Powertrain & Powertrain & Calibration 101Calibration 101

John BucknellJohn Bucknell

DaimlerChrysler DaimlerChrysler

Powertrain Systems EngineeringPowertrain Systems Engineering

December 4, 2006December 4, 2006

Powertrain & Calibration Powertrain & Calibration TopicsTopics

BackgroundBackground Powertrain Powertrain

termsterms ThermodynamiThermodynami

cscs Mechanical Mechanical

DesignDesign CombustionCombustion

ArchitectureArchitecture Cylinder Filling Cylinder Filling

& Emptying& Emptying AerodynamicsAerodynamics

CalibrationCalibration Spark & FuelSpark & Fuel Transients & Transients &

DrivabilityDrivability

What is a Powertrain?What is a Powertrain?

Engine that converts thermal energy Engine that converts thermal energy to mechanical workto mechanical work Particularly, the architecture comprising Particularly, the architecture comprising

all the subsystems required to convert all the subsystems required to convert this energy to workthis energy to work

Sometimes extends to drivetrain, Sometimes extends to drivetrain, which connects powertrain to end-which connects powertrain to end-user of poweruser of power

Characteristics of Internal Characteristics of Internal Combustion Heat EnginesCombustion Heat Engines

High energy density of fuel leads to high High energy density of fuel leads to high power to weight ratio, especially when power to weight ratio, especially when combusting with atmospheric oxygencombusting with atmospheric oxygen

External combustion has losses due to External combustion has losses due to multiple inefficiencies (primarily heat loss multiple inefficiencies (primarily heat loss from condensing of working fluid), internal from condensing of working fluid), internal combustion has less inefficienciescombustion has less inefficiencies

Heat engines use working fluids which is the Heat engines use working fluids which is the simplest of all energy conversion methodssimplest of all energy conversion methods

Reciprocating Internal Reciprocating Internal Combustion Heat EnginesCombustion Heat Engines

CharacteristicsCharacteristics Slider-crank mechanism has high Slider-crank mechanism has high

mechanical efficiency (piston skirt rubbing mechanical efficiency (piston skirt rubbing is source of 50-60% of all firing friction)is source of 50-60% of all firing friction)

Piston-cylinder mechanism has high single-Piston-cylinder mechanism has high single-stage compression ratio capability – leads stage compression ratio capability – leads to high thermal efficiency capabilityto high thermal efficiency capability

Fair to poor air pump, limiting power Fair to poor air pump, limiting power potential without additional mechanismspotential without additional mechanisms

Reciprocating Engine Reciprocating Engine TermsTermsVVcc = Clearance Volume = Clearance Volume

VVdd = Displacement or Swept = Displacement or Swept VolumeVolume

VVtt = Total Volume = Total Volume

TC or TDCTC or TDC = =

Top or Top Dead Center Top or Top Dead Center PositionPosition

BC or BDCBC or BDC = =

Bottom or Bottom Dead Center Bottom or Bottom Dead Center PositionPosition

Compression Ratio (CR)Compression Ratio (CR)c

cd

VVV

CR

Further explanation of aspects of Compression Ratio

Reciprocating Reciprocating EnginesEngines Most layouts Most layouts

created during created during second World War second World War as aircraft as aircraft manufacturers manufacturers struggled to make struggled to make the least-the least-compromised compromised installationinstallation

ThermodynamicsThermodynamics

Otto CycleOtto Cycle Diesel CycleDiesel Cycle Throttled CycleThrottled Cycle Supercharged Supercharged

CycleCycle

Source: Internal Comb. Engine Fund.

Thermodynamic TermsThermodynamic TermsMEPMEP – Mean Effective Pressure– Mean Effective Pressure Average cylinder pressure over measuring Average cylinder pressure over measuring

periodperiod Torque Normalized to Engine Displacement (VTorque Normalized to Engine Displacement (VDD))BMEPBMEP – Brake Mean Effective Pressure – Brake Mean Effective Pressure

IMEPIMEP – Indicated Mean Effective Pressure – Indicated Mean Effective PressureMEP of Compression and Expansion StrokesMEP of Compression and Expansion Strokes

PMEPPMEP – Pumping Mean Effective Pressure – Pumping Mean Effective PressureMEP of Exhaust and Intake StrokesMEP of Exhaust and Intake Strokes

FFMEPFFMEP – Firing Friction Mean Effective Pressure – Firing Friction Mean Effective Pressure

BMEP = IMEP – PMEP – FFMEPBMEP = IMEP – PMEP – FFMEP

)liter(V)Nm(Torque4

)kPa(BMEPD

.)in.cu(V

)ftlb(Torque48)psi(BMEP

D

Thermodynamic Terms continuedThermodynamic Terms continued

WorkWork = =

PowerPower = Work/Unit Time = Work/Unit Time

Specific PowerSpecific Power – Power per unit, – Power per unit, typically displacement or weighttypically displacement or weight

Pressure/Volume DiagramPressure/Volume Diagram –– Engineering tool to graph cylinder Engineering tool to graph cylinder pressurepressure

dVP

Cycle/volutionsReSecond/CyclesWork

Power

Indicated WorkIndicated Work

TDC BDC

Source: Design and Sim of Four Strokes

TDC BDC

Source: Design and Sim of Four Strokes

Pumping WorkPumping Work

History of Internal History of Internal CombustionCombustion

1878 Niklaus Otto 1878 Niklaus Otto built first successful built first successful four stroke enginefour stroke engine

1885 Gottlieb Daimler 1885 Gottlieb Daimler built first high-speed built first high-speed four stroke enginefour stroke engine

1878 saw Sir Dougald 1878 saw Sir Dougald Clerk complete first Clerk complete first two-stroke engine two-stroke engine (simplified by Joseph (simplified by Joseph Day in 1891)Day in 1891)

1891 Panhard-Levassor vehicle with front engine built

under Daimler license

Energy Distribution in Passenger Car Engines

Source: SAE 2000-01-2902 (Ricardo)

Source: Advanced Engine

Technology

Using Exhaust EnergyUsing Exhaust Energy

Highest expansion Highest expansion ratio recovers most ratio recovers most thermal energythermal energy

Turbines can Turbines can recover heat energy recover heat energy left over from gas left over from gas exchangeexchange Energy can be used Energy can be used

to drive turbo-to drive turbo-compressor or fed compressor or fed back into crank trainback into crank train

Source: Internal Comb. Engine Fund.

