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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.

Lean-burn is the most attractive way to lower emissions of NOx while improving the fuel consumption simultaneously in spark ignition engines. A Pulsed Combustion Jet (PCJ) ignition system has a great potential to enhance ignition reliability and burning rate of lean fuel-air mixtures. Its action is based on the utilization of turbulent plumes formed by jets produced by generators, in the shape and size of an ordinary spark plug, that embody a small (500 mm3 or less) cavity, capped with an orifice plate and outfitted with a hollow electrode. Performance characteristics of PCJ were established by combustion tests carried out in a diskshaped, constant volume combustion chamber using lean methane-air mixtures. The results were compared to those obtained with Pulsed Plasma Jet (PPJ) an standard spark plug ignition systems. Lean limit was extended most by PCJ ignition under both quiescent and swirl conditions.

In order to confirm quantitatively the performance and characteristics of the plasma jet ignition in turbulent lean mixtures, combustion tests were carried out in a disk-shaped combustion chamber with lean turbulent methane-air mixtures. In the tests, the governing parameters of the plasma jet ignition such as the plasma cavity size, the orifice diameter, and the discharge energy were varied. A characteristic lifetime and a characteristic length of the plasma jet and an entrainment volume of the mixture into the plasma jet are defined theoretically and expressed by the parameters of the plasma jet ignition. A series of combustion tests revealed that lean flammability limits, a comparing parameter, and a combustion index are correlated with these characteristic values, where the comparing parameter shows the degree of combustion enhancement by the plasma jet ignition in its initial stage and the combustion index represents the total combustion performance of the plasma jet ignition.