Figure 2-58. Forms of Energy.
braking device is tightened until the engine is
exerts a force of 300 lb. on the scale through a 2-ft-
slowed to a predetermined rpm. As the braking
long arm when the brake device holds the
device slows the engine, the arm attached to it
engine's speed at 3,000 rpm. By using the'
exerts pressure on a scale. Based on the reading
formula, calculate the brake horsepower as
at the scale and the engine rpm, a brake
horsepower value is calculated by using the
6.28 x length of arm x engine rpm x scale reading
It must be noted that the figures 6.28 and 33,000
a. General The modern method for checking
are constants in the formula, meaning that they
engine power output is by using a dynamometer.
The dynamometer can be used to check the output
of the engine at the crankshaft or the horsepower
of the engine can be measured at the driving
wheels of the automobile by using a chassis
b. Types of Dynamometers. The dynamom-
eter, like the prony brake, loads an engine down
to a given rpm and measures the torque that it
produces at that given speed. There are two basic
(1) One type of dynamometer-uses a large
electrical generator to which the engine is
attached. The engine brake horsepower then can
be calculated by converting the electrical power
generated into horsepower readings.
(2) Another type of dynamometer uses a
water brake to absorb engine power and calculate
Figure 2-59. Horsepower.
never change. For example, a given engine