LECTURE NOTES
ON
SUB: INTERNAL COMBUSTION ENGINE &
GAS TURBINES
8
th
SEMESTER, B MECHANICAL ENGINEERING
COURSE CODE – BME 423
Prepared by:
Mrs. Dulari Hansdah
Assistant Professor
DEPARTMENT OF MECHANICAL ENGINEERING
VEER SURENDRA SAI UNIVERSITY OF
TECHNOLOGY, BURLA, ODISHA
####### DISCLAIMER
This document does not claim any originality and cannot be used as a substitute for
prescribed text books. The information presented here is merely a collection by the
committee members for their respective teaching assignments. Various sources as mentioned
at the reference of the document as well as freely available material from internet were
consulted for preparing this document. The ownership of the information lies with the
respective authors or institutions. Further, this document is not intended to be used for
commercial purpose and the committee members are not accountable for any issues, legal or
otherwise, arising out of use of this document. The committee members make no
representations or warranties with respect to the accuracy or completeness of the contents of
this document and specifically disclaim any implied warranties of merchantability or fitness
for a particular purpose. The committee members shall be liable for any loss of profit or any
other commercial damages, including but not limited to special, incidental, consequential, or
other damages.
####### LESSON PLAN
Sl. No.
Lecture No.
Topics to be covered
1
Lecture-01 What is IC engines and components of IC engine, IC engine terminology, classification of IC engines, comparison of Two stroke &four stroke engines, Comparison between SI & CI engines, valve and port timing diagram 2 Lecture-02 Working cycles-Otto, Diesel and Dual cycle, problem solving 3 Lecture-03 Fuel- structure & composition of IC engine fuel, properties of SI and CI engine fuel, fuel rating 4 Lecture-04 Fuel additives and non-petroleum fuels (alternative fuels)
5 Lecture-05 Fuel air requirement for ideal normal operation, maximum power & quick acceleration, simple carburettor and its parts, problem solving 6 Lecture-06 Drawback of simple carburettor, types of carburettor 7 Lecture-07 Petrol injection, Lucas petrol injection system, electronic petrol injection system 8 Lecture-08 Requirements & type of diesel injection system 9 Lecture-09 fuel pump, types of injectors 10 Lecture-10 Types of nozzles, spray formation and its direction, injection timing 11 Lecture-11 Ignition system- requirements of ignition system, Battery and magneto ignition system 12 Lecture-12 Ignition timing, spark plug, spark advance mechanism 13 Lecture-13 Disadvantage of conventional ignition system, electronic ignition system
14
Lecture-14 Factors affecting energy requirement of ignition system
15 Lecture-15 Stages of SI engine combustion, effect of engine variables on ignition lag flame front propagation
16 Lecture-16 Abnormal combustion, pre-ignition & detonation, theory of detonation, effect of engine variables on detonation
17 Lecture-17 Control of detonation, requirement of good combustion chambers for SI engines 18 Lecture-18 Stages of CI engine combustion, effect of engine variables on delay periods 19 Lecture-19 Diesel Knock & methods of control in CI 20 Lecture-20 Diesel engine combustion chambers 21 Lecture-21 Testing and performance- Indicated power (indicator diagram-piston indicator, balanced-diaphragm type of indicator)
22 Lecture-
Measurement of brake power (prony brake, rope brake, eddy current, hydraulic dynamometer), Measurement of friction power (Willian‟s line method, Morse test, Motoring test) 23 Lecture-23 Fuel consumption measurements (volumetric and gravimetric method), air consumption measurements 24 Lecture-24 Variables affecting performance of SI engine 25 Lecture-25 Variables affecting performance of CI engine, problem solving 26 Lecture-26 Engine emissions, measurement method of smoke emission, measurement of unburnt hydrocarbon emission
27 Lecture 27 Measurement of CO 2 , NOx, engine emission control 28 Lecture 28 Requirement of cooling of the engine, types of cooling, air cooling system 29 Lecture 29 Water cooling (thermo-syphon, forced or pump, evaporative cooling system)
30 Lecture 30 Comparison of cooling system, Effect of cooling on power output & efficiency
31
Lecture 31 Lubrication- requirement of lubrication of the engine, effect of variables on engine friction, principle and function of lubricating system, properties of lubricating oil 32 Lecture 32 Types of lubricating system, additives to lubricating oil
33 Lecture 33 Turbine definition, types of turbines, comparison of gas turbine with reciprocating IC engine and steam turbine, classification of gas turbine 34 Lecture-34 Thermodynamic cycle or Brayton cycle, problem solving 35 Lecture 35 Regenerative gas turbine cycle, reheat gas turbine cycle, problem solving 36 Lecture 36 Gas turbine cycle with both reheat and heat exchange method, gas turbine with inter cooler, problem solving 37 Lecture 37 Real gas turbine, losses calculation, problem solving 38 Lecture 38 Linking components of turbine, combustion chamber 39 Lecture 39 Fuels for turbine, emission from turbine 40 Lecture 40 Application of gas turbine, automotive gas turbine
- According to the fuel supply and mixture preparation- (a) Carburetted type (fuel supplied
through the carburettor), (b) Injection type (fuel injected into inlet ports or inlet manifold,
fuel injected into the cylinder just before ignition).
