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8/4/2019 1-History Andd Classification
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INTERNAL COMBUSTIONENGINES AND GAS
TURBINES
Prof S. K. Acharya
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IS
Gasoline-fueledreciprocatingpiston engine
Diesel-fueledreciprocatingpiston engine
Gas turbine
Rocket
IS NOT
Steam powerplant
Solar power
plant Nuclear power
plant
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ENGINES!BOON OR BANE?
Greatest invention since thewheel?
Made transportation easy! Made life easy!
OR DID IT?
Increased pollution
Increased fossil fuelconsumption
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BUT..
WHETHER WE LIKE IT OR NOT.
CAN WE DO WITHOUT IT?
DO WE HAVE VIABLEALTERNATIVES?
THINK AS OF TODAY WE HAVE NO
ANSWER
MAY BE FOR AT LEAST 20 YEARS
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SO WE STUDY IT.!
And so on to the course:
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Background on IC Engines
An internal combustion is defined asan engine in which the chemicalenergy of the fuel is released inside
the engine and used directly formechanical work, as opposed to anexternal combustion engine in whicha separate combustor is used to burn
the fuel.1 IC engines can deliver power in the
range from 0.01 kW to 20x10^3 kW,
depending on their displacement.2
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History
The internal combustionengine was firstconceived anddeveloped in the late
1800s The man who is
considered the inventorof the modern IC engineand the founder of the
industry is pictured tothe right.Nikolaus Otto(1832-1891).
Otto developed a four-
stroke engine in 1876,most often referred to as
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History
The impact on society is quiteobvious, almost all travel andtransportation is powered by the IC
engine: trains, automobiles, airplanesare just a few.
The IC engine largely replaced the
steam engine at the turn of thecentury (1900s)
Another important cycle is the Dieselcycle developed by Rudolph Diesel in
1897. This cycle is also known as a
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CLASSIFICATION OFINTERNAL COMBUSTION
ENGINES
VARIOUS TYPES OF ENGINES
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CLASSIFICATION OF INTERNAL COMBUSTIONENGINES
1. Application
2. Basic Engine Design
3. Operating Cycle
4. Working Cycle5. Valve/Port Design and Location
6. Fuel
7. Mixture Preparation
8. Ignition
9. Stratification of Charge
10. Combustion Chamber Design
11. Method of Load Control
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
1. 1. Application
2. Automotive: (i) Car
(ii) Truck/Bus
(iii) Off-highway
2. Locomotive
3. Light Aircraft
4. Marine: (i) Outboard
(ii) Inboard
(iii) Ship
5. Power Generation: (i) Portable (Domestic)
(ii) Fixed (Peak Power)
6. Agricultural: (i) Tractors
(ii) Pump sets
7. Earthmoving: (i) Dumpers
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
2. Basic Engine Design:
1. Reciprocating (a) Single Cylinder
(b) Multi-cylinder (I) In-
line(ii) V
(iii)Radial
(iv)Opposed
Cylinder
(v)
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Types of ReciprocatingEngines
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
3. Operating Cycle
Otto (For the Conventional SIEngine)
Atkinson (For Complete Expansion SIEngine)
Miller (For Early or Late Inlet ValveClosing type SI Engine)
Diesel (For the Ideal Diesel Engine)
Dual (For the Actual Diesel Engine)
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
4. Working Cycle (Strokes)
1. Four Stroke Cycle:(a) Naturally
Aspirated
(b)Supercharged/Turbocharged
2. Two Stroke Cycle: (a) Crankcase
Scavenged(b) Uniflow Scavenged
(i) Inlet valve/Exhaust Port
(ii) Inlet Port/Exhaust Valve
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
5. (a) Valve/Port Design
1. Poppet Valve
2. Rotary Valve
3. Reed Valve
4. Piston Controlled Porting
5. (b) Valve Location
1. The T-head2. The L-head
3. The F-head
4. The I-head: (i) Over head Valve (OHV)
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
6. Fuel
1.Conventional: (a) Crude oil derived (i) Petrol
(ii) Diesel
(b) Other sources: (i) Coal
(ii) Wood (includes bio-mass)
(iii)Tar Sands
(iv)Shale
2. Alternate: (a) Petroleum derived (i) CNG
(ii) LPG
(b) Bio-mass Derived (i) Alcohols (methyland ethyl)
(ii) Vegetable oils
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
7. Mixture Preparation
1. Carburetion
2. Fuel Injection (i) Diesel(ii) Gasoline
(a) Manifold
(b) Port
(c) Cylinder
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
8. Ignition
1. Spark Ignition
(a) Conventional(i) Battery
(ii) Magneto
(b) Other methods
2. Compression Ignition
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
10. Combustion Chamber Design
1. Open Chamber: (i) Disc type
(ii) Wedge
(iii) Hemispherical
(iv) Bowl-in-piston
(v) Other design
2. Divided Chamber: (For CI): (i) Swirlchamber
(ii) Pre-chamber
(For SI) (i) CVCC
(ii) Other designs
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
11.Method of Load Control
1. Throttling: (To keep mixturestrength constant) Also called
Charge Control
Used in the Carbureted S.I. Engine
2. Fuel Control (To vary the mixture
strength according to load)
Used in the C.I. Engine
3. Combination
Used in the Fuel-injected S.I. Engine.
