<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (July 2012) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (July 2012) (Learn how and when to remove this template message) </Td> </Tr> <P> A glowplug (alternatively spelled as glow plug or glow - plug) is a heating device used to aid starting diesel engines . In cold weather, high speed diesel engines can be difficult to start because the mass of the cylinder block and cylinder head absorb the heat of compression, preventing ignition (which relies on that heat). Pre-chambered engines use small electric heaters (glowplugs) inside the pre-chambers . Direct - injected engines have these glowplugs in the combustion chamber . The glowplug is a pencil - shaped piece of metal with a heating element at the tip . This heating element, when electrified, heats due to its electrical resistance and begins to emit light in the visible spectrum, hence the term glowplug . The visual effect is similar to the heating element in a toaster . The fuel injector spray pattern then impinges directly upon the hot tip of the glow plug during the injection of fuel at top dead center . This ignites the fuel even when the engine is insufficiently hot for normal operation, which reduces the cranking time to start the engine . </P> <P> Diesel engines, unlike gasoline engines, do not use spark plugs to induce combustion . Instead, they rely solely on compression to raise the temperature of the air to a point where the diesel combusts spontaneously when introduced to the hot high pressure air . The high pressure and spray pattern of the diesel ensures a controlled, complete burn . The piston rises, compressing the air in the cylinder; this causes the air's temperature to rise . By the time the piston reaches the top of its travel path, the temperature in the cylinder is very high . The fuel mist is then sprayed into the cylinder; it instantly combusts, forcing the piston downwards, thus generating power . The pressure required to heat the air to that temperature, however, requires a large and strong engine block . </P>

What do glow plugs do in a diesel engine