Abstract
In diesel engines, most of the fuel is burned in a diffusion combustion phase, which inherently leads to the formation of excessive amount of soot and NOx emissions. In order to decrease soot and NOx emissions simultaneously, the concept of lean premixed compression ignition engine has been proposed. The onset of the combustion of the engine depends on the autoignition of the fuel, so it is quite difficult to control the ignition timing. 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. In PFJ, the combustion is initiated in the jet issuing from the 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. In this paper, autoignition characteristics of n-butane/air mixtures in a rapid compression machine (RCM) were shown first. The appearance of low temperature flames was observed in autoignition of n-butane in the RCM used here, and it was realized that the final compression conditions in the RCM correspond to the upper end of the low-temperature range of the positive temperature dependence region of ignition delay. Then the combustion tests with PFJ were carried out and it was demonstrated that the onset of combustion can be controlled by PFJ, and it was revealed that PFJ has a potential for the ignition timing control of the compression ignition premixed charge engine.
