Combustion System with Premixture-controlled Compression Ignition

The purpose of this study is to create a new combustion concept that offers a high thermal efficiency and very low NOx and soot emissions. To this end, we performed 3D-CFD simulations to identify problems with an actual PCCI that is characterized by in-cylinder mixture nonhomogeneity that arises through the direct injection of diesel fuel. We compared the combustion characteristics with an ideal 'HCCI' with homogeneous mixture conditions. Then, to overcome PCCI problems such as difficulties in combustion controllability and the limited operating range, we identified the key parameters impacting the HCCI/PCCI process through experiments with a variety of paraffinic hydrocarbon fuels. Finally, based on the knowledge gained through these steps, we developed a new concept for dual-fuel PCCI combustion using highand low-RON fuels to achieve extremely low NOx and smoke emissions. In this system, gasoline was supplied from the intake air port and diesel fuel was injected directly into the engine cylinder to act as an ignition trigger at a timing before TDC. It was found that the ignition phasing of this PCCI combustion can be controlled by changing the ratios of the two injected fuels, such that combustion proceeds very mildly, even without EGR, thanks to the spatial stratification of ignitability in the cylinder, which prevents the entire mixture from igniting instantaneously. The operable load range, where the NOx and smoke emissions were less than 10 ppm and 0.1 FSN, respectively, was extended up to an IMEP of 12 bar using an intake air boosting system together with dual fueling.