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Idealized thermodynamic cycles

Idealized cycles are simplified models of real engines and power plants, where each step is a pure process (isothermal, isobaric, isochoric or adiabatic). The models differ in how and when heat is added, and let you calculate efficiency without knowing every detail of a real machine.

\text{Otto: heat at constant } V

gasoline engine, instantaneous ignition

\text{Diesel: heat at constant } p

diesel engine

\text{Brayton: compression–heat–expansion}

gas turbine/jet engine, heat at constant p

Symbols

$V$	volume	m³
$p$	pressure	Pa

Example

In the Otto cycle the fuel ignites instantaneously, so heat is added before the piston has time to move much – approximately at constant volume.

What distinguishes the cycles is how heat is added: constant volume (Otto), constant pressure (Diesel/Brayton), or isentropic compression and expansion in both.

Practise thermodynamic cycles for free →

← Heat pump and COP · Throttling and isentropic processes →

Part of Thermodynamics: Thermodynamic cycles.