Volumetric Efficiency and Air-Fuel Ratio Analysis For Flex Fuel Engines

Stringent vehicle emissions limits, fuel economy and driveability requirements demand an accurate air-fuel ratio management system. A flex fuel (ethanol capable) engine system without an ethanol sensor requires a precisely tuned air fuel ratio control system. In flex fuel systems without an ethanol sensor, the ethanol content is estimated based on the closed loop adaptation values, therefore; it is important to have a very good open loop estimate of cylinder trapped air and consumed fuel since an error in either of these values will cause a shift in the closed loop adaptation values and ultimately, in the estimated fuel ethanol content. This paper analyzes the effect of volumetric efficiency and stoichiometric air-fuel ratio variation of OTTO port fuel injection (PFI) engines when operating on ethanol. Proposals for correction of these parameters are compared to experimental data.