Numerical Study on Skin Temperature and Heat Loss of Vehicle Exhaust System

The ability to accurately predict skin temperatures of catalytic converter and manifold is very important for a robust/durable design of the vehicle exhaust system, especially in the development of close coupled converter system. In this paper, Computational Fluid Dynamics (CFD) is used to calculate the skin temperature of complicated components in vehicle exhaust system such as catalytic converter. Generally, a catalytic converter consists of substrate, mat, outer shell, inner cone, cone insulation, and outer cone. 3-D compressible turbulent fluid flow with heat transfer involved in force and natural convections, heat conduction and radiation is numerically simulated. First, both numerical calculation and experimental tests are conducted for a catalytic converter under the same operation conditions to evaluate the accuracy of current numerical method. Good agreement is found between CFD prediction and experimental tests. Next, the method developed is employed to investigate the effect of different mat materials and thickness, different cell structures of substrate and different kinds of cone insulations on skin temperature. Furthermore, the heat loss of exhaust gas through the dual pipe duct is studied. The effect of air gap between inner and outer tubes and inlet gas temperature on heat loss is investigated and the optimization of the air gap is obtained to minimize the total heat loss. A general correlation of temperature loss through the dual pipe is given at end as a function of tube air gap and inlet exhaust gas temperature. The analytical simulations have highlighted the benefits of using numerical tools in optimizing the exhaust system design.