Variations of engine particulate matter in a miniature dilution tunnel

Measurement of diesel and spark ignition engine particulate emissions is of wide interest due to current research demonstrating that inhalation of nanoparticles may cause serious health problems. Both experimental and computational methods were used to investigate fluid and particle flows through a miniature dilution tunnel similar to those commonly used to sample particulate emissions from engines to help explain observed varabilities and bias, and to improve the repeatability of results. Laser Doppler Velocimetry, flow visualization, and a commercial CFD code were used to measure the flow field inside the apparatus. Slugs of NOx calibration gas and a high speed NOx concentration meter were used to measure mean velocities through the apparatus. An artificial aerosol generator was used in conjunction with a Scanning Mobility Particle Sizer (SMPS) to determine how tunnel geometry affects particle size distributions. These results were compared to a Monte Carlo type numerical simulation, accounting for Brownian motion and fluctuating turbulent velocities.;A comparison between the flow field measurement techniques, CFD results and published literature show the behavior similar to that expected from an enclosed turbulent jet. Centerline velocities of the jet decay as predicted by the literature with radial velocity profiles matching closely. A comparison between the SMPS results and the predicted size distribution at a particular point downstream from the Monte Carlo model exhibit similar magnitudes but do not follow the same trends, indicating that more refined modeling is needed. Nevertheless, this research strongly indicates that sampled submicron particle size distributions in dilution tunnels will be heavily influenced by the character of the turbulent mixing and the axial and radial locations of the sampling probe.