Calibration 101 by Kim Lyon

7/30/2019 Calibration 101 by Kim Lyon

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Calibration 101Kim LyonFEV Inc. Senior Engineer

Calibration Specialist GM PowertrainChrysler LLC Senior Technical Specialist -Retired


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Acknowledgement

Many of the following slides were originallycreated by former Chrysler engineer, JohnBucknell and originally presented at theCollegiate Roadshow in 2006.


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Overview

Covers what you will need to know about thesystem to be calibrated

Wont cover knob turning which isdependent on the specifics of the controlsystem being used.

Topics are typical of questions encountered inDesign Judging of the engine/powertrain area.


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Calibration PhilosophyFundamentals

In order to calibrate anything, you must understandthe physics of the system.

In order to be a good calibration engineer one mustcultivate a sense of being a good engine -ear. Useall your senses to assess.

The system defines the calibration, not the calibrator.The system will tell you what it needs if you aresmart enough to listen.


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What Is An I.C. Engine?

The primary function of an internalcombustion engine is to pump air in and outof a combustion chamber where acombustible fuel is mixed at a ratio whichmaximizes power output and minimizes fuelconsumption under all operating conditions.

In a gas engine at full throttle, which is moredifficult to increase (control), air or fuel?


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Part One Engine Fundamentals


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Powertrain & Calibration Topics Background

Powertrain terms Thermodynamics Mechanical Design Combustion

Architecture Cylinder Filling &

Emptying Aerodynamics

Calibration Spark & Fuel Transients &

Drivability


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Reciprocating Engine TermsVc = Clearance VolumeVd = Displacement or Swept VolumeVt = Total VolumeTC or TDC=

Top or Top Dead Center PositionBC or BDC =Bottom or Bottom Dead CenterPosition

Compression Ratio (CR)

c

cd

V

V V CR


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Further Aspects of Geometric Compression Ratio


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Thermodynamics

Otto Cycle Diesel Cycle Throttled Cycle

SuperchargedCycle

Source: Internal Comb. Engine Fund.


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Thermodynamic TermsMEP Mean Effective Pressure Average cylinder pressure over measuring period Torque Normalized to Engine Displacement (V D)BMEP Brake Mean Effective Pressure

IMEP Indicated Mean Effective PressureMEP of Compression and Expansion Strokes

PMEP Pumping Mean Effective Pressure

MEP of Exhaust and Intake StrokesFMEP Firing Friction Mean Effective Pressure

BMEP = IMEP PMEP FMEP

)liter( V

)Nm(Torque4)kPa(BMEP

D

.)in.cu( V

)ftlb(Torque48)psi(BMEP

D


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Thermodynamic Terms continued

Work =

Power = Work/Unit Time

Specific Power Power per unit, typically

displacement or weightPressure/Volume Diagram Engineering tool to

graph cylinder pressure

dVP

Cycle /volutionsReSecond /CyclesWork

Power


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Indicated Work

TDC BDC

Source: Design and Sim of Four Strokes


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TDC BDC

Source: Design and Sim of Four Strokes

Pumping Work


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Engine Breathing Volumetric Efficiency (or V.E.) is how we describe the engines

ability to pump air.

Stated as a percentage of the theoretical volume of air thatthe engine can move for one cylinder cycle.

Well tuned engines (such as race engines) can exceed thetheoretical 100% limit because of boosting or tuning effects(aftercharging).


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Momentum Effects Pressure loss influences dictate that duct diameter be as large

as possible for minimum friction

Increasing charge momentum enhances cylinder filling byextending induction process past unsteady direct energytransfer of induction stroke

Decreasing duct diameter increases available kinetic energyfor a given mass flux

Therefore duct diameter is a trade-off between velocity andwall friction of passing charge


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Pressure Wave Effects Induction process and exhaust blowdown both cause pressure

pulsations

Abrupt changes of increased cross-section in the path of a

pressure wave will reflect a wave of opposite magnitude backdown the path of the wave

Closed-ended ducts reflect pressure waves directly, thereforea wave will echo with same amplitude


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Pressure Wave Effects cont Friction decreases energy of pressure waves, therefore the 1 st

order reflection is the strongest but up to 5 th order havebeen utilized to good effect in high speed engines (thus activerunners in F1)

Plenums also resonate and through superposition increasethe amplitude of pressure waves in runners small impactrelative to runner geometry


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Effects of Intake Runner Geometry


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Aerodynamics Losses due to poor aerodynamics can be equal in magnitude

to the gains from pressure wave tuning

Often the dominant factory in poorly performing OEcomponents

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


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Aerodynamics cont Flow Separation

