Warming automotive catalysts with pulsating flows

Temperatures of an automotive catalyst substrate warmed by convection pre-l ight-off have been measured. Direct comparison has been made of warm-up by steady and pulsating flow for a one-dimensional flow case. The 32 Hz pulsat ing mass flow did not feature flow reversal. Pulsations were achieved by in terruption of the airflow by a rotating disc. Very small differences betwee n steady and pulsating cases were observed because the effect of mass flow pulsations on heat transfer is minimal. Two different computational fluid d ynamics methods were used to predict temperature. A one-dimensional porous medium model, which required input of an assumed heat transfer coefficient, was compared with a single-channel model. Predictions agreed closely and t here was also qualitative agreement with measurements. Similar mass flow pu lsations in the range 32-100 Hz have been studied for a case with a larger diameter automotive catalyst supplied via a conical diffuser. The radial fl ow distribution is controlled by pulsation frequency and the effect of freq uency on temperature at different depths in the substrate was observed expe rimentally. Pulsations will affect catalyst warm-up in practical systems be cause of their effect on flow distribution, rather than on heat transfer.