SupercharginSuperchargingg Increases specific Increases specific

output by increasing output by increasing charge density into charge density into reciprocatorreciprocator

Many methods of Many methods of implementation, cost implementation, cost usually only limiting usually only limiting factorfactor

Mechanical DesignMechanical Design

Two Valve ValvetrainTwo Valve Valvetrain

Pushrod OHV (Type Pushrod OHV (Type 5)5)

HEMI 2-Valve (Type HEMI 2-Valve (Type 5)5)

SOHC 2-Valve (Type SOHC 2-Valve (Type 2)2)

Four Valve ValvetrainFour Valve Valvetrain

SOHC 4-Valve (Type 3)SOHC 4-Valve (Type 3)DOHC 4-Valve (Type 2)DOHC 4-Valve (Type 2)

DOHC 4-Valve (Type 1)DOHC 4-Valve (Type 1)DesmodromiDesmodromicc

Specific Power = Specific Power = f(Air Flow, Thermal Efficiency)f(Air Flow, Thermal Efficiency) Air flow is an easier variable Air flow is an easier variable

to change than thermal to change than thermal efficiencyefficiency

90% of restriction of induction 90% of restriction of induction system occurs in cylinder system occurs in cylinder headhead

Cylinder head layouts that Cylinder head layouts that allow the greatest airflow will allow the greatest airflow will have highest specific power have highest specific power potentialpotential

Peak flow from poppet valve Peak flow from poppet valve engines primarily a function of engines primarily a function of total valve areatotal valve area

More/larger valves equals More/larger valves equals greater valve areagreater valve area

ValvetrainValvetrain

Combustion TermsCombustion Terms Brake PowerBrake Power – Power measured by the – Power measured by the

absorber (brake) at the crankshaftabsorber (brake) at the crankshaft BSFCBSFC - Brake Specific Fuel Consumption - Brake Specific Fuel Consumption

Fuel Mass Flow Rate / Brake Fuel Mass Flow Rate / Brake PowerPower grams/kW-h or lbs/hp-grams/kW-h or lbs/hp-hh

LBT FuellingLBT Fuelling - Lean Best Torque - Lean Best Torque Leanest Fuel/Air to Achieve Best TorqueLeanest Fuel/Air to Achieve Best Torque

LBT = 0.0780-0.0800 FA or 0.85-0.9 LambdaLBT = 0.0780-0.0800 FA or 0.85-0.9 Lambda Thermal EnrichmentThermal Enrichment – Fuel added for cooling – Fuel added for cooling

due to component temperature limitdue to component temperature limit Injector Pulse WidthInjector Pulse Width - Time Injector is Open - Time Injector is Open

Combustion Terms Combustion Terms continuedcontinued

Spark AdvanceSpark Advance – – Timing in crank degrees prior to Timing in crank degrees prior to TDC for start of combustion event (ignition)TDC for start of combustion event (ignition)

MBT SparkMBT Spark – Maximum Brake Torque Spark – Maximum Brake Torque Spark Minimum Spark Advance to Achieve Minimum Spark Advance to Achieve Best TorqueBest Torque

Burn RateBurn Rate – Speed of Combustion – Speed of Combustion Expressed as a fraction of total heat released versus Expressed as a fraction of total heat released versus crank degreescrank degrees

MAPMAP - Manifold Absolute Pressure - Manifold Absolute Pressure Absolute not Gauge (does not reference barometer)Absolute not Gauge (does not reference barometer)

Combustion Terms Combustion Terms continuedcontinued

KnockKnock – Autoignition of end-gasses in combustion – Autoignition of end-gasses in combustion chamber, causing extreme rates of pressure rise. chamber, causing extreme rates of pressure rise.

Knock Limit SparkKnock Limit Spark - - Maximum Spark Allowed due Maximum Spark Allowed due to Knock – can be higher or lower than MBTto Knock – can be higher or lower than MBT

Pre-IgnitionPre-Ignition – – Autoignition of mixture prior to Autoignition of mixture prior to spark timing, typically due to high temperatures of spark timing, typically due to high temperatures of componentscomponents

Combustion Stability Combustion Stability – – Cycle to cycle variation in Cycle to cycle variation in burn rate, trapped mass, location of peak pressure, burn rate, trapped mass, location of peak pressure, etc. The lower the variation the better the stability.etc. The lower the variation the better the stability.

Engine Architecture Engine Architecture Influence on PerformanceInfluence on Performance

Intake & Exhaust Manifold TuningIntake & Exhaust Manifold Tuning Cylinder Filling & EmptyingCylinder Filling & Emptying

MomentumMomentum Pressure WavePressure Wave

AerodynamicsAerodynamics Flow SeparationFlow Separation Wall FrictionWall Friction Junctions & BendsJunctions & Bends

Induction RestrictionInduction Restriction Exhaust Restriction (Backpressure)Exhaust Restriction (Backpressure) Compression RatioCompression Ratio Valve EventsValve Events

Intake Tuning Intake Tuning for WOT Performancefor WOT Performance

Intake manifolds have ducts (“runners”) Intake manifolds have ducts (“runners”) that tune at frequencies corresponding that tune at frequencies corresponding to engine speed, like an organ pipeto engine speed, like an organ pipe Longer runners tune at lower frequenciesLonger runners tune at lower frequencies Shorter runners tune at higher frequenciesShorter runners tune at higher frequencies

Tuning increases local pressure at intake Tuning increases local pressure at intake valve thereby increasing flow ratevalve thereby increasing flow rate

Duct diameter is a trade-off between Duct diameter is a trade-off between velocity and wall friction of passing velocity and wall friction of passing chargecharge

Exhaust Tuning Exhaust Tuning for WOT Performancefor WOT Performance

Exhaust manifolds tune just as intake Exhaust manifolds tune just as intake manifolds do, but since no fresh charge manifolds do, but since no fresh charge is being introduced as a result – not as is being introduced as a result – not as much impact on volumetric efficiency much impact on volumetric efficiency (~8% maximum for headers)(~8% maximum for headers)

Catalyst performance usually limits Catalyst performance usually limits production exhaust systems that flow production exhaust systems that flow acceptably with little to no tuningacceptably with little to no tuning

Tuned HeadersTuned HeadersTuned Headers generally do not appear on production engines due to the impairment to catalyst light-off performance (usually a minimum of 150% additional distance for cold-start exhaust heat to be lost). Performance can be enhanced by 3-8% across 60% of the operating range.

