Experimental Study On HC And CO Formation Mechanism Of Homogeneous Charge Compression Ignition Combustion

In the mode of Homogeneous Charge Compression Ignition (HCCI) combustion, homogeneous mixtures are compressed to ignite. There are several points igniting at the same time in the combustion chamber, which decreases the flame spreading distances and the combustion durations, and also reduces the heat transfer loss. As a result, the thermal efficiency can be as high as the traditional diesel engine combustion. Besides, the HCCI combustion is operated under a totally homogeneous and lean charge condition, and there are no regions in the chamber with too thick mixtures that can cause high temperature. So the HCCI combustion can reduce NOx and soot at the same time. Even so, there are some typical problems with the actual applications of the HCCI combustion mode, such as higher HC and CO emissions, and controlling problem of ignition phase and reaction rate. The reason of HC and CO formation is incomplete combustion of fuel, which causes lower heat efficiency. Besides, the current oxidation catalytic converter technology can not use to process exhaust gases with too much HC and CO emissions.In order to effectively control HC and CO emissions of HCCI combustion, a lot of studies are carried out to investigate the HC and CO formation mechanism. But most of current studies are numerical simulations, and there are few experimental studies. As a result, this study was carried out to investigate HC formations, distributions and consumptions of HCCI combustion in different regions of the chamber, the contributions of different regions to final HC emissions and also the factors which have influences on the final HC emissions. The study on formation mechanism of CO and CO₂ was carried out, too. The study on combustion characteristics of HCCI combustion was also carried out. Study results are as follows:(1) The variations of compression ratio have influences on boundary layer effects, as well as the contributions of different regions of the chamber to the final HC emissions.(2) The different configurations of flat piston and squish piston can cause different flow conditions in the compression stroke. That causes differences in HC formations, distributions and consumptions and also differences in contributions of different regions in the chamber to final HC emissions.(3) The variations of compression ratio and fuel composition have great effects on the final HC emissions.(4) The process of CO oxidized into CO₂ occurs during the high temperature reaction stage and the corresponding in-cylinder temperature of this process is about 1400K.(5) The variations of compression ratio and fuel composition have certain influences on the moment of CO oxidized into CO₂ and also the CO emissions.(6) The variations of compression ratio and fuel composition have great influences on HCCI combustion characteristics. Changing compression ratio and fuel composition can effectively control the ignition phase and reaction rate of HCCI combustion.