Abstract: A liquid primary fuel is ignited by HCCI with the assistance of the early injection of a liquid pilot fuel. Pilot fuel injection and/or ignition are preferably controlled so as to permit the injected pilot fuel to become thoroughly distributed through and mixed with the primary fuel/air charge in the combustion chamber and vaporized prior to ignition. Pilot fuel having a lower autoignition temperature will be ignited by compression ignition, followed by the ignition of the homogeneous mixture of the primary fuel and air. HCCI combustion of the primary fuel is facilitated by 1) selection of the properties of the primary and pilot fuels and 2) obtaining a homogenous mixture of primary fuel and air by injecting primary fuel into the engine's intake air stream in the form of finely atomized droplets having a mean diameter in the micron range.

Abstract: Pilot fuel injection and/or ignition are controlled in a pilot ignited, gas-fueled, compression ignition engine so as to maintain a relationship Dp/Di of <1, where Dp is the duration of the pilot injection event and Di is the ignition delay period as measured from the start of initiation of pilot fuel injection (Tp) to the start of pilot fuel autoignition (Ti). Dp/Di is less than 1 when a mixing period Dm exists between the end of pilot fuel injection and the start of autoignition. This mixing period permits the injected pilot fuel to become thoroughly distributed through and mixed with the gaseous fuel/air charge in the combustion chamber and vaporized prior to ignition, resulting in improved premixed burning of a heterogeneous mixture of the pilot fuel, the gaseous fuel, and air and dramatically reduced NOx emissions.