Question

Which one of the following event would reduce the volumetric efficiency of a vertical compression ignition engine?

(a) inlet valve closing after bottom dead center

(b) inlet valve closing before bottom dead center

(c) inlet valve opening before top dead center

(d) exhaust valve closing after top dead center

The question was asked during a job interview.

I'd like to ask this question from Engine Efficiencies in section Measurements and Testing/Performance Parameters and Characteristics of IC Engine

Answer 1

The correct answer is:

(a) inlet valve closing after bottom dead center

In a vertical compression ignition engine, the inlet valve closing after bottom dead center would reduce the volumetric efficiency. This happens because, if the inlet valve remains open too long (after the piston has passed bottom dead center), some of the intake air may be lost back into the intake manifold before the piston begins its compression stroke. This reduces the amount of air available for combustion, lowering the engine's efficiency in filling the cylinder with air, which is a key factor in volumetric efficiency.