废气中残留小分子碳氢对汽油HCCI着火的影响-动力机械及工程专业论文.docxVIP

ABSTRACT Homogeneous charge compression ignition (HCCI) combustion has been considered as one of the most promising methods to realize energy conservation and emissions resuction of internal combustion engine. However, the clear understanding of HCCI ignition mechanism is pressed for achieving optimized auto-ignition timing control. In our previous experiment of the gasoline HCCI combustion based on the recompression of residual gas, it is found that some experimental results of auto-ignition timing can not be explained well using the exsisting knowledge of the effects of residual gas on auto-ignition. It has been proved that the auto-ignition could be influenced in chemical aspect by the low-concentration components in residual gas. Consequently, more concerns should be paid on this issue. In this research, a fast instantaneous in-cylinder sampling system is developed to study the compositions and concentrations of micromolecular hydrocarbons in residual gas under the different operating conditions. And comparisons of evolutions of the micromolecular hydrocarbons are made between internal and external exhaust gas. Furthermore, a zero-dimensional chemical kinetic model with detailed chemical mechanism for gasoline surrogate is used to model the gasoline HCCI combustion. The effects of these micromolecular hydrocarbons on auto-ignition are analyzed through chemical kinetics simulation. It indicates that the micromolecular hydrocarbons with concentrations more than 10 ppm in residual gas are mainly CH4, C2H6, C2H4, C3H6, C2H2, CH2O and CH3CHO. Under the stoichiometric condition, CH4, C2H4 and C2H2 occupy about 80 percent of the total concentration of these 7 kinds of micromolecular hydrocarbons. It is found that C2H2 and C2H4 have the greatest contribution for promoting auto-ignition, while CH4 presents the potential of retrading auto-ignition. Under the condition of partial lean mixture, CH2O contributes more in promoting auto-igntinon. The combined effect of these