-
According to the number of cylinder- (a) Single cylinder and (b) multi-cylinder engine
-
Method of cooling- water cooled or air cooled
-
Speed of the engine- Slow speed, medium speed and high speed engine
-
Cylinder arrangement-Vertical, horizontal, inline, V-type, radial, opposed cylinder or
piston engines.
- Valve or port design and location- Overhead (I head), side valve (L head); in two stroke
engines: cross scavenging, loop scavenging, uniflow scavenging.
- Method governing- Hit and miss governed engines, quantitatively governed engines and
qualitatively governed engine
- Application- Automotive engines for land transport, marine engines for propulsion of
ships, aircraft engines for aircraft propulsion, industrial engines, prime movers for electrical
generators.
Comparison between external combustion engine and internal combustion engine:
External combustion engine Internal combustion engine *Combustion of air-fuel is outside the engine cylinder (in a boiler)
-
Combustion of air-fuel is inside the engine cylinder (in a boiler)
-
The engines are running smoothly and silently due to outside combustion
-
Very noisy operated engine
*Higher ratio of weight and bulk to output due to presence of auxiliary apparatus like boiler and condenser. Hence it is heavy and cumbersome.
- It is light and compact due to lower ratio of weight and bulk to output.
*Working pressure and temperature inside the engine cylinder is low; hence ordinary alloys are used for the manufacture of engine cylinder and its parts.
- Working pressure and temperature inside the engine cylinder is very much high; hence special alloys are used
*It can use cheaper fuels including solid fuels *High grade fuels are used with proper filtration *Lower efficiency about 15-20% *Higher efficiency about 35-40%
- Higher requirement of water for dissipation of energy through cooling system
*Lesser requirement of water
*High starting torque *IC engines are not self-starting
Main components of reciprocating IC engines:
Cylinder: It is the main part of the engine inside which piston reciprocates to and fro. It
should have high strength to withstand high pressure above 50 bar and temperature above
2000 oC. The ordinary engine is made of cast iron and heavy duty engines are made of steel
alloys or aluminum alloys. In the multi-cylinder engine, the cylinders are cast in one block
known as cylinder block.
Cylinder head: The top end of the cylinder is covered by cylinder head over which inlet and exhaust valve, spark plug or injectors are mounted. A copper or asbestos gasket is provided
between the engine cylinder and cylinder head to make an air tight joint.
Piston: Transmit the force exerted by the burning of charge to the connecting rod. Usually
made of aluminium alloy which has good heat conducting property and greater strength at
higher temperature.
Figure 1 shows the different components of IC engine.
Fig. 1. Different parts of IC engine
Piston rings: These are housed in the circumferential grooves provided on the outer surface
of the piston and made of steel alloys which retain elastic properties even at high temperature. 2 types of rings- compression and oil rings. Compression ring is upper ring of the piston
which provides air tight seal to prevent leakage of the burnt gases into the lower portion. Oil
ring is lower ring which provides effective seal to prevent leakage of the oil into the engine
cylinder.
Connecting rod: It converts reciprocating motion of the piston into circular motion of the
crank shaft, in the working stroke. The smaller end of the connecting rod is connected with
the piston by gudgeon pin and bigger end of the connecting rod is connected with the crank
(i) Suction stroke (suction valve open, exhaust valve closed)-charge consisting of fresh air mixed with the fuel is drawn into the cylinder due to the vacuum pressure created by the movement of the piston from TDC to BDC. (ii) Compression stroke (both valves closed)-fresh charge is compressed into clearance volume by the return stroke of the piston and ignited by the spark for combustion. Hence pressure and temperature is increased due to the combustion of fuel (iii) Expansion stroke (both valves closed)-high pressure of the burnt gases force the piston towards BDC and hence power is obtained at the crankshaft. (iv) Exhaust stroke (exhaust valve open, suction valve closed)- burned gases expel out due to the movement of piston from BDC to TDC.
