Control of the Start of HCCI Combustion by Pulsed Flame Jet

Homogeneous Charge Compression Ignition (HCCI) engines with lean fuel/air mixtures have a number of advantages over conventional spark ignition engines and compression ignition engines, such as decrease in soot and NOx emissions simultaneously, while achieving high thermal efficiency. As the onset of HCCI combustion depends on the autoignition of the fuel, it is quite difficult to control the start of combustion directly. On the other hand, it has been revealed that Pulsed Flame Jet (PFJ) has a great potential to enhance ignition reliability and burning rate in lean mixtures within the flammability limit. In PFJ, the combustion is initiated in the jet issuing from the orifice of the PFJ igniter, that is, the combustion is initiated volumetrically. This volumetric combustion initiation must behave as a trigger for the autoignition of the fuel in the combustion chamber. Presented here is an experimental proof of direct ignition timing control of HCCI combustion by PFJ. In the experiments, a compact rapid compression machine (RCM) was used to create a high pressures and high temperatures environment. The fuels used were lean n-butane/air mixtures. The experimental results showed that the start of combustion of lean n-butane/air mixtures has changed appropriately with varying the ignition timing of the PFJ igniter. The combustion phenomena were photographed by high-speed video, and it was obvious that the jet issuing from the PFJ igniter behaved as a trigger for the autoignition of the fuel in the combustion chamber. Therefore it was revealed that PFJ has a potential for controlling the start of HCCI combustion directly.