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