1. The problem statement, all variables and given/known data I'm trying to find an expression for the efficiency of a stirling engine operating with an ideal diatomic gas, and cycling through a volume V and a multiple of its compression ratio, r, Vr. 2. Relevant equations processes: 1-2 isothermal expansion 2-3 isochoric cooling 3-4 isothermal compression 4-1 isochoric heating r=compression ratio Th=high temperature Tl=low temperature Work=W1 proc. 1-2 (nRTh)ln(r) Work=W2 proc. 3-4 (nRTl)ln(1/r) Work Net= W1-W2= nRln(r)(Th-Tl) since ln=-ln(1/r) Heat Input=Qh=nCv(Th-Tl)=(5/2)R(Th-Tl) Efficiency=e=W Net/Heat Input=[nRln(r)(Th-Tl)]/[(5/2)nR(Th-Tl) Canceling:e=(5/2)ln(r) This does not Make sense since efficiency for an engine with an equal compression ration of say r=10 operating at a Temp high of 300k and low of 200k would have a carnot efficiency of (1/3) while with the above equation e=.92 which is impossible.