Automobile Exhaust-System Steady-State Heat Transfer

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. They also find application in the modeling of transient heat transfer in fully warmed-up exhaust systems.

Double-wall construction of the takedown pipe led to reduced heat losses and decreased exterior surface temperatures. Because of the steady-state heat conservation, the catalytic converter temperatures were higher for the systems with advanced technologies. Higher temperatures may have a negative impact on converter durability.