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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES
12. Cooling
1. Direct Air-cooling
2. Indirect Air-cooling (Liquid
Cooling)
.
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Basic Piston Engine Definitions
TDC
BDC
Stroke
Bore
Intake valve
Exhaust valve
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Nomenclature for Engines
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Basic Engine Definitions
Clearance volume
Displaced volume
Compression ratio
r
V
V
V
V
BDC
TDC
= =max
min
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Background on the OttoCycle
The Otto Cycle has fourbasic steps or strokes:
1. An intake stroke thatdraws a combustiblemixture of fuel and air intothe cylinder
2. A compression strokewith the valves closedwhich raises thetemperature of themixture. A spark ignites themixture towards the end ofthis stroke.
3. An expansion or powerstroke. Resulting fromcombustion.
4. An Exhaust stroke thepushes the burned
contents out of thecylinder.
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Why
The Otto cycle IC engine has remainedfundamentally unchanged, besides slightimprovements, for over 100 years. Itspopularity has continually increased
because Relatively low cost
Favorable power to weight ratio
High Efficiency
Relative simple and robust operatingcharacteristics
Improvements are mainly lower emissions
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Common terms used tocompare engine performance
Brake power (bp): net power outputof an IC engine
Torque: A force acting through aradius
RPM: engine speed, in rotations perminute
Specific fuel consumption (sfc): rateof fuel consumption per unit of brakepower
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Mean Effective Pressure
MEP: a fictitious pressure that, ifacted on the piston during the entirepower stroke, would produce the
same amount of net work as thatproduced during the actual cycle(Cengel & Boles, 2006)
If the MEP goes up, the cylinder
volume can go down and still achievethe same power output
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Mean Effective Pressure,cont.
Indicated MEP (imep): uses the totalpower output minus the powerneeded for the intake and exhaust
stokes (indicated power) Brake MEP (bmep): the power used
to overcome friction in the cylinder isalso subtracted; this term is usedmore often than the imep
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Brake Thermal Efficiency
Brake thermal efficiency: brakepower/rate of heat output forcomplete combustion
Brake thermal efficiency=indicatedthermal efficiency* mechanicalefficiency
Mechanical efficiency: related to theamount of power used to overcomefriction
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Carnot Efficiency
To see how well our engine is doing, wecan compare our brake thermal efficiencyto the Carnot efficiency
Remember that the Carnot efficiency is thebest we can do!
=1-(Tlow/Thigh), where Ts are in absolute
scale We could estimate Thigh as our exhaust
temperature
Tlow is our ambient temperature
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P
v
1
2
3
4
rr( )cycle 3 4 1 234 12 4 1in 23 3 2 3 2
4 14 1 1 4 1v
3 2 3 2 2 3 2
4 1
Thermal efficiency of the system:
W [ ( )] ( )= 1
Q ( ) ( )
( )( ) / 1For an ideal gas, u=C , =1 1 1
( ) ( ) / 1
Since /
v
v
m u u u uW W u u
Q m u u u u
C T Tu u T T T T
u u C T T T T T
T T
+ + = = =
= =
3 2
1
2
1
1 2 1
1
2 1 2
/ (why?)
1 . From isentropic compression relation for an ideal gas
1, where r= is the volume compression ratio
k
k
T T
T
T
T V V
T V r V
=
=
= =
1-2 isentropiccompression 2-3 constant volumeheat transfer 3-4 isentropicexpansion 4-1 constant volumeheat rejection
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0 3 6 9 12 15
0
20
40
60
80
100
compression ratio
thermalefficie
ncy
( )r
r
Thermal efficiency of an Ottocycle,
= 1
11
rk
Typical value of r for a realengine: between 7 and 10
The higher the compression ratio, the higher the thermal
efficiency. Higher r will led to engine knock (spontaneous ignition)problem.
