Experimental Study On Combustion Characteristics And Load Expansion Of Gasoline HCCI Engine Based On The OKP Technology

With challenges of energy situation and environment protection, improving engine thermal efficiency and reducing emissions have become a main approach to deal with these problems. Homogeneous Charge Compression Ignition (HCCI) which is taken as the third combusion mode with higher efficiency and cleaner properties has shown great potentials. However, HCCI has its own problems which are auto-igintion controlling and load expansion. The Optimized Kinetic Process (OKP) technology as one of gasoline HCCI technologies has shown some advantages for these two problems. So, this thesis experementally explored problems of gasoline HCCI combustion which based on OKP technoloty.Based on principles of the OKP technology, some reforms have been carried out on a commercial 4-cylinders gasoline engine. Meanwhile, other systems for the engine experimental platform have been designed and built. Finally, the stable gasoline HCCI combustion has been realized. In order to study the gasoline HCCI combustion characteristics, statistical analysis method is adopted to analyze cycle-to-cycle and cylinder-to-cylinder variation characteristics at different switching points and different operation modes under the same load. The results shown that, for the switching process at engine speed 1400 rpm, properly increasing the load could make HCCI combustion more stable after switching process; at the same load, combustion parameters' variation in HCCI mode were remarkable less than parameters in SI mode, the cycle-to-cycle variation of IMEP was less than 2.5% and cylinder-to-cylinder variation was less than 3%.Statistics also shown that each cylinder-to-cylinder combustion parameters had regular differences. Experimentally studied the load range of gasoline HCCI engne whcih based on the pure OKP technolgy, the parameters which could be used to indicate upper boundary and lower boundary of HCCI load has been discussed. And then, the effects of Exhaust Gas Recirculation (EGR) and Boost on combustion characteristics of gasoline HCCI engine which based on OKP have been studied respectively.The test results indicated that, with increasing the external EGR rate, the combustion phase retarded, the duration of combustion prolonged, the HC and CO emissions increased; but with increasing intake air pressure, the combustion phase advanced, the duration of combustion shortened, the HC and CO emissions increased. The NOx emissions stayed at a low level under these two methods.Based on these results, experimentally explored potential of HCCI load expansion with these two methods.The results indicated that the load range of HCCI is expanded greatly towards up boundary and low boundary, the minimum effective specific fuel comsumption dropped to 230g/kW.h, the indicated thermal efficiency is much higher than traditional Spark Ignition engine's, the NOx emissions basically stays at a low level (<60ppm), but CO and HC emissions has increased.Finally, main combustion parameters' distributions have been analysed for all test points during the load expanding process. To sum up, the HCCI load range could be further expanded if the structural strength of engine had been improved.