So today in this article we are discus about working of 4-stroke diesel engine and their parts. One more thing guys In 1876 a German engineer Nikolaus Otto designed a working model of a four stroke diesel engine.
Parts of four stroke diesel engine
- Injector
- Inlet Port
- Exhaust Port
- Rocker Arm
- Hot Plug
- Push rod
- Piston
- Water Jackets
- Cylinder
- Connecting rod
- Cam
- Piston Pin
- Crank
- Crank Case
- Fuel injector
- High Pressure Fuel Pipe
(1) Cylinder
It is the heart of the engine. The piston reciprocate in the cylinder. and It has two withstand high pressure and temperature and thus it is made as strong, generally it is made from cast iron.
It is provided with cylinder linear on the inner side and a cooling arrangement on it’s outer side for two stroke engine. and it houses exhaust and transfer port.
(2) Cylinder port
The top cover of the cylinder towards TDC is know as cylinder head. and hence it houses the spark plug in petrol engine and fuel injector on diesel engine.
For 4-stroke cycle engines, the cylinder head has the housing of inlet and exhaust valve.
(3) Piston
It is the reciprocating member of the engine. So it reciprocate in the cylinder and it is usually made of cast iron or aluminum alloy surface is called piston screed. and It’s top surface is make flat four stroke engine and dedicate for two stroke engine.
(4) Piston rings
Two or three piston rings are provided on the piston. The piston rings seal the space between the cylinder linear and piston in order to prevent leakage (below by losses) of high pressure gases from cylinder to crank case.
(5) Crank
It is rotating member and it makes circular motion in the crank case. So its one end is connect with a shaft know as crank shaft and the other end is connect with a connecting rod.
(6) Crank case
It is the housing of the crank and body of the engine to which cylinder and other engine parts are fasten. So it is act as a ground for lubricating oil.
(7) Connecting rod
It is a link between the piston and crank. So it is connect its one end with a circuit and at the other end with a piston and it transmits power developed on the piston to a crank shaft through crank. And it is usually make of medium carbon steel.
(8) Crank shaft
It is a shaft, a rotating member which connects the crank. and the power developed by the transmitted out side through this shaft. And it is make of medium carbon or alloy steel.
(9) Cooling fins
During combustion, the engine releases a large amount of heat. Thus the engine parts may be subject to a temperature at which engine parts cannot maintain their properties such as hardness etc.
The cooling fins are provided on light duty engine, while cooling water jacket is provided on and heavy duty.
(10) Cam shaft
It is provided on four stroke engines, and it carries two cams for controlling the opening and closing of inlet and exhaust valve.
(11) Valve inlet
This valve controls the admission of charge into the the engine during a suction stroke.
(12) Exhaust valve
The removal of exhaust gases after doing work on the piston is control by the valve.
(13) Fuel injector
It is provided on diesel engines, Hence the diesel fuel is inject in the cylinder at the end of the compression through a fuel injector under very high pressure.
(14) Fuel pump
It is provided with diesel engine, The diesel is taken from the fuel tank. and Its pressure is raised in the fuel pump and then it is delivered to fuel injector.
(15) Air filter
It is use to filter (separate from unwanted particles) the air before it passed through inlet valve.
(16) Fly wheel
It is mount on the crank shaft and is make of cast iron. and It stores energy in the form of inertial, when energy is exes and it gives back energy when it is in deficit. and It minimize the speed fluctuation on the engine.
Working of a 4 stroke diesel engine
The 4 stroke diesel engine works on diesel cycle or constant pressure pressure cycle. Heavy motor vehicle, stationary power plants, large industrial units and ships mostly employ this engine.
Diesel or compression ignition engines, which mostly use diesel oil as fuel, differ from petrol engines in that the air fuel mixture is ignited by an electric spark from the spark plug after the latter is compressed under high pressure in the engine cylinders. While the pre-fuel is ignite by injecting it into an engine cylinder containing compressed air under very high pressure.
The temperature of this air is sufficiently high to ignite the fuel. and diesel engine have no spark plugs.
The temperature of compressed air itself is sufficient to ignite the fuel which is inject at a controlled rate as a very fine spray so that the combustion proceeds at constant pressure.
Four stroke diesel engine has four stroke or stages and that is suction stroke, compression stroke, expansion stroke, exhaust stroke. A schematic of a four stroke diesel engine you can see in the below
Suction stroke
The inlet valve opens the exhaust valve remains closed, only air is drawn into the cylinder as the piston moves from top dead center (TDC) to the bottom dead center (BDC). and this stroke ends as the piston approaches the bottom dead center.
Compression stroke
As the piston moves from the bottom dead center to the top dead center, the inlet valve closes, exhaust valve remains closed as shown in the figure.
The air dropped into the cylinder is compressed into the cylinder until the piston reaches top dead center. So the air temperature reaches about 800°C by compression.
At the end of the compression stroke, the fuel is inject under very high pressure, which is sufficient to ignite the injected fuel. Thus ignition takes place inside the cylinder.
Expansion stroke
During this stroke both the valves are remain closed as shown in the figure, the piston at the top dead center is pushed by expansion of burning gases.
Actual work is obtain during this stroke due to the force obtained by high pressure burning gases. Therefore this stroke is know as power stroke or working stroke.
Exhaust stroke
During this stroke, the piston moves from the bottom dead center to the top dead center the exhaust valve opens and the inlet valve remains closed. and the burnt gases of the previous stroke are cut off from the cylinder by the upward movement of the piston.
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Application of 4 stroke diesel engine
It is one of the most popular prime movers. So it is manufactured from 50 mm to 1000 mm cylinder both with speeds ranging from 100 rpm to 4500 rpm.
From the above article we learned about the four stroke diesel engine and how it works. So in a four stroke diesel engine has a total of four stage and the crankshaft has to be rotate twice to complete these four stages.
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