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ABE 223: ABE Principles – Machine Systems
Power Measurement
Tony Grift
Dept. of Agricultural & Biological EngineeringUniversity of Illinois
Agenda
• Power measurement• Dynamometers, waterbrake, eddy current• Torque and Power curve
• Power computation• Pressure-Volume curves• Indicated Mean Effective Pressure• Power computation in cylinder, engine
Power Measurement
Belt-driven Prony brake dynamometer.
PTO dynamometer
• Dyno’s• Mechanical
(friction)• Electrical
(generator)• Hydraulic (water,
eddy current)• ? What type is
this ?
Brake Power Measurement
Engine Speed
Engine Torque
TP
Compare Torque in a 430 HP Caterpillar C12 truck and a 437 HP Mustang Cobra. What is the difference?
Exercise
• Compute the Torque of the following vehicles• Audi GT Coupe 1985 136 HP @ 6000 RPM• MyHeavyChevy• Dodge Viper 500 HP @ 7000 RPM• DU Sulzer Ships Engine 100,000 HP @ 100
RPM• Ferrari F1 V12 Engine 800 HP @
18,000 RPM
s
rad
srev
radrev
s
NmWattHP
NmTs
radPow
1047.0min
60
1
1
2
min1
7457451
*
Fig 2.5 Typical diesel engine performance curves
Power Computation
Physical Model of Mean Effective Pressure
F = p* A
p
•Mean pressure in thecombustionchamber provides adownward force oneach piston.
Mean Effective Force of the Stroke
A•The piston area and thecycle mean effectivepressure provide a measureof the average forceexerted.
Work
F = p* A
F
W = F * L
L
•Simply the averageforce exerted times the
length of the stroke.
Power Measurement
Dynamometer
Power and efficiencies
Power in fuel
RejectedHeat
Friction Power
ip
Indicated
thermal
efficiency
Mechanicalefficiency
bp
Ideal Otto Engine Simulation
Credit: Wolfgang Christian
Compression stroke
BDC TDC
p
ApF CC *
sApW CC **
Power stroke
BDC TDC
p
ApF PP *
sApW PP **
Compression and Power Combined
BDC TDC
p
CWime ppp
CP WWW
sApsAppsApsApWWW ime
p
CPCPCP
ime
********
Power per Cylinder
s
revRPM
60
MECHime
ENGINE
sApW
W
t
W
s
NmP
*2
****
1
Power for whole Engine
MECHime
ENGINE
NsAp
s
NmP
*2
****
Indicated Mean Effective Pressure during Compression and Power strokesA Area of the pistons Stroke of the piston
Number of revolutions per secondN Number of cylinders
Mechanical efficiency of the engine 2 Factor since only 2/4 strokes produce Indicated Mean Effective Pressure (four stroke engine)
imep
MECH
Homework
120 mm
100 mm
The indicated mean effective pressure measured in the cylinder is 10 Bar (that is or ). The engine is a V8 four-stroke. The engine is running at 3600 and the mechanical efficiency is 90%.
Required:
1) Compute the average Force acting on the piston during the compression/work strokes.
2) Compute the Work being done in one cylinder during compression/work strokes.
3) Compute the work done in 1 second for the whole engine, which is the
Power
