Study of Effects of Thermal Insulation Techniques on a Catalytic Converter for Reducing Cold Start Emissions 2018-01-1431

Previous work done at the University of Michigan shows the capability of the vacuum-insulated catalytic converter (VICC) to retain heat during soak and the resulting benefits in reducing cold start emissions. This paper provides an improved version of the design which overcomes some of the shortcomings of the previous model and further improves the applicability and benefits of VICC. Also, newer materials have been evaluated and their effects on heat retention and emissions have studied using the 1-D after treatment model.

Cold start emissions constitute around 60% to 80% of all the hydrocarbon and CO emissions in present day vehicles. The time taken to achieve the catalyst light-off temperature in a three-way catalytic converter significantly affects the emissions and fuel efficiency. The current work aims at developing a method to retain heat in catalytic converter, thus avoiding the need for light-off and reducing cold start emissions effectively. Various techniques under study involve recovering heat from exhaust gases downstream of catalyst bricks, composite insulation with different materials and geometry optimization of the phase change material (PCM) around the catalyst bricks to increase the heat absorption rate and storage capacity for prolonged cool down periods. Analytical models were developed and the variants were tested using real-world cycle data. Two variants were studied, with modifications made to the thickness of the insulation layer and PCM layer. Furthermore, a target heat transfer curve was constructed and a set of simulations were performed to identify the physical properties of the PCM that would closely imitate the target curve and this was used to search for alternate PCM materials that favor this application.