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Chapter 1.1: Introduction
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What is an Internal Combustion Engine? The internal combustion engine is a mechanical device in which the
rapid oxidation of gas and air occurs in a confined space called acombustion chamber. This exothermic reaction of a fuel with an oxidizer
creates gases of high temperature and pressure, which are allowed toexpand.
The defining feature of an internal combustion engine is that useful workis performed by the expanding hot gases acting directly on the piston,causing movement of the piston inside the cylinder.
This contrasts with external combustion engines, such as steam enginesand Stirling engines, which use an external combustion chamber to heata separate working fluid, which then in turn does useful work e.g. bymoving a piston.
The term Internal Combustion Engine(ICE) is almost always used torefer specifically to reciprocating engines, Wankel engines and similardesigns in which combustion is intermittent. However, continuouscombustion engines, such as jet engines, most rockets and many gasturbines are also internal combustion engines.
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Brief Historical Perspective 1860s: Lenoir engine burned coal gas-air mixtures at atmospheric pressure before combustion. 5000
engines built up to 6 hp; efficiency up to 5%
1862: Beau de Rochas, a French civil engineer, patents but does not build a four-stroke engine
1866: Otto and Langen build 5,000 atmospheric engines with up to 11% efficiency and 2 hp.
1876: Otto builds a four-stroke engine. Enormous reduction in engine weight and volume. 50,000engines sold in Europe and U.S.
1882: Atkinson invents the two-stroke engine with a longer expansion than compression stroke.Compression ratios 4 to avoid knock.
1893: Diesel received a patent for compression-ignition internal combustion engine using petrol oilwhich achieves high thermal efficiency due to greater compression ratios.
1908: Production of the Model T begins. One of the first mass produced, affordable automobiles(average cost ~ $550). 2.9 L spark ignited engine, ~ 20 HP, 13-21 mpg, CR = 4.5:1.
1923: Bosch develops a number of designs for fuel injection pumps. 1939: First volume production car to be fitted with diesel (Mercedes 260D)
1946: Stratified-charge, spark-ignition engine developed by Texaco
1961: Wankel patents rotary engine
1970s: First direct-injection SI engine by Ford
1975: Three way catalysts appear on spark-ignited vehicles within the US. The catalysts significantly
reduce NOx, HC and CO emissions, however, the vehicles must be operated stoichiometrically forefficient catalyst operation.
1980s: Electronic SI Engine Controllers
1990s: Electronic Diesel Engine Controllers
2000s: Hybridization is introduced for production cars
2000s: High-pressure common rail injection system for Diesel engines
2010s: Downsized, boosted SI engines
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Todays ICE Spark-Ignition (SI) and Compression Ignition (CI or
Diesel) Engines
Difference in combustion defines engine: use either spark orcompression to ignite air-fuel mixture
Gasoline and Diesel are primarily used
U.S. Diesel Popularity
2005: 3.2% of market share* 2015 forecast: ~10% of market share*
Nearly 50% of New Registrations for WesternEuropean Vehicles are Diesel Powered with Some
Countries over 70%**
* J.D. Power and Associates (2006)** Schindler, DEER Conference (2006)
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Engine Classificationa. Applicationsb. Basic Engine Design
c. Working Cycled. Method of Gas Exchangee. Valve and Port Design
f. Fuelsg. Method of Mixture Preparation,Ignition and Combustion
h. Method of Load Control
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Chapter 1.2: IntroductionEngine Classification (a-b)
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Approx.
