Experimental verification of hydrodynamic similarity in hot flows

Abstract

[EN] This paper examines a common hypothesis in the design of internal combustion engine exhaust lines, namely that the ratio of the total pressure drop across the line to the inlet dynamic head should be a function only of the Reynolds number. While incompressible flow theory, provided that some simplifications are considered, is often used in support of this hypothesis, detailed experimental verification in actual exhaust lines is absent from the literature. Production exhaust lines contain non-trivial flow complexities such as muffler devices and catalytic converters and, in the case of high-performance engines, often operate at high temperature and high mass flow conditions, thereby rendering the usual theoretical simplifications doubtful. In this work, a production exhaust line composed of cold and hot ends, featuring a muffler and a catalytic converter, is tested at a variety of conditions. Analysis of the results shows that compressibility corrections must be factored in at certain conditions routinely found in actual high-performance engines, and that for hot ends, laminar flow at the converter monolith channels may pose a challenge to the hydrodynamic similarity hypothesis.