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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 internal combustion engines, lean-burn is particularly attractive for minimizing pollutant emissions, in particular NOx, with a concomitant improvement in fuel economy. For combustion in lean fuel-air mixtures, achievement of adequate reliability of ignition and sufficiently high burning rate requires special devices. The most effective among them is the injection of active radicals by means of PFJ (Pulsed Flame Jet) ignition system. Presented here is an experimental proof of the action of the hydroxyl (OH) radical produced by such an ignition system. The measuring apparatus used for this purpose was based on PLIF (Planar Laser-Induced Fluorescence), and the effects of equivalence ratio of the mixture in the cavity, cavity volume, and orifice diameter on the variation of OH fluorescence area in the jet and their intensity were revealed quantitatively.