Direct injection assisted HCCI combustion of natural gas

Direct injection of n-heptane is investigated as a means of providing a measure of direct control over the ignition and combustion timing in a natural gas fuelled HCCI engine.This study examines the use of a direct injection event to extend the load range and control the ignition of a natural gas HCCI engine. The injection can be varied on a cycle-to-cycle basis to meet transient loading conditions without requiring changes in inherently slower control mechanisms. The load range of the engine is extended with the direct injection event at the cost of increased NOx emissions, with no significant efficiency penalty.The benefits of HCCI engines include reduced NOx emissions and increased efficiency. HCCI combustion is inherently difficult to control due to the lack of a timed ignition event. Slower control mechanisms such as intake temperature, intake pressure, and EGR are insufficient for constant speed engines.