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Icengine
1. UNIT- I (I.C. Engine)
• Internal Combustion Engines
• Introduction and Classification,
• Engine details,
• four-stroke/ two-stroke cycle
• Petrol/Diesel engines,
• Indicated power, Brake Power, Efficiencies
COURSE OUTCOME:
After learning the course the students should be able to
• To understand the fundamentals of mechanical systems
• To understand and appreciate significance of mechanical engineering in different fields of
engineering
2. Introduction
• “Engine refers to a device which transforms one form of energy into the other
form”.
• “Heat engine is a modified form of engine used for transforming chemical
energy of fuel into thermal energy and subsequently for producing work”.
Based on the mechanism used for adding thermal energy they can be
classified into the following:
(a) External combustion engine
(b) Internal combustion engine.
• External combustion engine have combustion occurring outside engine and
adding heat to the working fluid used in the engine.
• Thus, in external combustion engines heat released during combustion is
indirectly utilized by the working fluid in external combustion engine.
• Internal combustion engines have combustion occurring in engine itself and
heat released during combustion is directly utilized for getting shaft work
3. • Internal Combustion Engines (IC-engines) produce mechanical power from the
chemical energy contained in the fuel, as a result of the combustion process
occurring inside the engine.
• IC engine converts chemical energy of the fuel into mechanical energy, usually
made available on a rotating output shaft.
• Chemical energy of the fuel is first converted to thermal energy by means of
combustion or oxidation with air inside the engine, raising the T and p of the gases
within the combustion chamber.
• The high-pressure gas then expands and by mechanical mechanisms rotates the
crankshaft, which is the output of the engine.
• Crankshaft is connected to a transmission/power-train to transmit the rotating
mechanical energy to drive a vehicle.
4. Advantages of I.C. Engine over E.C. Engine
Internal combustion engines have numerous advantages over
external combustion engines
• such as lower weight to power output ratio,
• simplicity,
• smaller initial cost,
• higher efficiency etc.
5. APPLICATIONS
Internal combustion engines are exhaustively used in
• Automobiles,
• Gas Turbine etc.
External combustion engines are used in
• steam turbine,
• steam engine,
• nuclear power plant etc.
6. CLASSIFICATION OF IC ENGINES
• BASED ON NUMBER OF STROKES
• BASED ON THERMODYNAMIC CYCLE
• BASED ON MECHANISM OF IGNITION
• BASED ON TYPE OF FUEL USED
• BASED ON FUEL ADMISSION
• BASED ON TYPE OF COOLING
• BASED ON TYPE OF MOTION
7. CLASSIFICATION OF IC ENGINES
(a) BASED ON NUMBER OF STROKES : Number of strokes involved in a cycle of IC
engine can be two strokes or four strokes. Such engine can be;
(i) Two stroke engines
(ii) Four stroke engines
(b) BASED ON THERMODYNAMIC CYCLE : Depending upon thermodynamic cycle used
in the internal combustion engines these can be classified as:
(i) Engines based on Otto cycle (‘Constant Volume Cycle’)
(ii) Engines based on Diesel or Dual cycle (‘Constant Pressure Cycle’)
(c) BASED ON MECHANISM OF IGNITION: Internal combustion engines have
combustion as the basic process.
(i) Spark ignition engines (S.I. Engines)
(ii) Compression ignition engines. (C.I. Engines)
The spark ignition engines may have “magneto ignition system” or “battery ignition
system” for creating necessary electric potential for producing spark.
8. (d) BASED ON TYPE OF FUEL USED: IC engines may be classified depending upon the
type of fuel being used. These can be:
(i) Petrol engines (petrol being used as fuel)
(ii) Gas engines (gaseous fuel being used)
(iii) Diesel engines (diesel being used as fuel)
(iv) Multi-fuel engines (more than one fuel being used)
(e) BASED ON FUEL ADMISSION: IC engines can be of different types depending upon
arrangement used for fuel admission:
(i) Carburettor type engines (use carburettor fuel metering)
(ii) Injection type engines (use fuel injector and injection system)
(f) BASED ON TYPE OF COOLING: IC engines have inherent requirement of continuous
cooling of engine. Based on type of cooling these can be classified as:
(i) Air cooled engines (Generally used in small sized engines)
(ii) Water cooled engines (Generally used in large sized engines)
9. (g) BASED ON TYPE OF MOTION: IC engines may have reciprocating motion of piston
or it may also have rotary motion. Such engines can be:
(i) Reciprocating engines
(ii) Rotary engines
Reciprocating engines may have different cylinder arrangements such as:
(i) Opposed cylinder engines
(ii) Inclined cylinder engines
(iii) V-shaped cylinder arrangement.
Rotary engines may be further classified as single rotor engines or multi rotor engines
i.e.
