A modeling study has been conducted in order to characterize the heat transfer in an automotive diesel exhaust system.
The exhaust system model, focusing on 2 exhaust pipes, has been created using a transient 1-D engine flow network simulation program. Model results are in excellent agreement with experimental data gathered before commencement of the modeling study. Predicted pipe exit stream temperatures are generally within one percent of experimental values.
Sensitivity analysis of the model was the major focus of this study. Four separate variables were chosen for the sensitivity analysis. These being the external convective heat transfer coefficient, external emissivity, mass flow rate of exhaust gases, and amplitude of incoming pressure fluctuations. These variables were independently studied to determine their contribution to changes in exhaust gas stream temperature and system heat flux.
There are two primary benefits obtained from conducting this analysis. First, by obtaining variable sensitivities, one can estimate the accuracy of future modeling studies. Second, by ranking the relative sensitivities, proper effort can be directed towards variables of great importance while avoiding time consuming studies of unimportant variables.
All sensitivity levels were found to be relatively low, within acceptable ranges. This gives confidence that 1-D modeling can be used to accurately estimate gas temperatures throughout diesel exhaust systems.