A Spark Plug is used in vehicles that run on petrol but the ones with a diesel engine do not use it. Petrol and diesel have dissimilar properties, one of which is auto-ignition. Diesel has low auto-ignition temperature. The Auto-ignition temperature means that a fuel which starts burns automatically at a particular temperature.Because of low auto-ignition temperature, diesel can easily ignite.
In a diesel engine, the highly compressed air (compression ratios of 18 to 25) is introduced into the combustion chamber, this compressed air increases the temperature of diesel fumes or vapors to kindling point, and thus the mixture self-ignites.
But, to introduce such high compression ratios, the engine cost drastically increases, thus to keep engine cost economical, we use the auxiliary assistance of glow plugs. They help in reaching the kindling point of diesel fume air mixture. They also come handy, during cold start, and when there is heat leak from the cylinder block and cylinder head.Diesel has low volatility and thus it cannot form the desired air-fuel mixture to be ignited by spark plugs.
1.) The diesel engine (also known as a compression-ignition or CI engine) is named after Rudolf Diesel.
2.) Diesel engines can operate at high compression ratios.
3.) The ignition temperature of diesel ranges around 473 K.
4.) The diesel engine has the highest thermal efficiency (engine efficiency) of any practical internal or external combustion engine due to its very high expansion ratio and inherent lean burn which enables heat dissipation by the excess air.