Internal Combustion Engine. (I C Engine)
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Transcript of Internal Combustion Engine. (I C Engine)
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 11
Internal Combustion Engine.Internal Combustion Engine.(I C Engine)(I C Engine)
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 22
Classification of I C Engines• According to:
• (i) (i) Nature of Thermodynamic CycleNature of Thermodynamic Cycle : :– 1. Otto cycle engine. – 2. Diesel cycle engine. – 3. Dual combustion cycle engine.
• (ii)(ii) Type Type of the Fuel- used of the Fuel- used ::– 1. Petrol engine. – 2. Diesel engine. – 3. Gas engine. – 4. Bi-fuel Engine. – 5. Dual Fuel Engine
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 33
Classification of I C Engines
(iii) Number of Strokes :-– 1. 2 - stroke engine– 2. 4 - stroke engine
(iv) (iv) Method of Ignition: Method of Ignition: – 1. Spark ignition engine, [S.I. Engine].– 2. Compression ignition engine, [C.I. engine].
(v) (v) Number of Cylinders Number of Cylinders – 1. Single cylinder engine. – 2. Multi-cylinder engine.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 44
Classification of I C Engines• (vi) Position of the Cylinder:vi) Position of the Cylinder:
– 1. Horizontal engine – 2. Vertical engine– 3. V- engine.– 4. Radial engine.
• (vii) Method of Cooling :(vii) Method of Cooling :– 1. Air cooled engine. – 2. Water cooled engine
• (viii) Speed of the Engineviii) Speed of the Engine ::– 1. Low speed engine.– 2. Medium speed engine.– 3. High speed engine.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 55
I C Engine Parts
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 66
I C Engine terms & Definition
TDC (top dead center):TDC (top dead center):
It is the top most position of the piston towards head side of the cylinder
BDC (bottom dead center):
The lowermost position of the piston towards the crank end side of the cylinder.
Clearance volume
Valve
Spark plug
TDC
BDC
Bore
Stroke
Piston
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 77
Stroke: It is the linear distance traveled by the piston when it moves from one end of the cylinder to the other end
Bore: It is the inside diameter of the cylinder.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 88
Swept volume or (Displacement volume)It is the volume swept through by the piston in moving between TDC and BDC
Clearance volume: It is the volume contained in the cylinder above the top of the piston, when the piston is at TDC.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 99
Total volume = swept volume + clearance volume.
Compression ratio: “r”
It is the ratio of total cylinder volume to clearance volume.
r = Total volumeclearance volume
Value of “r” for,petrol engine lies between 7 to 9Diesel engine lies between 15 to 22
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1010
Working of 4-S Petrol engine
• The petrol engines work on the principle of “OTTO CYCLE”, also known as constant Volume cycle.
• The engines operating on this cycle use either petrol or other spirit fuels or the gases such as LPG / CNG as their fuels.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1111
• In a 4-Stroke petrol engine, the charge is admitted to the engine cylinder is a homogeneous mixture of petrol and air.
• Depending on the load on the engine, the fuel and air is mixed in proper proportions and sent in to the cylinder by a popular device known as “carburetor”.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1212
In a 4-stroke petrol engine there are four main events taking place, they are
1. Suction 2. Compression3. Working or power or expansion, and 4. Exhaust
So in a cycle there are four events to take place, and each of this is performed during a single stroke of the piston
Since ignition in these engines is due to a spark, they are also called spark ignition engines .
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1313
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1414
1. INTAKE [Suction]: During the intake stroke, the piston moves down ward, drawing a fresh charge of vaporized fuel-air mixture, This operation is represented by the line AB on the P-V diagram.
