why spark is needed in case of gasoline engines?

Answer by JGMagoo
Submitted on 1/19/2005
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If you are asking why a spark is needed in a gasoline engine when it is NOT needed in a diesel engine, this is an excellent question! Since it is quite obvious from observation that gasoline is far more flammable than diesel fuel one would think it would be easier to start the combustion process with gasoline than it would be with diesel fuel. The truth is that a gasoline-air mixture WOULD self-ignite if subjected to enough pressure and temperature such as is found in a diesel engine. The problem is that when this gasoline self-ignition took place in the cylinder the resulting explosion would be TOO violent and of too short duration to effectively push the piston down the cylinder. By using a spark from a spark plug the combustion can be started earlier and at a lower pressure and temperature and the resulting "explosion" is more of a "WHOOSH" rather than a "BANG", resulting in a much more efficient power stroke and much less punishment to the mechanical parts of the engine. Diesel fuel, by nature, is slower burning and produces a wonderful "WHOOSH" effect, pushing the piston all the way down the cylinder very smoothly in comparison to gasoline.

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Question by ravi
Submitted on 6/26/2004
Related FAQ: Gasoline FAQ - Part 4 of 4
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why spark is needed in case of gasoline engines?

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