COMPARISON OF PETROL AND DIESEL ENGINES. • • • • • • • • • • • • • • • • • • • • • • • • • ★ Petrol Engine:- * A petrol engine draws a mixture of petrol and air during suction stroke. * The carburettor is employed to mix air and petrol in the required proportion and to supply it to the engine during suction stroke. * The pressure at the end of compression is about 10 Bar. * The charge (petrol and air mixture) is ignited with the help of a spark plug. * The combustion of fuel takes place approximately at constant volume. In other words, it works on otto cycle. * A petrol engine has compression ratio approximately from 6 to 10. * The starting is easy due to low compression ratio. As compression ratio is low the petrol engines are lighter and cheaper. * The thermal efficiency is upto about 26%. Overheating trouble is more due to low thermal efficiency. These are high speed engines. ★ Diesel Engines:- * A diesel engine draws only air during suction stroke. * The injector or atomiser is employed to inject the fuel at the end of compression stroke. * The pressure at the end of compression is about 35 bar. * The fuel is injected in the form of fine spray. The temperature of the compressed air ( about 600°C at a pressure of about 35 bar) is sufficiently high to ignite the fuel. * A diesel engine has compression ratio approximately from 15 to 25. * The combustion of fuel takes place approximately at constant pressure. In other words it works on diesel cycle. * The starting is little difficult due to high compression ratio. As the compression ratio is high the diesel engines are heavier and costilier. * The thermal efficiency is upto about 40%. Overheating trouble is less due to high thermal efficiency. These are relatively low speed engines.
Posted on: Sat, 18 Oct 2014 15:54:55 +0000
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