WOT IMEP Exhaust Manifold Comparison4-2-1 Tubular Header vs 4-1 Close Coupled Cast

1000

1050

1100

1150

1200

1250

1300

1350

1400

1450

1500

Engine Speed (rpm)

IME

P (

kPa)

/PM

EP

(kP

a)

-150

-135

-120

-105

-90

-75

-60

-45

-30

-15

0

IMEP 4-2-1 1044.1 1122.8 1188.5 1226.6 1269.2 1290.5 1337.9 1390.1 1445.7 1427 1445.8 1435.4 1411.7 1337.9

IMEP 4-1 Cast 1102.5 1162.2 1225.5 1252.3 1248 1262.4 1320.9 1403.6 1403.5 1406.3 1398 1367.2 1294.6

PMEP 4-2-1 -5.3 -9.7 -14.2 -19.7 -23.0 -29.9 -38.4 -52.3 -64.0 -78.5 -90.8 -107.9 -122.8 -136.2

PMEP 4-1 Cast -12.5 -16.8 -20.8 -26.1 -32.0 -40.3 -54.0 -68.6 -81.0 -89.0 -99.8 -111.5 -119.5

1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400

Momentum EffectsMomentum Effects Pressure loss influences dictate that duct Pressure loss influences dictate that duct

diameter be as large as possible for minimum diameter be as large as possible for minimum frictionfriction

Increasing charge momentum enhances Increasing charge momentum enhances cylinder filling by extending induction cylinder filling by extending induction process past unsteady direct energy transfer process past unsteady direct energy transfer of induction stroke (ie piston motion)of induction stroke (ie piston motion)

Decreasing duct diameter increases available Decreasing duct diameter increases available kinetic energy for a given mass fluxkinetic energy for a given mass flux

Therefore duct diameter is a trade-off Therefore duct diameter is a trade-off between velocity and wall friction of passing between velocity and wall friction of passing chargecharge

Pressure Wave EffectsPressure Wave Effects Induction process and exhaust blowdown Induction process and exhaust blowdown

both cause pressure pulsationsboth cause pressure pulsations Abrupt changes of increased cross-Abrupt changes of increased cross-

section in the path of a pressure wave section in the path of a pressure wave will reflect a wave of opposite magnitude will reflect a wave of opposite magnitude back down the path of the waveback down the path of the wave

Closed-ended ducts reflect pressure Closed-ended ducts reflect pressure waves directly, therefore a wave will waves directly, therefore a wave will echo with same amplitudeecho with same amplitude

Pressure Wave Effects con’tPressure Wave Effects con’t Friction decreases energy of pressure Friction decreases energy of pressure

waves, therefore the 1waves, therefore the 1stst order order reflection is the strongest – but up to reflection is the strongest – but up to 55thth order have been utilized to good order have been utilized to good effect in high speed engines (thus effect in high speed engines (thus active runners in F1 in Y2K)active runners in F1 in Y2K)

Plenums also resonate and through Plenums also resonate and through superposition increase the amplitude superposition increase the amplitude of pressure waves in runners – small of pressure waves in runners – small impact relative to runner geometryimpact relative to runner geometry

Effects of Intake Runner Effects of Intake Runner Geometry Geometry

Tuning in Production I4 Tuning in Production I4 EngineEngine

350

370

390

410

430

450

470

Engine Speed (rpm)

Air

Mas

s p

er C

ylin

der

(m

g)

Trapped Mass 372 381 373 421 428 402 397 430 454 453 458 460 431 401

1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400

AerodynamicsAerodynamics Losses due to poor aerodynamics can Losses due to poor aerodynamics can

be equal in magnitude to the gains be equal in magnitude to the gains from pressure wave tuningfrom pressure wave tuning

Often the dominant factory in poorly Often the dominant factory in poorly performing OE componentsperforming OE components

If properly designed, flow of a single-If properly designed, flow of a single-entry intake manifold can approach entry intake manifold can approach 98% of an ideal entrance on a 98% of an ideal entrance on a cylinder head port (steady state on a cylinder head port (steady state on a flow bench)flow bench)

Aerodynamics con’tAerodynamics con’t Flow SeparationFlow Separation

Literally same phenomenon as stall in Literally same phenomenon as stall in wing elements – pressure in free stream wing elements – pressure in free stream insufficient to ‘push’ flow along wall of insufficient to ‘push’ flow along wall of short side radiusshort side radius

Recirculation pushes flow away from Recirculation pushes flow away from wall, thereby reducing effective cross-wall, thereby reducing effective cross-section: so-called “vena contracta”section: so-called “vena contracta”

Simple guidelines can prevent flow Simple guidelines can prevent flow separation in ducts – studies performed separation in ducts – studies performed by NACA in the 1930s empirically by NACA in the 1930s empirically established the best duct configurationsestablished the best duct configurations

Aerodynamics con’tAerodynamics con’t Wall FrictionWall Friction

Surface finish of ducts need to be as Surface finish of ducts need to be as smooth as possible to prevent ‘tripping’ smooth as possible to prevent ‘tripping’ of flow on a macro levelof flow on a macro level