engine power Predominant TypeClass Service range, kW CI or SI Cycle Cooling
Road vehicles Motorcycles, scooters 0.75-70 SI 2, 4 ASmall passenger cars 15-75 CI, SI 4 A, WLarge passenger cars 75-200 CI, SI 4 W
Light truck 35-150 CI, SI 4 WHeavy (long-distance) truck 120-400 CI 2, 4 W
Off-road vehicles Light vehicles (factory, airport, etc.) 1.5-15 SI 2, 4 A, WAgricultural 3-150 CI, SI 2, 4 A, WEarth moving 40-750 CI 2, 4 WMilitary 40-2000 CI 2, 4 A, W
Railroad Rail cars 150-400 CI 2, 4 W
Locomotives 400-3000 CI 2, 4 W
Marine Outboard 0.4-75 SI 2 WInboard motorcrafts 4-750 CI, SI 4 W
Light naval craft 30-2200 CI 2, 4 WJet skis 5-10 SI 2, 4 A, WShips 3500-80000 CI 2, 4 W
Ships' auxiliaries 75-750 CI 4 W
Airborne Vehicles Airplanes 45-2700 SI 4 AHelicopters 45-1500 SI 4 A
Home use Lawn mowers 0.7-5 SI 2, 4 A
Snow blowers 2-5 SI 2, 4 ALight tractors 2-8 SI 4 A
Stationary Building service 7-400 CI 2, 4 WElectric power 35-22000 CI, SI 2, 4 W
Gas pipeline 750-5000 SI 2, 4 W
Heywood (1988), Internal Combustion Engines; Taylor (1985), The Internal Combustion Engine in Theory and Practice
A Air
W Water
a. Applications
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Extreme Engine Sizes
the small
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Extreme Engine Sizes
the big
http://www.emma-maersk.com/engine/Wartsila_Sulzer_RTA96-C.htm
Engine Sulzer RTA-96C
Engine weight 2087 metric tonsLength 27.1 m
Height 13.4 m
Cylinders 14
Bore 960 mmStroke 2500 mm
Maximum power 81220 kW at 102 rpm
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b. Basic Engine Design
Reciprocating In-line
V-shaped Radial
Rotary (Wankel)
Keep these in mind as we gothrough the basic designs:
Working CycleMethod of BreathingValve or Port DesignMethod of Mixture
Preparation, Ignition
and CombustionMethod of Load Control
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SI designs
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Readers Digest (1981), Complete Car Care Manual
In-Line Four
CylinderSI Engine(pushrod)
Cylinder head:communicates with intakeand exhaust systems.Contains passageways thatthe air (& fuel) passthrough. Contains cooling
passageways.
Engine block: housescylinders and alsocontains passagewaysfor coolant to prevent
extreme temperatures(water and oil jackets).
Flywheel: stores angularmomentum so that itsmoothens power
pulses from individualpistons.
uses under head camshaft
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Readers Digest (1981), Complete Car Care Manual
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In-Line Four
CylinderSI Engine
(OHC)
Society of Automotive Engineers, 1981
Filters intake air
Older methodfor
introducingfuel
Overhead
Activates valves withone lobe per valve
Controls camshaft,but parasitic loss of
power
Translates force onpiston to crankshaft
Breathing ofengine.Have
machinedsurfaces for
uniformcombustionchamber.
Engine designers areconcerned about packaging.In-line 4-cylinder is relatively
compact, but in-line 8-cylinder is impractical.
Connected totransmission for
translating enginepower to wheels
F = pA
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Courtesy of Ford Motor Company
V-Design
SI Engine(pushrod)
Blue fresh airRed exhaust gasesYellow lubricating oil
Green coolant to reducetemperature (or warm-up)
In this case, the engineuses low pressure fuelinjection (~ 2 bar) in theintake ports. Need goodatomization at low flow
rates.
Throttle in fullyclosed position.
Different Working Fluids
and runners
WOT Wide open throttle,minimum pressure drop through
throttle plate (most time
operated at part load)
partial vacuum
puddles
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SI Piston Detail
Pistons provide the forcethat drives the engine
Depending on theapplication, there are many
different types of pistonshapes Two compression rings
seal working fluid inchamber
Oil ring scrapes off oil to
prevent from enteringchamber Most 4-valve engines have
cut-outs at the pistonsurface to avoid contactwith the valves
Readers Digest (1981), Complete Car Care Manual
Piston crown
Skirt
ConnectingRod
CompressionRings (2)
Oil Ring
Top Land
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CI/Diesel designs
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Design Features
of a Heavy-DutyTruck Engine
Courtesy of Caterpillar Inc.
High-pressure injection system is alarge cost factor for CI engines ~ 20-
30% of total cost.
To account for the high pressures (1500-2000bar vs. 50 bar in SI) during combustion, these
engines have robust components (ex:
connecting rod)
MEUI Fuel Injector
Notice the bowl shape in the piston toaccount for the fuel injection spray. Have tomake sure of correct injection timing. (soot,
turbulence, mixing)
Cylinder liner may be press-fitted so theblock material and the piston material
are different. May reduce the weight ofthe engine.
