Question

The delay period in petrol engine is of the order of
A) 0.002 sec
B) 0.001 sec
C) 0.01 sec
D) 0.02 sec

Answer 1

The difference of time between injection and combustion of any fuel in a fuel cylinder is known as the delay period of that engine. This time depends both upon the mechanism of the engine and the type of fuel used.

Complete step by step answer:
Delay period of any engine is also known as the Ignition delay. It is the definite period of time of inactivity inside the engine after the start of fuel injection and before the ignition starts. This delay period mainly consists of two types of delay. One is physical delay and another is chemical delay. Physical delay is the time delay between the beginning of fuel injection and attaining proper chemical reaction condition. Within this time period, fuel undergoes vaporization, atomization and mixing with air. Then comes the chemical delay. During this period chemical reactions start slowly and accelerate for the ignition to happen. Usually chemical delay is larger than physical delay. And their sum gives the total delay time for that engine. For petrol engines this period is typically of the order of 0.002 sec.

Correct answer:
The delay period of the petrol engine is of the order of (a) 0.002 sec.

Note: Some students might think that the delay period of an engine is completely a waste of a few fractions of seconds and reducing the delay period is always necessary. But in case of petrol engine delay period is deliberately kept a little longer to avoid knocking effect due to which charge far from spark plug auto-ignites and thus generated pressure wave collides with the original pressure wave (generated by original spark plug).