Junctions & BendsJunctions & Bends Everything from your fluid dynamics Everything from your fluid dynamics

textbook applies textbook applies Radiused inlets and free-standing pipe Radiused inlets and free-standing pipe

outletsoutlets Minimize number of bendsMinimize number of bends Avoid ‘S’ bends if at all possibleAvoid ‘S’ bends if at all possible

Induction RestrictionInduction Restriction

Air cleaner and intake manifolds Air cleaner and intake manifolds provide some resistance to incoming provide some resistance to incoming chargecharge

Power loss related to restriction Power loss related to restriction almost directly a function of ratio almost directly a function of ratio between manifold pressure (plenum between manifold pressure (plenum pressure upstream of runners) and pressure upstream of runners) and atmosphericatmospheric

Exhaust RestrictionExhaust RestrictionBack Pressure Effects on Peak Power - 2.0L SOHC R/T

145

146

147

148

149

150

151

152

0 2 4 6 8 10 12 14 16

Back Pressure (in-Hg)

Cor

rect

ed P

ower

(c

Bhp

)

Peak Power Back Bhp

Compression RatioCompression Ratio

The highest possible compression ratio is The highest possible compression ratio is always the design point, as higher will always always the design point, as higher will always be more thermally efficient with better idle be more thermally efficient with better idle qualityquality

Knock limits compression ratio because of Knock limits compression ratio because of combustion stability issues at low engine combustion stability issues at low engine speed due to necessary spark retardspeed due to necessary spark retard

Most engines are designed with higher Most engines are designed with higher compression than is best for low speed compression than is best for low speed combustion stability because of the associated combustion stability because of the associated part-load BSFC benefits and high speed powerpart-load BSFC benefits and high speed power

Valve EventsValve Events

Valve events define how an engine Valve events define how an engine breathes all the time, and so are an breathes all the time, and so are an important aspect of low load as well as important aspect of low load as well as high load performancehigh load performance

Valve events also effectively define Valve events also effectively define compression & expansion ratio, as compression & expansion ratio, as “compression” will not begin until the “compression” will not begin until the piston-cylinder mechanism is sealed – piston-cylinder mechanism is sealed – same with expansionsame with expansion

Valve Event Valve Event Timing Timing

DiagramDiagram Spider PlotSpider Plot - -

Describes timing Describes timing points for valve points for valve events with respect events with respect to Crank Positionto Crank Position

Cam CenterlineCam Centerline - - Peak Valve Lift with Peak Valve Lift with respect to TDC in respect to TDC in Crank DegreesCrank Degrees

Valve Events for PowerValve Events for Power Maximize Trapping EfficiencyMaximize Trapping Efficiency

Intake closing that is best compromise between Intake closing that is best compromise between compression stroke back flow and induction momentum compression stroke back flow and induction momentum (retard with increasing engine speed)(retard with increasing engine speed)

Early intake closing usefulness limited at low engine Early intake closing usefulness limited at low engine speed due to knock limitspeed due to knock limit

Early intake opening will impart some exhaust Early intake opening will impart some exhaust blowdown or pressure wave tuning momentum to blowdown or pressure wave tuning momentum to intake charge intake charge

Maximize Thermal EfficiencyMaximize Thermal Efficiency Earliest intake closing to maximize compression ratio Earliest intake closing to maximize compression ratio

for best burn rate (optimum is instantaneous after TDC)for best burn rate (optimum is instantaneous after TDC) Latest exhaust opening to maximize expansion ratio for Latest exhaust opening to maximize expansion ratio for

best use of heat energy and lowest EGT (least thermal best use of heat energy and lowest EGT (least thermal protection enrichment beyond LBT)protection enrichment beyond LBT)

Valve Events for PowerValve Events for Power Minimize Flow LossMinimize Flow Loss

Achieve maximum valve lift (max flow usually at Achieve maximum valve lift (max flow usually at L/D > 0.25-0.3) as long as possible (square lift L/D > 0.25-0.3) as long as possible (square lift curves are optimum for poppet valves)curves are optimum for poppet valves)

Minimize Exhaust Pumping WorkMinimize Exhaust Pumping Work Earliest exhaust opening that blows down Earliest exhaust opening that blows down

cylinder pressure to backpressure levels before cylinder pressure to backpressure levels before exhaust stroke (advance with increasing engine exhaust stroke (advance with increasing engine speed)speed)

Earliest exhaust closing that avoids Earliest exhaust closing that avoids recompression spike (retard with increasing recompression spike (retard with increasing engine speed)engine speed)

Centerline Effects On Torque

420

430

440

450

460

470

480

490

500

510

520

530

540

550

560

570

1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600

Engine Speed (rpm)

Tor

que

(ft-

lbs)

115 degree centerline 120 degree centerline 124 degree centerline

10

20

30

40

50

60

70

80

90

100

110120

240

250

250

275

275

300

300

350

400450500

600 700

1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400

d Speed [rpm]

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

BM

EP

SI

[ kP

a]

2006 2.4L WE BSFC MAP (g/kW-h) Engine Power and BSFC vs Engine Speed

SummarySummary Component’s Relative Impact on Component’s Relative Impact on

PerformancePerformance1.1. Cylinder Head Ports & Valve AreaCylinder Head Ports & Valve Area2.2. Valve EventsValve Events3.3. Intake Manifold Runner GeometryIntake Manifold Runner Geometry4.4. Compression RatioCompression Ratio5.5. Exhaust Header GeometryExhaust Header Geometry6.6. Exhaust RestrictionExhaust Restriction7.7. Air Cleaner RestrictionAir Cleaner Restriction

Powertrain Closing RemarksPowertrain Closing Remarks Powertrain is compromisePowertrain is compromise

Four-stroke engines are volumetric flow rate Four-stroke engines are volumetric flow rate devices – the only route to more power is devices – the only route to more power is increased engine speed, more valve area or increased engine speed, more valve area or increased charge densityincreased charge density

More speed, charge density or valve area are More speed, charge density or valve area are expensive or difficult to develop – therefore expensive or difficult to develop – therefore minimizing losses is the most efficient path minimizing losses is the most efficient path within existing engine architectureswithin existing engine architectures

Highest average power during a vehicle Highest average power during a vehicle acceleration is fastest – peak power values don’t acceleration is fastest – peak power values don’t win raceswin races

BreakBreak

CalibrationCalibration What is it?What is it?