Wet liner means that the cooling fluidflows over the liner, whereas for a dry
liner does not.
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Radial Engines
Gasoline engines can also bedesigned using a radialconfiguration.
These engines are mostly used inthe aircraft industry and not inautomobiles
Differences with in-line and V
configurations are mostly justpackaging still four-stroke,reciprocating combustion
Schwaller, Anthony E., Motor Automotive Technology
Radial Engine
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Wankel (Rotary) Engine
Uses a rotor instead ofreciprocating pistons.
This design delivers smooth
high-rpm power from acompact, lightweight engine.
Mobil Technical Bulletin, Rotary Engines, 1971
Wankel Engine
Same thermodynamic
working cycle asprevious engine designs Mechanicalarrangement is verydifferent Typically lowerefficiency, due in part to
the high surface area tovolume ratio of thecombustion chamber,which effects heattransfer Smoother torqueproduction (lessimbalance)
Fewer moving partsMazda productionengines (RX-8)
Seals package
3 power strokes perone revolution of rotor
no valves
Spins 3 times fasterthan rotor
Why not Wankel?Used to have sealing
problems and high fuelconsumption
Rotor controlsworking space.
Each facecreates onecombustionchamber.
analogous to engine block
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Chapter 1.3: IntroductionEngine Classification (c-e)
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Engine Classification
a. Applicationsb. Basic Engine Designc. Working Cycle
d. Method of Breathinge. Valve or Port Designf. Fuelsg. Method of Mixture Preparation, Ignition
and Combustionh. Method of Load Control
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c. Working Cycle
Four-stroke
The four strokes refer to intake, compression,
combustion/expansion and exhaust strokes that occur duringtwo crankshaft rotations per working cycle.
Two-stroke
The two-stroke cycle of an internal combustion engine differs
from the more common four-stroke cycle by completing thesame four processes (intake, compression,combustion/expansion, exhaust) in only two strokes of thepiston rather than four.
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Four-Stroke SI Engine Cycle
Readers Digest (1981), Complete Car Care Manual; Car Bibles: The Fuel and Engine Bible (four-stroke animation)
Intake Stroke:Piston descends drawingin air/fuel mixture whilethe intake valve is open(exhaust valve closed).
Intake valve closing endsprocess.
Compression Stroke:While both valves are
closed, piston rises in thecylinder compressing fuel/air
mixture.
Combustion/ExpansionStroke:
Compressed gas is ignitedby spark plug. Expandingburning gases push piston
down.
Exhaust Stroke:Exhaust valve opens and thepiston rises to expel burned
gases. Exhaust valveclosing and intake valveopening ends process.
TDC (0) BDC (180) BDC (180) TDC (360) TDC (360) BDC (540) BDC (540) TDC (720)
Geometric stroke is defined as Top Dead Center (TDC)to Bottom Dead Center (BDC) or vice-versa
One power stroke per two revolutions (720) of crankshaft
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Four-Stroke CI Engine Cycle
Readers Digest (1981), Complete Car Care Manual
Intake Stroke:Piston descends drawing
in air while the intakevalve is open
(exhaust valve closed).Intake valve closing ends
process.
Compression Stroke:While both valves are
closed, piston rises in thecylinder compressing the air.
Just before maximumcompression, diesel fuel isinjected into the chamberunder very high pressure.
Combustion/ExpansionStroke:
Fuel vaporizes and ignitesafter very short delay in the
hot compressed air.Expanding burning gases
push piston down.
Exhaust Stroke:Exhaust valve opens and thepiston rises to expel burned
gases. Exhaust valve
closing and intake valveopening ends process.
One power stroke per two revolutions (720) of crankshaft
Geometric stroke is defined as Top Dead Center (TDC)to Bottom Dead Center (BDC) or vice-versa
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Two Stroke SI or CI Engine Cycle
HowStuffWorks (2007)
Car Bibles: The Fuel and Engine Bible (two-stroke animation)
One power stroke per one revolution (360) of crankshaft
Crankcaseflow can bringoil with air or
air/fuel
Ports activated bymotion of piston.
Piston shape helpswith breathing by
driving flowdirection.
