The expression for the Otto cycle efficiency,
ηotto=1−1rγ−1
Substitution of the values:
Compression ratio, r = 10.0, and
Ratio of heat capacities,γ=1.4 gives
ηotto=1−110.01.4−1=0.602
=60.2%
ηbrake=ηi×ηmech=0.5×ηotto×ηmech
=0.5×0.602×0.9=0.271
Equation can be used to calculate the specific fuel consumption (sfc)
sfc=1(ηbrake×CV)=1(0.271×44×106)=83.9g/MJ