The esters in biodiesel are superior to petrol diesel in centane rating, which is similar to octane rating for gasoline. The cetane rating is a measure of how well a fuel combusts under compression ignition. This is different from octane, which measure combustion under spark combustion. What is the difference?
In spark combustion, an electric spark (from a spark plug), is used to ignite a fuel. This is similar to putting a flame to a can of gasoline. Compression ignition works differently. In this process, a gas is compressed to well above atmospheric pressure. Compressing a gas causes its temperature to increase because pressure and temperature are related by one of the three gas laws as follows: