Diesel and petrol engines are most commonly used in I.C engines (internal combustion engines). Both diesel and petrol engines convert chemical energy from a fuel into mechanical energy through a series of explosions. Even though their operation looks quite similar, they have some interesting differences:
The Basic Operation of a 4 Stroke diesel or Petrol Engine:
A 4 stroke engine is an internal combustion engine in which the piston while turning the crankshaft completes 4 separate strokes:
(a) intake (b) compression (c) power (d) exhaust.
During the intake stroke, air fuel mixture (in a petrol engine) or fresh air ( in a diesel engine) is sucked by producing the vacuum pressure into the cylinder. This gas is compressed in the compression stroke to produce a hot gas. The Combustion of Fuel takes place followed by the power stroke where the energy is generated and is absorbed by the piston. This stroke produces mechanical work from the engine to turn the crankshaft. During the exhaust stroke, burnt gasses are exhausted to the atmosphere.
What are the major differences between diesel and petrol engine?
Being highly volatile in nature, Petrol readily evaporates and mixes with air efficiently. Hence, just a spark of an electric charge is enough to initiate a smooth combustion process of the air-fuel mixture in a petrol engine.
Being less volatile in nature diesel does not mix properly with air. Therefore, to initiate a spontaneous ignition process, diesel is generally broken into finite fuel particles before it is sprayed into the high-temperature air.
In petrol engines, the air and fuel are premixed whereas, in a diesel engine mixing happens during the process of compression. For this purpose diesel engines have a fuel injector whereas petrol engines are using the spark plug.
Why is Diesel Engine much Heavier than petrol engine?
The process of combustion in a Petrol engine propagates smoothly. However, in a diesel engine, it is an uncontrollable process and could initiate anywhere in the combustion chamber. Therefore, the vehicles running on petrol engines are less noisy and vibrate less in comparison to vehicles running on Diesel engines. A heavy flywheel is generally attached for normalizing the huge unbalanced production of power in diesel engines. This is the main reason why petrol engines are used in lightweight automobiles like bikes, small cars etc.
Why are diesel engines more Fuel Economical than Petrol engines?
In a diesel engine, only the air is compressed hence, a good ratio of compression can be achieved without having any risk of self-ignition. However, it is not possible to achieve such a high ratio of compression in a premixed petrol engine. Chances of self-ignition of air-fuel mixture become high if the compression ratio of a petrol engine is increased. This phenomenon is called as knocking. Thus, the higher compression ratio of diesel engines is the prime reason to have a better fuel economy and more mileage in comparison to petrol engines.
What happens when Petrol is added to a Diesel Engine or Vice Versa?
Case 1: Diesel used in Petrol Engines
Since Diesel is less volatile in comparison to Petrol, therefore, diesel will not get mixed with air properly and it will result in poor quality of air-diesel mixture. On applying the spark to such a poor quality mixture will not initiate any combustion hence, Diesel if added to a petrol engine will not even burn the air-fuel mixture and you just need to drain the fuel lines to get rid of diesel.
Case 2: Petrol used in Diesel Engines
If petrol is added to a diesel engine, then it will result in detonations instead of smooth combustion because a highly volatile fuel (Petrol) is sprayed in a chamber of highly compressed hot air. Resulting in the damaging of engine components.
Diesel generally acts as a lubricant for the injection system and the fuel pump whereas Petrol doesn’t have any lubrication property. Hence, the addition of petrol will spoil the lubrication system and the intricate components will wear down over the time.
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