Difference Petrol and Diesel Engine - Otto Engine - Gasoline Engine

Basically there are two types of thermal engines which are Otto engines and diesel engine. Thermal engines are converting the internal energy of the fuel into mechanical energy to produce some work. So, these are two classifications of thermal engines. Both are different from each other.

Difference-petrol-diesel-engine

 

The major difference between them is found in its theoretical cycle which is important for study the working of these both engines. The working of Otto engine is based on the Otto cycle by spark ignition on the other hand the diesel engine is work according to the diesel cycle by compression ignition. Thus there are two types of ignition in the Otto engine spark ignition and in the diesel engine compression ignition.

 Another difference is in the ignition of the fuel in both engines. In the Otto engine the ignition is made by spark plug, due to that it is also known as the spark ignition engine, while, in the diesel engine, the ignition is done by the compression of the fuel and air. Due to this reason, the diesel engine is also called a compression ignition engine.

 There is no major difference between both different engines in terms of mechanical level. Although, we should remember that in the diesel engine the combustion of fuel is at very high pressure so diesel engines needs more strong structure.

The basic differences between the two types of engines derive from the differences in their theoretical cycles:

Difference In- Inlet of the Fuel

Fuel inlet or input into the diesel engines and the Otto engines is one of the most significant differences between both types of alternative thermal engines:

Fuel inlet into the Otto engine.

In most Otto engines (Otto cycle), air and fuel are entered into the combustion chamber in the form of a gas mixture (contains feel and air).the mixture of air and gasoline is carried out in the carburetor.

Now days, that type of mixture is produced electrically and its proportions is very dependent on different factors like the temperature of the fuel and engine.

Fuel inlet in diesel engine

In diesel engine the air is entered into the chamber of combustion that reaches to the suction valve. In this type of thermal engines the fuel (diesel) is come out with directly by means of an injector.

In this type of diesel engine it is important to remember that the pressure inside the cylinder is much higher than in the Otto engine. Functions of the injector are to produce enough pressure on the fuel so that it can enter and take combustion.

 The mixture of fuel and air is committing in the combustion chamber. In the diesel engine there is no regulation of the supply amount of air, there is only a regulation of the amount of fuel to be supplied in.

Different in- the Ignition of the fuel

Once the fuel enters into the cylinder, the way that it ignites is different between both types of alternate engines. In the one case fuel ignited by supplying temperature and in the other engine the fuel ignition is carried out by increasing the pressure of inside the cylinder. As per the laws of thermodynamics and the law of gases, both state variables pressure and temperature are related to each other. If the volume is constant during process, increasing one variable is resulting into increases the other.

Ignition of fuel in the gasoline engine

In the internal combustion engines (i.c. Engines), the explosion cycle is caused by the heating of the mixture of the air and fuel placed in the cylinder.

In Otto engine, the fuel gets ignition by a spark. This type of spark ignition engines requires an ignition system to create a spark between the spark plug electrodes in the combustion chamber. This spark indicates an increase in the temperature or heat of the mixture (air + fuel). This temperature increase is enough to allow the starting of combustion.

Ignition of fuel in the diesel engine

In the diesel engine the fuel is ignited by compression. This type of compression ignited engines uses the high temperature and high pressure exist by compressing the air in the cylinder to start the combustion when the fuel is injected in combustion chamber.

In the diesel engine this high temperature is created by air compression. During the obtained enters cycle the air enters the explosion chamber that will be compressed in the next following cycle, that compression generates an addition in air temperature until the auto ignition temperature value is achieved.

It is at when the injectors put the fuel under high pressure, in a way for a better mixture with the air, and the combustion of the same takes place in combustion chamber.

Difference in compression ratio

The compression ratio (volume of the cylinder at the beginning of process divide by volume of cylinder at the end of the process) in an endothermic engine is the number that makes it possible to measure the proportion in which the mixture of air and fuel (in case of Otto engine) or air (in case of diesel engine) has been compressed in the combustion chamber of a cylinder.

The value of compression ratio in Otto engines(Otto cycle) varies from 6 to 10 in ideal condition, while in diesel engines or diesel cycle the compression ratio varies from 14 to 22.

Difference in weight of the Petrol engine and Diesel Engine

In this case, the ignition form of the fuel affects on the weight of the engine. In the diesel engine, the ignition of the fuel is done by compression. As we noted in the mechanical differences of the engine, this means that it must be made with a design that can withstand these high pressures and high temperature.

The diesel engine is generally heavy weighted than the Otto engine of equal movement. The weight of the engine will also have to be shifted, with moving of vehicle so the engine will requires more power to have equal performance.

Difference in the brake of the engine

Another difference between engines that does not affect performance, which is braking of the engine.

 In the gasoline engines or Otto engines, the engine brake is created by the air intake mechanism or system. When we stop the accelerating the throttle in an atom mobile, the air flow closes, at that moment the air stops entering into  the combustion chamber of engine and a vacuum is generated due to that. The energy that the piston in cylinder has to make to create that vacuum is the energy that is achieved by braking or braking force.

 In the diesel vehicles, it is not possible to close the air flow to generate that vacuum. The natural process is as following: the valves opened and air enters in cylinder, the valves are closed and the air is compressed with pressure, when the piston reaches the top dead center (T.D.C.) in the cylinder it begins its enough helped by the pressure of the compressed air.

Conclusion:

We can conclude that diesel engine and petrol engine are different in various factors which are we discussed in this post which are difference by compression ratio, by weight, by ignition, by inlet of the fuel.

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