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Measuring Engine Performance The main goal of this chapter is to determine functional horsepower through different measurements and formulas Small Gasoline Engine – Internal Combustion Small Gasoline Engine – Internal Combustion • Air/fuel mixture is ignited inside the engine Small Gasoline Engine – Internal Combustion • Air/fuel mixture is ignited inside the engine • The gasses (when ignited ) expand in all directions 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 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 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. 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 Performance • Defined as the work engines do Performance • Defined as the work engines do also, • Defined as how well they do the work Bore • The diameter or width across the top of the cylinder – Measured using caliper or telescoping gauges and micrometers Stroke • The up or down movement of the piston. – Measured from TDC to BDC. – Determined by the amount of offset on the crankshaft. 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 Square? • An engine is considered square if the bore and stroke measurements are identical Square? • 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? • 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. Engine Displacement • The total volume of space increase in the cylinder as the piston moves from the top to the bottom of its stroke. 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. 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 r2 x stroke) or (V = .7854 D2 x stroke) 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 r2 x stroke) or (V = .7854 D2 x stroke) • Engine Displacement: .7854 x D2 x Length of stroke Engine Displacement • Example – Bore = 2 ¼ in – Stroke = 2 ¼ in Engine Displacement • Example – Bore = 2 ¼ in – Stroke = 2 ¼ in • .7854 x D2 x Length of stroke Engine Displacement • Example – Bore = 2 ¼ in – Stroke = 2 ¼ in • .7854 x D2 x Length of stroke • .7854 x (2.25 in)2 x 2.25 in Engine Displacement • Example – Bore = 2 ¼ in – Stroke = 2 ¼ in • .7854 x D2 x Length of stroke • .7854 x (2.25 in)2 x 2.25 in • .7854 x 5.0625 in2 x 2.25 in Engine Displacement • Example – Bore = 2 ¼ in – Stroke = 2 ¼ in • • • • .7854 x D2 x Length of stroke .7854 x (2.25 in)2 x 2.25 in .7854 x 5.0625 in2 x 2.25 in 8.95 in3. or 8.95 cubic inches Engine Displacement • Example – Bore = 2 ¼ in – Stroke = 2 ¼ in • • • • .7854 x D2 x Length of stroke .7854 x (2.25 in)2 x 2.25 in .7854 x 5.0625 in2 x 2.25 in 8.95 in3. or 8.95 cubic inches – 2 cylinder? Engine Displacement • Example – Bore = 2 ¼ in – Stroke = 2 ¼ in • • • • .7854 x D2 x Length of stroke .7854 x (2.25 in)2 x 2.25 in .7854 x 5.0625 in2 x 2.25 in 8.95 in3. or 8.95 cubic inches – 2 cylinder? • Multiply 8.95 in3 x 2 = 17.89 in3 Problem • Bore = 2 inches • Stroke = 2 inches • 4 cylinder engine • Determine the displacement using the above data and the formula below (.7854 x D2 x Stroke = Displacement) Problem .7854 x D2 x Stroke = Displacement/Cylinder Problem .7854 x D2 x Stroke = Displacement/Cylinder .7854 x 22 in x 2 in = Displacement/Cylinder Problem .7854 x D2 x Stroke = Displacement/Cylinder .7854 x 22 in x 2 in = Displacement/Cylinder .7854 x 4 in2 x 2 in = Displacement/Cylinder Problem .7854 x D2 x Stroke = Displacement/Cylinder .7854 x 22 in x 2 in = Displacement/Cylinder .7854 x 4 in2 x 2 in = Displacement/Cylinder 6.28 in3 = Displacement/Cylinder Problem .7854 x D2 x Stroke = Displacement/Cylinder .7854 x 22 in x 2 in = Displacement/Cylinder .7854 x 4 in2 x 2 in = Displacement/Cylinder 6.28 in3 = Displacement/Cylinder 6.28 in3 x 4 cylinder = Total Displacement Problem .7854 x D2 x Stroke = Displacement/Cylinder .7854 x 22 in x 2 in = Displacement/Cylinder .7854 x 4 in2 x 2 in = Displacement/Cylinder 6.28 in3 = Displacement/Cylinder 6.28 in3 x 4 cylinder = Total Displacement 25.12 in3 Total Displacement 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 Force • The pushing or pulling of one body on another. Force • The pushing or pulling of one body on another. – Weight of you on a chair 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 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) 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 Work • Accomplished only when a force is applied through some distance Work • Accomplished only when a force is applied through some distance • Work = Distance x Force Work • Accomplished only when a force is applied through some distance • Work = Distance x Force – Distance (ft), Force (lb) Work • Accomplished only when a force is applied through some distance • Work = Distance x Force – Distance (ft), Force (lb) – Work Unit = ft·lb Power • The rate at which work is done Power • The rate at which work is done • Power = Work / Time Power • The rate at which work is done • Power = Work / Time • Power = Pounds x Distance / Time 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 • 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 • 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 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 Horsepower • Calculate the amount of work and engine does and divide it by 550 ft·lb/sec. This will give the rated horsepower. 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 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 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 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) Horsepower • Increases with increased speeds. Horsepower • Increases with increased speeds. • Engines generally run at 3600 rpm. Torque • A twisting or turning force Torque • A twisting or turning force • Torque = Distance (radius) x Force Torque • A twisting or turning force • Torque = Distance (radius) x Force • Torque = Feet x Pounds Torque • • • • A twisting or turning force Torque = Distance (radius) x Force Torque = Feet x Pounds Torque = ft·lb Torque • • • • • A twisting or turning force Torque = Distance (radius) x Force Torque = Feet x Pounds Torque = ft·lb 1 ft·lb = 12 in·lb 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. 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