* Dead zonesmay not get
properly purged*
EGRhappenswithouttrying
Short-circuitingmay occur (loss of
fresh mixture)
Timing decided bythe location ofexhaust ports
versus intake ports
Uniflow Scavenging
Crank Scavenging
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d. Method of Breathing
Naturally Aspirated
Turbocharged
Supercharged
Crank Scavenged
Intercooling / Aftercooling
Ambient air input
Used to increase air mass intocylinder for higher power output
Used to cool the inlet air effectively increasingthe density (from the ideal gas law)
p RT=
Ideal Gas Law
Compressing the mixture
will raise the pressure,density and temperature ofthe mixture subject to theideal gas law. For a given
volume of air, the moredense it is, the more masswe can put in the cylinder.
m V=
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Turbocharger Principle
The amount of power that an engine canproduce is limited by the amount of air and fuelthat can be drawn into the cylinders.
Turbochargers use the high-speed flow ofexhaust gases to power a small turbine wheelcompressing the intake mixture.
The greater the flow of exhaust gases, thefaster the turbine spins and the morecompression that takes place.
A waste gate prevents the process from
getting out of hand sensor on inlet pressureis utilized to bypass some exhaust energy.
No direct coupling to engine May lead to knock in SI engines. Aerodynamic compressor may not have
constant volume flow rate during operation;
hence susceptible to surging and choking Surge: flow detached from blades causing non-ideal accel/deceleration of compressor wheel
Choking: critical flow is reached
Readers Digest (1981), Complete Car Care Manual
Up to 35% of fuel energycan exit in the exhaust gas,
however not all of this
energy can be convertedinto useful work (2nd law).
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Turbocharging
Utilization of exhaust gas energy thatwould otherwise be lost
However, the turbocharger adds arestriction on the system, which
may affect pumping work.
Turbochargers can suffer from turbolag When acceleration is needed, exhaust
energy initially is not enough to keep upwith the demand.
Inertia of turbocharger must beovercome.
Compressed air must travel throughthe intake pipes to reach the cylinders.
Depending on operating conditions,boosting the engine generally provideshigher overall thermal efficiency.
Fairbanks (2004), Engine Maturity, Efficiency and Potential Improvements
Q: Why not use T/C on all engines?
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Supercharger Principle
While turbochargers use the exhaust flow,superchargers are powered mechanically by abelt- or chain-drive from the enginescrankshaft Driven parasitically from engine crankshaft
Superchargers do not suffer from any lagbecause they respond directly to the speed ofthe engine As the engine power increases, the
supercharger immediately spins faster
Positive Displacement Pump every rotationit will output the same amount of volume flowrate (not subject to surging or choking)
* Howstuffworks How Superchargers Work* Supercharging
Roots type Twin screw type
Centrifugal type
Advantage always onDisadvantage parasitic loss
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Two-StrokeDiesel Engine
OperationWith Uniflow
Scavenging
Supercharging canhelp with the
scavenging processby increasing intake
air pressure
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Intercooling / Aftercooling
An Intercooler lowers the temperature of theintake mixture, which will increase the densityaccording to the Ideal Gas Law.
This is especially important in Turbocharging
and Supercharging applications becausecompression also increases the temperature. A small pressure drop occurs through the
Intercooler but at a much larger gain indensity.
The Inter-in the name refers to its locationcompared to the compressors.
In aircraft engines, coolers were typicallyinstalled between multiple stages ofsupercharging.
Modern automotive designs are technicallyAftercoolers.
Design of the size of the Intercooler is also
important due to the volume of air it containswhich can lead to a larger turbo lag.
Dinkel (2000), Road & Track Illustrated Automotive Dictionary
p RT=
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e. Valve or Port Design
Poppet Valves (Four-Stroke Scavenging Methods) Used to bring in the fresh charge (consisting of air or air + fuel)
during intake and to expel burned gases during the exhaust stroke Valve actuation:
Pushrod and rocker-arm
Overhead camshaft
Ports (Two-stroke Scavenging Methods) Also used for intake and exhaust
Most common methods: Loop-scavenged porting
Uniflow-scavenged
Intake ports combined with a poppet exhaust valve Crank Scavenged
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Overhead Camshaft Valvetrain
Overhead camshaftsoperate the valves moredirectly than rocker-armdesign.
Fewer parts and lessinertia allow engines to runfaster.
One or more overheadcamshafts may be used.
V-type engine with dualoverhead camshafts hasfour camshafts in total.
