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**Measuring Engine Performance page 91**

Chapter Brian Measuring Engine Performance page 91

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**Basic Terminology Bore & Stroke Engine Displacement Compression Ratio**

Force Work Power Energy Horsepower

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Bore Diameter of cylinder 2 X Radius

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Stroke Distance TDC-BDC Distance piston travels up or down

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**Cylinder Displacement**

x D2 x stroke or Π x r2 x Stroke

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**Engine Displacement 0.7854 x D2 x stroke X # of cylinders or**

Π x r2 x Stroke # of cylinders in3 / 62 = Liters

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**Compression Ratio Area of cylinder at BDC compared to**

Area of cylinder at TDC 63 in3 to 9 in3 = 7:1 compression ratio

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**Force pushing or pulling stationary force moving force**

Centrifugal force spinning FORCE does NOT = Pressure

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**Pressure Pressure is force per given area or Force/Area PSI**

Force = psi X area Area = force / psi Area = Π R2

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**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

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

500# 2’

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**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?

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**Energy Energy can not be created or destroyed**

Potential—has the potential to . . . Kinetic Mechanical Chemical Thermal (heat) Light

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**Horsepower Power = work / time P= w/t**

Hp = 33,000 ft-lb (work) / 1 minute (time) or Hp = 550 ft-lb / 1 second

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**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

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**Kinds of Horsepower Brake Horsepower Indicated Horsepower**

Frictional Horsepower Rated Horsepower Corrected Horsepower

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Brake Horsepower bhp actual hp delivered what we can use

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**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

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**Frictional Horsepower**

fhp HP lost because of drag fhp = ihp-bhp

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Rated Horsepower rhp 80% of bhp

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**Corrected Horsepower corrected for elevation (sea level)**

corrected for temperature barometric pressure quality of fuel humidity

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

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**Torque is not Constant Torque will change w/ engine speed**

More pressure on piston = more torque

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**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

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**Volumetric Efficiency**

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

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Practical Efficiency how efficiently an engine uses the fuel

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**Mechanical Efficiency**

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

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**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%

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**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

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