The actual cycle does not have these sharp transitions between the different processes and might be as sketched in figure 2A-2 ISentropic Spark Exhaust Exhaust valve closes Figure 2A-2: Sketch of actual Otto cycle Efficiency of an ideal otto cycle The starting point is the general expression for the thermal efficiency of a cycle york L=1+L heat input engine, So QL Is negative. The heat absorbed occurs during combustion when the spark occp or The convention, as previously, is that heat exchange is positive if heat is flowing into the system or roughly at constant volume. The heat absorbed can be related to the temperature change from state 2 to state 3 as Qn=Q23=AU23(W23=0 C=C(T3-T2) The heat rejected is given by(for a perfect gas with constant specific heats) (T1-T4) Substituting the expressions for the heat absorbed and rejected in the expression for thermal efficiency yields T 2A-22A-2 The actual cycle does not have these sharp transitions between the different processes and might be as sketched in Figure 2A-2 Spark Exhaust valve opens Not isentropic Exhaust valve closes P P0 V Figure 2A-2: Sketch of actual Otto cycle Efficiency of an ideal Otto cycle The starting point is the general expression for the thermal efficiency of a cycle: η = = + = + work heat input Q Q Q Q Q H L H L H 1 . The convention, as previously, is that heat exchange is positive if heat is flowing into the system or engine, so QL is negative. The heat absorbed occurs during combustion when the spark occurs, roughly at constant volume. The heat absorbed can be related to the temperature change from state 2 to state 3 as: QQ U W C dT C T T H T v T v == = ( ) = ∫ = − ( ) 23 23 23 2 3 3 2 ∆ 0 The heat rejected is given by (for a perfect gas with constant specific heats) Q Q U CT T L v == = − 41 41 1 4 ∆ ( ) Substituting the expressions for the heat absorbed and rejected in the expression for thermal efficiency yields η = − − − 1 4 1 3 2 T T T T