HEAVY DUTY VEHICLE EXHAUST PLUME STUDY IN THE NASA/LANGLEY WIND TUNNEL

Concern over health effects associated with diesel exhaust and debate over the influence of high number counts of particles in diesel exhaust prompted research to develop a methodology for diesel particulate matter (PM) characterization. As part of this program, a tractor truck with an electronically managed diesel engine and a dynamometer were installed in the Old Dominion University (ODU) Langley full-scale wind tunnel. This arrangement permitted repeat measurements of diesel exhaust under realistic and reproducible conditions and permitted examination of the steady exhaust plume at multiple points. Background particle size distribution was characterized using a Scanning Mobility Particle Sizer (SMPS). In addition, a remote sampling system consisting of a SMPS, PM filter arrangement, and carbon dioxide (CO₂) analyzer, was attached to a roving gantry allowing for exhaust plume sampling in a three dimensional grid. Raw exhaust CO₂ levels and truck performance data were also measured. The plume centerline was mapped and dilution ratios were determined and mapped. At 55 mph truck wheel speed and steady wind speed operation, at 200 inches behind the stack at the plume centerline, the dilution ratio was about 75, and at 337 inches behind the stack the dilution ratio was about 125. The truck was also operated through repeated transient tests, from 40 to 55 mph, with a wind speed of 47 mph. CO₂ variations in the plume were clearly detected during the transients. Steady state PM size measurements were made at scan rates of 90 seconds. Ambient samplers located in the tunnel determined PM loading by mass. This paper presents the methodology used, discusses the plume location and dilution, and discusses results from ambient samplers. Particle sizing results are given in a companion paper.