High Cell Density Flow Through Substrate for New Regulations

This paper, written in collaboration with Ford, evaluates the effectiveness of higher cell density combined with higher porosity, lower thermal mass substrates for emission control capability on a customized, RDE (Real Driving Emissions)-type of test cycle run on a chassis dynamometer using a gasoline passenger car fitted with a three-way catalyst (TWC) system. Cold-start emissions contribute most of the emissions control challenge, especially in the case of a very rigorous cold-start. The majority of tailpipe emissions occur during the first 30 seconds of the drive cycle. For the early engine startup phase, higher porosity substrates are developed as one part of the solution. In addition, further emission improvement is expected by increasing the specific surface area (GSA) of the substrate. This test was designed specifically to stress the cold start performance of the catalyst by using a short, 5 second idle time preceding an aggressive, high exhaust mass flowrate drive cycle. The evaluation results showed that the substrate with the lowest ratio of bulk density to GSA had the best cold-start emissions control capability, with 21% lower NMHC and 30% lower NOx during the first phase of the aggressive cold start drive cycle compared to a standard porosity substrate. A cell density higher than 1000 cells/in² was found to be 32% more effective than a standard 900 cells/in² substrate at controlling high space velocity, higher temperature NMHC+NOx emissions. The paper concludes with the development status of next generation higher porosity, higher cell density ceramic substrates.