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Unlike gasoline engines in which spark plugs ignite a premixed air-fuel mixture in the combustion chamber, diesel engines work according to the so-called self-ignition process. With this process, intake air is compressed and close to top dead center diesel fuel is injected into the combustion chamber. The injected fuel mixes with the compressed air, evaporates and ignites almost simultaneously because the intake air heats up during compression and diesel fuel has a relatively low ignition temperature. No external ignition device like a spark plug is needed. However, with a cold diesel engine, the compression temperature might not be high enough to ensure proper ignition of the injected diesel fuel, causing inconvenience to the driver and increased exhaust emissions. The glow plug - an electrical heating device - helps to solve this problem.