Volume [V]
Pressure [P]
AB
TDC
BDC
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1515
2. Compression Stroke: During compression stroke, the piston moves from BDC to TDC, thus compressing air petrol mixture. Due to compression, the pressure and temperature are increased and is shown by the line BC on the P- V diagram. Just before the end of this stroke the spark - plug initiates a spark which ignites the mixture and combustion takes place at constant volume as shown by the line CD
Volume [V]
Pressure [P]
AB
TDC
BDC
C
D
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1616
3. Working Stroke: The expansion of gases due to the heat of combustion exerts a pressure on the piston. Under this impulse, the piston moves from TDC to BDC and thus the work is obtained in this stroke as shown by the line DE
Volume [V]
Pressure [P]
AB
TDC
BDC
C
D
E
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1717
4. Exhaust Stroke: At the end of the power stroke, the exhaust valve is opened & greater part of the burnt gases escapes because of their own expansion. The drop in pressure at constant volume is represented by the line EB. During this stroke the piston moves from BDC to TDC and pushes the remaining gases to the atmosphere. This stroke is represented the line BA on the P-V diagram.
Volume [V]
Pressure [P]
AB
TDC
BDC
C
D
E
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1818
P V diagram for SI Engine / Otto cycle engineD
TDC
BDC
C
A B
E
D
Pressure
Volume
Theoretical Otto cycle
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 1919
Working of 4-S Diesel engine
The basic construction of a four stroke diesel engine is same as that of four stroke petrol engine.
Except that instead of a spark plug, a fuel INJECTOR is mounted in its space.
Fuel injector injects the fuel in to the cylinder as a fine spray at very high pressure
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2020
In case of diesel engine, the air enters the inside the cylinder during suction, and it will get compressed during the compression stroke. (i.e.. charge is only air)At the end of the compression stroke the diesel is injected in to the cylinder in the form of fine spray
When this fine spray diesel comes in contact with hot air in the cylinder, it auto ignites and results in a combustion of injected diesel fuel.
Since ignition in these engines is due to the temperature of the compressed air, they are also called compression ignition engines.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2121
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2222
1. INTAKE [Suction]: During the intake stroke, the piston moves down ward, drawing a fresh charge [AIR]. This operation is represented by the line AB on the P-V diagram.
TDC
BDC
Volume [V]
Pressure [P]
AB
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2323
2. Compression Stroke: During compression stroke, the piston moves from BDC to TDC, thus compressing air. Due to compression, the pressure and temperature are increased and is shown by the line BC on the P- V diagram. Just before the end of this stroke, a metered quantity of Diesel is injected into the hot compressed air in the form of fine sprays by means of fuel injector. The fuel starts burning at constant pressure shown by the line CD.
TDC
BDC
Volume [V]
Pressure [P]
AB
CD
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2424
3. Working Stroke: The expansion of gases due to the heat of combustion exerts a pressure on the piston. Under this impulse, the piston moves from TDC to BDC and thus the work is obtained in this stroke as shown by the line DE
TDC
BDC
Volume [V]
Pressure [P]
AB
CD
E
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2525
4. Exhaust Stroke: At the end of the power stroke, the exhaust valve is opened & greater part of the burnt gases escapes because of their own expansion. The drop in pressure at constant volume is represented by the line EB. During this stroke the piston moves from BDC to TDC and pushes the remaining gases to the atmosphere. This stroke is represented the line BA on the P-V diagram.
TDC
BDC
Volume [V]
Pressure [P]
AB
CD
E
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2626
C
A B
E
D
Pressure
Volume
Theoretical Diesel cycle
P V diagram for CI Engine / Diesel cycle engineD
TDC
BDC
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2727
Comparison between Petrol & Diesel Engine
Petrol engine Diesel engine1 It works on Otto cycle. It works on diesel cycle.2 Air and petrol are
mixed in the carburetor before they enter into the cylinder.
Diesel is fed into the cylinder by fuel injection and is mixed with air inside the cylinder.
3 It compresses a mixture of air and petrol and is ignited by an electric spark. (Spark Ignition)
It compresses only air and ignition is accomplished by the heat of compression. (Compression Ignition)
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2828
4Cylinder is fitted with a spark plug.
