Nano Particulate Matter Evolution in a CFR1065 Dilution Tunnel 2009-01-2672
Dual primary full-flow dilution tunnels represent an integral part of a heavy-duty transportable emissions measurement laboratory designed and constructed to comply with US Code of Federal Regulations (CFR) 40 Part 1065 requirements. Few data exist to characterize the evolution of particulate matter (PM) in full scale dilution tunnels, particularly at very low PM mass levels. Size distributions of ultra-fine particles in diesel exhaust from a naturally aspirated, 2.4 liter, 40 kW ISUZU C240 diesel engine equipped with a diesel particulate filter (DPF) were studied in one set of standard primary and secondary dilution tunnels with varied dilution ratios. Particle size distribution data, during steady-state engine operation, were collected using a Cambustion DMS500 Fast Particulate Spectrometer. Measurements were made at four positions that spanned the tunnel cross section after the mixing orifice plate for the primary dilution tunnel and at the outlet of the secondary dilution tunnel. Gaseous emissions measurements were utilized as surrogate confirmation of adequate mixing at the various measurement locations. A computational fluid dynamic (CFD) model was employed to predict primary tunnel mixing and to determine the locations of primary tunnel sampling ports. These predicted gaseous emissions concentration levels were compared with measured levels to verify the CFD model. Results indicated varying size distributions across the tunnel cross sections where the flow was still developing. Homogenous particle size distributions were observed across the sections at locations where the primary flow was fully mixed. However, the profile of particle size distributions continued to evolve, due to residence time, even for fully mixed primary flow conditions. Variability of size distributions at the end of the secondary dilution tunnel was also observed with varied secondary dilution ratios. The effects of dilution ratios, dilution speeds, and residence time on diesel particulate matter (DPM) particle size distributions and particle mass concentration levels were analyzed and discussed.