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Increase the compression ratio
Increase the engine displacement: more power
Compress more air into the cylinder duringintake: using supercharger and turbocharger.
Cool the air before allowing it to enter thecylinder: cooler air can expand more, thus,increase the work output.
Reduce resistance during intake and exhauststages: multiple valve configuration: 4 cylinders/16valves engine
Fuel injection: do away with the carburetor andprovide precise metering of fuel into the cylinders.
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Diesel Cycle
T
s
1
2
3
4
P
v
2 3
4
1
2-3: a constantpressure process
(instead of a constantvolume process) andis the only differencebetween an idealizedDiesel cycle and anidealized Otto cycle.
Fuel injection for an extended period during the power strokeand therefore maintaining a relatively constant pressure. Diesel cycle has a lower thermal efficiency as compared toan Otto cycle under the same compression ratio. In general, Diesel engine has a higher thermal efficiencythan spark-ignition engine because the Diesel engine has amuch higher compression ratio. Compression-ignition: very high compression ratio 10 to 20or even higher.
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CI vs. SI Engines
SI engines draw fuel and air into thecylinder.
Fuel must be injected into the cylinder atthe desired time of combustion in CIengines.
Air intake is throttled to the SI engine -- nothrottling in CI engines.
Compression ratios must be high enoughto cause auto-ignition in CI engines.
Upper compression ratio in SI engines islimited by the auto-ignition temperature.
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CI vs. SI Engines
Flame front in SI engines smooth andcontrolled.
CI combustion is rapid anduncontrolled at the beginning.
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Diesel vs Otto engine
qHigher thermal efficiencyas a consequence of a higher compression ratio (16-20 vs9-12) needed for the self ignition of the mixture
q Higher efficiency at part load condition (city driving) because of the different loadcontrol with much inferior pumping loss for aspirating air into the cylinder: load controldirectly by varying the fuel delivery, while in the Otto engine by varying the air through anintake throttle
qLess energyspent to produce Diesel fuel
q Higher weight for same power delivery, because of higher thermal and mechanicalstresses due to higher temperatures and pressures , almost double vs Otto engine, at theend of compression and combustion phases
q Lower maximum engine speed because a slower combustion process and higherweight of the rotating an oscillating masses
qEngine roughness that generates higher structural and airborne vibration/noise.
Advantages
Disadvantages
4141
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4-stroke engine
High volumetric efficiency over a wideengine speed rangeLow sensitivity to pressure losses in theexhaust systemEffective control of the chargingefficiency trough appropriate valve timingand intake system design
2-stroke engine
Very simple and cheap engine designLow weightLow manufacturing costBetter torsional forces pattern
2-stroke engine
Higher fuel consumption
Higher HC emissions because of aproblematic cylinder scavengingLower mean effective pressure becauseof poorer volumetric efficiencyHigher thermal load because no gasechange strokePoor idle because of high residual gaspercentage into the cylinder
4-stroke engine
High complexity of the valve control
Reduced power density because thework is generated only every secondshaft rotation
Four stroke vs Two-stroke cycle
Advantages
Disadvantages
4242
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EXHAUST GAS RECIRCULATION (EGR) -SI AND CI ENGINES
Dilutes Air/Fuel mixture with exhaust gases therebyreducing peak combustion temperatures and NOxformation
There are limits to how lean an air-fuel-exhaust gas
mixture can be for ignition
Ignition systems (spark plugs etc.) and combustionchambers can be designed to improve performance withthese lean mixtures
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Exhaust Gas Recirculation
Returns ~ 5% of Exhaust toIntake Charge
Displaces Air/Fuel ChargeWithout Affecting Ratio
Reduces Peak Temperature
Reduces NOx Emissions
HCCI
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HCCI
Importance
SI engines have very low NOx and PM emissions
CI engines have high efficiency
Homogeneous Charge Compression Ignition(HCCI) is
a promising alternative combustion technologywith high efficiency and lower NOx andparticulate matter emissions
P i i l
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Principle
HCCI is characterized by the fact that the fueland air are mixed before combustion starts andthe mixture auto-ignites as a result of the
temperature increase in the compression stroke
Optical diagnostics research shows that HCCI
combustion initiates simultaneously at multiple
siteswithin the combustion chamber and that thereis no discernable flame propagation.
