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Optimization of the mechanical aspects of a heated conical oxygen sensor for desired performances, such as low heater power, good poison resistance, fast light-off, and broad temperature range, etc. was achieved with computer modeling. CFD analysis was used to model the flow field in and around a sensor in an exhaust pipe to predict the convection coefficients, poisoning, and switching time. Heat transfer analysis coupled with electrical heating was applied to predict temperature and light-off time. Results of the optimization are illustrated, with good agreements between modeling and testing.

A numerical model was developed for the transient heat transfer phenomena occurring in automotive exhaust systems. The model considers heat convection along the gas flow, convection between the gas and the pipe wall, conduction in the pipe wall, and radiation and convection to ambient. The model is capable of modeling pipes fabricated with layered materials or multiple walls with air gaps or insulation. The model correlates well with experimental data measured in a takedown pipe with cold start exhaust gas from a typical engine. Parametric studies provided an understanding of the effects of various pipe designs and materials on the temperature of the exhaust gas entering a downstream catalytic converter for a more efficient light-off response.

A previously developed three-dimensional, transient numerical model was extended to Pt/Rh catalyzed oxidations. The numerical model has been applied to a metal monolith converter for simulations of the light-off conversion performances and thermal response during a thermal cycling test. In this study, we consider an oval converter with a metal monolith substrate which has fully orthotropic thermal properties. The analysis accounts for transient inlet exhaust gas conditions and non-uniform inlet flow distributions. The simulation covers a wide range of exhaust gas stoichiometrics. The predicted light-off conversion efficiencies are very close to the test results. The simulated temperatures compare favorably with the measured data throughout the converter. Temperature contours are also illustrated and the temperature gradients can be as high as 500°C/cm at the monolith edge during thermal cycling.

Recent advanced heat engine development has led to the use of a ceramic port liner casted into the aluminum cylinder head as a thermal insulation between aluminum and exhaust gas to reduce the weight of the engine and improve its performance. This study evaluates the high transient tensile stresses generated in the port liner due to thermal shock during casting and the compressive shrinkage stresses during cool-down by finite element simulation. The survivability of the liner under thermal shock was assessed by a statistical failure criterion and the results showed that both cordierite and aluminum titanate survive. Shrinkage stress analyses indicated that the shrinkage stresses in the aluminum titanate were less than its compressive strength except at the sharp edge around the valve guide hole while the shrinkage stresses in the cordierite were greater than its compressive strength in most of the region.

A transient three-dimensional model has been developed to simulate the thermal and conversion characteristics of nonadiabatic monolithic converters operating under flow maldistribution conditions. The model accounts for convective heat and mass transport, gas-solid heat and mass transfer, axial and radial heat conduction, chemical reactions and the attendant heat release, and heat loss to the surroundings. The model was used to analyze the transient response of an axisymmetric ceramic monolith system (catalyzed monolith, mat, and steel shell) during converter warm-up, sustained heavy load, and engine misfiring. The simulation indicates that high solid temperatures are encountered during sustained heavy load or engine misfiring, while steep temperature gradients are developed during the converter warm-up period. Flow maldistribution and radial heat loss are major sources for the thermal gradients.