Optimizing the control system (once hardware is Optimizing the control system (once hardware is finalized) for drivability, durability & emissionsfinalized) for drivability, durability & emissions

It’s just spark and fuel – how hard could it It’s just spark and fuel – how hard could it be?be? Knowledge of Thermodynamics, Combustion and Knowledge of Thermodynamics, Combustion and

Control Theory all play inControl Theory all play in Fortunately race engines have no emissions Fortunately race engines have no emissions

constraints and use race fuel (usually eliminates constraints and use race fuel (usually eliminates any knock) – therefore are relatively easy to any knock) – therefore are relatively easy to calibratecalibrate

Calibration TermsCalibration Terms StoichiometryStoichiometry – Chemically correct ratio of fuel – Chemically correct ratio of fuel

to air for combustionto air for combustion F/A F/A – Fuel/Air Ratio– Fuel/Air Ratio

Mass ratio of mixture, a determination of Mass ratio of mixture, a determination of richness or leanness. richness or leanness. Stoichiometry = 0.0688-Stoichiometry = 0.0688-0.0696 FA0.0696 FA

LambdaLambda – Excess Air Ratio – Excess Air RatioStoichiometry = 1.0 LambdaStoichiometry = 1.0 Lambda

Rich F/ARich F/A – F/A greater than Stoichiometry – F/A greater than StoichiometryRich < 1.0 LambdaRich < 1.0 Lambda

Lean F/ALean F/A – F/A less than Stoichiometry – F/A less than StoichiometryLean > 1.0 LambdaLean > 1.0 Lambda

Calibration Terms continuedCalibration Terms continued Brake PowerBrake Power – Power measured by the – Power measured by the

absorber (brake) at the crankshaftabsorber (brake) at the crankshaft BSFCBSFC - Brake Specific Fuel Consumption - Brake Specific Fuel Consumption

Fuel Mass Flow Rate / Brake Fuel Mass Flow Rate / Brake PowerPower grams/kW-h or lbs/hp-grams/kW-h or lbs/hp-hh

LBT FuellingLBT Fuelling – Lean Best Torque – Lean Best Torque Leanest Fuel/Air to Achieve Best TorqueLeanest Fuel/Air to Achieve Best Torque

LBT = 0.0780-0.0800 FA or 0.85-0.9 LambdaLBT = 0.0780-0.0800 FA or 0.85-0.9 Lambda Thermal EnrichmentThermal Enrichment – Fuel added for cooling – Fuel added for cooling

due to exhaust component temperature limitdue to exhaust component temperature limit Injector Pulse WidthInjector Pulse Width - Time Injector is Open - Time Injector is Open

Calibration Terms continuedCalibration Terms continued

Spark AdvanceSpark Advance – – Timing in crank degrees prior to Timing in crank degrees prior to TDC for start of combustion event (ignition)TDC for start of combustion event (ignition)

MBT SparkMBT Spark - Maximum Brake Torque - Maximum Brake Torque Minimum Spark Advance to Achieve Best Minimum Spark Advance to Achieve Best TorqueTorque

Burn RateBurn Rate – Speed of Combustion – Speed of Combustion Expressed as a fraction of total heat released versus Expressed as a fraction of total heat released versus crank degreescrank degrees

MAPMAP - Manifold Absolute Pressure - Manifold Absolute Pressure Absolute not Gauge (which references barometer)Absolute not Gauge (which references barometer)

Lean Best Torque Fuel Air Sweeps

76%

78%

80%

82%

84%

86%

88%

90%

92%

94%

96%

98%

100%

102%

0.0660 0.0690 0.0720 0.0750 0.0780 0.0810 0.0840 0.0870 0.0900 0.0930 0.0960 0.0990 0.1020 0.1050 0.1080 0.1110

F/A FN

To

rqu

e D

elta

Fac

tor

Fro

m L

BT

1856 RPM, 70 kPa MAP 3296 RPM, 98 kPa MAP 3296 RPM, 56 kPa MAP 3296 RPM, 84 kPa MAP

4544 RPM, 70 kPa MAP 3296 RPM, 98 kPa MAP 2688 RPM, 70 kPa MAP

Spark Held Constant During Fuel A ir Sw eep

Spark Advance vs Torque

84%

86%

88%

90%

92%

94%

96%

98%

100%

102%

-22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12

Delta Spark Advance From MBT

To

rqu

e D

elta

fro

m M

BT

Control System TypesControl System Types Alpha-NAlpha-N

Engine Speed & Throttle AngleEngine Speed & Throttle Angle Speed-DensitySpeed-Density

Engine Speed and MAP/ACTEngine Speed and MAP/ACT MAFMAF

Engine Speed and MAFEngine Speed and MAF

Alpha-NAlpha-N Fuel and spark maps are based on Fuel and spark maps are based on

throttle angle – which is very non-throttle angle – which is very non-linear and requires complete linear and requires complete mapping of engine mapping of engine Good throttle response once dialed inGood throttle response once dialed in Density compensation (altitude and Density compensation (altitude and

temperature) is usually absent – needs temperature) is usually absent – needs to be recalibrated every time car goes to be recalibrated every time car goes outout

Speed-DensitySpeed-Density Fuel and spark maps are based on MAP – Fuel and spark maps are based on MAP –

density of charge is a strong function of density of charge is a strong function of pressure, corrected by air temp and coolant pressure, corrected by air temp and coolant temp therefore air flow is simple to temp therefore air flow is simple to calculatecalculate Less time-intensive than Alpha-N, once Less time-intensive than Alpha-N, once

calibrated is good – most common type of calibrated is good – most common type of controlcontrol

Needs less mapping – can do WOT line and mid-Needs less mapping – can do WOT line and mid-map then curve-fit air flow (spark needs a little map then curve-fit air flow (spark needs a little more in-depth for optimal control)more in-depth for optimal control)

