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A modelling study is presented in this paper, whose objective is to obtain design criteria for optimum layouts and dimensions of exhaust manifolds in automotive engines. The first step has been the characterisation of the pulsating flow phenomena in the exhaust manifold, focusing on the pressure wave propagation process and on the interaction between cylinders across the manifold. Two relevant phenomena have been studied: the reflection of under-pressure pulses at pipe junctions and open ends, and the interference between exhaust processes of different cylinders. These phenomena have been characterised respectively by non-dimensional parameters, related to the layout and dimensions of the manifold. A parametric modelling study has been performed in order to evaluate the effects of the manifold dimensions on the engine performance. The work has been focused on a four-cylinder engine with a four-branch manifold.

An original calculation model based on the acoustic-wave theory is presented in this paper, capable of calculating the overall dimensions of an optimum intake manifold, with the aim of improving the gas exchange process in the engine. Some parameters depicting the dynamic interaction between the engine and the manifold are defined, which also allows the assessment of the manifold quality. By employing these parameters, the model can be applied in two complementary modes: the acoustic analysis of an existing manifold and the synthesis of an optimum geometry according to the design requirements and restrictions. The model results are assessed by the test on engine of some prototype intake manifolds, designed following the guidelines of the model.

The results of a predictive modelling study on the transient load response of a heavy-duty turbocharged diesel engine are presented in this paper. The model is based on a wave-action calculation code, whose input parameters are managed by an external module, which updates their value according to the changing engine running conditions. The transient operation aimed at is a load increase from idle to full load, at constant engine speed. Several modifications to the engine design have been simulated: valve size and timing, inlet manifold dimensions, insulation of the exhaust manifold, and turbine design. The response of the engine operation to these modifications has been evaluated by means of the transient duration and of the evolution of relevant engine parameters.