Inertial effects on fluid flow through manifolds of internal combustion engines

Abstract

The flows in intake and exhaust manifolds of internal combustion engines play a major role in determining the different (volumetric, scavenging, and trapping) efficiencies, indicated power, performance, and emissions and in establishing the flow field within the engine cylinder. When the gas flows unsteadily through these systems, friction, pressure, and inertial forces are present. The relative importance of these forces depends on gas velocity and the size and shape of such systems. Traditionally, these flows are studied by means of the one dimensional (1D) gas dynamics equations, where the 3D phenomenon of the flow and the pressure wave's deformation, turbulence, and viscosity are ignored or neglected. The thermodynamic (0D) approach is also used where the important effect of fluid inertia related to the size of manifold components is ignored. In this study, the filling and emptying method is completely revised and a new method, based on the thermodynamic formulation of the filling and emptying and on the fundamental equation of momentum conservation, is developed. The objective is then to take into account the fluid inertial effects on the fluid behaviour without the use of a one-dimensional 1D code (due to the computational times). In this objective, a computational fluid dynamics analysis is made in order to calculate the tuning parameters of the ‘inertial capacitive method’ corresponding to the new model. In this study, it appears that the ignored inertial effects from the formulation of the filling and emptying method is the reason why theis latter becomes only appropriate for the compact manifolds. To validate the new model, experimental investigation is carried out on a single-cylinder four-stroke engine. The volumetric efficiency of the engine is then calculated with the new model. The result is compared to the experimental one and a correct agreement is obtained.