Abstract: An improved engine control in which the fuel volatility is detected based on a measure of the fired-to-motored cylinder pressure ratio, and used to trim fuel and spark timing controls during engine warm-up and transient fueling periods. In a first embodiment, a matrix of empirically determined pressure ratio values that occur with fuels of differing volatility is stored and compared to the measured pressure ratio to identify the closest stored pressure ratio, and the fuel volatility is determined based on the fuel volatility associated with the identified pressure ratio. In a second embodiment, the actual fuel vapor-to-air equivalence ratio is computed based on the measured pressure ratio, and the fuel volatility is determined based on the deviation between the actual ratio and the desired fuel vapor-to-air equivalence ratio.

Abstract: An improved engine fuel control method which divides the liquid fuel into a plurality of components characterized by relative volatility. The mass and evaporation characteristics of each fuel volatility component are determined separately within the fuel puddle, with the overall puddle behavior being characterized as the sum of the behaviors of the individual volatility components. The method involves determining, for each engine cycle, the mass of fuel that will evaporate from the puddle, the mass of vapor required to achieve the desired air/fuel ratio for the engine cylinder, the fraction of the injected fuel that will vaporize, and the mass of fuel that needs to be injected in order to achieve the desired air/fuel ratio in the cylinder. Finally, the puddle mass is updated for the next intake event.