AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Dynamic Modeling Study for In-cabin Ultrafine Particle Transport: Evaluation of Infiltration and Passive Ventilation in a Wide Range of Driving Speed
EON LEE, Michael Stenstrom, Yifang Zhu, University of California, Los Angeles
Abstract Number: 187 Working Group: Indoor Aerosols
Abstract A few recent studies have proposed in-cabin ultrafine particle (UFP) models. However, these models did not incorporate infiltration and passive ventilation as a function of driving speed. This study presents a zero-dimension pseudo-steady-state model coupled with two sub-models describing infiltration and passive ventilation. The infiltration term was formulated using vehicle envelope leakage parameters (i.e., flow coefficient and pressure exponent) to address the dynamic behavior of infiltration as a result of the two competing processes: aerodynamic pressure on moving vehicle surface and mechanical cabin pressurization. The passive ventilation term was empirically derived from extensive field measurements. This model allows infiltration and passive ventilation to affect in-cabin UFPs at any driving speed in time. Model predictions agreed well with the experimental measurements in 12 different vehicle models as well as previously published data in the literature. In outdoor air (OA) mode, UFP I/O increases at increasing driving speed due to mechanical ventilation, passive ventilation, and infiltration. While mechanical ventilation dominantly controlled the I/O, passive ventilation and infiltration could also increase the I/O by 0.45 under fan off. In this case, surface deposition mechanism reduced the I/O in driving speed up to 60 and 90 km/hr in sedan and minivan, respectively. Above these driving speeds, passive ventilation and more importantly infiltration increased the I/O. When operating fan in OA mode, mechanical ventilation reduced the effects from infiltration and passive ventilation. Thus, in-cabin UFP concentration significantly changes by different particle gain/loss mechanisms and the magnitude of change depends on driving speed, ventilation condition, and vehicle type.