(i) Single rotor engine
(ii) Multi rotor engine
17. 1. CYLINDER: It is a cylindrical block having cylindrical space inside for piston to make
reciprocating motion. Upper portion of cylinder which covers it from the top is called
cylinder head. This is manufactured by casting process and materials used are cast iron
or alloy steel.
2. PISTON AND PISTON RINGS: Piston is a cylindrical part which reciprocates inside the
cylinder and is used for doing work and getting work. Piston has piston rings tightly
fitted in groove around piston and provide a tight seal so as to prevent leakage across
piston and cylinder wall during piston’s reciprocating motion. Pistons are manufactured
by casting or forging process. Pistons are made of cast iron, aluminium alloy. Piston rings
are made of silicon, cast iron, steel alloy by casting process.
3. COMBUSTION SPACE: It is the space available between the cylinder head and top of
piston when piston is at farthest position from crankshaft (TDC).
4. INTAKE MANIFOLD: It is the passage/duct connecting intake system to the inlet valve
upon cylinder. Through intake manifold the air/air-fuel mixture goes into cylinder.
ENGINE DETAIL
18. 5. EXHAUST MANIFOLD: It is the passage/duct connecting exhaust system to the exhaust
valve upon cylinder. Through exhaust manifold burnt gases go out of cylinder.
6. VALVES: Engine has both intake and exhaust type of valves which are operated by valve
operating mechanism comprising of cam, camshaft, follower, valve rod, rocker arm, valve
spring etc. Valves are generally of spring loaded type and made out of special alloy steels by
forging process.
7. SPARK PLUG: It is the external ignitor used for initiating combustion process. Spark plug
is activated by electrical energy fed by electrical system with engine. It delivers spark with
suitable energy to initiate combustion at appropriate time for suitable duration.
8. BEARING: Bearings are required to support crank shaft. Bearings are made of white metal
leaded bronze.
9. CONNECTING ROD: It is the member connecting piston and crankshaft. It has generally I
section and is made of steel by forging process.
19. 10. CRANK: It is the rigid member connecting the crankshaft and connecting rod. Crank is
mounted on crankshaft. Crank transfers motion from connecting rod to crankshaft as it is
linked to connecting rod through crank pin.
11. CRANKSHAFT: It is the shaft at which useful positive work is available from the piston-
cylinder arrangement. Reciprocating motion of piston gets converted into rotary motion of
crankshaft. Crankshaft are manufactured by forging process from alloy steel.
12. CRANKCASE: Crankcase actually acts like a sump housing crank, crankshaft, connecting
rod and is attached to cylinder. These are made of aluminium alloy, steel, cast iron etc. by
casting process.
13. GUDGEON PIN: It is the pin joining small end of the connecting rod and piston. This is
made of steel by forging process.
14. Cams and Camshafts: Cams are mounted upon camshaft for opening and closing the valves
at right timings and for correct duration. Camshaft gets motion from crankshaft through
timing gears.
15. CARBURETTOR: Carburettor is device to prepare the air fuel mixture in right proportion
and supply at right time.
20. I.C. ENGINE TERMINOLOGY
1. BORE: It is nominal inner diameter of the cylinder.
2. PISTON AREA: It is the area of a circle of diameter equal to bore.
3. STROKE: It is the nominal distance travelled by the piston between two extreme
positions in the cylinder. It is denoted by L.
4. DEAD CENTRE: It refers to the extreme end positions inside the cylinder at which piston
reverses it’s motion. Thus, there are two dead centres in cylinder, called as ‘top dead
centre’ or ‘inner dead centre’ and ‘bottom dead centre’ or ‘outer dead centre’. Top dead
centre (TDC) is the farthest position of piston from crankshaft. It is also called inner dead
centre (IDC). Bottom dead centre (BDC) refers to the closed position of piston from
crankshaft. It is also called outer dead centre (ODC).
5. SWEPT VOLUME : It is the volume swept by piston while travelling from one dead centre
to the other. It may also be called stroke volume or displacement volume.
Mathematically, Swept volume = Piston area × Stroke
21. 6. CLEARANCE VOLUME: It is the volume space above the piston inside cylinder, when
piston is at top dead centre. It is provided for cushioning considerations and
depends, largely upon compression ratio.
7. COMPRESSION RATIO: It is the ratio of the total cylinder volume when piston is at
BDC to the clearance volume.
Compression ratio (r)= Total cylinder Volume/Clearance volume
– For Petrol engine r varies from 6 to 10
– For diesel engine r varies from 14 to 20
8. PISTON SPEED: It is the average speed of the piston
Vp=2LN/60 m/s
26. TWO STROKE PETROL ENGINE
• It is a modified form of 4-stroke petrol engine.
• All the four processes required for completion of one
cycle of SI engine get completed in two strokes.
