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Temperatures were measured in the exhaust manifolds, takedown pipes, and post-converter components (tailpipe section) of several passenger cars under equilibrium conditions on a chassis dynamometer. Cast and fabricated exhaust manifolds of several designs were instrumented, as were single-wall and double-wall takedown pipes. Steady-state heat fluxes in exhaust components correlated with interior Reynolds numbers regardless of the engine operating condition. Nusselt numbers on component interior and exterior wall surfaces also correlated with Reynolds number. The interior Nusselt number was greater than that calculated for ideal flow with fully developed boundary layers. The ratio of measured to ideal-flow Nusselt numbers was relatively constant for a given component. These parameters are required for analytical modeling of the heat transfer performance of exhaust components, e.g., for the study of underhood and underbody heat loads.

Catalytic converters will be required in some future truck exhaust systems because of recently enacted emission standards. A computer model was developed to evaluate means to cool the exhaust to protect the converters to improve their durability. The model showed that changing the pipe diameter or wall thickness had little effect on exhaust cooling. Adding internal ribbing or exterior fins improved the exhaust cooling by only a few degrees C. Counterflow air-cooling was not found to be effective, but counterflow water-cooling was able to cool the muffler-out exhaust gas below the target temperature £or all test conditions.

The peak power of some vehicles can be limited by exhaust system backpressure contributed by a catalytic converter. A computer model was developed for flow and pressure drop in a generalized single-bed bead-bed catalytic converter to determine the sources of converter pressure drop and suggest improved designs with lower restriction. In an accompanying experimental study, pressure losses in the components of two different converters were determined in an engine-dynamometer test cell over a wide range of engine operating conditions. The measured and predicted pressure drops were in good agreement. The experience gained in this study was used to develop a low-restriction converter for truck applications.