Influence of Intake Manifold Heat Transfer Effects on Accuracy of SI Engine Air Charge Prediction

Estimation of the actual cylinder air charge and air-charge prediction several engine events into the future are needed to implement an air-fuel ratio feedforward controller. The estimator/predictor is usually based on the isothermal intake manifold model which assumes constant temperature of manifold air. However, fast thermocouple measurements have pointed to significant changes of manifold air temperature during typical tip-in/tip-out engine transients. In order to capture the temperature change effect, the manifold dynamics should be described by the so-called polytropic model. This paper presents an algebraic and simulation analyses of the influence of manifold modeling errors on the accuracy of air-charge prediction. The analysis is conducted for a typical predictor given in two variants depending on whether the throttle mass flow sensor or the manifold pressure sensor is used.