Literally same phenomenon as stall in wing elements pressure in free stream insufficient to push flow alongwall of short side radius

Recirculation pushes flow away from wall, therebyreducing effective cross-section so- called venacontracta

Simple guidelines can prevent flow separation in ducts studies performed by NACA in the 1930s empiricallyestablished the best duct configurations


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Induction Restriction Air cleaner and intake manifolds provide some resistance to

incoming charge

Power loss related to restriction almost directly a function of

ratio between manifold pressure (plenum pressure upstreamof runners) and atmospheric


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Valve Events

Valve events define how an engine breathes all thetime, and so are an important aspect of low load aswell as high load performance

Valve events also effectively define compression &expansion ratio, as compression will not begin untilthe piston-cylinder mechanism is sealed same withexpansion. VVT can change the engines effectivecompression ratio as opposed to the geometriccompression ratio.


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Valve Event

Timing Spider Plot - Describes

timing points for valveevents with respect toCrank Position

Cam Centerline - PeakValve Lift with respect toTDC in Crank Degrees


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Valve Events for Power Maximize Trapping Efficiency

Intake closing that is best compromise between compressionstroke back flow and induction momentum (retard with increasingengine speed)

Early intake closing usefulness limited at low engine speed due toknock limit

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

Maximize Thermal Efficiency Earliest intake closing to maximize compression ratio for best burn

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

of heat energy and lowest EGT (least thermal protectionenrichment beyond LBT)


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Valve Events for Power

Minimize Flow Loss Achieve maximum valve lift (max flow usually at L/D >

0.25-0.3) as long as possible (square lift curves areoptimum for poppet valves)

Minimize Exhaust Pumping Work Earliest exhaust opening that blows down cylinder

pressure to backpressure levels before exhaust stroke

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

spike (retard with increasing engine speed )


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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

T o r q u e

( f t - l b s )

Engine Speed (rpm)

Centerline Effects On Torque

115 degree centerline 120 degree center line 124 degree centerline


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Combustion Terms

Open Brake Power Power measured by theabsorber (brake) at the crankshaft

BSFC - Brake Specific Fuel Consumption

Fuel Mass Flow Rate / Brake Powergrams/kW-h or lbs/hp-h

LBT Fueling - Lean Best TorqueLeanest Fuel/Air to Achieve Best Torque

LBT = 0.0780-0.0800 FA or 0.85-0.9 Lambda Thermal Enrichment Fuel added for cooling due to

component temperature limit Injector Pulse Width - Time Injector is on


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Source: Advanced Engine Technology

Using Exhaust Energy

Highest expansion ratiorecovers most thermalenergy

Turbines can recoverheat energy left overfrom gas exchange

Energy can be used todrive turbo-compressor orfed back into crank train


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Valvetrain Specific Power = f(Air Flow,

Thermal Efficiency) Air flow is an easier variable to

change than thermal efficiency 90% of restriction of induction

system occurs in cylinder head Cylinder head layouts that allow

the greatest airflow will havehighest specific power potential

Peak flow from poppet valve

engines primarily a function of total valve area More/larger valves equals greater

valve area


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Combustion Terms continued Spark Advance Timing in crank degrees prior to TDC for

start of combustion event (ignition) MBT Spark Maximum Brake Torque Spark

Minimum Spark Advance to Achieve Best Torque Burn Rate Speed of Combustion

Expressed as a fraction of total heat released versus crankdegrees

MAP - Manifold Absolute PressureAbsolute not Gauge (does not reference barometer)


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Combustion Terms continued Knock Autoignition of end-gasses in combustion chamber,

causing extreme rates of pressure rise. Knock Limit Spark - Maximum Spark Allowed due to Knock

can be higher or lower than MBT Pre-Ignition Autoignition of mixture prior to spark timing,

typically due to high temperatures of components Combustion Stability Cycle to cycle variation in burn

rate, trapped mass, location of peak pressure, etc. The lowerthe variation the better the stability.


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Engine ArchitectureInfluence on Performance

Intake & Exhaust Manifold Tuning Cylinder Filling & Emptying

Momentum Pressure Wave

Aerodynamics Flow Separation Wall Friction Junctions & Bends

Induction Restriction Exhaust Restriction (Backpressure) Compression Ratio Valve Events


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Force Relates to Pedal Position

Pedal Position

Foot off Pedal

Floored

F o r c e

A p p

l i e d

t o V e h

i c l e

Wh D th F C F ?


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Where Does the Force Come From? Power- the rate at which work is done:

Power is Force times Velocity (linear)

Power is Torque times Rotational Speed (rotary)

VFVelocityForcePower

T

SpeedRotationalTorquePower


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Where Does the Force Come From?


