Question

At what value of compression ratio, a knock can be heard?

(a) At the minimum value

(b) At the maximum value for power output

(c) At the maximum value above the power output

(d) In between of lowest and highest value

This question was addressed to me in quiz.

The query is from Knocking in chapter Fuels and Combustion of Engineering Chemistry II

Answer 1

The correct choice is (c) At the maximum value above the power output

Easy explanation: The compression rate, corresponding to the maximum power output is known as a useful compression ratio at which a slight metallic knock can be heard. This knock becomes louder when the compression ratio goes on increasing.