Cutoff ratio The term ' cut-off ratio'  applies specifically to diesel engines and does not pertain to petrol engines. In petrol engines, there is no cut-off. Cut-off refers to the cessation of fuel spray, which occurs in diesel engines but not in petrol engines. Therefore, this term is exclusive to diesel engines. Please note the PV diagram of the diesel cycle below. Air is isentropically compressed in process 1-2. Once the compression process is complete, the fuel spray initiates at point 2. With the onset of the fuel spray, combustion begins, leading to gas expansion. This spray and combustion phase continues until point 3, representing the gas expansion from point 2 to point 3. At this stage, V3/V2 equals the cutoff ratio, where V3 represents the volume at point 3, and V2 represents the volume at point 2. A potential question may arise: why does the fuel spray organize combustion? The answer lies in the fact that the compression of air during process 1-2 elevates its temper