In engineering, the study of heat and work comes under the branch of thermodynamics. When a thermodynamic system changes from one state to another it is called a process. A process in which the initial state is identical to the final state is called a cycle. Thermodynamic cycles are the basis of all internal combustion engines.
The petrol and gas engines work on the principle of a thermodynamic cycle called Otto cycle and diesel engine works on a cycle called the diesel cycle.
WORKING PRINCIPLE OF DIESEL ENGINES
Diesel engine works on the diesel cycle devised by Rudolph diesel.
In the diesel engine atmospheric air is drawn into the engine cylinder and is compressed by the piston to high pressure and temperature. This temperature is above the ignition temperature of the fuel. Just before the end of the compression stroke, the fuel is injected as a fine spray by means of a fuel injector.
Due to the extreme conditions inside the compressed cylinder the FUEL LITERALLY EXPLODES and the gases expand the cylinder, and this is what we obtain as the mechanical power from the engine.
As the ignition of the fuel takes place due to high pressure and temperature brought about by the compression of air inside the cylinder, the engine is called the CI ENGINE or the compression ignition engine.
WORKING PRINCIPLE OF PETROL ENGINE
Petrol engine operates on the Otto cycle. Petrol is a highly volatile fuel than diesel. As most of you may have noticed, it vapourises very easily.
In the petrol engine, many of you may have seen a carburetor associated with it. The device is used to mix a desired quantity of petrol and air. This fuel air mixture is injected into the engine cylinder, as only air is compressed and fuel is injected later in the diesel engine. This fuel air mixture in the engine cylinder is BURNT BY USING THE SPARK provided by the spark plug. The gases expand, and we get the power output.
As the ignition takes place with the help of the spark plug, the petrol engine is called a Spark ignition engine or the SI ENGINE. The number of spark plugs in a cylinder can be varied, and that is what DTSi stands for in the pulsar. It has two spark plugs, so it is called the digital twin spark ignition.
COMPARISON OF PETROL AND DIESEL ENGINES
1. FUEL: in the SI engine, a highly volatile fuel such as petrol is used. As Arnab explained in his review, petrol is much more refined than diesel and so it costs a lot more. So diesel engines are going to be lighter on your pockets as far as the fuel efficiency is concerned.
2. Fuel introduction: In petrol engines, fuel air mixture is introduced into the engine, whereas in the diesel engine, fuel is injected directly into the engine in the form of a fine spray.
3. WEIGHT: in the diesel engine, due to the high pressure and temperature the fuel literally explodes. So the engine is subjected to a lot of pressure and since it is combustion ignition also, it has to stand very high pressures than the petrol engine. So the diesel engine has to be built much more stronger than the average petrol engine. This makes the engine and the car heavier.
4. MAINTENANCE COST: the maintenance costs are almost similar. But in the long run, diesel engines require most cost on maintenance because diesel is less refined than petrol and so there can be many deposits clogging up the engine which may require cleaning, and also it subjected to tougher working conditions than the petrol engine.
5. FUEL ECONOMY: in diesel engines, diesel is injected into the engine in the form of a fine spray. The engine has better fuel economy at all working conditions. Combined with the fact that diesel is cheaper, this is definitely going to be much more pocket friendly.
6. INITIAL COST: the initial coat of a diesel engine is more than that of a petrol engine as it is to be built tougher and also the injection of fuel in the form of the fine spray require highly modern laser technology, which explains for the fact that diesel engine technology is not fully developed in India.
7. ENGINE VIBRATION: In the diesel engine, due to the vigorous explosion of the fuel, the engine vibration and noise is lot more as compared to the petrol engine in which the fuel is nicely burnt.
Overall speaking, if you want to financially sound in the long run, and is prepared to risk somewhat the joy of driving, and is prepared to bear the high initial cost, go for a diesel engine. But there are some things to look for before buying a diesel car.
1. Look for a TURBOCHARGER with the engine. They increase the performance of the car several fold.
2. Don’t go in for outdated diesel technology. Prefer a CRDI (COMMON RAIL DIRECT INJECTION) system, which decreases pollution, engine vibration and engine noise.
3. Don’t push the vehicle too hard to make it behave as a sport. It can be really harmful to the engine.
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Good Information.
Thank you