Experimental and Simulation Study of Zero Flow Impact on Hybrid Vehicle Emissions 2024-37-0036

Combustion engines in hybrid vehicles turn on and off several times during a typical passenger car trip. Each engine restart may pose a risk of excessive tailpipe emissions in real-drive conditions if the after-treatment system fails to maintain an adequate temperature level during zero flow. In view of the tightening worldwide tailpipe emissions standards and real-world conformity requirements, it is important to detect and resolve such risks via cost-effective engineering tools relying on accurate 3d analysis of the thermal and chemical behavior of exhaust systems. In this work, we present a series of experiments to examine the impact of zero-flow duration on the exhaust system cooling and subsequent emissions risk. We also present a catalyst model calibrated to predict the 3d thermal and chemical behavior under normal and zero flow conditions. Particular emphasis is given to the phenomena of free convection and thermal radiation dominating the heat transfer at zero flow. Following the model validation against temperature and emissions measurement, the model can subsequently be used to study several scenarios of vehicle hybridization schemes, as well as techniques to minimize the risk of zero flow operation by proper design and control. Overall, the model is able to accurately predict the temperature distribution inside the catalyst and tail pipe emissions, under a broad range of operating conditions, which tend to underline the robustness of the followed methodology.