• Thus, obviously in each stroke two processes get
completed.
• Here all four processes occur during two strokes and
one revolution of crank shaft.
• Thermodynamic cycle followed by 2-stroke SI engine is
Otto cycle.
• Scooter engines are generally two stroke engines.
• 2-stroke SI engines are used for smaller applications.
27.
28.
29. PERFORMANCE EVALUATION
•Internal combustion engines have combustion taking place inside and power is available
at crankshaft.
•The shaft work available is less than the total energy released inside the cylinder due to
frictional and other losses.
•For performance evaluation of internal combustion engine one is interested in following
different powers.
(I) INDICATED POWER (I.P):
•It refers to the power available inside the cylinder i.e. the power provided to piston.
•It is the power actually developed by the engine cylinder.
• It is measured from the indicator diagram which is obtained using indicator mechanism.
30. • Mathematically,
A = cross-sectional area of cylinder. A = π D2/4, where D is bore.
L = length of stroke. N = Speed of the engine in rpm
N=N (For 2-stroke cycle), N=N/2 (For 4-stroke Cycle)
k = no. of cylinders. Pm = Mean effective pressure= as/l
b) FRICTION POWER: It refers to the power lost due to friction and other reasons.
It is quantified by the difference between indicated power and brake power.
Friction power = Indicated power – Brake power
31. 31
(C) BRAKE POWER: It refers to the power available at crankshaft i.e. it is the useful
shaft work.
•It is usually measured by means of brake mechanism (Prony brake or rope brake)
Brake power is usually measured by absorption or transmission type dynamometers. It
can be given as:
Let, W= Net load acting on the brake drum, N
R=Radius of the brake drum, m . N= R.P.M. of crank shaft,
T= resisting torque N-m
34. (3) Relative efficiency:
It is the ratio of indicated thermal efficiency of an engine to
air standard cycle efficiency
∴ ƞrel=
(4) Air Standard efficiency: It is the efficiency of
thermodynamic cycle of engine.
for petrol engine, ƞair= 1 -
for diesel engine, ƞair= 1 -
where, r = compression ratio,
= Cut-off ratio, V3/V2
and = Adiabatic index, c /c
•
35. (5) Volumetric efficiency: It is the ratio of the volume of
charge/air actually sucked at atmospheric condition to swept
volume of engine.
It indicates breathing capacity of the engine.
Ƞvol=
(6) Specific output : The specific output of the engine is
defined as the power output per unit piston area.
specific output =
(7) Specific fuel consumption: Specific fuel consumption
(SFC) is defined as the amount of fuel consumed by and
engine for one unit of power production.
SFC = kg/kWh
•
38. Q1. A four cylinder diesel engine of 4-stroke type has stroke to bore ratio
as 1.2 and the cylinder diameter is 12 cm. Estimate indicated power of
the engine using the indicator diagram arrangement. Indicator card
shows the diagram having area of 30 cm2 and length as half of stroke.
Indicator spring constant is 20 × 103 kN/m3 and engine is running at
2000 rpm. Also find out mechanical efficiency of engine if 10% of power
is lost in friction and other losses.
Q2. A four cylinder two stroke cycle petrol engine develops 23.5 KW brake
power at 2500 r.p.m. The mean effective pressure on each piston is 8.5
bar and the mechanical efficiency is 85%. Calculate the diameter and
stroke of each cylinder, assuming the length of stroke equal to 1.5 times
the diameter of cylinder.
Q3. A four stroke single cylinder petrol engine has a bore of 150 mm and
stroke of 250mm. At 500 r.p.m and full load, the net load on friction
brake is 435N and torque arm is 0.45m. The indicator diagram gives a
net area of 580 mm2 and a length of 70mm with a spring rating of 0.85
bar/mm. Determine indicted power, brake power, Friction power and
mechanical efficiency.
39. Q4. During trial of four stroke single cylinder engine the
load on dynamometer is found 20 kg at radius of 50 cm.
The speed of rotation is 3000 rpm. The bore and stroke
are 20 cm and 30 respectively. Fuel is supplied at the
rate of 0.15 kg/min. The calorific value of fuel may be
taken as 43 MJ/kg. After some time the fuel supply is
cut and the engine is rotated with motor which required
5 kW to maintain the same speed of rotation of engine.
Determine the brake power, indicated power,
mechanical efficiency, brake thermal efficiency,
indicated thermal efficiency, brake mean effective
pressure, indicated mean effective pressure.
Q5. Determine the power required to drive a double
acting reciprocating pump having indicator diagram
with area 40 cm2 and length 8 cm. Bore and stroke of
the pump are 15 cm and 20 cm. The pump motor runs
40. • 1. Indicated power = 90479.6 W
• Mechanical efficiency = 90%
• 2.
