A. Work
- Moving an object against an opposing force either by a
push, pull, or lift. It is measured in terms
of distance and force.
Example: A 5 pound weight
lifted 2 feet would equal 10 foot-pounds.
B. Energy
- The ability or capacity to do work. When work is done on
an object, energy is stored in that object.
C. Power
- Rate at which work is done (rapidly or slowly).
D. Torque
- A twisting or turning effort. Turning a lid on a jar or
turning a steering wheel.
Example: Pushing on a 1 1/2
foot crank with 20 lbs. of force equals 30 pound feet of torque.
Horsepower (hp) - The power of one horse.
hp = ft. lbs. per minute
= L * W
L = Length in feet
33,000
33,000 *
time
W = Force in pounds
t = Time in minutes
hp = torque * RPM
5252
RPM =
Revolutions per minute
Example: You have a heavy box loaded with sand
that you must drag across a level lot for 500 feet in 2 minutes.
A pull of 2000 lbs. is required to move the box. What is the
horsepower?
hp = 500
* 2000 = 15.15 horse power
33,000 * 2 Inertia - The property of all
material objects that causes them to resist any change in speed or
direction of travel.
Friction - Resistance to motion
between two objects in contact with each other.
Bore and Stroke - Indicates the
size of an engine cylinder.
1. Bore -
Diameter of the cylinder.
2. Stroke -
Distance the piston travels from BDC (Bottom Dead Center) to TDC (Top
Dead Center).
Example: A cylinder 3 by 2
1/2 has a 3 inch bore and a 2 1/2 inch stroke.
Piston displacement - Volume that the piston displaces, or sweeps out,
as it moves from BDC to TDC.
Example: You have a
cylinder 3 X 2.
2
Formula: PD=3.14 * (1/2
bore) * stroke
2
So :: PD = 3.14
* (1/2 3) * 2
PD = 14.13 cubic inches
If the engine has 4 cylinders,
the total displacement is 56.52 cubic inches PD * # of Cylinders. 2 OR Engine
displacement ED = 3.14 * (1/2 bore) *
stroke * # of Cyl.
Compression ratio - The
measure of how much the air/fuel mixture is compressed in an engine
cylinder. It is calculated by dividing the air volume in one
cylinder with the piston at BDC by the air volume in the cylinder when
the piston is at TDC (also refereed to as clearance volume) to 1.
Example: Volume at BDC is
42.35 the volume at TDC is 4.45. 42.35/4.45 = 9.5:1
Engine performance measurement.
Volumetric efficiency - The
amount of air/fuel mixture taken into the cylinder on the intake
stroke. The ratio is determined by the amount of air/fuel mixture
that actually enters the cylinder to the amount that could possibly
enter.
Example: A cylinder can
hold 0.034 ounces of air. The engine is running at a high speed
and 0.027 ounces get in so the volumetric efficiency is 0.027/0.034 or
80%. The volumetric efficiency should be at least 50% at high
speeds.
Ways to increase volumetric efficiency
a. Widen intake ports and passages and keep ports and
passages as straight as possible.
b. Smooth the inside surfaces of the intake ports.
c. Use more carburetors or carburetors with a larger
air passages.
Brake horsepower (bhp) -
Horsepower output or power delivered by the engine. This is measured
with a Prony Brake or Dynomometer.
Indicated horsepower (ihp) -
The power that develops inside the combustion chamber of the engine
during the combustion process. This calculated horsepower which does
not take into effect losses.
Friction horsepower (fhp) - The
power required by the engine to overcome the friction of the moving
parts in the engine (the greatest loss occurs when the rings scrape on
the cylinder walls).
The
relationship is bhp = ihp - fhp.
Engine efficiency - The relationship between power delivered
and power that could be obtained.
Mechanical efficiency
- The relationship between bhp and ihp.
Mechanical
efficiency = bhp / ihp
Example:
At a certain speed the bhp of an engine is 116 and the ihp is
135.
The mechanical
efficiency is 116
= .86 or 86%.
135
The remaining
14% is loss due to fhp.
Thermal efficiency - The
relationship between power output and the energy of the fuel burned.
The potential energy is calculated