Cylinder is fitted with a fuel injector.
5 Less thermal efficiency and more fuel consumption.
More thermal efficiency and less fuel consumption.
6 Compression ratio ranges from 4:1to10:1
Compression ratio ranges from 12:1 to 22:1
7 Less initial cost and more running cost.
More initial cost and less running cost.
8 Light weight and occupies less space.
Heavy and occupies more space.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 2929
9Easy to start even in cold weather.
Difficult to start in cold weather and requires heater plugs.
10Requires frequent overhauling.
They run for longer periods between overhauls.
11
Fuel (petrol) is costlier and more volatile.
Fuel (diesel) is cheaper and less volatile.
12
Used in light vehicles like cars, motor cycle, scooters, etc.
Used in heavy duty vehicles like tractors, trucks, buses, locomotives, etc.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3030
Working of the Two Stroke engine.
In a two stroke engine, a cycle is completed by the two strokes of the piston.Out of the four strokes, the two strokes that are eliminated are, suction and exhaust strokes.However, the exhaust process is achieved by the admission of charge which is extremely compressed, which drives out the burnt gases out and this process is popularly called as SCAVENGING.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3131
In case of the two stroke engines instead of valves, ports are used.
Ports in the cylinder liner, opened and closed by the piston motion itself
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3232
Working of Two Stroke Petrol Engine
First stroke First stroke
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3333
Working of Two Stroke Petrol Engine
• First stroke (Downward) As soon as the charge is ignited, the hot gases force the piston to move downwards, rotating the crankshaft, thus doing the useful work. During this stroke the inlet port is covered by the piston and the new charge is compressed in the crank case as shown in the fig.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3434
• As soon as the transfer port opens, the compressed charge from the crankcase flows into the cylinder.
• As the compressed charge enters into the cylinder, it pushes out the exhaust gases from the cylinder.
• The process of removal of exhaust gases by the fresh incoming charge is known as scavenging.
• Further downward movement of the piston uncovers first the exhaust port and then the transfer port.
• The burnt gases escape through the exhaust port.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3535
• Second stroke: (upward)
Here the piston moves from BDC to TDC, during the process the exhaust port and transfer port are covered and the charge in the cylinder is compressed. Simultaneously, vacuum is created in the crankcase, and a new charge is drawn into the crankcase through the uncovered inlet port.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3636
• The compressed charge is ignited in the combustion chamber by a spark provided by the spark plug and the cycle of events is then repeated.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3737
Working of Two Stroke Diesel Engine
First stroke Second stroke
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3838
• First stroke (Downward) Combustion starts once the diesel is injected in to the hot compressed air, the hot gases force the piston to move downwards, rotating the crankshaft, thus doing the useful work. During this stroke the inlet port is covered by the piston and the new charge [air] is compressed in the crank case as shown in the fig.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 3939
• As soon as the transfer port opens, the compressed charge from the crankcase flows into the cylinder.
• As the compressed charge enters into the cylinder, it pushes out the exhaust gases from the cylinder.
• The process of removal of exhaust gases by the fresh incoming air is known as scavenging.
• Further downward movement of the piston uncovers first the exhaust port and then the transfer port.
• The burnt gases escape through the exhaust port.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4040
• Second stroke: (upward)
Here the piston moves from BDC to TDC, during the process the exhaust port and transfer port are covered and the fresh air in the cylinder is compressed. Simultaneously, vacuum is created in the crankcase, and a new charge [air] is drawn into the crankcase through the uncovered inlet port.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4141
• At the end of the compression diesel is injected to the compressed air which is at a temperature higher than the self ignition temperature of diesel. Hence, the injected diesel auto ignites when it comes in contact with hot air. And the cycle of events is then repeated.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4242
Comparison between 4 - stroke & 2 - stroke Engine
4 – stroke engine 2 – stroke engine1 One Working stroke for
every two revolution of the Crank shaft
One working stroke for each revolution of the crank shaft
2 Turning moment on the crank shaft is not even, hence heavier flywheel is required
Turning moment on the crank shaft is more even, hence lighter flywheel is required
3 Less fuel consumption More fuel consumption.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4343
4
More output due to full fresh charge intake and full burnt gases exhaust.
