Turbulent Flow Fields Analysis and Aerosol Dynamics of Exhaust from a Diesel Engine inside Two Dilution Sampling Tunnels

BO YANG (1,2), Yan Wang (2), Ke Max Zhang (2), Eric M. Lipsky (3), Allen L. Robinson (4)

(1) College of Automotive Engineering, Jilin University, Changchun, China, (2) Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY, USA, (3) Engineering, Pennsylvania State University, McKeesport, PA, USA, (4) Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

     Abstract Number: 453
     Last modified: May 12, 2010

Abstract
The development of emission inventories and regulations rely on the results from emission testing. A fabricated dilution system is used by many emission testing procedures, and for almost all major combustion sources. The main objective of our study is to investigate the effects of mixing processes in fabricated dilution systems on diesel engine emission measurements. As the first step, turbulent flow fields and aerosol dynamics of two dilution sampling tunnels were investigated using a coupled computational fluid dynamics (CFD) and aerosol dynamics model, developed at Cornell University. One dilution tunnel is a variation of the widely cited Caltech design (referred to as Caltech dilutor), and the other is a portable dilution sampler designed by Carnegie Mellon University (CMU), referred to as CMU dilutor. Turbulent flow fields were modeled by k-epsilon model and the aerosol dynamic processes, including nucleation, condensation and coagulation were simulated using the Eulerian method. Computational results show a reasonable agreement with the experimental data reported by Lipsky and Robinson (AS&T, 2005) for diesel exhaust. The exhaust and the ambient air mixed well at the downstream location of both dilution tunnels. The CMU dilutor could provide more rapid mixing as compared with the Caltech dilutor resulting in large differences in total particle number between the two tunnels. Nucleation occurred in the Caltech dilutor but not in the CMU dilutor. Turbulent flow separation and recirculation regions are likely factors affecting the nucleation phenomena inside the tunnels according to computational results.