Q115
The efficiency of Diesel cycle approaches to Otto cycle efficiency when
A.
Cut-off is decreased
B.
Cut-off is constant
C.
Cut-off is increased
D.
Cut-off is zero
AnswerAnswer: Option D
Solution
Answer: Option D
Solution:
In the Diesel cycle, the efficiency approaches the efficiency of the Otto cycle when the cut-off is zero.
The Diesel cycle consists of constant pressure heat addition followed by constant volume heat rejection. When the cut-off ratio is zero, the heat addition process in the Diesel cycle becomes constant volume (isochoric) instead of constant pressure. This is analogous to the heat addition process in the Otto cycle, where heat is added at constant volume.
As a result, when the cut-off ratio is zero in the Diesel cycle, its thermal efficiency approaches that of the Otto cycle, which is higher due to the constant volume heat addition process. Therefore, the correct option is Option D: Cut-off is zero.