The air standard efficiency of an Otto cycle is given by

where r = Compression ratio and

γ = Ratio of specific heats.

Concept:

Otto cycle

The air-standard-Otto cycle is the idealized cycle for spark-ignition internal combustion engines.

The Otto cycle 1-2-3-4 consists of the following four processes:

• Process 1-2: Reversible adiabatic compression of air
• Process 2-3: Heat addition at constant volume
• Process 3-4: Reversible adiabatic expansion of air
• Process 4-1: Heat rejection at constant volume

The thermal efficiency of the Otto Cycle:

\({\eta _{otto}} = 1 - \frac{1}{{{r^{\gamma - 1}}}}\)

Compression ratio: r = v1/v2

The air standard efficiency of an Otto cycle is \(1 - \frac{1}{{r^{\gamma - 1}}}\) 

Important Points

The air standard efficiency of a Diesel cycle is \(1 - \frac{1}{{{r^{\gamma - 1}}}}\frac{{\rho^\gamma - 1}}{{\gamma \left( {{\rho} - 1} \right)}}\)