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.