1,263 10.0

1,177 23.5

FOR DYNAMOMETER
POWER CALIBRATION

This appendix describes the method for de-
termining the road horsepower absorbed by
a chassis dynamometer. The measured ab-
sorbed road horsepower includes the dyna-
mometer friction as well as the power ab-
sorbed by the power absorption unit. The
dynamometer is driven above the test speed
range. The device used to drive the dyna-
mometer is then disengaged from the dyna-
mometer and the roll(s) is allowed to coast
down. The kinetic energy of the system is
dissipated by the dynamometer friction and
absorption unit. This method neglects the
variations in roll bearing friction due to the
drive axle weight of the vehicle. The differ-
ence in coast down time of the free (rear)
roll relative to the drive (front) roll may be
neglected in the case of dynamometers with
paired rolls.

This procedure shall be followed:

1. Devise a method to determine the speed
of the drive roll if not already measured. A
fifth wheel, revolution pickup or other
suitable means may be used.

2. Place a vehicle on the dynamometer or
devise another method of driving the
dynamometer.

3. Engage inertia flywheel for the most
common vehicle weight class for which the
dynamometer is used.

4. Drive dynamometer up to 50 m.p.h.
5. Record indicated road horsepower.
6. Drive dynamometer up to 60 m.p.h.
7. Disengage the device used to drive the
dynamometer.

8. Record the time for the dynamometer
drive roll to coast down from 55 m.p.h. to
45 m.p.h.

9. Adjust the power absorption unit to a
different level.

10. Repeat steps 4 to 9 above sufficient
times to cover the range of road horsepower
used.

11. Calculate absorbed road horsepower
from:

HP (1/2) (W1/32.2) (V12-V2)/(550t)
HPa 0.06073 (W1/t)
Where:

W1 = Equivalent inertia in lb.
V1

Initial velocity in ft./sec. (55 m.p.h.
80.67 ft./sec.).

V2 Final velocity in ft./sec. (45 m.p.h.

=66 ft./sec.).

t Elapsed time for rolls to coast from

55 m.p.h. to 45 m.p.h.

ROAD

HORSE-

CONSTANT VOLUME SAMPLER FLOW CALIBRATION The following procedure is used in Federal laboratories to calibrate the gas flow of constant volume samplers which use positive displacement pumps. First, the gas flow as a function of the pressure increase across the pump is determined. Second, the whole system, including the instruments, is checked to determine if it accounts for an amount of pure propane or carbon monoxide introduced into the system.

The following steps are followed to determine the gas flow as a function of the pressure increase across the pump, in cubic feet per pump revolution.

1. The pump inlet pressure depression during a typical test is determined.

2. A variable flow restrictor, such as a slide valve, is attached to the CVS at a point upstream of the sample point and the positive displacement pump The dilution air filter system may or may not be in use during calibration, depending on the particular CVS design.

3. A flow measuring device (laminar flow element) is attached ahead of the flow restrictor.

4. The CVS is operated at several diferent pump inlet pressure settings (controlled by the flow restrictor) and the measurements as specified in § 1201.83 (h), (j), (1), and (m), the time per test, and the measurements

7. Vo is plotted versus pressure increase across ahe pump, AP.

8. The flow measuring device is removed and attached to the exit of the CVS. Steps No. 4, No. 5, No. 6 and No. 7 are repeated. If the resulting two Vo versus AP plots differ significantly, the procedure is repeated with the flow measuring device ahead of the flow restrictor, steps being taken to eliminate the leaks which caused the discrepancy in the original data.

9. If the CVS exhaust system configuration and pressure are constant, the pressure inlet depression is substituted for the independent variable, JP.

The following procedure is followed to check the CVS calibration using a known quantity of injected gas. It assumes a reliable analyzer calibration.

1. A small cylinder is charged with pure propane or carbon monoxide gas.

2. The cylinder is weighed.

3. The CVS is operated in the normal manner and a quantity of pure propane or carbon monoxide is released into the system.

4. The calculations of § 1201.87 are performed in the normal way except the density of propane (17.30 grams/cu. ft./carbon atom) is used in place of the density of exhaust hydrocarbons.

5. The CVS measured mass is compared to the gravimetric measured mass.

6. The reason for any discrepancy is found and corrected.