Internal Combustion Engine Intake-Manifold Aspiration Dynamics

Abstract

A model is developed for simulating and predicting the dynamics of intake-manifolds for automotive internal combustion engines. A thermodynamic control volume approach and bond graphs are used to derive mass and energy conservation equations. Simulation outputs include time histories of pressure, temperature, mass flow, energy flow, heat flow and overall volumetric efficiency. Cylinder pressure when the intake valve closes is intensively examined because it determines the volumetric efficiency. Increases in volumetric efficiency result from increases in pressure caused by dynamic effects. Volumetric efficiency versus rpm is used to evaluate the dynamic effects of certain intake-manifold configurations. Major design parameters are the length of the intake manifold pipe, diameter of the intake manifold pipe and length of the pipe upstream of the throttle valve. Changing manifold parameters can yield improvements in volumetric efficiency at certain engine speeds but can also cause deterioration at other speeds. Shortening the length of the upstream pipe moves the volumetric efficiency peaks to higher engine speeds.