference especially in the suburbs. Suburbs were once described by Betty Friedan in The Feminine Mystique as comfortable concentration camps (Friedan). Suburban is ideally characterized in the form of domesticity, cooperation, conformity and family. Unfortunately in the 1950s, the new suburban life Americans enjoy is excludes African Americans. Racism grew more prominent. The United States was significantly richer and more conservative than any other time in history where the middle class grew but the population of the poor did not decrease.Advertising Looking for essay on history? Let's see if we can help you! Get your first paper with 15% OFF Learn More The hypocrisy of inequality between the whites and colored in the United States drew many white youth into civil rights movements. The massive spread of racism even resulted in many states forbidding interracial marriages at the same time most communities have restrictive housing covenants. Interstate Commerce Commission even ordered the desegregation of trains, buses, waiting rooms while the Supreme Court ordered the desegregation of restaurants in 1958. Racism became a major issue in the 1950s. Racism and the US government’s constant participation in foreign wars gave rise to civil rights groups and protesters. Of all the social protest movements of the 1960’s, student movements would have the most affect on middle class Americans. Political In terms of political aspects, President Truman justified the use of the atomic bombs in Hiroshima and Nagasaki to save both American and Japanese lives for the use of such destructive device seized the war. In the 1950s racism became intrinsic in the US government and throughout its agencies. The Truman Doctrine was produced after the war where the US pronounced its intentions to stop the spread of communism. The doctrine allowed the US to give monetary aid and military support to the Greek right during its civil war in 1946 – 49. Limited wars were also created which circumvent Congress and traditional Pentagon procurement system. When the Cold War came money from social programs were diverted to national defense. In the 1950s the United States begun testing nuclear weapons in the Pacific namely in Bikini Atoll and on the mainland in Utah. The new nuclear world and anti-communist rhetoric which developed in the United States created national anxiety. In 1956, Eisenhower was reelected as president. He filled the cabinet with business leaders who determined the domestic policy of the United States. The president’s conservative fiscal policy as well as his dynamic conservatism resulted in the increase of the average family income of Americans. During the Cold War the Americans help in funding the war expenses of the French in the Vietnam War. 80% of the expenditure was paid by the American government as of 1954 (Addington). Vietnam was divided into two parts namely the North which is controlled by the communists and the south which is controlled by the democratic French and Americans. The United States was on the verge of civil war in 1968 because of the government’s intervention on the Vietnam War. The people were angry because about 14,650 Americans had been killed in 1968 alone – almost one-half of the 30,610 who had died since 1961 (Addington). Many Americans criticized the government for spending money on Asia when the said money could be spent at home developing new jobs and infrastructure as the poverty level in the United States had increased.Advertising We will write a custom essay sample on Social, Political and Economic Conditions of the 1950s specifically for you for only $16.05 $11/page Learn More Economic After the war FHA loans were provided to individuals and VA loans for war veterans. Social programs such as the Social Security subsidized housing program called â€Å"Levittowns† were offset by the Fed because of the insecurity the people felt towards bombs. The FHA did not lend to African Americans despite the ruling of the Supreme Court. The blacks suffered because of the restrictive covenants where it resulted to higher costs of loans, poorer housing and worse schools for the ethnic group (Wolfe). Many Americans were forced into the cities to find work as federal subsidies to business and agriculture exacerbated problems for small farmers and business people. During the 1950s, about 1.5 million people left Appalachia for cities. The poor educational system left Americans with few opportunities for apprenticeships which meant there were fewer skilled workers available. In 1953 to 1959, about 1.5 million blue collar jobs were lost. 11% of which were lost forever. Between 1956 and 1959, 30,000 meat packing jobs were lost. Discussion In the 1950s the suburban life was very prominent in the American society where the ideal life of every American was to live in the suburbs. The man was the bre ed winner of the family thus he was the decision maker. On the other hand femininity was best described as being passive. Women were expected to be submissive to their husbands and they were considered the homemaker. They did not need to work for the man would be the sole provider. The American government had provided loans for the white families unfortunately there was racial discrimination thus African Americans did not enjoy such benefits. The rise of racism also gave rise to civil rights movements formed and led by white American youths who contradicted the way of life. These movements would later become prominent in the American society in the 1960s where mostly students would lead such groups. Political leaders after the war were characterized by their alertness to new ideologies that may oppose the democratic way of thinking in the world. After the war the US government’s priority was to rebuild the American economy. The federal government had devised programs which wo uld recover the American economy through loans that would help in the construction of homes to citizens and war veterans and serve as capitals to start up businesses.Advertising Looking for essay on history? Let's see if we can help you! Get your first paper with 15% OFF Learn More America’s fear of communism led to the government’s down fall in the 1960s when the government allocated most of its budget to national security and defense. The Vietnam War is an example of the government’s expensive aid to the French allies in winning the war. This expenditure angered the American public and almost cost a civil war to occur. In terms of the American economy, the 1950s showed the height of America as a rich nation where the middle class grew but ironically the poor population remained the same. During this time the American government aided citizens in building their homes and businesses to stabilize the US economy. White collared jobs were created but unfortunately blue collared ones decreased thus explaining the constant population of the poor in the United States. African Americans were not given the same benefits as their white counterparts. They were the ones who suffered the most for they had poor housing, bad education and their standard of livings have worsened during the 1950s. Conclusion The United State’s social upheaval in the 1960s was caused by racism in the 1950s where only the white population benefited from the government’s social programs. This led to civil rights groups which lobbied for the equal treatment of citizens. The same group gave rise to the popular student hippies in the 1960s that almost cost civil war because of the US government’s support in the Vietnam War. In terms of the political sector, the US government’s constant intervention with other foreign nations’ concerns with regards to wars against communism led to the anger of US citizens in the 1960s because budgets were allocated to national security and defense as well as financial supports in wars. Such move greatly affected the US economy. Works Cited Addington, Larry. America’s War in Vietnam: A Short Narrative History, Bloomington, Indiana: Indiana University Press, 2000. Print. Friedan, Bet ty. The Feminine Mystique, New York, United States of America: W.W. Norton and Company, Inc., 1963. Print. Henriksen, Margot. Dr. Stragelove’s America: Society and Culture in the Atomic Age, Los Angeles, California: University of California Press, 1997. Print. Wolfe, Tom. The Electric Kool-Aid Acid Test, New York, United States of America: Random House Inc., 1968. Print. This essay on Social, Political and Economic Conditions of the 1950s was written and submitted by user S1lverclaw to help you with your own studies. You are free to use it for research and reference purposes in order to write your own paper; however, you must cite it accordingly. You can donate your paper here.