Readers Digest (1981), Complete Car Care Manual
Roller finger follower2.2L GM Ecotec
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2 Valve vs. 4 Valve Designs in CI engines
The effective flow area forthe intake and exhaustprocess can be increasedby increasing the numberof valves This impacts the flow velocity
and resulting friction losses,which influence volumetricefficiency
The flow will choke if theflow area is too small
Volumetric efficiency: theeffectiveness of the engine atinducting air
The valve configurationcan also be used for
turbulence enhancementor flow arrangement
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Ideal Timing Diagram
Introduction to timingdiagrams
Reference four-stroke cycle
Geometric processes
define the intake andexhaust events
Not really what happens
V l Lift
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The inlet and exhaust valve opening is
a function of the crank angle andvaries from a closed position to a
maximum lift position.
Valve Lift
Readers Digest (1981), Complete Car Care Manual
Valves do not open instantly takes time to reach max lift
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Intake Fluid Dynamics Effect
In addition to geometric concerns, fluiddynamics must be considered
At BDC, piston has effectively zerovelocity
During reversion of piston, flow velocitiesare initially low; hence, the loss due topiston movement is small
Can take advantage of the high speedmomentum of inlet air flow to continue tocharge cylinder: IVC occurs after BDC
(180) Momentum effect depends on length anddiameter of intake runner.
Must consider momentum whenspecifying valve timing: Low engine speeds (rpm) dictate earlier
closing (closer to BDC) High engine speeds dictate later closing May get backflow if improper timing: loss
in fresh charge back through inlet valve
RAM effect: high speed
momentum of air flow continues
to charge cylinder as piston moves
from BDC
BDC
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Exhaust Fluid Dynamics Effect
Why not follow same methodology asintake for exhaust by opening afterBDC? Will act to purge the cylinder However, now we perform negative
work by using the piston to push outthe exhaust gas
There is a thermodynamic advantageby opening the exhaust valve early
Large pressure drop across valvecauses significant blowdown andpurging of combustion gases fromcylinder, P ~ 5-10 bar
Open during late expansion after mostof the combustion has occurred totake advantage of pressure drop
Balance between expansion, exhaustand compression work
BDC
1 bar
There exists a balance betweenexpansion work and purging of the
exhaust gases during blowdownprocess
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Overlap Period
Valve overlap = both valves open When both the intake and exhaust valves
are open, backflow may occur from theexhaust into the intake side
Is this desirable? Yes or no depending on the gas exchangetarget
Exhaust Gas Recirculation (EGR) reducesNOx emissions and may be used for part-load operation
Internal (i-EGR) or External (e-EGR) The fact that pintake in an SI engine is normallybelow pexhaust accentuates the backflowprocess, especially at idle This decreases volumetric efficiency even
more than for engines with no overlap. Thisis why race engines with large overlap idle
so poorly as shown on next slide.
pexhaust > pcylinder > pintake
i-EGR
e-EGR
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Four Stroke Valve Timing: Conventional vs. Formula SAE
High-speed timing (12,000 rpm):Use momentum of air intake to
close extremely lateEarly blowdown because of high
engine speed (time/breathing)Poor idling capabilities
A single set of valve timingswill not work for all enginesand all desired conditions
Conventional Engine Formula SAE Engine
IVO IVO
IVC
IVC
EVO
EVO
EVC
EVC
More overlap for scavenging(make sure all exhaust gases
leave the cylinder)
T S k S i M h d
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Two-Stroke Scavenging Methods
Loop scavenging
No valvetrain required
Possibility of shortcircuiting air through theexhaust ports
Uniflow scavenging
Improved volumetric
efficiency relative to loopscavenging
More complicated design(exhaust valve andmechanism)
Crank scavenging
See slide 1-28
Loop Scavenging Uniflow Scavenging
EXHAUST VALVE
marineengineeringonline.com
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Helps push outexhaust gases
May lose freshmass Short-circuiting can
occur during this time
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Chapter 1.4: IntroductionEngine Classification (contd)
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f F l
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f. Fuels
Gasoline
Diesel
Natural Gas, LPG
Alcohols (methanol, ethanol)
Synthetic diesel
Bio-diesel
Dual Fuel Gas to Liquid / Coal to Liquid
Hydrogen
F l Ch i
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Fuel Choices
Crunching the Numbers on Alternative Fuels Popular Mechanics
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g. Methods of Mixture Preparation, Ignition and
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MIT Laboratory for Energy and the Environment