MAFMAF Fuel and spark maps are based on MAF – Fuel and spark maps are based on MAF –

airflow measured directlyairflow measured directly MAF sensor isn’t the most robust deviceMAF sensor isn’t the most robust device

Pressure pulses confuse signal, each application has Pressure pulses confuse signal, each application has to be mapped with secondary damped MAF sensor to be mapped with secondary damped MAF sensor (usually a 55 gallon drum inline)(usually a 55 gallon drum inline)

Least noisy signal is usually at air cleaner – so Least noisy signal is usually at air cleaner – so separate transport delay controls need to be separate transport delay controls need to be calibrated for transients and leaks need to be calibrated for transients and leaks need to be absolutely eliminatedabsolutely eliminated

Boosted applications usually add a MAP as wellBoosted applications usually add a MAP as well

Control System Control System ComponentsComponents

Fuel SystemFuel System Injectors, Fuel pump & RegulatorInjectors, Fuel pump & Regulator

Basic SensorsBasic Sensors Manifold Absolute Pressure (MAP) or Mass Manifold Absolute Pressure (MAP) or Mass

Air Flow (MAF)Air Flow (MAF) Crank Position (Rpm & TDC)Crank Position (Rpm & TDC) Cam Position (Sync)Cam Position (Sync) Air Charge Temp (ACT)Air Charge Temp (ACT) Engine Coolant Temp (ECT)Engine Coolant Temp (ECT) Knock SensorKnock Sensor Lamda SensorLamda Sensor

Fuel SystemFuel System InjectorsInjectors

Volumetric flow rate solenoids, linear relationship Volumetric flow rate solenoids, linear relationship between pulsewidth and flow for given pressure between pulsewidth and flow for given pressure deltadelta

Battery offset is time necessary to open and close Battery offset is time necessary to open and close solenoid – time is fixed for any voltagesolenoid – time is fixed for any voltage

Duty cycle is injector on time – it’ll go static above Duty cycle is injector on time – it’ll go static above 95%95%

Bernoulli relationship for different pressure deltas – Bernoulli relationship for different pressure deltas – allowing differing flow rates for a given injectorallowing differing flow rates for a given injector

High impedance injectors have lower dynamic range High impedance injectors have lower dynamic range and lower amperage and thus less heat in controllerand lower amperage and thus less heat in controller

Fuel Pump & RegulatorFuel Pump & Regulator Pressure needs to be sufficiently high to prevent Pressure needs to be sufficiently high to prevent

vapour lock (>4bar) and low enough that engine can vapour lock (>4bar) and low enough that engine can idleidle

In-tank regulation adds least heat but has line-loss In-tank regulation adds least heat but has line-loss as flow rate increases, ie fuel pressure changes with as flow rate increases, ie fuel pressure changes with flowflow

Manifold-referenced regulation can help injectors Manifold-referenced regulation can help injectors achieve higher flow rates at elevated boost or lower achieve higher flow rates at elevated boost or lower flows at low vacuum – making calibration more flows at low vacuum – making calibration more complicatedcomplicated

1

2

1

2

P

P

V

V

Bernoulli Effect of Fuel Pressure

Pulsewidth

Pulsewidth + Battery Offset

Pin

tle H

eigh

t

SensorsSensors Manifold Absolute Pressure (MAP)Manifold Absolute Pressure (MAP)

A variable-resistance diaphragm with perfect vacuum on A variable-resistance diaphragm with perfect vacuum on one side and manifold pressure on otherone side and manifold pressure on other

Mass Air Flow (MAF)Mass Air Flow (MAF) A heating element followed by a temperature-sensitive A heating element followed by a temperature-sensitive

element. Heated element is maintained at a constant element. Heated element is maintained at a constant temperature and based upon the measured downstream temperature and based upon the measured downstream temperature the mass flow rate can be determinedtemperature the mass flow rate can be determined

Crank PositionCrank Position High resolution for spark advance, less-so for crank speed High resolution for spark advance, less-so for crank speed

and with once-per-rev can indicate TDCand with once-per-rev can indicate TDC Cam PositionCam Position

Low resolution for syncronization for sequential fuel Low resolution for syncronization for sequential fuel injection and individual cylinder sparkinjection and individual cylinder spark

Air Charge Temp and Engine Coolant TempAir Charge Temp and Engine Coolant Temp Thermistors used for air density correction and startup Thermistors used for air density correction and startup

enrichmentenrichment

Sensors, contSensors, cont Knock SensorKnock Sensor

A piezoelectric load cell that measures structural A piezoelectric load cell that measures structural vibration. Knock is a pressure wave that travels at local vibration. Knock is a pressure wave that travels at local sonic velocity and ‘rings’ at a frequency that is a function sonic velocity and ‘rings’ at a frequency that is a function of bore diameter (typically between 14-18kHz). When of bore diameter (typically between 14-18kHz). When the structure of the engine (typically the block) is hit with the structure of the engine (typically the block) is hit with this pressure wave it rings as well, but at a frequency this pressure wave it rings as well, but at a frequency that is a function of the structure (ie materials and that is a function of the structure (ie materials and geometry). A FFT analysis of different mounting positions geometry). A FFT analysis of different mounting positions (nodes not anti-nodes) is necessary to determine the (nodes not anti-nodes) is necessary to determine the ‘center frequency’ to listen for knock (which is measured ‘center frequency’ to listen for knock (which is measured via in-cylinder pressure measurements) without picking via in-cylinder pressure measurements) without picking up other structure-borne noise.up other structure-borne noise.

Sensors, contSensors, cont Lamda Sensor (EGO)Lamda Sensor (EGO)

Compares ambient air to Compares ambient air to exhaust oxygen content exhaust oxygen content (partial pressure of (partial pressure of oxygen). Sensor output is oxygen). Sensor output is essentially binary (only essentially binary (only indicates rich or lean of indicates rich or lean of stoichiometry).stoichiometry).

