Fundamental Research On The Effects Of Fuel Additives On Homogeneous Charge Compression Ignition Combustion

1970s, a new combustion mode, Homogeneous Charge Compression Ignition (HCCI), was proposed by Onishi. Because it has potential to be energy conservation with ultra-low emissions, attention has been focused on HCCI combustion in 1990s, which was considered as an important technology to satisfy the strict emission rules in future and was great progress in combustion technology. But it is difficult to control the ignition point and easy to misfire and knock.In this research, the theoretical principal and technical route were investigated to improve the ignition for HCCI engine by employing fuel additives. At the same time, the mechanism of improving HCCI ignition by additives was also studied. The works of searching the radicals of improving HCCI ignition, selecting additives that can produce the radicals, designing the chemical constructure of additives and synthesizing the more effective additives were done. Besides, we have set up a new experimental approach for investigation of fuel (with additives) homogeneous combustion (pyrolysis). The experimental results showed that fuel ignition was effectively improved by peroxide additives. The suitable temperature range for fuel additive to improve the ignition is 500K~900K. The laboratory results have a good agreement with the outcome of the engine bench test, indicating that the approach is simple and reliable for screening HCCI additives. At the same time, it will be a rapid and high effective tool that can be used in this field in future.We further studied on the mechanism of fuel additive improving the ignition. Different type peroxides and peroxides with the same function group but different structure unit were investigated by homogeneous combustion (pyrolysis). The experimental results showed that the ability to improve HCCI ignition had a correlation with amount and the type of radicals. Methyl radical and ethyl radicals were key species for improving the ignition, the amount of radical produced in fuel combustion was proportional to the ability of improving HCCI ignition. For knock at high load, an antiknock agent and a microemulsion were used to meet with this problem in HCCI engine bench test. Experimental results showed that the antiknock agent used could improve the knock, but at the same time the ignition was inhabited. Microemulsion fuel not only can improve the knock, but also has no effect on the ignition at the low load.