\[\eta=1-\frac{1}{r^{\gamma-1}}\]
Variables
eta[η]Otto cycle thermal efficiency (dimensionless)
rcompression ratio V1/V2 (dimensionless)
gamma[γ]heat capacity ratio Cp/Cv (dimensionless)
Description
What is this formula?
The Otto cycle efficiency gives the theoretical thermal efficiency of an ideal spark-ignition internal combustion engine operating on the Otto cycle. The efficiency depends primarily on the compression ratio and the heat capacity ratio of the working gas.
When to use it
Use this formula when analyzing gasoline engines, spark-ignition engines, or ideal Otto cycle thermodynamic models. It is commonly used to estimate the maximum achievable efficiency for a given compression ratio.
Example
Given:
r = 10
gamma = 1.4
Formula:
η = 1 - 1/r^(gamma - 1)
Substitution:
η = 1 - 1/10^(1.4 - 1)
Result:
η = 0.602 = 60.2%
Applications
Gasoline engines, automotive engineering, engine design, thermodynamic cycle analysis, power generation studies, and mechanical engineering education.