The Diesel cycle comprises which sequence of processes?

• A. Isothermal, Isobaric, Isothermal, Adiabatic
• B. Isobaric, Isothermal, Adiabatic, Isochoric
• C. Isothermal, Isothermal, Adiabatic, Isobaric
• D. Adiabatic, Isobaric, Adiabatic, Isochoric

Answer: (D)

In the Diesel cycle, the four processes occur in this order: a rapid, almost adiabatic compression where the gas heats up; heat is added at nearly constant pressure as combustion occurs with the piston moving; the gases then expand adiabatically, doing work and cooling; finally, heat is rejected at constant volume as the cycle returns to the initial state. This sequence matches: adiabatic compression, constant-pressure heat addition, adiabatic expansion, and constant-volume heat rejection. The other options don’t fit because the compression is not isothermal or isobaric in the Diesel cycle, and the heat rejection happens at constant volume rather than at constant pressure or a different mode.