Which of the following fuels detonates readily?

Question

Question

This question was previously asked in

BPSC AE Paper 5 (Mechanical) 2012 Official Paper

Answer 1

Explanation:

Detonation is a rapid and violent form of combustion due to which strong shock wave propagates into the explosion.
It is the spontaneous combustion of the end gas in the chamber.
It is generally caused by:
- Excessive heat
- Excessive cylinder pressure
- Improper ignition timing
Octane Number
- Octane Number is a measure of the quality of petrol.
- It is the percentage of iso-octane in the mixture of iso-octane and n-heptane which has the same knocking properties as the fuel sample.
- Iso-octane chemically being a very good antiknock fuel, is arbitrarily assigned a rating of 100 octane number.
- Normal heptane (C₇H₁₈) has very poor antiknock qualities i.e. readily detonates and is given a rating of 0 octane number. So, if normal heptane (C₇H₁₈) is present in the fuel then it will create knocking which will result in the auto-ignition.

Important Points

A fuel having higher self-ignition temperature detonates less, n-heptane fuel detonates readily. While iso-octane has little tendency towards detonation.
Detonation in petrol engines can be reduced by the addition of a small amount of lead ethide or ethyl fluid into the fuel commonly known as doping