Flow measurements across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser

Abstract

Flow measurements are presented across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser. Particle image velocimetry measurements were obtained in the diffuser and the flow distribution within the monolith was obtained from hot wire anemometry at the monolith exit. Flow separation at the diffuser inlet resulted in the formation of a jet that traversed the diffuser before spreading just prior to entering the monolith. The jet featured a potential core and saddle-type velocity profiles. A free shear layer separated the jet core from two large recirculation regions that developed in the diffuser narrowing the potential core. The flow field in the main body of the diffuser was observed to be independent of Re in contrast to that within the monolith. Increasing monolith length gave greater flow uniformity in the monolith as a consequence of jet spreading. Comparing the axial velocity flow profiles ∼ 3 mm upstream of the monolith to that downstream showed that significant flow redistribution occurred as the flow entered the monolith, resulting in more flow entering peripheral channels. It is inferred that pressure loss arising from oblique entry into monolith channels significantly affects the flow distribution within the monolith.

Pulsating flow in a planar diffuser upstream of automotive catalyst monoliths

“…Re is defined as U in d h / v where U in is the mean velocity at the diffuser inlet, d h the hydraulic diameter of the nozzle (38.4 mm) and v the kinematic viscosity. The shear layers at the sides of the jet are clearly shown as are the saddle-shape profiles in its potential core; similar features have been observed by Quadri et. al.…”

“…Ilgner et al (2001), made PIV measurements upstream of an auto-thermal gas reformer but significant image distortion due to wall curvature restricted the field of view where reliable data could be obtained. Using a planar diffuser optical distortion was minimised by Quadri et al (2009a). By comparing the upstream flow field (PIV) with that measured downstream of the monolith using HWA it was demonstrated that the monolith radically redistributes the flow as it enters the channels.…”

On the effects of flow pulsation upon the performance of flow deflector for catalytic converter

“…So, to explain the present results more comprehensibly, we should discuss the flow in the catalyticconverter diffuser part which will bring us deeper and fruitful understanding, engineering innovation and so on. Recently, Quadri et al (2009) and Yamin et al (2013) have visualised the flow in the catalytic-converter diffuser part using a twodimensional model for steady and pulsating flows, respectively. While they are in the no-flow-deflector case of course, they have shown the importances of the catalyst-converter substrate part, the frequency of flow pulsation and so on.…”