The process which runs from the initial state andreturns again to that initial state after the gas doeswork is called cycle.
In the process a - b, the gas expands in adiabatic process andthe work done by the gas is the area of plane abV2Vp its value isnegative.In process b - c the compressed gas in isothermal process is thearea of plane bcV1V2, its value is positive.In process c - a . The gas does not do any work because itsvolume is constant.The process c – a is an isochoric process which is done to makethe gas return to its initial state.
The total external work done by the gas in one cycle a – b – c – a is thearea of plane abca.A thermodynamics cycle can occurs in a heat engine, such as otto engine,diesel engine, and steam engine. In an Otto engine, the cycle occuring iscalled Otto cycle. In a diesel engine, the cycle occurring is called dieselcycle. While in a steam engine, the cycle occuring is called Rankinecycle.
This Carnot engine isassumed as an ideal heatengine which workscyclically and is reversiblebetween two temperatureswithout any loss of energy.This imaginary Carnotengine consist of a cylindercontaining ideal gas andcovered with a piston thatcan move alternatingly inthe cylinder.Figure 8.16 shows the workprocess of Carnot engine toproduce Carnot cycle. Entireof process in the Carnotcycle can be represented inpressure (P) against volume(V) graph as follows.
Based on the graph above, then the carnot cycle consist of the followingsteps.Step 1 The engine absorbs heat from the heat source or hightemperature reservoir T1 so that the ideaL gas in the engineexperiences isothermal expansion (temperature of system is equal totemperature of reservoir). The expanded gas applies a work on thepiston, so that the gas volume are changes from v1 to v2. Thisexpansion is shown in Figure 8.16, with changes from state a to b alongan isothermal graph. During this isothermal gas expansion, the gasreceives heat equal to Q1.
Step 2 The heat source is removed so that there is no heat input to thesystem. The gas still expands adiabatically and applies works to changegas volume from V2 to V3 In this process the gas temperature decreasesto T2. This process is shown in Figure 8.16 with change of state from bto c along an adiabatic graph.
Step 3. The gas experiences isothermal compression by giving awayan amount of Q2 heat the low temperature reservoir T2, In this process,the gas volume decreases from v3 to v4. This compression is shown inFigure 8.16, with change of state from c to d along an isothermalgraph.
Step 4. The gas experiences adiabatic. compression and returns to itsinitial state. In this process, a work is applied on the gas so that the gasvolume decreases from V4 to V1. This compression is shown in Figure8.l6, with change of state from d to a along an adiabatic graph.
Total work which done by gas in one cycle is equal to wide of area incycle.Because during process of Carnot cycle the gas accept kalor Q1 from hightemperature reservoir and free a heat Q2 to low temperature reservoir.Hence the work is done by gas according to first law of Thermodynamic isQ = U + W atau Q1 - Q2 = 0 + WW = Q1 − Q2
The Otto engine was made by Nikolaus August Otto (1832-1891),a technician born in Holzhausen, Germany. This Otto engine is usu-ally used in automobiles and airplanes.An Otto cycle is an idealized thermodynamic cycle which describesthe functioning of a typical spark ignition reciprocating piston engine.The Otto cycle is constructed out of: TOP and BOTTOM of the loop: apair of parallel adiabatic processes. LEFT and RIGHT sides of the loop:a pair of parallel isochoric processes.Otto cyclea – b and c - d process : adiabatic processb – c and d - a process : isochoric process
The Diesel engine was made by the German engineer Rudolf Chris-tian Karl Diesel (1858-1913). The Diesel cycle is the thermodynamiccycle which approximates the pressure and volume of the combustionchamber of the Diesel engine.The Diesel engine is usually used in electric generators, trucks, buses,and several types of cars.Diesel cyclea - b process : isobaric processb - c and d - a process : adiabatic processc - d process : isochoric process
The Rankine engine was made by William John Macquorn Rankine, aScottish polymath and Glasgow University professor.The Rankine cycle is a cycle that converts heat into work.The Rankine cycle is the fundamental thermodynamic underpinning ofthe steam engine.The Rankine cycle is sometimes referred to as a practical Carnot cyclebecause, when an efficient turbine is used, the TS diagram begins toresemble the Carnot cycle. The main difference is that heat addition (inthe boiler) and rejection (in the condenser) are isobaric in the Rankinecycle and isothermal in the theoretical Carnot cycle.a - b and c - d process : isobaric processb – c and d - a process : adiabatic process