11

Chapter BrianChapter Brian

Measuring Engine PerformanceMeasuring Engine Performance

page 91page 91

22

Basic TerminologyBasic Terminology

Bore & StrokeBore & Stroke

Engine DisplacementEngine Displacement

Compression RatioCompression Ratio

ForceForce

WorkWork

PowerPower

EnergyEnergy

HorsepowerHorsepower

33

BoreBore

Diameter of Diameter of cylindercylinder

2 X Radius2 X Radius

44

StrokeStroke

Distance Distance TDC-BDCTDC-BDC

Distance piston travelsDistance piston travels up or downup or down

55

Cylinder DisplacementCylinder Displacement

0.7854 x D2 x stroke0.7854 x D2 x stroke

oror

ΠΠ x r2 x Stroke x r2 x Stroke

66

Engine DisplacementEngine Displacement

0.7854 x D0.7854 x D22 x stroke X # of cylinders x stroke X # of cylinders

oror

ΠΠ x r x r22 x Stroke # of cylinders x Stroke # of cylinders

inin33 / 62 = Liters / 62 = Liters

77

Compression RatioCompression Ratio

Area of cylinder at BDCArea of cylinder at BDC

compared to compared to

Area of cylinder at TDCArea of cylinder at TDC

63 in3 to 9 in363 in3 to 9 in3

==

7:1 compression ratio7:1 compression ratio

88

ForceForce

pushing or pullingpushing or pulling

stationary forcestationary force

moving forcemoving force

Centrifugal forceCentrifugal force spinningspinning FORCE does NOT = PressureFORCE does NOT = Pressure

99

PressurePressure

Pressure is force per given areaPressure is force per given area

or or

Force/AreaForce/Area

PSIPSI

Force = psi X areaForce = psi X area

Area = force / psiArea = force / psi

Area = Area = ΠΠ R R22

1010

WorkWork

force applied resulting in movementforce applied resulting in movement

Work = Force x DistanceWork = Force x Distance

W = F x DW = F x D

Mechanical advantage (lever, ramp, etc)Mechanical advantage (lever, ramp, etc)

Effort distance / resistance distance = Effort distance / resistance distance = Mechanical advantageMechanical advantage

1111

Mechanical AdvantageMechanical Advantage

2’2’

10’

10’ / 2’ = 5 = MA

E(effort) = R(resistance)/ MA

or

E = 500# / 5 = 100 #

500#

1212

PowerPower

Power is time taken to do the workPower is time taken to do the work

P = work/timeP = work/time

P=W/TP=W/T

Power = feet x Pounds / timePower = feet x Pounds / time

or Foot pounds per second?or Foot pounds per second?

1313

EnergyEnergy

Energy can not be created or destroyedEnergy can not be created or destroyed

Potential—has the potential to . . .Potential—has the potential to . . .

Kinetic Kinetic

MechanicalMechanical

ChemicalChemical

Thermal (heat)Thermal (heat)

LightLight

1414

HorsepowerHorsepower

Power = work / time P= w/tPower = work / time P= w/t

Hp = 33,000 ft-lb (work) / 1 minute (time)Hp = 33,000 ft-lb (work) / 1 minute (time)

oror

Hp = 550 ft-lb / 1 secondHp = 550 ft-lb / 1 second

1515

Horsepower FormulaHorsepower Formula

100 ft x 330 lb / 6 seconds = 5500 ft lb / sec100 ft x 330 lb / 6 seconds = 5500 ft lb / sec

dividing this by 550 ft lb / sec (1hp)dividing this by 550 ft lb / sec (1hp)

==

(5500 ft-lb /sec) / (550 ft lb / sec) = 10 hp(5500 ft-lb /sec) / (550 ft lb / sec) = 10 hp

thusthus

1 hp = rate of work in ft-lb/sec 1 hp = rate of work in ft-lb/sec / / 50 ft-lb / sec50 ft-lb / sec

1616

Kinds of HorsepowerKinds of Horsepower

Brake HorsepowerBrake Horsepower

Indicated HorsepowerIndicated Horsepower

Frictional HorsepowerFrictional Horsepower

Rated HorsepowerRated Horsepower

Corrected HorsepowerCorrected Horsepower

1717

Brake HorsepowerBrake Horsepower

bhpbhp

actual hp deliveredactual hp delivered

what we can usewhat we can use

1818

Indicated HorsepowerIndicated Horsepowerihp (perfect world)ihp (perfect world)power developed by the burning fuelpower developed by the burning fuelaverage of power on 4 strokes (mean)average of power on 4 strokes (mean)PLANK / 33,000PLANK / 33,000PP = mep in in lb/in = mep in in lb/in22

LL = length of stroke = length of strokeAA = Cylinder Area = Cylinder AreaNN = power strokes per minute = power strokes per minute oror RPM / 4 RPM / 4KK = # of cylinders = # of cylinders

1919

Frictional HorsepowerFrictional Horsepower

fhpfhp

HP lost because of dragHP lost because of drag

fhp = ihp-bhpfhp = ihp-bhp

2020

Rated HorsepowerRated Horsepower

rhp rhp

80% of bhp80% of bhp

2121

Corrected HorsepowerCorrected Horsepower

corrected for elevation (sea level)corrected for elevation (sea level)

corrected for temperaturecorrected for temperature

barometric pressurebarometric pressure

quality of fuelquality of fuel

humidityhumidity

2222

TorqueTorque

Twisting forceTwisting force

force x distanceforce x distance

ft - lbft - lb

in – lbin – lb

Newton - MetersNewton - Meters

2323

Torque is not ConstantTorque is not Constant

Torque will change w/ engine speedTorque will change w/ engine speed

More pressure on piston = more torqueMore pressure on piston = more torque

2424

Torque and HorsepowerTorque and Horsepower

Unlike torque. . .Unlike torque. . .

Horsepower increases with engine speedHorsepower increases with engine speed

Torque measure of engine’s twisting forceTorque measure of engine’s twisting force

Hp measures engine’s ability to do workHp measures engine’s ability to do work

2525

Volumetric EfficiencyVolumetric Efficiency

How well an engine breathesHow well an engine breathes draws air/fuel into cylinderdraws air/fuel into cylinder

Can decrease as engine speed increasesCan decrease as engine speed increases

many factorsmany factors

2626

Practical EfficiencyPractical Efficiency

how efficiently an engine uses the fuelhow efficiently an engine uses the fuel

2727

Mechanical EfficiencyMechanical Efficiency

% of power developed in cylinder (ihp)% of power developed in cylinder (ihp)

compared to compared to

power delivered to crankshaft (bhp)power delivered to crankshaft (bhp)

friction, friction,

Mechanical efficiency = bhp/ihpMechanical efficiency = bhp/ihp

2828

Thermal EfficiencyThermal Efficiency

Heat efficiencyHeat efficiencyhow much power produced is used to how much power produced is used to push the piston downpush the piston downPower is lost to :Power is lost to : coolingcooling exhaustexhaust 20-25% efficient20-25% efficient Exhaust 35% . . .Exhaust 35% . . . Cooling & Lubrication 35%Cooling & Lubrication 35%

2929

Brake thermal efficiencyBrake thermal efficiency

= =

Brake horsepower (bhp x 33,000)Brake horsepower (bhp x 33,000)

778 778 Fuel heat valueFuel heat value x x weight of burned fuel per weight of burned fuel per minuteminute

778 is Joule’s equivalent778 is Joule’s equivalent

it is a constantit is a constant