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Measuring Engine Performance

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The main goal of this chapter is to determine functional horsepower through different measurements and formulas

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Small Gasoline Engine –Internal Combustion

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Small Gasoline Engine –Internal Combustion Air/fuel mixture is ignited inside the engine

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Small Gasoline Engine –Internal Combustion Air/fuel mixture is ignited inside the engine The gasses (when ignited ) expand in all directions

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Small Gasoline Engine –Internal Combustion Air/fuel mixture is ignited inside the engine The gasses (when ignited ) expand in all directions Only the piston is allowed to move

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Small Gasoline Engine –Internal Combustion Air/fuel mixture is ignited inside the engine The gasses (when ignited ) expand in all directions Only the piston is allowed to move –Inertia

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Small Gasoline Engine –Internal Combustion Air/fuel mixture is ignited inside the engine The gasses (when ignited ) expand in all directions Only the piston is allowed to move –Inertia A physical law that states an object in motion will continue in motion or an object at rest will continue at rest unless an additional force is applied.

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Small Gasoline Engine –Internal Combustion Air/fuel mixture is ignited inside the engine The gasses (when ignited ) expand in all directions Only the piston is allowed to move –Inertia A physical law that states an object in motion will continue in motion or an object at rest will continue at rest unless an additional force is applied. –The piston reaches TDC then reverses direction, repeating the process at BDC. This places extreme stress on the engine by changing the inertia

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Performance Defined as the work engines do

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Performance Defined as the work engines do also, Defined as how well they do the work

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Bore The diameter or width across the top of the cylinder –Measured using caliper or telescoping gauges and micrometers

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Stroke The up or down movement of the piston. –Measured from TDC to BDC. –Determined by the amount of offset on the crankshaft.

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Stroke The up or down movement of the piston. –Measured from TDC to BDC. –Determined by the amount of offset on the crankshaft. or by the vernier depth gauge

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An engine is considered square if the bore and stroke measurements are identical Square?

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An engine is considered square if the bore and stroke measurements are identical An engine is considered over square if the bore diameter is greater than the stroke Square?

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An engine is considered square if the bore and stroke measurements are identical An engine is considered over square if the bore diameter is greater than the stroke An engine is considered under square if the bore diameter is smaller than the stroke.

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The total volume of space increase in the cylinder as the piston moves from the top to the bottom of its stroke. Engine Displacement

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The total volume of space increase in the cylinder as the piston moves from the top to the bottom of its stroke. –Determined by the circular area of the cylinder then multiplied by the total length of the stroke. Engine Displacement

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The total volume of space increase in the cylinder as the piston moves from the top to the bottom of its stroke. –Determined by the circular area of the cylinder then multiplied by the total length of the stroke. (V = π r 2 x stroke) or (V =.7854 D 2 x stroke)

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Engine Displacement The total volume of space increase in the cylinder as the piston moves from the top to the bottom of its stroke. –Determined by the circular area of the cylinder then multiplied by the total length of the stroke. (V = π r 2 x stroke) or (V =.7854 D 2 x stroke) Engine Displacement:.7854 x D 2 x Length of stroke

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Example –Bore = 2 ¼ in –Stroke = 2 ¼ in Engine Displacement

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Example –Bore = 2 ¼ in –Stroke = 2 ¼ in.7854 x D 2 x Length of stroke Engine Displacement

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Example –Bore = 2 ¼ in –Stroke = 2 ¼ in.7854 x D 2 x Length of stroke.7854 x (2.25 in) 2 x 2.25 in Engine Displacement

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Example –Bore = 2 ¼ in –Stroke = 2 ¼ in.7854 x D 2 x Length of stroke.7854 x (2.25 in) 2 x 2.25 in.7854 x 5.0625 in 2 x 2.25 in Engine Displacement

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Example –Bore = 2 ¼ in –Stroke = 2 ¼ in.7854 x D 2 x Length of stroke.7854 x (2.25 in) 2 x 2.25 in.7854 x 5.0625 in 2 x 2.25 in 8.95 in 3. or 8.95 cubic inches Engine Displacement

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Example –Bore = 2 ¼ in –Stroke = 2 ¼ in.7854 x D 2 x Length of stroke.7854 x (2.25 in) 2 x 2.25 in.7854 x 5.0625 in 2 x 2.25 in 8.95 in 3. or 8.95 cubic inches –2 cylinder? Engine Displacement

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Example –Bore = 2 ¼ in –Stroke = 2 ¼ in.7854 x D 2 x Length of stroke.7854 x (2.25 in) 2 x 2.25 in.7854 x 5.0625 in 2 x 2.25 in 8.95 in 3. or 8.95 cubic inches –2 cylinder? Multiply 8.95 in 3 x 2 = 17.89 in 3 Engine Displacement

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Problem Bore = 2 inches Stroke = 2 inches 4 cylinder engine Determine the displacement using the above data and the formula below (.7854 x D 2 x Stroke = Displacement)

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Problem.7854 x D 2 x Stroke = Displacement/Cylinder

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Problem.7854 x D 2 x Stroke = Displacement/Cylinder.7854 x 2 2 in x 2 in = Displacement/Cylinder

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Problem.7854 x D 2 x Stroke = Displacement/Cylinder.7854 x 2 2 in x 2 in = Displacement/Cylinder.7854 x 4 in 2 x 2 in = Displacement/Cylinder

