For the same capacity of engine, the efficiency of spark ignition engine is

For the same capacity of engine, the efficiency of spark ignition engine is ____

Options:

a. less than the efficiency of compression ignition engine
b. equal to the efficiency of compression ignition engine
c. greater than the efficiency of compression ignition engine
d. cannot say

Correct Answer: a. less than the efficiency of compression ignition engine

Explanation:

Efficiency of an internal combustion engine directly relates the compression ration an engine. Because, more mechanical energy is generated at the power stroke, if the the expansion of combusted fuel takes place at higher pressure and this pressure is produced in compression ignition engine as it has higher compression ratio than that of spark ignition engine.

Also in spark ignition engine the fuel and air is mixed in carburetion process before entering the combustion chamber. Therefore, there is a limit for oxygen supply for burning the fuel. Engine speed is restricted by the air supply as well as fuel supply. But in compression ignition engine, there is no restriction for the air supply as it is already available in the combustion chamber. There is always enough oxygen available for the burning process. The engine speed is restricted only by the fuel supply rate. Therefore for the same capacity of engine, the efficiency of spark ignition engine is less than the efficiency of compression ignition engine.