California Partners for Advanced Transportation Technology

The purpose of this report is to experimentally determine the air flow through the cooling module (air-conditioning condenser plus engine radiator) of a Ford Windstar minivan when the van is operated at a fraction of a vehicle length behind a lead van. Pressures and temperatures are measured across the cooling module while the vans are in operation, and a standard calibration relates the pressure drop to the flow velocity through the cooling module. The Windstars are connected in tandem and driven on a test track at spacings of 0.22, 0.28, 0.38, 0.62, 0.88, and 1.0, expressed as fractions of the Windstar length. For the purposes of the test, an override switch is installed to allow the close-following van to be operated either with both cooling fans remaining on or with both fans disabled. Air flow is expressed either as a volume flow, in cubic meters per second, or as the fraction of the flow for a van operating in isolation at the same forward speed. With both fans disabled, the air flow is approximately twenty per cent of the isolation value at the shortest spacing, and increases to about sixty per cent at a spacing of one vehicle length. With both fans operating, the air flow is approximately fifty per cent of the isolation value at the shortest separation, and increases to about seventy per cent at one vehicle length separation. These represent substantial decreases in air flow, and will result in a diminished operating envelope for the vehicle in close-following.