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Problem.7854 x D 2 x Stroke = Displacement/Cylinder.7854 x 2 2 in x 2 in = Displacement/Cylinder.7854 x 4 in 2 x 2 in = Displacement/Cylinder 6.28 in 3 = Displacement/Cylinder

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Problem.7854 x D 2 x Stroke = Displacement/Cylinder.7854 x 2 2 in x 2 in = Displacement/Cylinder.7854 x 4 in 2 x 2 in = Displacement/Cylinder 6.28 in 3 = Displacement/Cylinder 6.28 in 3 x 4 cylinder = Total Displacement

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Problem.7854 x D 2 x Stroke = Displacement/Cylinder.7854 x 2 2 in x 2 in = Displacement/Cylinder.7854 x 4 in 2 x 2 in = Displacement/Cylinder 6.28 in 3 = Displacement/Cylinder 6.28 in 3 x 4 cylinder = Total Displacement 25.12 in 3 Total Displacement

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Compression Ratio The relationship between the total cylinder volume when the piston is a BDC and the volume remaining when the piston is at TDC. Small engines generally have 5-6:1 Some motorcycles have 9-10:1

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Force The pushing or pulling of one body on another.

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Force The pushing or pulling of one body on another. –Weight of you on a chair

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Force The pushing or pulling of one body on another. –Weight of you on a chair –Centrifugal force The ball at the end of a string tries to move outward from its path when twirled

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Force The pushing or pulling of one body on another. –Weight of you on a chair –Centrifugal force The body tries to move outward from its path when twirled –Tensile Stress the pushing or pulling stress (on the string)

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Force The pushing or pulling of one body on another. –Weight of you on a chair –Centrifugal force The body tries to move outward from its path when twirled –Tensile Stress the pushing or pulling stress –Ex. The piston reversing direction several times a second

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Work Accomplished only when a force is applied through some distance

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Work Accomplished only when a force is applied through some distance Work = Distance x Force

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Work Accomplished only when a force is applied through some distance Work = Distance x Force –Distance (ft), Force (lb)

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Work Accomplished only when a force is applied through some distance Work = Distance x Force –Distance (ft), Force (lb) –Work Unit = ft·lb

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Power The rate at which work is done

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Power The rate at which work is done Power = Work / Time

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Power The rate at which work is done Power = Work / Time Power = Pounds x Distance / Time

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Power The rate at which work is done Power = Work / Time Power = Pounds x Distance / Time –Example: a horse can lift 100 lb a distance of 330 ft in 1 minute. How much Power is used?

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Power The rate at which work is done Power = Work / Time Power = Pounds x Distance / Time –Example: a horse can lift 100 lb a distance of 330 ft in 1 minute. How much Power is used? –Power = 330 ft x 100 lb / 60 sec

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Power The rate at which work is done Power = Work / Time Power = Pounds x Distance / Time –Example: a horse can lift 100 lb a distance of 330 ft in 1 minute. How much Power is used? –Power = 330 ft x 100 lb / 60 sec –Power = 550 ft·lb/sec

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Power The rate at which work is done Power = Work / Time Power = Pounds x Distance / Time –Example: a horse can lift 100 lb a distance of 330 ft in 1 minute. How much Power is used? –Power = 330 ft x 100 lb / 60 sec –Power = 550 ft·lb/sec –1 horse power = 550 ft·lb/sec

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Horsepower Calculate the amount of work and engine does and divide it by 550 ft·lb/sec. This will give the rated horsepower.

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Horsepower Calculate the amount of work and engine does and divide it by 550 ft·lb/sec. This will give the rated horsepower. Brake Horsepower

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Horsepower Calculate the amount of work and engine does and divide it by 550 ft·lb/sec. This will give the rated horsepower. Brake Horsepower –Usable horsepower

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Horsepower Calculate the amount of work and engine does and divide it by 550 ft·lb/sec. This will give the rated horsepower. Brake Horsepower –Usable horsepower –Measured by

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Horsepower Calculate the amount of work and engine does and divide it by 550 ft·lb/sec. This will give the rated horsepower. Brake Horsepower –Usable horsepower –Measured by Prony brake (fiction) Dynamometer (hydraulics)

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Horsepower Increases with increased speeds.

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Horsepower Increases with increased speeds. Engines generally run at 3600 rpm.

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Torque A twisting or turning force

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Torque A twisting or turning force Torque = Distance (radius) x Force

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Torque A twisting or turning force Torque = Distance (radius) x Force Torque = Feet x Pounds

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Torque A twisting or turning force Torque = Distance (radius) x Force Torque = Feet x Pounds Torque = ft·lb

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Torque A twisting or turning force Torque = Distance (radius) x Force Torque = Feet x Pounds Torque = ft·lb 1 ft·lb = 12 in·lb

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Torque A twisting or turning force Torque = Distance (radius) x Force Torque = Feet x Pounds Torque = ft·lb 1 ft·lb = 12 in·lb Engine Torque increases with increased rpm, but decreases if rpm is becomes too high.

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Review Why do we check engine performance? What type of forces are working in an internal combustion engine? Explain the difference between bore & stroke. How is displacement measured? What is the unit for work? What is the unit for power? What is 1 horsepower? Torque is measured in ______ for units

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