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Petrol's and Diesel Engines

By : Asad Ali Arshad

Petrol’s and Diesel Engines:


What is Engine? An engine is a machine that is designed to convert one form of energy into mechanical form.
The main parts of Engines:
Cam Shaft takes up and down motion of piston and converts it into rotating motion. Valves there are two types of value intake and exhaust as from the name intake value are used to transfer fuel inside the cylinders and exhaust value is used to exhaust the burning fuel outside to the environment. Engine head is the head of engine on which the spark plug in mounted. Spark plug is used to provide the spark in each cycle to burn the petrol (in petrol engine). Injector it sprays the fuel (used in diesel engine). Cylinders combustion is take place in cylinder. Piston oil control ring. Connecting Rod connects the piston and crankshaft. Crankshaft is used when the multiple pistons are used in an engine in order to convert the each piston up and down movement into rotation. Flywheel is attached with the gear train and delivers the power. Gear Train is used to increase or decrease the speed.
Important Terminologies we learn.
Internal Combustion Engine? is an engine in which the combustion of a fuel occurs in a combustion chamber. External Combustion Engine? Is an engine in which the combustion takes place in an external source it is also known as heat engine. Top dead Center the furthest point of a piston's travel, at which it changes from an upward to a downward stroke. Bottom dead center the furthest point of a piston's near to crankshaft, at which it changes from downward to upward stroke. Stroke a stroke refers to the full travel of along the cylinder. Intake Stroke this stroke of the piston begins at top dead center. The piston descends from the top of the cylinder to the bottom of the cylinder. A mixture of fuel and air is forced by atmosphere pressure into the cylinder through the intake port. Compression Stroke when both the intake and exhaust valves are closed, the piston returns to the top of the cylinder compressing the air or air-fuel mixture. Power Stroke while the piston is close to top death center, the compressed air-fuel mixture in a gasoline engine is ignited, by a spark plug. The resulting pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward the bottom dead center. Exhaust during the exhaust stroke piston once again returns to top dead center while the exhaust valve is open.


Four functions known as intake, compression, combustion and exhaust these four functions are required to produce a final power stroke. Without these function no internal combustion engine in the world can work whether it is a two strokes, four strokes or Wankel engine.
2 Stroke Engines is a type of internal combustion engine which completes a power cycle in only one crankshaft revolution and with two stroke, or up and down movements, in short it complete the above four functions intake, compression, combustion and exhaust in two stroke. Intake and compression in one stroke and combustion and exhaust in second stroke.
4 Stroke Engine is a type of internal combustion engine in which the piston completes four separate strokes which comprise a single thermodynamics cycle.

Two Stroke Engines
Four Stroke Engines
It completes power cycle within two strokes.
It completes power cycle within four strokes.
In two strokes the end of the combustion stroke and beginning of the compression stroke take place simultaneously.
In four strokes the end of the combustion stroke occurs separately and beginning of the compression stroke occurs separately.
Two stroke engines have high power to weight ratio.
Four stroke engines have low power to weight ratio.
Two stroke engines have a greatly reduced number of moving parts and so can be more compact.
It has more parts.
Don’t have valve. It has ports.
Don’t have ports. It has valve.
Cheaper to construct.
Expensive to construct.
It is not fuel efficient.
It is fuel efficient as compared to two stroke.
Low life.
High life.

Which one is better?
At the end of the day the winner is probably going to be the one that has had more money and technology spent on it. In these days of quick and cheap international production schedules you can’t take it for granted that the 4 stroke will be better. So for a particular application, we should try to line up the options and make a decision based on what’s available, not based on lists that miss the key points of difference.

Petrol Engines
Diesel Engines
It works on Otto Cycle.
It works on diesel cycle.
§        In petrol engine the air and petrol are mixed in carburetor and it enters into the cylinder.
§   
In diesel engine the fuel is first fed into the cylinder by a fuel injector and then gets mixed with air inside the cylinder.
In petrol engine first the compression of air and petrol is done and then it is ignited by an electric spark.
In diesel engine only the charge of air is compressed and ignition is done by the heat of compressed air.
Its compression is low.
Its compression ratio is high.
In petrol engine we use spark plug for ignition.
In diesel engine we use injector for ignition.
Power developed is low due to low compression ratio.
Power developed is high due to high compression ratio.
The fuel that burns has high volatility.  
The fuel that burns has low volatility.
It used in light weight vehicles like in cars, motorcycles, scooters etc.
It used in heavy weight vehicles like in cars, motorcycles, scooters etc.








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