Powertrain & Calibration 101 John Bucknell DaimlerChrysler Powertrain Systems Engineering December...
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Transcript of Powertrain & Calibration 101 John Bucknell DaimlerChrysler Powertrain Systems Engineering December...
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