The Simulation Study On On-board Fuel Reformation Of HCCI Combustion Fueled With Methanol

Under the great pressure of energy conservation and emission reduction, HCCIengine is approved by the majority of researchers because of its excellent performance.HCCI engine is different from conventional diesel engine, because it runs with thecompression of homogeneous charge and there is no flame propagation obviously in thecylinder. The in-cylinder charge is considered as the homogeneous mixture when the inletvalve is closed, so there is no very rich mixture in the local part of the cylinder which wouldlead to high emissions of NOx and PM. Thus, it became the important part in the field ofinternal combustion engine. The viewpoint of HCCI combustion is dominated by thechemical kinetics and has been accepted by the public. Therefore, the problems ofuncontrollability of combustion starting and narrow operation range are going to be solvedurgently.To solve these problems, our research team has proposed an on-board fuelreformation system. The system is mainly made of the reforming chamber mounted on thecylinder head and its driving mechanism. The reforming chamber and the main cylinder areconnected by an independent and controllable valve. The valve is opened during thecombustion process and it is closed after the combustion, so some residual gas will betrapped in the reforming chamber. Reforming fuel will be injected into the reformingchamber and reforming reaction happens. In the proper time of the next cycle, the valve isopened and the reforming products mix with the in-cylinder charge. There are a lot of activesubstances in the reforming products, including H₂, CO, H, O, OH, and so on. Thesesubstances will have an important effect on combustion control. Thus, through controllingof the valve, the fact of HCCI combustion is dominated by the chemical kinetics which willbe converted into the mechanical motion of the connected valve. Consequently, combustionphase control and operation range extension will be solved.The on-board fuel reformation model has been built based on CHEMKIN softwareand the simulation of fuel reforming and combustion has been finished. The results showedthat H₂is the most important constituent that will affect the in-cylinder ignition and combustion. So the product of H₂in the reforming reaction will be regarded as the goal ofoptimizing the parameters of reforming system. Of course, there are other constituents likeCO, O and H radicals, but results of these radicals are not better than that of H₂. Byoptimizing the parameters like volume of reforming chamber, the phase of trapping theresidual gas, the phase of adding the reforming products into the main cylinder and so on,the reforming system will be optimized. In the end, the results also indicated that the systemwill work on the extension of operation range at low intake-temperature and high speed butkeeping a relative high thermal efficiency. Therefore, the combustion phase will becontrolled precisely, and to some extent extending the operation range because of theaddition of reforming gas. As a result, HCCI engine will run under a steady condition andwide operation range.