The ignition system of an internal combustion engine is an important part of the overall engine system. All conventional petrolhttp://en.wikipedia.org/wiki/Petrol (gasoline)http://en.wikipedia.org/wiki/Gasoline engines require an ignition system. By contrast, not all engine types need an ignition system - for example, a diesel engine relies on compression-ignition, that is, the rise in temperature that accompanies the rise in pressure within the cylinder is sufficient to ignite the fuel spontaneously.