Figure 2 show the cycle of operation of four stroke engine.
Fig. 2. Cycle of operation in four stroke engine
Two stroke engine:
-No piston stroke for suction and exhaust operations
-Suction is accomplished by air compressed in crankcase or by a blower
-Induction of compressed air removes the products of combustion through exhaust ports
-Transfer port is there to supply the fresh charge into combustion chamber
Figure 3 represents operation of two stroke engine
Fig. 3. Cycle of operation in two stroke engine
Comparison of Four-stroke and two-stroke engine:
Four-stroke engine Two-stroke engine
- Four stroke of the piston and two revolution of crankshaft
Two stroke of the piston and one revolution of crankshaft 2. One power stroke in every two revolution of crankshaft
One power stroke in each revolution of crankshaft 3. Heavier flywheel due to non-uniform turning movement
Lighter flywheel due to more uniform turning movement 4. Power produce is less Theoretically power produce is twice than the four stroke engine for same size 5. Heavy and bulky Light and compact 6. Lesser cooling and lubrication requirements Greater cooling and lubrication requirements 7. Lesser rate of wear and tear Higher rate of wear and tear 8. Contains valve and valve mechanism Contains ports arrangement 9. Higher initial cost Cheaper initial cost 10. Volumetric efficiency is more due to greater time of induction
Volumetric efficiency less due to lesser time of induction 11. Thermal efficiency is high and also part load efficiency better
Thermal efficiency is low, part load efficiency lesser 12. It is used where efficiency is important.
Ex-cars, buses, trucks, tractors, industrial engines, aero planes, power generation etc.
It is used where low cost, compactness and light weight are important. Ex-lawn mowers, scooters, motor cycles, mopeds, propulsion ship etc.
Opening and closing of inlet valve
- Inlet valve opens 12 to 30ᵒ CA before TDC to facilitate silent operation of the engine under high speed. It increases the volumetric efficiency.
-Inlet valve closes 10-60ᵒ CA after TDC due to inertia movement of fresh charge into cylinder i. ram effect.
Figure 5 represents the actual valve timing diagram for low and high speed engine.
####### Fig. 5. Actual valve timing diagram for low and high speed engine
Opening and closing of exhaust valve
Exhaust valve opens 25 to 55ᵒ CA before BDC to reduce the work required to expel out the burnt gases from the cylinder. At the end of expansion stroke, the pressure inside the chamber is high, hence work to expel out the gases increases.
Exhaust valve closes 10 to 30ᵒ CA after TDC to avoid the compression of burnt gases in next cycle. Kinetic energy of the burnt gas can assist maximum exhausting of the gas. It also increases the volumetric efficiency.
####### Note: For low and high speed engine, the lower and upper values are used
####### respectively
####### Valve overlap
During this time both the intake and exhaust valves are open. The intake valve is opened before the exhaust gases have completely left the cylinder, and their considerable velocity assists in drawing in the fresh charge. Engine designers aim to close the exhaust valve just as the fresh charge from the intake valve reaches it, to prevent either loss of fresh charge or unscavenged exhaust gas.
Port timing diagram:
-Drawn for 2-stroke engine
-No valve arrangement
-3 ports- inlet, transfer and exhaust
Figure 6 shows port timing diagram for 2-stroke engine
Fig. 6. Port timing diagram for 2-stroke engine
Working cycle:
(a) Otto cycle- thermodynamic cycle for SI/petrol engine -Reversible adiabatic compression and expansion process -Constant volume heat addition (combustion) and heat rejection process (exhaust) Figure 7 depicts the Otto cycle
Fig. 7. Otto cycle Heat supplied, qs=Cv(T 3 -T 2 ) Heat rejection, qR=Cv(T 4 -T 1 ) Compression ratio, =
Thermal efficiency,
( ) ( ) ( ) Fig. 8. Diesel cycle Heat supplied, Q 1 =Cp(T 3 -T 2 ) Heat rejection, Q 2 =Cv(T 4 -T 1 ) Compression ratio, =
Cut off ratio, =
Thermal efficiency,
( ) ( ) ( ) ( ) ( ) In adiabatic compression process i. 1-2,
(
)
( )
In process 2-3, pressure constant, then
( ) In adiabatic expansion process i. 3-4,
(
) (
) =( ) ( ) ( ) ( ) = ( )
( ) ( ) ( ) ( ) ( )
[
( ) ]
Work done (W)
( )
( )
since * ( )( ) ( ) ( )
- ( ) ( )
Mean effective pressure,
[ ( )
( ) ] [ ( ) ( )] ( )( )
(c) Dual cycle or limited pressure cycle-thermodynamic cycle for high speed diesel and hot spot ignition engine -Reversible adiabatic compression and expansion process -Constant pressure and constant volume heat addition (combustion) and heat rejection process
Total heat supplied, Q 1 = Cv(T 3 -T 2 )+ Cp(T 4 -T 3 ) Heat rejection, Q 2 =Cv(T 5 -T 1 ) Compression ratio, =
Cut off ratio, =
Pressure ratio, =
Figure 9 shows the P-V diagram of Dual cycle.
