The concept of turning the chemical energy into mechanical energy is not new. A petrol engine was patented as early as 1876 but the primate engines were not very fuel efficient. Those engines used only 10% of the fuel energy while the rest went into useless heat. With the passage of time, improvements were made to the engines and their fuel combustions. Diesel engine was introduced in late 1890s to overcome the fuel inefficiency problem faced by the other engines at that time.
In theory, there is no difference between the working of diesel and petrol engines. Both are four stroke engines and both use combustion to convert the chemical energy stored inside the fuels to mechanical energy. In reality, the only difference between these two engines is of air and fuel mixing method.
A petrol engine mixes the fuel with air and compresses it inside the piston tube for combustion while a diesel engine compresses the air inside the piston tube and then adds fuel to it for combustion. In petrol engines, the chemical reaction occurs when the mixture of air and fuel is compressed while in case of a diesel engine, the air is compressed first which heats it up and when fuel is added to it, the combustion initiates due to the heated and compressed air.
The typical operation of a four stroke diesel engine can be divided into four parts
The intake stroke open up a valve allowing the piston tube to be filled with air and moves the piston down.
The air inside the piston tube is compressed with the upward movement of the piston.
Fuel is injected at the right time just before the piston reaches up and ignited which forces the piston back down.
The piston is moved at the top pushing the combustion exhaust out through the exhaust valve.
The piston is connected to a crankshaft which converts the linear motion of the piston into circular motion necessary for the movement of a vehicle. The efficiency of the fuel is maximised in diesel engines which use 14:1 to 25:1 air to fuel ratio as compared to 8:1 to 12:1 ratio in petrol engines. The air to fuel ratio affects the efficiency. The more the air, the more efficient will be the combustion process.
Diesel engines are very fuel efficient and perform better than petrol engines. Diesel engines are quite useful for carrying loads over long distance. This is the main reason that diesel engines are utilised in trucks and loaders however diesel engines create higher noise pollution and environment pollution in the form of carbon, oxygen, hydrogen and sulphur compound emissions.
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