Wide-band Lamda Sensor Wide-band Lamda Sensor (UEGO)(UEGO) Compares partial pressure Compares partial pressure

of oxygen (lean) and partial of oxygen (lean) and partial pressure of Hpressure of HmmCCnn, H, H22 & CO & CO (rich) with ambient. Gives (rich) with ambient. Gives output from ~0.6 to 2 output from ~0.6 to 2 Lamda.Lamda. UEGO Schematic

EGO Schematic

Calibration GoalsCalibration Goals Combustion & ThermodynamicsCombustion & Thermodynamics

Work, Power & Mean Effective PressuresWork, Power & Mean Effective Pressures Knock, Pre-IgnitionKnock, Pre-Ignition Burn RateBurn Rate

TransientsTransients Wall filmWall film

Thermal EnrichmentThermal Enrichment DrivabilityDrivability

KnockKnock Causes of KnockCauses of Knock

Knock = f(Time,Temperature,Pressure,Octane)Knock = f(Time,Temperature,Pressure,Octane) Time – Higher engine speeds or faster burn rates reduce Time – Higher engine speeds or faster burn rates reduce

knock tendency. Burn rate can come from multiple knock tendency. Burn rate can come from multiple spark sources, more compact combustion chambers or spark sources, more compact combustion chambers or increased turbulenceincreased turbulence

Temperature – Reduced combustion temperatures Temperature – Reduced combustion temperatures reduce knock through reduced charge temperatures reduce knock through reduced charge temperatures (cooler incoming charge or reduced residual burned (cooler incoming charge or reduced residual burned gases), increased evaporative cooling from richer F/A gases), increased evaporative cooling from richer F/A mixtures and increased combustion chamber coolingmixtures and increased combustion chamber cooling

Pressure – Lower cylinder pressures reduce knock Pressure – Lower cylinder pressures reduce knock tendency through lower compression ratio or MAP tendency through lower compression ratio or MAP pressurepressure

Octane – Different fuel types have higher or lower Octane – Different fuel types have higher or lower autoignition tendencies. Octane value is directly related autoignition tendencies. Octane value is directly related to knocking tendencyto knocking tendency

Knock continuedKnock continued Effects of KnockEffects of Knock

Disrupts stagnant gases that form boundary layer Disrupts stagnant gases that form boundary layer at edge of combustion chamber, increasing heat at edge of combustion chamber, increasing heat transfer to components and raising mean transfer to components and raising mean combustion chamber temp that can lead to pre-combustion chamber temp that can lead to pre-ignitionignition

Scours oil film off cylinder wall, leading to dry Scours oil film off cylinder wall, leading to dry friction and increased wear of piston ringsfriction and increased wear of piston rings

Shockwave can induce vibratory loads into piston Shockwave can induce vibratory loads into piston pin, piston pin bore and top land - reducing oil pin, piston pin bore and top land - reducing oil film thickness and accelerating wearfilm thickness and accelerating wear

Shockwave can be strong enough to stress Shockwave can be strong enough to stress components to failurecomponents to failure

In-cylinder Pressure In-cylinder Pressure MeasurementMeasurement

Piezoelectric pressure Piezoelectric pressure transducers develop transducers develop charge with changes charge with changes in pressurein pressure

Installed in Installed in combustion chamber combustion chamber wall or spark plug to wall or spark plug to measure full-cycle measure full-cycle pressurespressures

Typical pressure probe Typical pressure probe installationinstallation

Passage drilled through deck face (avoiding coolant jacket)Passage drilled through deck face (avoiding coolant jacket)

Cylinder Pressure Trace Cylinder Pressure Trace No KnockNo Knock

Cylinder Pressure Trace Cylinder Pressure Trace Knock Limit or Trace Knock - Best PowerKnock Limit or Trace Knock - Best Power

Cylinder Pressure TraceCylinder Pressure TraceSevere Damaging KnockSevere Damaging Knock

Pre-IgnitionPre-Ignition Effects of Pre-IgnitionEffects of Pre-Ignition

Increases peak cylinder pressure by beginning Increases peak cylinder pressure by beginning heat release too soonheat release too soon

Increased cylinder pressure also increases heat Increased cylinder pressure also increases heat load to combustion chamber components, load to combustion chamber components, sustaining the pre-ignition (leading to ‘run-sustaining the pre-ignition (leading to ‘run-away pre-ignition’)away pre-ignition’)

Increases loads on piston crown and piston pinIncreases loads on piston crown and piston pin Sustained pre-ignition will typically put a hole Sustained pre-ignition will typically put a hole

in the center of the piston crownin the center of the piston crown

Burn RateBurn Rate Burn Rate = Burn Rate = f(Spark, Dilution Rate/FA Ratio, Chamber Volume f(Spark, Dilution Rate/FA Ratio, Chamber Volume

Distribution, Engine Speed/Mixture Motion/Turbulent Intensity)Distribution, Engine Speed/Mixture Motion/Turbulent Intensity) SparkSpark

Closer to MBT the faster the burn with trace knock the fastestCloser to MBT the faster the burn with trace knock the fastest Dilution Rate/FA RatioDilution Rate/FA Ratio

Least dilution (exhaust residual or anything unburnable) fastestLeast dilution (exhaust residual or anything unburnable) fastest FA Ratio best rate around LBTFA Ratio best rate around LBT

Chamber Volume DistributionChamber Volume Distribution Smallest chamber with shortest flame path best (multiple ignition Smallest chamber with shortest flame path best (multiple ignition

sources shorten flame path)sources shorten flame path) Engine Speed/Mixture Motion/Turbulent IntensityEngine Speed/Mixture Motion/Turbulent Intensity

Crank angle time for complete burn nearly constant with increasing Crank angle time for complete burn nearly constant with increasing engine speed indicating other factors speeding burn rateengine speed indicating other factors speeding burn rate

Mixture motion-contributed angular momentum conserved as cylinder Mixture motion-contributed angular momentum conserved as cylinder volume decreases during compression stroke, eventually breaking down volume decreases during compression stroke, eventually breaking down into vortices around TDC increasing kinetic energy in chargeinto vortices around TDC increasing kinetic energy in charge

Turbulent Intensity a measure of total kinetic energy available to move Turbulent Intensity a measure of total kinetic energy available to move flame front faster than laminar flame speed. More Turbulent Intensity flame front faster than laminar flame speed. More Turbulent Intensity equals faster burn. equals faster burn.

