Difference between 4 stroke petrol and diesel engine [with Pdf]

The basic difference between these two engines is that the four stroke petrol engines use a spark plug for the ignition while the four stroke diesel engine uses a higher compression ratio so that the fuel can undergo auto-ignition.

Four stroke petrol engine:

These are the spark ignition (SI) engines that work on a principle of the Otto cycle. In these engines, the fuel is mixed with air before it reaches the combustion chamber.

In this, the air-fuel mixture is ignited by the generation of a spark with the help of a spark plug. As these engines don’t have autoignition, these engines work at a comparatively lower compression ratio.

These internal combustion engines are noticed mostly in light-duty applications like cars, two-wheelers, smaller generators, ATVs, etc.

Four stroke diesel engine:

These are the compressed ignition engines that work on the Diesel cycle. In these engines, the air is compressed at high pressure to reach the auto-ignition temperature of the diesel. Then the fuel is spread in the hot air with the help of a fuel injector.

As the fuel is directly injected into the pressurized air in the combustion chamber, it requires a high-pressure fuel injection system.

These engines are used in heavy-duty applications like trucks, tractors, Diesel generators, cargo ships, etc.

Difference between four-stroke petrol and diesel engine:

Sr. No.	Four Stroke Diesel Engine	Four Stroke Petrol Engine
1	The higher compression ratio helps for the auto-ignition of the fuel.	In this engine, Combustion starts due to the generation of a spark in the Air-Fuel Mixture.
2	It works on Diesel Cycle.	It works on Petrol or Otto Cycle.
3	In this engine, Diesel is used as fuel.	In this engine, Petrol (gasoline), ethanol, CNG, etc. are used as Fuel.
4	Fuel mixes with air in the carburetor or in the intake manifold before going to the combustion chamber.	Spark Plug generates a spark to ignite the charge.
5	Fuel mixes with air inside the combustion chamber.	Fuel mixes with air in the carburettor or in the intake manifold before going to the combustion chamber.
6	It requires a high-pressure fuel injection system.	The high-pressure fuel injection system is not necessary.
7	These engines produce more torque.	It produces comparatively lower torque.
8	It runs at a lower RPM.	It runs at a comparatively higher RPM.
9	The fuel used is less volatile.	Less fuel consumption as the fuel used is more dense.
10	Lower wear of cylinder due to the lubricating properties of diesel.	The gasoline can wear the engine components faster.
11	The compression Ratio is High.	It works at a lower compression ratio.
12	It has a more rigid design because of the higher compression ratio.	These engines are less rigid than four-stroke diesel engines.
13	These engines last longer than petrol engines.	It has a lower lifespan than four-stroke diesel engines.
14	Less fuel consumption as the fuel used is higher dense.	The initial cost of a four-stroke diesel Engine is High.
15	The initial cost of Four Stroke Diesel Engine is High.	It has a lower initial cost.
16	More maintenance costs as it uses costly components.	Less maintenance cost.
17	It is used in heavy-duty applications like buses, trucks, farm tractors, etc.	It is used in light-duty vehicles like two-wheelers, cars, ATVs, etc.
18	Difficult to a cold start.	Cold starting is easier because of the spark plug.

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