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Transmission:

Ignoring Losses, of Course

enginetransengineengine

trans

enginetransengine

transtranstrans

PP

TnnT

TP


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Where Does the Force Come From? Tire:

Ignoring Losses, of Course

enginetransaxlevehicle

axleaxle

axleaxle

vehiclevehiclevehicle

PPPP

T

T

VFP

2

er TireDiamet

2er TireDiamet


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Engine Performance Optimization Criteria


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Engine Performance Optimization Criteria Typically engine program goals are a peak

torque value and a peak power value Assuming different sets of engine hardware

could meet the program goals, only one setof hardware will perform the best in avehicle

The best performing vehicle will have thehighest average power delivered to thewheels during an acceleration event, whichis dependent on transmission capability


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I t k T i g


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Intake Tuningfor WOT Performance

Intake manifolds have ducts (runners) thattune at frequencies corresponding to enginespeed, like an organ pipe

Longer runners tune at lower frequencies Shorter runners tune at higher frequencies

Tuning increases local pressure at intake valvethereby increasing flow rate

Duct diameter is a trade-off between velocityand wall friction of passing charge

Exhaust Tuning


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Exhaust Tuningfor WOT Performance

Exhaust manifolds tune just as intakemanifolds do, but since no fresh charge isbeing introduced as a result not as much

impact on volumetric efficiency (~8%maximum for headers)

Catalyst performance usually limits production

exhaust systems that flow acceptably withlittle to no tuning


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Tuning in Production I4 Engine

350

370

390

410

430

450

470

Engine Speed (rpm)

A i r M a s s p e r

C y

l i n

d e r ( 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


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Powertrain Closing Remarks Powertrain is compromise

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

More speed, charge density or valve area areexpensive or difficult to develop thereforeminimizing losses is the most efficient path withinexisting engine architectures

Highest average power during a vehicle acceleration isfastest peak power values dont win races


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Calibration Terms

Stoichiometry Chemically correct ratio of fuel to air forcombustion

F/A Fuel/Air Ratio Mass ratio of mixture, a determination of richness or

leanness. Stoichiometry = 0.0688-0.0696 FA Lambda Excess Air Ratio

Stoichiometry = 1.0 Lambda Rich F/A F/A greater than Stoichiometry Rich

1.0 Lambda


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Calibration Terms continued Spark Advance Timing in crank degrees prior to

TDC for start of combustion event (ignition) MBT Spark - Maximum Brake Torque

Minimum Spark Advance to Achieve Best Torque Burn Rate Speed of Combustion

Expressed as a fraction of total heat releasedversus crank degrees

MAP - Manifold Absolute PressureAbsolute not Gauge (which references barometer)


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Control System Types Alpha-N

Engine Speed & Throttle Angle Speed-Density

Engine Speed and MAP/ACT MAF

Engine Speed and MAF


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Speed-Density Fuel and spark maps are based on MAP density of

charge is a strong function of pressure, corrected byair temp and coolant temp therefore air flow issimple to calculate

Less time-intensive than Alpha-N, once calibrated is good most common type of control

Needs less mapping can do WOT line and mid-map thencurve-fit air flow (spark needs a little more in-depth foroptimal control)


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MAF Fuel and spark maps are based on MAF airflow

measured directly MAF sensor isnt the most robust device

Pressure pulses confuse signal, each application has to bemapped with secondary damped MAF sensor (usually a 55 gallondrum inline)

Least noisy signal is usually at air cleaner so separate transportdelay controls need to be calibrated for transients and leaks needto be absolutely eliminated

Boosted applications usually add a MAP as well


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Control System Components Fuel System

Injectors, Fuel pump & Regulator Basic Sensors

Manifold Absolute Pressure (MAP) or Mass Air Flow

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


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Sensors


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Sensors Manifold Absolute Pressure (MAP)

A variable-resistance diaphragm with perfect vacuum on one side andmanifold pressure on other

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

element is maintained at a constant temperature and based upon themeasured downstream temperature the mass flow rate can bedetermined

Crank Position High resolution for spark advance, less-so for crank speed and with once-

per-rev can indicate TDC Cam Position

Low resolution for syncronization for sequential fuel injection andindividual cylinder spark

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

S t


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Sensors, cont Knock Sensor

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

noise.

