Modeling the effect of fuel ethanol concentration on cylinder pressure evolution in Direct-Injection Flex-Fuel engines

A physics-based lumped-parameter model for the cylinder pressure evolution during the compression stroke in Flex-Fuel Direct-Injection (DI) engines is developed in this paper. The proposed model captures the fuel vaporization process for ethanol-gasoline fuel blends and the associated charge cooling effect. In addition, a detection residue is introduced to process cylinder pressure measurements under two different fuel injection patterns and extract the charge cooling effect caused by fuel vaporization during the compression stroke. The residues calculated from the proposed model were validated with those generated from experimental cylinder pressure for different gasoline-ethanol blends and various speeds and loads on a 2.0 L Turbocharged Spark Ignited Direct Injection (SIDI) engine with Variable Valve timing (VVT). Residues generated from both measured and modeled cylinder pressure exhibit a monotonic correlation with the fuel ethanol content for all the tested engine operating conditions. The promising results point to the potential of the proposed model to be integrated with the residue generation algorithm into a real-time model-based scheme for ethanol detection.