A brief explanation of 4 stroke SI Engine.

1. National Institute Of
Technology,
Arunachal Pradesh
Subject: Basic Thermodynamics
Semester: Third Semester (2017)
Group Number: Three
Group Members: Indrakesh (09),
Shubham(10), Adarsh(11), Ravi(12), Pooja(14)

2. Four Stroke Compression- Ignition
Engine (Diesel Engine)

4. Brief Introduction
 Rudolf Christian Karl Diesel was a German inventor and
mechanical engineer, famous for the invention of the 4- stroke
diesel engine.
 Four stroke engine was first demonstrate by Nikolaus Otto in
1876, hence it is also known as Otto Cycle.
 It consist of 4 stroke, one cycle operation is completed in 4
stroke of the piston.
 Each stroke consist of 180 degree, of crankshaft rotation and
hence a cycle of 720 degree, of crankshaft rotation.
 The engine operates at a high Compression Ratio of the order of
16 to 20.

5. Components
 The major components of a four stroke compressed ignition
engine are:
1. Cylinder: It is a cylindrical vessel in which a piston makes up
and down motion.
2. Piston: It is a cylindrical component making up and down
movement in the cylinder.
3. Combustion Chamber: It is the portion above the cylinder in
which the combustion of the Fuel air mixture takes place.
4. Inlet and Exhaust Valves: The inlet valves allow the fresh fuel
air mixture to enter the combustion chamber and the exhaust
valve discharges the products of combustion.

6.  Crank Shaft: It is a shaft which converts the reciprocating
motion of piston into the rotary motion.
 Connecting Rod: The connecting rod connects the Piston with
the crankshaft.
 Cam Shaft: The cam shaft controls the opening and closing of
inlet and Exhaust valves.
 Fuel Injector: It is located at the top of head to inject the
fuel into the combustion chamber.

7. Working of four Stroke Diesel
Engine
 Following are the four strokes:
1. Intake / suction stroke,
2. Compression stroke,
3. Expansion stroke,
4. Exhaust stroke.

8. 1.Intake Stroke
 In suction stroke piston starts at Top Dead Centre (TDC) of the
cylinder and moves to the Bottom Dead Centre (BDC).
 Outlet Valve will be closed and inlet valve will be open to
allowing the fresh charge of mixed fuel and air into the
cylinder.

9. 2.Compression Stroke
 In compression stroke, Once piston reaches BDC and moves
back TDC, inlet valve will be closed.
 As the piston moves towards TDC.
 It compress air inside the cylinder and compression takes
place. Hence it is called compression stroke.

10. 3.Power Stroke
 In expansion stroke, Both the valves are closed. When piston
reaches top of its stroke, the fuel is sprinkled by the Fuel
Injector and the fuel mixture is ignited due to high
temperature and pressure generated inside the cylinder and
push down the piston to BDC.
 Hence it is known as Power generated in this stroke is stored in
the flywheel for its further utilisation in the other strokes.

11. 4.Exhaust Stroke
 In this stroke exhaust valve is opened when piston reaches to
BDC and moves to upward.
 Piston pushes out the burnt gases to the atmosphere through
the exhaust valve.
 Hence called exhaust stroke and the engine is ready to begin
the cycle again.

12. Advantages
 The most important advantage of the diesel engine is that it gets
great mileage. It delivers 25 to 30 percent better fuel economy
compared to that of similarly performing gasoline engines.
 The efficiency of the diesel engine is highest and is energy dense
fuel.
 Better fuel economy is delivered by diesel engine than gasoline
because it contains more usable energy.
 The diesel engine has advantage of higher torque compared to
petrol powered engine of the same volume.
 Due to high torque, diesel engine poses an advantage because
high torque helps in the city traffic allowing the movement
minimal engine turnover in traffic jams.

13. Disadvantages
 The cost of diesel engine is almost same or more than that of
gasoline. Therefore, it is not cost effective.
 Due to high cost factor, diesel engine is posing to be as a
disadvantage.
 Diesel fuel is largely used at homes, for commercial trucks and
heating oil. Hence the demand for the diesel engine is growing
resulting in increases price of diesel fuel which is more likely
continue to rise because of competition from those other users.

14. Difference between CI & SI
Engines