Combustion & Combustion & Thermodynamics SummaryThermodynamics Summary

Peak Specific PowerPeak Specific Power LBT fuelling for best compromise between available LBT fuelling for best compromise between available

oxygen and charge densityoxygen and charge density MBT spark if possible, fast burn rate assumed at peak MBT spark if possible, fast burn rate assumed at peak

loadload Highest engine speed to allow highest compression ratioHighest engine speed to allow highest compression ratio Highest octaneHighest octane

Peak Thermal Efficiency at desired loadPeak Thermal Efficiency at desired load Highest compression ratio will have best combustion, Highest compression ratio will have best combustion,

usually with highest expansion ratio for best use of usually with highest expansion ratio for best use of thermal energythermal energy

MBT spark with fastest burn rateMBT spark with fastest burn rate 10% lean of stoichiometry will provide best compromise 10% lean of stoichiometry will provide best compromise

between heat losses and pumping work, but not used between heat losses and pumping work, but not used because of catalyst performance impacts in pass carsbecause of catalyst performance impacts in pass cars

Transient FuellingTransient Fuelling Liquid fuel does not burn, only fuel vapourLiquid fuel does not burn, only fuel vapour Heat from somewhere must be used to make vapour – Heat from somewhere must be used to make vapour –

which is why up to 500% more fuel must be used on a which is why up to 500% more fuel must be used on a cold start to provide sufficient vapour for engine to run cold start to provide sufficient vapour for engine to run (relationship between temperature and partial pressure (relationship between temperature and partial pressure of fuel fractions)of fuel fractions)

Most of heat during fully warm operation comes from Most of heat during fully warm operation comes from back side of intake valve and port wallsback side of intake valve and port walls Because of geometry a large portion of fuel wets wall – this film Because of geometry a large portion of fuel wets wall – this film

travels at some fraction of free stream. Therefore some fuel travels at some fraction of free stream. Therefore some fuel from every pulse goes into engine and some onto port wall.from every pulse goes into engine and some onto port wall.

On a fast acceleration, additional fuel must be added to offset On a fast acceleration, additional fuel must be added to offset the slowly moving wall film. Opposite true on decels.the slowly moving wall film. Opposite true on decels.

If injector is positioned far upstream volumetric efficiency If injector is positioned far upstream volumetric efficiency increases due fuel heat of vapourization cooling incoming increases due fuel heat of vapourization cooling incoming charge, but a large amount of wall is wetted – leading to poor charge, but a large amount of wall is wetted – leading to poor transient fuel controltransient fuel control

Injector TargetingInjector Targeting

Bad Tip Location

Targets Valve

Targets Port Wall

Better Tip Location

Thermal EnrichmentThermal Enrichment DurabilityDurability

Combustion temperatures can reach 4000 deg K Combustion temperatures can reach 4000 deg K and drop to 1800 deg K before Exhaust Valve and drop to 1800 deg K before Exhaust Valve Opening (EVO)Opening (EVO)

Materials must operate at sufficiently low Materials must operate at sufficiently low temperature to maintain strength, so Exhaust Gas temperature to maintain strength, so Exhaust Gas Temperature (EGT) limits must be adhered to for Temperature (EGT) limits must be adhered to for sufficient durabilitysufficient durability

Usually 950 deg C runner temperature is Usually 950 deg C runner temperature is acceptable for a developed package, as low as acceptable for a developed package, as low as 800 deg C for undeveloped components may be 800 deg C for undeveloped components may be necessarynecessary

Primary path for cooling is additional fuel beyond Primary path for cooling is additional fuel beyond LBT, as heat of vapourization cools the charge LBT, as heat of vapourization cools the charge before ignition (pressure-charged engines before ignition (pressure-charged engines primarily)primarily)

DrivabilityDrivability Throttle ResponseThrottle Response

Drivers expect some repeatability and Drivers expect some repeatability and resolution of thrust versus pedal position resolution of thrust versus pedal position – some degree of spark mapping – some degree of spark mapping (retard) and pedal to throttle cam can (retard) and pedal to throttle cam can help a driver’s confidencehelp a driver’s confidence

Usually least developed and of most Usually least developed and of most importance is tip-in (throttle closed to importance is tip-in (throttle closed to small opening) where torque can come small opening) where torque can come in as a step changein as a step change

Closing RemarksClosing Remarks Calibration is compromiseCalibration is compromise

Best spark for drivability may not Best spark for drivability may not produce sufficient combustion stability produce sufficient combustion stability or fuel consumptionor fuel consumption

Best fuelling for drivability is voracious Best fuelling for drivability is voracious fuel consumer - decel fuel shut off can fuel consumer - decel fuel shut off can improve economy by 20% but has tip-in improve economy by 20% but has tip-in torque bumps without careful calibrationtorque bumps without careful calibration

ReferencesReferences

Internal Combustion Engine Fundamentals, John B Internal Combustion Engine Fundamentals, John B Heywood, 1988 McGraw-HillHeywood, 1988 McGraw-Hill

The Design and Tuning of Competition Engines – The Design and Tuning of Competition Engines – Sixth Edition, Philip H Smith, 1977 Robert BentleySixth Edition, Philip H Smith, 1977 Robert Bentley

The Development of Piston Aero Engines, Bill The Development of Piston Aero Engines, Bill Gunston, 1993 Haynes PublishingGunston, 1993 Haynes Publishing

Design and Simulation of Four-Stroke Engines, Design and Simulation of Four-Stroke Engines, Gordon P. Blair, 1999 SAEGordon P. Blair, 1999 SAE

Advanced Engine Technology, Heinz Heisler, 1995 Advanced Engine Technology, Heinz Heisler, 1995 SAESAE

Vehicle and Engine Technology, Heinz Heisler, 1999 Vehicle and Engine Technology, Heinz Heisler, 1999 SAESAE

Q & AQ & A