A new modelling of air dynamics inside ICE intake manifolds

Abstract

Higher performances, lower fuel consumption, emission reduction and better derivability are strictly related to the Air to Fuel ratio control. So, the new technology challenges in this area need new control strategies able to satisfy near and far future demands: an increasing role of the mathematical modeling is expected to occur, mainly for on board applications ( A/F model based control ). This paper presents a new modeling for the air dynamics able to describe the transient effects inside engine intake manifolds. The model can be considered as a further evolution of the Mean Value Engine Models, widely used in literature, that compensates for transient effects. Through a suitable formulation of the mass, momentum and energy equations the model predicts mass flow rates during engine transients without renouncing to simplicity and possibility to be used in the on board applications ( compatible with the near future electronic capabilities ). In this sense, the model appears to be an intermediate stage between lumped and distributed parameter models. The model considers the engine intake manifold ducts as a collection of small interconnected capacities, and each capacity interacts with the surrounding capacities as boundary condition. In this way, it becomes more simple to model the complicated duct geometry, which characterize the practical designs of the internal combustion engine’s intake manifolds. The application of the conservation equations at the capacity under consideration gives a set of three first- order differential equations, whose solution describe the pressure and the temperature in the capacity, in addition to the air velocity between adjacent capacities. Transient processes can be therefore described and their effects on the air mass trapped into the cylinder.