An Improved Branched Pipe Model for Multi-Cylinder Automotive Engine Calculations

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Abstract
This paper describes a new mathematical model for calculating the behaviour of unsteady gas flow in engine manifold junctions of any configuration. The model, which allows for pressure losses at the junction, is arranged for use with engine simulation computer programs in which the gas dynamics analysis is based on the method of characteristics. Experimental coefficients obtained from steady flow tests are presented for use with existing momentum theory models and also with the generalized approach. Measured pressure-time histories and performance data for a multi-cylinder engine are compared with computer predictions using three different pipe branch calculations: constant pressure theory, momentum theory and the generalized procedure. This comparison shows the new technique gives correlations which are better than the constant pressure method but without the limitations and complexity of the model based on momentum theory.

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