This video lecture from Fundamental Principles of Organic Chemistry (F.Sc. second year Chemistry) covers briefly how a piston or an internal combustion engine works. The pre-ignition in between the compression and power stroke causes the knocking in the engine which is highly undesirable. The quality of a fuel is hence measured by its octane number which determines and relates the knocking characteristics of any fuel with standard fuels i.e. 2,2,4 trimethylpentane and n-heptane. Find more e-learning material and educational video lectures in Urdu at maktab.pk. These videos are free to use for promotional and commercial purpose by keeping the credits to Maktab.