TEST METHOD FOR MEASURING POWER CONSUMPTION OF ENGINE COOLING FANS
This SAE Recommended Practice is intended for use in testing and evaluating the approximate power consumption of engine cooling fans. This power consumption would then be used to estimate net engine power per SAE J1349. The procedure also provides a general description of equipment necessary to measure the approximate fan power consumption in a vehicle installation.
The test conditions in the procedure generally will not match those of the installation for which fuel consumption information is desired. The power required by a given fan depends on the geometric details of the installation, including the shroud and its clearance. These details should be duplicated in the test setup if accurate power measurement is expected. Required power at a given air density and speed also depend on the volumetric flow rate, or else the pressure rise across the fan, since these two parameters are mutually dependent. These parameters depend on the pressure drop across the radiator core and the ram pressure due to vehicle motion. Core drop and ram pressure tend to offset each other, but can be expected to cancel one another at only one vehicle speed at most. Tests run in the absence of the radiator core will not impose the proper pressure-rise requirement on the fan. Tests run with the radiator core in place will impose a greater pressure-rise requirement on the fan than it will likely experience at high vehicle speeds, when part of the rise will be provided by ram air. For these reasons, the test procedure should be recognized as providing only an approximate measure of installed fan power.
Although the test procedure is based on running the fan with a motoring dynamometer, the actual installation can be used as a test fixture if an accurate torque meter is available. In this case, the same qualifications discussed apply. Finally, for the effect of a fan clutch in reducing fan use and power consumption, which is not a part of this procedure, refer to SAE J1342.