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M a n u a l
AutoDyn
Section 4 - Page 8
AutoDyn manual Section 4. PM7, 5/2004
cleaning. An epoxy paint mixed with an abrasive material is commonly
used.
4.4. Technical issues
4.4.1. Problem statement
The two major problems you will face in a chassis dynamometer test
room are heat evacuation and exhaust gas extraction.
All power generated by the engine will be converted to heat: in the
engine cooling system(s), engine compartment, vehicle transmission
and exhaust system, and in the dynamometer itself.
4.4.2. Air supply
Chassis dynamometer testing produces a lot of heat. This heat is for the
most part released to the test room air. Significant ventilation is required
to evacuate this heat from the room. If the room temperature increases
during the test, or exhaust gas recirculates into the engine inlet, your
test results will vary in an unpredictable manner. Both the quantity and
the direction of air flow are critical for repeatable test results.
The tables at the end of this section provide some examples of esti-
mated cooling requirements as a function of engine power.
The fan(s) you select must be able to generate the required airflow at
the pressure drop caused by your inlet and outlet ducting. Keeping the
length and complexity of ducting to a minimum greatly reduces the
pressure drop and thus the fan power required. Axial fans are most
effective for high airflow at low pressure drops. The fan(s) are best
installed on the outlet side. This way, a slight negative pressure (about
0.5 to 1 inH
2
O or 100 to 200 Pa) is maintained in the test room; this
prevents noxious fumes from entering the rest of the building.
A cross-flow design is recommended for the ventilation system. The air
inlet should draw fresh air from outside the building, and should be
positioned away from the air outlet, to prevent air recycling. If engines
will be tested without air filter, appropriate air filters should be installed
on the inlet ducts. We recommend 92% efficient filters. In that case, it is
best to provide a pressure manometer across the filters; once the filters
become clogged, the ventilation system may not be able to overcome
the pressure drop and the air flow through the room will rapidly
decrease.
For pit installations of an Eddy Current dynamometer, a 24” (60 cm) or
larger duct with a suitable blower should be provided for adequate
absorber cooling air supply.
The large fans required to provide the necessary airflow are noisy. They
should be installed in a location where the noise causes minimal