A complete numerical and experimental investigation has been carried out on the thermal behavior of a diesel car exhaust system aimed to develop design tools for the exhaust system and thermal shields.
Both one and three dimensional analysis have been conducted by means of commercial codes.
The one dimensional model calculates the exhaust gas temperature evolution, from the engine to the tail pipe, due to convection with the system walls and estimates convective heat transfer coefficients between walls and external ambient. Starting data have been the inlet exhaust gas temperature, as measured on a complete vehicle, and average ambient air velocity, as estimated using external aerodynamics simulations.
Two three-dimensional models of the complete car underbody have been built. One is a FEM model that calculates radiation between components and uses fixed thermal coefficients for the convection. The second one is a complete CFD model, intended to precisely evaluate convective phenomena. Both models allow to detect the most critical points in terms of higher temperatures.
A prototype car has been instrumented to record the temperatures of the exhaust gas and exhaust system surface in different locations and the skin temperatures of many underbody components. These data have been used to validate and evolve the models.