Modelling warm-up of an automotive catalyst substrate using the equivalent continuum approach

To predict automotive catalyst light-off time, an understanding of the processes controlling warm-up prior to light-off is necessary. Warming substrate temperature is predicted by numerical solution of the energy equations using the equivalent continuum approach, and predictions are compared with measurements. The experimental studies on warm-up, without chemical reactions, were performed with the substrates supplied via a sudden expansion or a conical diffuser. Encouraging agreement is obtained for washcoated and non-washcoated, metal and ceramic samples. The important parameters which characterise the substrate and the warming process are (hAv), the product of the heat transfer coefficient and the wetted surface area per unit volume; (pwCw), the product of the bulk density and the wall material specific heat; m´, the mass flow rate; and ξ(t), the rate of rise with time of gas temperature at inlet. The significance of these parameters and their influence on warm up is reviewed.