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 doalso,

• 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

• 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?

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.

• 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

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

• 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

Engine Displacement

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