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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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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


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


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


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.


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


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


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



CI (Diesel) Stratified Compression Non-Premixed Flame1

SIDI (late) Stratified Spark Premixed Flame

SIDI (early)NearlyHomogeneous



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



CI (Diesel) Stratified Compression Non-Premixed FlameSIDI (late) Stratified Spark Premixed Flame

SIDI (early)NearlyHomogeneous



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

mec 523

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