Thermal Studies in the Exhaust System of a Diesel-Powered Light-Duty Vehicle

This paper is a continuation of an earlier paper, which examined the steady-state internal heat transfer in the exhaust system of a diesel powered, light-duty vehicle. The present paper deals with the heat transfer of the exhaust system during two types of transient testing, as well as, the estimation of the exhaust systems external heat transfer. Transient heat transfer was evaluated using: a simple fuel-step transient under constant speed and the New European Driving Cycle (NEDC). The thermal response of the external walls varied considerably for the various components of the exhaust system. The largest percent difference between the measured temperatures and the corresponding quasi-steady estimates were about 10%, which is attributed to thermal storage. Allowing for thermal storage resulted in an excellent agreement between measurements and analysis. External steady-state heat transfer analysis was performed on various exhaust-system components by estimating the relative importance of forced and free convection and radiation. Based on rough estimations of the external heat transfer from the takedown pipe, free convection contributed 50% of the total heat losses; forced convection and radiation contributed equally to the other half.