HCCI
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HCCI
POTENTIAL1. High efficiency, no knock limit on compression
ratio.2. Low NOx and no NOx after treatment systems
required.3. Low PM emissions, no need for PM filter.4. HCCI provides up to a 15-percent fuel savings,
while meeting current emissions standards.5. HCCI engines can operate on gasoline, diesel fuel,
and most alternative fuels.6. In regards to CI engines, the omission of throttle
losses improves HCCI efficiency.
HCCI
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HCCI
BARRIERS1. The auto-ignition event is difficult to
control, unlike the ignition event in spark
-ignition(SI) and diesel engines which arecontrolled by spark plugs and in-cylinderfuel injectors, respectively.
2. HCCI engines have a small power range,constrained at low loads by leanflammability limits and high loads by in-cylinder pressure restrictions
3. High HC and CO emissions.
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Multi-Port Fuel Injection
One injector percylinder
Mounts in intakemanifold, spraysdirectly at intake valve
Fired in groups orindividually (SFI)
Ram Tuning for denserair charge
Lower A/F temps
Leaner mixture during
warm-up
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M it f F l I j ti i
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Merits of Fuel Injection inthe SI Engine
Absence of Venturi NoRestriction in Air Flow/HigherVol. Eff./Torque/Power
Hot Spots for Preheating cold aireliminated/Denser air enters
Manifold Branch Pipes Notconcerned with MixturePreparation (MPI)
Better Acceleration ResponseMPI
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Merits (Continued)
Use of Greater Valve Overlap
Use of Sensors to MonitorOperating Parameters/Gives
Accurate Matching of Air/fuelRequirements: Improves Power,Reduces fuel consumption andEmissions
Precise in Metering Fuel in Ports
Precise Fuel DistributionBetween Cylinders (MPI)
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Merits (Continued)
Fuel Transportation in Manifoldnot required (MPI) so no WallWetting
Fuel Surge During Fast Corneringor Heavy Braking Eliminated
Adaptable and Suitable ForSupercharging (SPI and MPI)
Limitations of Petrol
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Limitations of PetrolInjection
High Initial Cost/HighReplacement Cost
Increased Care and
Attention/More ServicingProblems
Requires Special Servicing
Equipment to Diagnose Faultsand Failures
Special Knowledge of Mechanicaland Electrical Systems Neededto Dia nose and Rectif Faults
Limitations of Petrol
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Limitations of PetrolInjection (Continued)
Injection EquipmentComplicated, Delicate to Handleand Impossible to Service by
Roadside Service Units Contain More Mechanical and
Electrical Components Which
May Go Wrong Increased Hydraulic and
Mechanical Noise Due to
Pumping and Metering of Fuel
Limitations of Petrol
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Limitations of PetrolInjection (Continued)
Very Careful Filtration NeededDue to Fine Tolerances ofMetering and Discharging
Components More Electrical/Mechanical
Power Needed to Drive FuelPump and/or Injection Devices
More Fuel Pumping/InjectionEquip-ment and Pipe PlumbingRequired- May be Awkwardly
Placed and Bulky
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Dual Fuel SystemMechanical KitComponents
Electronic KitComponents
n Converts vehicle to run on up to 80% natural gas and 20%
dieseln Meets or exceeds CARB/EPA emission standards
n Retro fit for older engines
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Dual Fuel SystemCharacteristics
No mechanical or electrical modifications to theoriginal diesel engine
Diesel system can be either mechanical or electroniccontrolled
Electronic Control Unit provides completemanagement of natural gas
and diesel simultaneously, for reliable power andemissions control over a wide range of operatingconditions.
ECU contains 64-bit core micro-controller for fastcalculations of
required engine control parameters. The program isstored entirely in flash memory.
No ower loss or loss of milea e
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Lean Burn EngineLean Air/Fuel mixture as high as 65:1can be used.Engine can employ higher CR for betterperformance
Efficient fuel use.Low exhaust hydrocarbon emissionCan be achieved by GDIIt can not reduce Nox
Used in heavy duty natural gas ,biogas,LPG engines
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Stratified Charge Engine
In the cylinder air /fuel mixture is layeredUsed in direct injection systemFuel injection is at the cylinder head or at
peripheryRich charge in that area ignites and burnsCombustion proceeds to lean areaFlame front cools rapidly.
Nox is not formed.Extra O2 in lean area combines with CO toform CO2Also applied to diesel engineFuel economy 20%