g p , g
CombustionSI
Homogeneous ChargeSpark Ignition
CI (Diesel)Stratified Charge
Compression Ignition
HCCIHomogeneous ChargeCompression Ignition
SIDIHomogeneous orStratified Charge
Spark Ignition
Spark Ignited (SI) Compression Ignited (CI) Homogeneous Charge Compression Ignition (HCCI) also commonly referred to as Low Temperature Combustion (LTC) Spark Ignited Direct Injection (SIDI) also known as Gasoline Direct Injection (GDI)
MITSUBISHI GDI
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Indirect Injection (IDI) for diesels
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d ect ject o ( ) o d ese s
Antiquated system used in pre-chamber CI engines
Fuel only goes into pre-chamberwhere there is a great amplification of
turbulence Glow plug used to warm-up smallchamber for cold starts (resistanceheating element)
Relatively quiet compared to directinjection (following slides)
Subject to losses in heat transfer andpower Note tortuous path of fluid flow during
combustion
Fuel economy not as good becauseof throttling losses and combustion isdelayed
Society of Automotive Engineers, Inc., 1982
ReadersDigest(1981),Comp
leteCarCareManual
~ 300 bar
Methods of Direct Diesel Fuel Injection
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jPump-Line-Nozzle (PLN)
Fundame
ntalsofGasolineandDieselFuelSystems
Common Rail
BMW World
Fuel gets
pressurized,mechanical
system to injectfuel. Only onepulse allowed.
Have reservoir (rail) of fuel at high pressure (>2000 bar).Can tap from reservoir to provide multiple pulses of
different amounts of fuel at different times. Minimizessoot, noise and can maximize power output.
Methods of Fuel Injection for SIDI Engines
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Methods of Fuel Injection for SIDI Engines
Similar to common rail fuel
injection Lower injection pressures,
100-300 bar
Fuel injector may be centrally
or side mounted Piston design depends on
injector and spray orientation
Spark Plug
Fuel Injector
motivemag.com
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Port Fuel Injection
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j
Motivation for Port Fuel Injection Torque and Horsepower
Improved fuel distribution WOT enrichment closer to
optimum A/F Open intake valve injection
possible for WOT torqueimprovement
Emissions Improved air/fuel control during
warm-up & stabilized engine Closed intake valve injection
possible Individual cylinder adaptive
learning reduces C-T-C variation
Fuel pressures 4-10 bar Mechanical system illustrated,
however all electrical now
ECU dictates timing and durationof fuel injection
Readers Digest (1981), Complete Car Care Manual
Combustion in Homogeneous SI and SIDI Engines
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Combustion in Homogeneous SI and SIDI Engines
Concept
Homogeneous mixture composition
Control Heat Release Rate (HRR) through flame propagation
EngineType
MixturePreparation
Ignition Method Combustion
SI Homogeneous Spark Premixed Flame
CI (Diesel) Stratified Compression Non-Premixed Flame
SIDI (late) Stratified Spark Premixed Flame
SIDI (early) NearlyHomogeneous
Spark Premixed Flame
HCCI Homogeneous Compression Auto-Ignition
Images of Premixed Flame Propagation in an SI Engine
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Zigler, B., An Experimental Investigation of the Properties of Low Temperature Combustion in an Optical
Engine, PhD Thesis in Mechanical Engineering, The University of Michigan, Ann Arbor (2008)
Spark plug
+0.0 deg +4.2 deg +8.4 deg +12.6 deg +16.8 deg
View of Cylinder Head ThroughOptical Window in Piston Crown
Burned Gas
SI CombustionChamber Cross
Section
Fuel Air
Mixture(Unburned)
Piston
PropagatingThin Flame
Geometric compressionratios range from 8 to 14
(knock constraints)
Spark Flame kernel Laminar flame Turbulent flame
Crank Angle Degrees (CAD)
Valves
Combustion in CI (Diesel) Engines
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( ) g
1. The CI process typically begins with auto-ignition and transitions to a non-premixed flame
Concept
Use overall very lean mixture for high thermal efficiency
Locally, the mixture can range from lean to rich (stratification)
Control Heat Release Rate (HRR) by mixing air with fuel
Fast enough to consume all of the fuel
Slow enough to avoid global fast autoignition
EngineType
MixturePreparation
Ignition Method Combustion
SI Homogeneous Spark Premixed Flame
CI (Diesel) Stratified Compression Non-Premixed Flame1
SIDI (late) Stratified Spark Premixed Flame
SIDI (early)NearlyHomogeneous
Spark Premixed Flame
HCCI Homogeneous Compression Auto-Ignition
High Pressure Direct Injection Diesel Engine
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g j g
Utilize fluid mechanics, shape ofpiston and high pressure injectionto promote mixing of fuel with air
Within the fuel spray mixture will
be extremely rich (A/F = 0) andsoot can form
Geometric compressionratios 12 24
Can auto ignite lean overall mixtures(A/F = 100:1 is possible). Pockets ofconcentrated fuel/air mixture aroundinjector will be rich enough in fuel to
trigger autoignition.
