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An electromechanically driven valve train offers unprecedented flexibility to optimize engine operation for each speed load point individually. One of the main benefits is the increased fuel economy resulting from unthrottled operation. The absence of a restriction at the entrance of the intake manifold leads to wave propagation in the intake system and makes a direct measurement of air flow with a hot wire air meter unreliable. To deliver the right amount of fuel for a desired air-fuel ratio, we therefore need an open loop estimate of the air flow based on measureable or commanded signals or quantities. This paper investigates various expressions for air charge in camless engines based on quasi-static assumptions for heat transfer and pressure.

This paper presents heat release regressions for the combustion modes in a gasoline direct injected (GDI) engines. These heat release regressions can be used in one-dimensional flow codes and mean value models as a simplified representation of combustion. The heat release profiles are approximated as functions of crank angle, with some free parameters. These parameters are fitted as functions of engine operating conditions, so that a continuous family of curves is obtained. GDI engines have four distinct modes of combustion: homogeneous rich, homogeneous stoichiometric, homogeneous lean and stratified lean, each requiring its own functional approximation. We present the functional approximations, the dependence of the parameters on engine operating conditions, and the quality of the fit on data from a 1.8 liter production GDI engine.