| Homogeneous Charge Compression Ignition (HCCI), which combines the advantages of compression-ignited (CI) engine with that of spark-ignited (SI) engine, could provide highly effective and very clean combustion. It is considered as. a new generation combustion, which meets the stringent future emission law regulations and has gotten all attention from academic and industry area.Autoignition timing and burning rate of HCCI are controlled by chemical kinetics. And the chemical feature of fuel has great effect on its combustion and emission, so changing the chemical feature of fuel is an importance way that could control combustion process in HCCI. By mixing iso-octane with octane number 100 and n-heptane with octane number 0, it is possible to obtain an octane rating between 0 and 100. The effect of fuel octane number on HCCI combustion performance and emissions has been investigated in an experimental single cylinder engine. The results show that the increase of RON will delay the ignition timing, reduce the burning rate, prolong the lasting time, lower the maximum pressure in cylinder and augment the cycle fluctuation, especially at RON of 90.With the increase of fuel concentration, the ignition timing is advanced, the burning rate is increased and the combustion duration is shortened. However, combustion efficiency will be decreased by increasing RON and be increased by raising the concentration of mixture. When next to the boundary of knocking, the differences of combustion efficiency among different RON fuels become small. With higher RON, the operation region is expanded into large load condition, and the load at the boundary of partial combustion is also increased. And the operation region of high RON fuel is narrow. The combustion efficiency of low RON fuel is high with ignition timing advanced, while the combustion efficiency of high RON fuel is low with ignition timing delayed. In each condition, there is an optimal RON, which is corresponding to the highest indicated thermal efficiency. In the condition of low load, the fuel of low RON has the highest indicated thermal efficiency. And the optimal RON will rise up with the increase of load.HC and CO emission rise up with the increase of RON, but the increase of mixture concentration causes that fall down. When the concentration of the mixture is high, the fuel with RON of less 90 has less effect on HC emission. CO emission has close relationship with combustion temperature-temperature's up cause CO emission down, which means CO is a product of chemical kinetics. As for HC emission, besides temperature, the RON offuel also affects it. When the engine speeds up, ignition timing is delayed, combustion duration account by crack angle is prolonged, but its influence weaker when the mixture concentration become higher. Limited speed of engine falls with the increase of RON and the region of mixture concentration minishs with rises the of engine speed. With higher speed, the combustion efficiency falls down, HC and CO emission rises up. However, its influence becomes weaker at the knocking boundary.Exhaust Gas Recirculation (EGR) is one of the important ways to control combustion process in HCCI. The effect of EGR on combustion and emission characteristics of different RON fuels was investigated in the paper. The operation region of different RON fuels was expanded into large load condition by EGR in HCCI. As the RON of fuel increased, the larger maximum load was improved, and the load in condition of partial combustion was also raised. Because of its widest operation regions, the fuel with RON of 60 fits to HCCI best. And the increase of EGR rate will cause ignition timing of main combustion delay, combustion rate decrease, duration of main combustion prolong, the maximum pressure and the highest avenger temperature reduce. However, misfire will appear in the condition of too high EGR rate. With the increase of fuel's RON, the highest EGR ratio in misfire boundary falls down. For the fuel with RON of 80, the highest EGR ratio is 45%.The effects of EG...
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