Statement (I): To prevent knocking in SI engines the end gas should have a low density.
Statement (II): Pre-ignition is caused due to detonation.

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ESE Mechanical 2016 Paper 1: Official Paper

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Both Statements I) and Statement II) are individually true and Statement II) is the correct explanation of Statement I)
Both Statements I) and Statement II) are individually true but Statement II) is not the correct explanation of Statement I)
Statement I) is true but Statement II) is false
Statement I) is false but Statement II) is true

Answer 1

Explanation:

For Statement 1:

To prevent knock in SI engine the end gas should have low temperature, pressure and density, a long ignition delay and a non-reactive composition. If the density of the end gas is less, then the pressure and temperature of the end gas do not rise to achieve the ignition temperature as a result of which the auto-ignition cannot take place and the chance of detonation gets reduced.

For Statement 2:

Auto ignition:

A mixture of fuel and air can react spontaneously and produce heat by chemical reaction in the absence of flame to initiate the combustion or self-ignition.
This type of self-ignition in the absence of flame is known as Auto-Ignition. The temperature at which the self-ignition takes place is known as self-igniting temperature.
The pressure and temperature abruptly increase due to auto-ignition because of sudden release of chemical energy. This auto-ignition leads to abnormal combustion known as detonation.

⇒ The statement 2 is false and statement 1 is true