Load is controlled by amount offuel injected, not by air flow
through throttle plate
Never goes globally stoichiometric becauseof emissions issues (A/F ~ 30:1 max)
Combustion in a Direct Injection Diesel Engine
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Combustion happens over a range of fuel/airmixtures and temperatures. There will be
locations where there is too much fuel (soot),there will also be pockets where we havehigh temperatures and excess O2 (NOx)
http://picasaweb.google.com
Non-PremixedFlame , ~ 1
Rich Mix ~ 4
Sootformation
Flynn, P. F., et al. (1999) Diesel combustion: An integrated view combininglaser diagnostics, chemical kinetics, and empirical validation. SAE Paper
No. 1999-01-0509
Conceptual Model of MixingControlled Diesel Combustion
Fuel =
DI Diesel Fuel Spray Movie(http://www.youtube.com/watch?v=LnZmt5SViuY)
Combustion in Stratified SIDI Engines
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g
Concept
Use overall lean mixture for high thermal efficiency
Locally, the mixture can range from lean to rich (stratification)
Arrange fuel air mixture near spark plug to be stoichiometric (A/F = 14.6) for
ignition
Control Heat Release Rate (HRR) through flame propagation
EngineType
MixturePreparation
Ignition Method Combustion
SI Homogeneous Spark Premixed Flame
CI (Diesel) Stratified Compression Non-Premixed FlameSIDI (late) Stratified Spark Premixed Flame
SIDI (early)NearlyHomogeneous
Spark Premixed Flame
HCCI Homogeneous Compression Auto-Ignition
Gasoline Direct Injection
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SIDI with gasoline fuel
Used to take advantage of fuel economy benefits ofglobally lean mixtures at low load
Nearly premixed, stoichiometric operation athigh load through early injection
Control engine through fuel injection not throttle plateto eliminate pumping loss (more vacuum, more loss)
Can get 100% of fuel in cylinder versus PFI
Vaporization of fuel in cylinder removes energy fromsurrounding air which lowers temperature(evaporative cooling) can go to higher compressionratios
Homogeneous mixture at WOT is harder to create Still uses spark plug, so mixture composition around
plug is crucial (piston-guided design)
Use of intake air motion and fuel injection onmodified piston shape to get stoichiometricmixture around spark plug at desired time
Misfire is a strong likelihood for this engine, ifmixture is too lean or too rich
Premixed flame will propagate through fuel-airmixtures ranging from locally lean to locally rich
Can have issues with catalytic exhaust aftertreatment
What about knock and this design?
Mitsubishi GDI
Stratified charge engine that
runs at global A/F of 40 or 50:1
Compression ratios range fromaround 10 to 15
Gasoline Direct Injection Modes
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Stratified(Lean / Part Load)
Homogeneous(Stoichiometric / Full Load)
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Homogeneous Charge Compression Ignition (HCCI)
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How about a Gasoline-PoweredHCCI Hybrid?
Currently a promising research concept limited to low loads; use bigger engines or boostfor higher specific power
Combination of premixed charge and CI Homogeneous mixtures prevent generation of soot (absence of fuel rich pockets) No spark autoignition of charge due to high temperature near TDC No throttling
Use higher compression ratios for efficiency (also required for autoignition) Use lean mixtures (similar to CI) and/or large amounts of EGR (Dilute mixture) for Low
Temperature Combustion. This significantly lowers NOx emissions.
