Otto Cycle Efficiency
Otto Cycle Efficiency
The ideal Otto cycle efficiency depends only on the compression ratio and the gas properties — the theoretical ceiling for a petrol engine.
The efficiency is η = 1 − 1/CR^(γ−1). where CR is the compression ratio and γ the heat-capacity ratio.
Inputs
CR := 10=10
gamma := 1.4=1.4
Apply the air-standard Otto efficiency.
eta := 1 - 1/CR^(gamma - 1)=0.6
Results
A 10:1 ratio gives about 60% ideal efficiency; real engines reach roughly half that because of friction, heat loss and incomplete combustion. Higher compression raises the ceiling.
Assumptions & limitations
- Air-standard (ideal) Otto cycle.
- Constant specific heats.
- Reversible processes.