| With its excellent performance，the internal combustion engine has dominated themainstream status of power machinery for150years since it was birth. However, withthe concept of low-carbon and environment-friendly being supported widely, peopleput forward higher requirements on economical efficiency and emissioncharacteristics of the internal combustion engine. Combined with the new energyautomotive technology advances, the traditional internal combustion engine industryis facing unprecedented challenges. In the new century, a new type of combustiontheory—homogeneous charge compression ignition (HCCI) technology is striking byimproving fuel economy and emissions at the same time. But the combustion controlof HCCI engine is difficult and the scope of work is narrow. In this paper, the laws ofHCCI combustion are explored by simulation methods to find the ways to let thetheory to be practical.Firstly, the method to achieve HCCI combustion is summarized. Then, combinedwith the technical conditions of our laboratory, negative valve overlap (NVO) strategyis applied to achieve HCCI. In order to use NVO strategy and for the convenience ofcomparison with other internal EGR strategy, a new variable valve lift (VVL)mechanism is design. The dynamic performances are checked by software ADAMS,and the curves of different valve timing and valve lift are output by then.A single-zone HCCI combustion model coupled simplified chemical kineticmechanism is established based on the combined operating of AVL-Boost andCHEMKIN. Rely on this simulation platform; the study of HCCI can be carried out.The chemical reaction mechanism coupled in the model comes from the simplifiedmechanism established by Youngchul Ra and this mechanism is proved suitable forour prototype by calculation.In this paper, the influence to combustion and gas exchange process by NVO,compression ratio, valve lift and speed of engine are studied based on simulationplatform. The calculations of this model show that, the load control can be achievedby changing the size of NVO; the control of the combustion time can be realized bychanging the compression ratio; low-load region can be extended by increasing thecompression ratio, while there is limited effect to extend high-load region by the same way for roughness; increasing the valve lift of the engine can obtain smaller pressurerise rate in the same level of IMEP, which is good for the expansion of high-loadregion; the speed of engine can also affect operating range significantly. At speed of1000rpm, the high pressure rise rate limit the extension of high-load region; at speedof4000rpm, due to the misfire, its difficult to expand the low-load region. When thelift of intake and exhaust valves is not equal in the NVO strategy, it is potential toextend the high-load region. Compared to other internal EGR strategy, the NVOstrategy has advantages in expanding engine operating range. |