Nearly constant volume combustion which leads to extreme rates of pressure rise Compression ratios range from 10 to 21 with ignition controlled by charge temperature Use cooled or hot EGR to control charge temperature and hence ignition timing (variable
valve timing) Subject to low combustion efficiencies leading to higher amounts of CO and HC
Variable Valve Actuation (VVA) and HCCIPOSITIVE
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ConceptAdjust valve timings to get right amount of HOTresidual gas at beginning of compression and
adjust charge temperature to controlIGNITION TIMING near TDC
Rebreathing: draw back exhaust gas fromthe Exhaust port with additional exhaust
valve event
Recompression: trap burned gas in the
cylinder with negative valve overlap (NVO)
0 180720540
LIFT
CA deg
EXH 1 INT EXH 2
0 180720540
LIFT
CA deg
EXH INT
POSITIVE
OVERLAP
0 180720540
LIFT
CA deg
EXH INT
NEGATIVEOVERLAP
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h. Method of Load Control
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Throttling of fuel and air flow together (most current SI systems)
High pumping losses
Control of fuel flow alone (typical diesel, HCCI)
No throttling
Low pumping losses
Variable Valve Timing (VVT) (SI, HCCI)
Controls air flow without throttling (lower pumping losses)
More complicated, expensive
Load Control via Throttling
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Regulates load on the majority of currentproduction SI engines that operatestoichiometrically ( = 1)
The throttle position controls the flow areaand p across the throttle plate
Density of the air within the intakemanifold and cylinder varies with pacross the throttle plate
Trapped air mass varies with air density
Backflows of exhaust also occur with throttling,affecting trapped air mass
p adjusted in part with throttle position
Because A/F ratio is fixed (~14.7:1) forstoichiometric operation with gasoline, the
fuel delivery scales with the mass of airtrapped in the cylinder
Throttling is undesirable because of pumpinglosses at part load operation.
new-car365.blogspot.com
Pambient Pintake
p
RT=p= pambient - pintake
mair
mair
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Chapter 1.5: Impact of IC Engines on Society
U.S. Energy and Petroleum Consumption Trends
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U.S. Energy Information Administration/Annual Energy Review 2009
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Atmospheric Issues Facing Society
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Problematic Emissions Oxides of Nitrogen and Sulfur (NOx/SOx) Carbon Monoxide (CO) Unburned Hydrocarbons (UHC) Particulate Matter (PM)
Acid Rain, Smog and Tropospheric O3 Acidification of lakes and soil damage
Forest die-back
Greenhouse Gases (CO2/N2O/CH4)
Inevitable result of burning fossil fuels Can only be restricted by reducing fuel
consumption
Cannot sell cars unless they meet
emissions regulations!
Foust (2007)
UM (2005)
Acid Rain
HC + NO + hn
= SMOG
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Automotive Emission Regulation Trends
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UNITED STATES, FEDERAL
(g/mi)
Regulation Year HC CO NOx PM1970 4.1 341973 3.0 28 3.11975 1.5 15 3.1
1981 0.41 3.4 1.0Tier I (g) 1994 0.25 3.4 0.4 0.08Tier I (d) 1994 0.25 3.4 1.0 0.08Tier II, Bin 8 2009 0.143 4.2 0.20 0.02Tier II, Bin 5 2009 0.108 4.2 0.07 0.01Tier II, Bin 1 2009 0 0 0 0
EUROPE(g/km)HC+NOx CO NOx PM
Euro II 1996 0.90 0.1Euro III 2000 0.56 0.64 0.5 0.05
Euro IV 2005 0.30 0.50 0.25 0.025Euro V 2008 0.25 0.50 0.2 0.005
Source www.epa.gov
Exhaust Emission Certification Standards: Federal Test Procedure: Passenger Cars
Tier II Emissions
Vehicles can be made withemissions over a range of
bins, however, themanufacturers fleet
conform to an averagelevel (around Bin 5)
Europe NOx limitsare about 6x theUS limits. More
conscience about
greenhousegases, hence fuel
economy
Normalized numbers and approach are similar to passenger cars
EPA Heavy-Duty Engine Emissions Standards
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Detroit Diesel's Series 60 Heavy-Duty Diesel Engine (2007)
Continuous variation ofspeeds and loads to
mimic operating cycle
* Transient tests were met, butengine calibration shifted duringoperation at steady-state points.
*
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Potter (2006), Diesel Technology Challenges & Opportunities for North America