Less output due to mixing of fresh charge with the burnt gases.
5 Higher thermal efficiency Lower thermal efficiency
6 Engine design is complicated
Engine design is simple.
7 Lesser rate of wear and tear.
Greater rate of wear and tear.
8 It has inlet and exhaust valves
It has inlet and exhaust ports
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4444
9Engine is heavy & bulky.
For the same power, the engine is light and compact.
10
It requires lesser cooling and lubrication
It requires greater cooling and lubrication. (consumes more lubricating oil)
11 More initial cost Less initial cost.
12 Less running noiseMore running noise due to the sudden release of the burnt gases.
13
Used in cars, trucks, buses, tractors, etc.
Used in mopeds, motor cycles, scooters, etc.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4545
Important definitionsImportant definitions• Brake Power [B.P]: It is the power developed by
the engine at the output shaft.
kwNT
Brakepower60000
2,
Where, N = Speed of the crank shaft in rpm.
T =Torque applied on the brake drum due to load “W”, (N-m)
R = Radius of the brake drum (m)
T = W x R kg-m = 9.81 x W x R N-m
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4646
• Indicated Power [I.P]: It is the power developed inside the IC engine cylinder
kWnALPi
owerIndicatedp m
60000,
Where, n = No. of working cycles/ min.
n = N/2, for 4 stroke engine
= N, for 2 stroke engine
L = Stroke length (m), D = Bore diameter (m)
Pm = Indicated mean effective pressure (N/m2)
A = Area of the cylinder,
,
22 ,4
mDA
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4747
• Frictional Power [F.P]: It is the difference between the indicated power and the brake power.
F.P = [I.P – B.P] kW
,
%100.
.,
PI
PBefficiencyMechanical mech
• Mechanical Efficiency [ηmech ]: It is the ratio of the
brake power and the indicated power.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4848
• Indicated thermal Efficiency [ηith ]: It is the ratio of the indicated power to the heat supplied by the fuel.
%100*Cm
3600PI.
vf
ith
Where, mf = mass of the fuel supplied (kg/hr) CV = Calorific Value of the fuel (kJ/kg)
• Brake thermal Efficiency [ηbth ]: It is the ratio of
the brake power to the heat supplied by the fuel. %100*
Cm
3600 PB.
vf
bth
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 4949
Working of a Simple Carburetor
• The petrol enters the float chamber through the needle valve, Purpose of needle valve is to maintain the constant level of petrol in the float chamber.
• When engine runs, the air is sucked through the venturi tube. As a result pressure at throat reduces (-) and the petrol issues out of the main jet located at the throat.
• Thus amount of petrol issuing from jet proportional to the velocity of air through the venturi tube.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 5050
Working of a Diesel pump
• Plunger of the fuel pump is operated by the cam roller mechanism, which derives the power from the engine. El.
• As plunger moves up, the fuel filled above the plunger is pressurized and pressurized fuel flow through the barrel.
• The outlet of from the fuel pump barrel is closed by a spring loaded delivery valve which opens only at prescribed pressure of the fuel.
• As the fuel pressure rises, the delivery valve and is forced out towards the injector.
Dept. of Mech & Mfg. Engg.Dept. of Mech & Mfg. Engg. 5151
Working of a Diesel injector• Fuel under pressure from the
pump, passes down through passages in the injector body to an annular space in the nozzle and lifts the needle valve against pressure of the spring
• As a result fuel is forced through the holes of injector under high pressure resulting in finely atomized spray.