Browse Publications Technical Papers 2000-05-0038
2000-06-12

An approach of the engine charge efficiency ascertainment 2000-05-0038

Presented into this paper is a part of the research work carried out to upraise the charge efficiency of an automotive engine and subsequently to find a correlation between theoretical and experimental data concerning the airflow into the inlet duct. An airflow model for the charge efficiency ascertains was evaluated. The model is based on the evolution of pressure drop versus intake valve lift, considering the influence of the inlet valve through area and the layout of the valve came profile and inlet duct.
A two-step hybrid finite difference scheme was used to solve the differential system equations describing the specific processes, in the exhaust and intake systems of the engine. These equations use the laws of continuity of mass, conservation of momentum and energy applied to a small control volume. Estimation of the charge parameters was done using two different methods. First method considers the intake pipe and the cylinder as two control volumes. The flow between the two control volumes is a function of the flow characteristics through the inlet valve determined experimental, assuming in each computation step, the steady flow through the pipe. The second method assumes the unsteady flow through the pipe and takes into account the pipe junctions for each cylinder and flow dynamics including the throttle.
By processing the experimental data it was possible to have a response about the charge efficiency by considering the theoretical flow and maximum potential flow assured by the inlet duct during the intake air piston movement. A superposed of the results of the model concerning volumetric efficiency characteristic versus engine speed has demonstrated an increasing of the intake air rate in case of modified engine. During the engine tests, the conditions considered in the assumptions seemed justified by reasonably good agreement with some quantities and some qualitative data.

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