In which phase of the Diesel cycle,do the high pressure and high temperature gases expand and perform mechanical work?

Correct option is B

In the Diesel cycle, after the fuel is injected and combusted, the gases reach high pressure and high temperature. These gases then expand in the cylinder, pushing the piston and performing mechanical work on the crankshaft. This expansion process occurs without heat transfer, and ideally it is considered isentropic (reversible and adiabatic). Therefore, the phase in which the high-pressure, high-temperature gases expand and produce mechanical work is the isentropic expansion phase of the Diesel cycle.