 # Measuring Engine Performance page 91

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Measuring Engine Performance page 91
Chapter Brian Measuring Engine Performance page 91

Basic Terminology Bore & Stroke Engine Displacement Compression Ratio
Force Work Power Energy Horsepower

Bore Diameter of cylinder 2 X Radius

Stroke Distance TDC-BDC Distance piston travels up or down

Cylinder Displacement
x D2 x stroke or Π x r2 x Stroke

Engine Displacement 0.7854 x D2 x stroke X # of cylinders or
Π x r2 x Stroke # of cylinders in3 / 62 = Liters

Compression Ratio Area of cylinder at BDC compared to
Area of cylinder at TDC 63 in3 to 9 in3 = 7:1 compression ratio

Force pushing or pulling stationary force moving force
Centrifugal force spinning FORCE does NOT = Pressure

Pressure Pressure is force per given area or Force/Area PSI
Force = psi X area Area = force / psi Area = Π R2

Work force applied resulting in movement Work = Force x Distance
W = F x D Mechanical advantage (lever, ramp, etc) Effort distance / resistance distance = Mechanical advantage

Mechanical Advantage 10’ / 2’ = 5 = MA E(effort) = R(resistance)/ MA
500# 2’

Power Power is time taken to do the work P = work/time P=W/T
Power = feet x Pounds / time or Foot pounds per second?

Energy Energy can not be created or destroyed
Potential—has the potential to . . . Kinetic Mechanical Chemical Thermal (heat) Light

Horsepower Power = work / time P= w/t
Hp = 33,000 ft-lb (work) / 1 minute (time) or Hp = 550 ft-lb / 1 second

Horsepower Formula 100 ft x 330 lb / 6 seconds = 5500 ft lb / sec
dividing this by 550 ft lb / sec (1hp) = (5500 ft-lb /sec) / (550 ft lb / sec) = 10 hp thus 1 hp = rate of work in ft-lb/sec / 50 ft-lb / sec

Kinds of Horsepower Brake Horsepower Indicated Horsepower
Frictional Horsepower Rated Horsepower Corrected Horsepower

Brake Horsepower bhp actual hp delivered what we can use

Indicated Horsepower ihp (perfect world)
power developed by the burning fuel average of power on 4 strokes (mean) PLANK / 33,000 P = mep in in lb/in2 L = length of stroke A = Cylinder Area N = power strokes per minute or RPM / 4 K = # of cylinders

Frictional Horsepower
fhp HP lost because of drag fhp = ihp-bhp

Rated Horsepower rhp 80% of bhp

Corrected Horsepower corrected for elevation (sea level)
corrected for temperature barometric pressure quality of fuel humidity

Torque Twisting force force x distance ft - lb in – lb Newton - Meters

Torque is not Constant Torque will change w/ engine speed
More pressure on piston = more torque

Torque and Horsepower Unlike torque. . .
Horsepower increases with engine speed Torque measure of engine’s twisting force Hp measures engine’s ability to do work

Volumetric Efficiency
How well an engine breathes draws air/fuel into cylinder Can decrease as engine speed increases many factors

Practical Efficiency how efficiently an engine uses the fuel

Mechanical Efficiency
% of power developed in cylinder (ihp) compared to power delivered to crankshaft (bhp) friction, Mechanical efficiency = bhp/ihp

Thermal Efficiency Heat efficiency
how much power produced is used to push the piston down Power is lost to : cooling exhaust 20-25% efficient Exhaust 35% . . . Cooling & Lubrication 35%

Brake thermal efficiency
= Brake horsepower (bhp x 33,000) 778 Fuel heat value x weight of burned fuel per minute 778 is Joule’s equivalent it is a constant