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Petrol & Diesel Engines
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Petrol engines require a spark plug that receives electrical current to ignite the fuel and air mixture in a cylinder each cycle. Diesel engines provide ignition through compression of the heated fuel mixture. The spark plugs in a petrol motor are located in every cylinder to ignite the fuel mixture. In a diesel a glow plug is positioned in the cylinders. The purpose of the glow plug is to heat the engine block and cylinder space so that the fuel, will spontaneously combust when it is injected during operation.
The purpose of the glow plug is to provide heat to the block and not to cause ignition of the fuel itself. Glow plugs usually are only required when an engine has not been operated for a period of time. Starting a diesel engine is not the same as starting a petrol one. The diesel block is first heated by the glow plug. Owners of diesel vehicles will have to turn the key to the on position and wait for indication that the engine block has reached a temperature that will allow for ignition of the fuel. Usually a dashboard indicator light will be illuminated while the glow plugs are heating the engine. Once the block is hot enough to provide compression combustion the light will go out and the motor can then be started. Attempting to start a diesel prior to the block reaching the right temperature will cause it not to start and may cause damage to the block and components. Modern glow plugs can heat a block to operational temperatures in a very short space of time.
Once it has heated the block the glow plugs are usually not needed. The combustion in a diesel engine is caused when the fuel is injected into the cylinders near the top of the piston. The fuel that is injected into the cylinder will ignite due to the temperature of the engine. This will cause the piston to be forced down and provide power to turn the crank shaft moving the next piston into position for combustion in that cylinder.
Diesel applications provide more power across the entire operating spectrum and low end torque is a feature of all diesels. Since they are able to operate at higher compression they are generally more efficient than petrol engines. Diesel will provide better mileage figures and require less fuel overall to operate.
One problem with diesel over the years has been the emission quandary. The particulate emissions from a diesel engine are greater than those from a petrol engine. The thick black smoke clouds and noxious odours that come from the tailpipe of diesel engines have made them less desirable than petrol engines.