Question

The mean effective pressure of a diesel engine having fixed compression ratio will ____________ if cut off ratio decreases.

(a) increase

(b) decrease

(c) remain same

(d) none of the mentioned

The question was asked during an online interview.

This interesting question is from Comparison of Two Stroke S.I. and C.I. Engines topic in division Two Stroke Engines of IC Engine

Answer 1

The correct answer is:

(a) increase

Explanation:

The mean effective pressure (MEP) of an engine is directly related to the engine's efficiency and power output. The cutoff ratio in a diesel engine refers to the ratio of the cylinder volume at the point of injection cutoff (when the fuel injection stops) to the volume at the end of the compression stroke.

- Decrease in cutoff ratio means the fuel injection stops earlier in the cycle, leading to a shorter combustion duration.

- This results in more efficient combustion, where the fuel is burned in a smaller volume, increasing the pressure in the cylinder at the point of combustion.

Hence, as the cutoff ratio decreases, the mean effective pressure (MEP) will increase, improving the engine's efficiency and performance.

This is why, for a fixed compression ratio, reducing the cutoff ratio increases the mean effective pressure.