Diesel cycle

The Diesel cycle is an idealized thermodynamic cycle for compression-ignition engines, with heat added at constant pressure and rejected at constant volume.

Isentropic compression: A reversible adiabatic process in which a fluid’s entropy remains constant while its pressure and temperature change. The cycle’s first process compresses air without heat transfer.
Thermodynamic cycle: A sequence of thermodynamic processes that returns a system to its initial state. The Diesel cycle is one idealized sequence of this broader kind.
Otto cycle: An idealized cycle for spark-ignition engines, with heat added and rejected at constant volume. Its constant-volume heat addition differs from the Diesel cycle’s constant-pressure addition.
Compression ratio: The ratio of a cylinder’s maximum volume to its minimum volume. It is a principal geometric input to ideal Diesel-cycle efficiency.
Constant-pressure heat addition: An ideal process that adds heat to a working fluid while its pressure remains constant. This process represents fuel combustion in the ideal Diesel cycle.
Ideal gas law: An equation relating the pressure, volume, temperature, and amount of an ideal gas. It connects the working fluid’s state variables throughout the modeled cycle.
Dual cycle: An idealized engine cycle that adds heat partly at constant volume and partly at constant pressure. It combines the heat-addition assumptions of the Otto and Diesel cycles.
Cutoff ratio: The ratio of cylinder volume after heat addition to its volume before heat addition in the ideal Diesel cycle. It captures how long constant-pressure heat addition continues and affects efficiency.
Isentropic expansion: A reversible adiabatic expansion in which a fluid’s entropy remains constant as it performs work. The heated gas expands and delivers work during the cycle’s power stroke.
Specific heat capacity: The heat required to raise the temperature of a unit mass of a substance by one degree. The constant-pressure heating process depends on the working gas’s heat capacity.

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