S t


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Sensors, cont Lamda Sensor (EGO)

Compares ambient air to exhaustoxygen content (partial pressure of oxygen). Sensor output isessentially binary (only indicates

rich or lean of stoichiometry). Wide-band Lamda Sensor

(UEGO) Compares partial pressure of

oxygen (lean) and partial pressure

of HmCn, H2 & CO (rich) withambient. Gives output from ~0.6to 2 Lamda. Turns vehicle into arolling dyno.

UEGO Schematic

EGO Schematic

K k


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Knock Causes of Knock

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

Burn rate can come from multiple spark sources, more compactcombustion chambers or increased turbulence

Temperature Reduced combustion temperatures reduce knock throughreduced charge temperatures (cooler incoming charge or reducedresidual burned gases), increased evaporative cooling from richer F/Amixtures and increased combustion chamber cooling

Pressure Lower cylinder pressures reduce knock tendency throughlower compression ratio or MAP pressure

Octane Different fuel types have higher or lower autoignitiontendencies. Octane value is directly related to knocking tendency

K k i d


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Knock continued Effects of Knock

Disrupts stagnant gases that form boundary layer at edge of combustion chamber, increasing heat transfer to componentsand raising mean combustion chamber temp that can lead to

pre-ignition Scours oil film off cylinder wall, leading to dry friction andincreased wear of piston rings

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

Shockwave can be strong enough to stress components tofailure


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T pical press re probe installation


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Typical pressure probe installation

Passage drilled through deck face (avoiding coolant jacket)

Cylinder Pressure TraceNo Knock


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Cylinder Pressure TraceKnock Limit or Trace Knock - Best Power


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P I iti


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Pre-Ignition

Effects of Pre-Ignition Increases peak cylinder pressure by beginning heat release

too soon Increased cylinder pressure also increases heat load to

combustion chamber components, sustaining the pre-ignition(leading to run -away pre- ignition)

Increases loads on piston crown and piston pin Sustained pre-ignition will typically put a hole in the center of

the piston crown

B R t


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Burn Rate Burn Rate = f(Spark, Dilution Rate/FA Ratio, Chamber Volume Distribution,Engine Speed/Mixture Motion/Turbulent Intensity)

Spark Closer to MBT the faster the burn with trace knock the fastest

Dilution Rate/FA Ratio Least dilution (exhaust residual or anything unburnable) fastest

FA Ratio best rate around LBT Chamber Volume Distribution

Smallest chamber with shortest flame path best (multiple ignition sources shorten flamepath)

Engine Speed/Mixture Motion/Turbulent Intensity Crank angle time for complete burn nearly constant with increasing engine speed

indicating other factors speeding burn rate Mixture motion-contributed angular momentum conserved as cylinder volume decreases

during compression stroke, eventually breaking down into vortices around TDC increasingkinetic energy in charge

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


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Transient F eling


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Transient Fueling

Liquid fuel does not burn, only fuel vapour Heat from somewhere must be used to make vapour which is why

up to 500% more fuel must be used on a cold start to providesufficient vapour for engine to run (relationship betweentemperature and partial pressure of fuel fractions)

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

some fraction of free stream. Therefore some fuel from every pulse goesinto engine and some onto port wall.

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

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


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Thermal Enrichment


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Thermal Enrichment

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

Materials must operate at sufficiently low temperature tomaintain strength, so Exhaust Gas Temperature (EGT)

limits must be adhered to for sufficient durability Usually 950 deg C runner temperature is acceptable for adeveloped package, as low as 800 deg C for undevelopedcomponents may be necessary

Primary path for cooling is additional fuel beyond LBT, as

heat of vapourization cools the charge before ignition(pressure-charged engines primarily)

Drivability


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Drivability

Throttle Response Drivers expect some repeatability and resolution

of thrust versus pedal position some degree of spark mapping (retard) and pedal to throttle camcan help a drivers confidence

Usually least developed and of most importance istip-in (throttle closed to small opening) where

torque can come in as a step change

Calibration Summary


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Calibration Summary

Calibration is compromise Fueling level is a compromise between engine protection

and good V.E. Best spark advance for drivability may be too close to the

knock limit. Focus on calibration of primary functions first (fuel and

spark) Need to understand to understand why a dyno engine

calibration will be different than one derived from avehicle. Can the dyno replicate vehicle transients fully?

References


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References

Internal Combustion Engine Fundamentals, John BHeywood, 1988 McGraw-Hill The Design and Tuning of Competition Engines Sixth

Edition, Philip H Smith, 1977 Robert Bentley

Design and Simulation of Four-Stroke Engines, GordonP. Blair, 1999 SAE Advanced Engine Technology, Heinz Heisler, 1995 SAE Vehicle and Engine Technology, Heinz Heisler, 1999 SAE

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Calibration 101 by Kim Lyon