| Energy and environment are two main topics in today's world. The rapid development of automobile industry not only speeds up the consumption of finite energy resources but also causes serious environmental pollution. In order to alleviate the pressure of energy sources' limitation and reduce automobile exhaust pollution, the internal combustion engine workers committed to the efficient and clean combustion technology, which HCCI can achieve due to the high thermal efficiency and ultra low NO_x and dry soot emission, with increasingly stringent regulations of emission laws, HCCI has become a hot topic. Currently the difficulty of ignition control, the narrow range of working conditions, the high hydrocarbon (HC) and carbon monoxide (CO) emissions, the difficulty of cold start and other issues are the main problems on HCCI engine.Based on the current domestic and international HCCI development, the test and simulation of the HCCI technology was introduced, and a HCCI engine test bed was constructed. On the HCCI engine test bed, the 4100Q-1A engine's intake system was rebuilt and HCCI combustion was realized. The in-cylinder pressure and emission tests indicate that DME's HCCI has an obviously two-stage heat release characteristics. The first stage is the DME's low temperature reaction, the second stage is the DME's high temperature reaction, with the intake temperature increases, the ignition timing of low-emperature and high-temperature are advanced, the combustion duration is shortened. There is almost no dry soot emission, very low NO_x emission, but high emissions of CO and HC in DME's HCCI. In this paper, the single-zone model and the DME's oxidation reaction mechanism were used to numerical study the DME's HCCI combustion. In order to verify the reliability of the calculation method, the simulation results and the test results were compared, and then the simulation method was used to analyze effects of DME's HCCI combustion characteristics with different compreAssion ratio and EGR rate. The simulation results indicate that with the compression ratio increases, the ignition timing gradually advanced, the in-cylinder pressure and temperature both increased, the combustion duration gradually shortened. At this point the IMEP (Indicated mean effective pressure ) increased first and then decreased. Using EGR technology is a highly effective HCCI combustion control method. In addition, this paper analyzes the reaction flow of the detailed chemical reaction kinetics of the DME oxidation, and gets the simplified mechanism of the chemical reaction kinetics. And then the comparative studies were given between the simplified model and the detailed mechanism model for DME's HCCI. The simulation results of the ignition timing, the rate of heat release, in-cylinder peak pressure and peak temperature which based on the simplified model indicate that the calculation results of the simplified model is basically in consistence with the detailed mechanism models. The simplified mechanism has good predictive capability for the altering initial temperature, the altering concentration of mixture, the altering intake pressure and the altering engine speed. It can be applied to the combustion process of DME's HCCI. |