Fig. 9. Dual cycle
Thermal efficiency,
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
In adiabatic compression process i. 1-2,
(
) ( )
In constant volume combustion process i. 2-3,
( ) ( ) ( )
(c) For same maximum pressure and temperature
( ) ( ) ( )
(d) For same maximum pressure and output
( ) ( )
####### FUELS &FUEL INJECTION
In IC engines, the chemical energy contained in the fuel is converted into mechanical power by burning (oxidizing) the fuel inside the combustion chamber of the engine.
Fuels suitable for fast chemical reaction have to be used in IC engines, they are following types-
(a) Hydrocarbons fuels derived from the crude petroleum by proper refining process such as thermal and catalytic cracking method, polymerisation, alkylation, isomerisation, reforming and blending.
(b) Alternative fuels such as-Alcohols (methanol, ethanol) Natural gas (methane) LPG (propane, butane) Hydrogen
*Classification of petroleum fuels used for IC engine:
Liquid hydrocarbons- Engine fuels are mainly mixtures of hydrocarbons, with bonds between hydrogen and carbon atoms. During combustion these bonds are broken and new bonds are formed with oxygen atoms, accompanied by the release of chemical energy. Principal products are carbon dioxide and water vapour. Fuels also contain small amounts of S, O 2 , N 2 , H 2 O. The different constituents of crude petroleum which are available in liquid hydrocarbons are- paraffins, naphthenes, naphthenes, olefins, aromatics.
(i) Paraffin-
-Paraffins or alkanes can in general be represented by-CnH2n+ -All the carbon bonds are single bonds – they are "saturated" high number of H atoms, high heat content and low density (620 – 770 kg/m3) -The carbon atoms can be arranged as a straight chain or as branched chain compounds. -Straight chain group (normal paraffins) shorter the chain, stronger the bond not suitable for SI engines – high tendancy for autoignition according to the value of "n" in the formula, they are in gaseous (1 to 4), liquid (5 to 15) or solid (>16) state.
-Hexan C 6 H 14 (normal paraffin) H H H H H H H – C – C – C – C – C – C – H H H H H H H
- Branched chain compounds (isoparaffins) When four or more C atoms are in a chain molecule it is possible to form isomers, they have the same chemical formula but different structures, which often leads to very different chemical properties.
Example: Iso-octane- C 8 H 18
(ii) Naphthenes-
-Also called as cycloparaffins and represented as CnH2n -Saturated hydrocarbons which are arranged in a circle have stable structure and low tendancy to autoignite compared to alkanes (normal paraffins) -Can be used both in SI-engines and CI-engines -Low heat content and high density (740 – 790 kg / m 3 )
(iii) Olefins-
-Olefins or alkenes are represented as Mono olefins-CnH2n or Dio-olefins CnH2n- -Olefins have the same C-to-H ratio and the same general formula as naphthenes, their behavior and characteristics are entirely different -They are straight or branch chain compounds with one or more double bond. The position of the double bond is indicated by the number of first C atom to which it is attached, i., CH2=CH.CH2.CH2 called pentene- CH3=CH3 called butene- -Olefinic compounds are easily oxidized, have poor oxidation stability -Can be used in SI-engines, obtained by cracking of large molecules low heat content and density in the range 620 – 820 kg / m 3
Alkenes are such as, Hexen (mono-olefin) H H H H H H H – C – C – C – C – C = C - H H H H H Butadien (dio-olefin) H H H H H – C = C – C = C – H
(iv) Aromatics-
-These are so called due to aromatics odour and represented as CnH2n- -They are based on a six-membered ring having three conjugated double bonds -Aromatic rings can be fused together to give polynuclear aromatics, PAN, also called polycyclic aromatic hydrocarbons, PAH simplest member is benzene (C 6 H 6 )
Source: https://www.studocu.com/in/document/university-of-delhi/mechanical-vibration/lecture-1429900545-nptel/8576646
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