Mechanical Engineering - Thermodynamics - Discussion

The correct answer is: cut-off is decreased.

The Diesel cycle and Otto cycle are both idealized thermodynamic cycles used to model internal combustion engines. The main difference between them is the way heat is added to the system.

As the cut-off ratio (the ratio of the volume at the end of combustion to the volume at the beginning of combustion) in a Diesel cycle decreases, the cycle approaches the Otto cycle. This is because a smaller cut-off ratio means that the combustion process is more similar to the constant-volume heat addition process in the Otto cycle.

In contrast, a large cut-off ratio means that the combustion process is more similar to the constant-pressure heat addition process in the Diesel cycle. A cut-off ratio of zero would mean no heat addition and a constant cut-off ratio would not change the fundamental characteristics of the cycle.