正丁醇/柴油喷雾特性及缸内混合气形成过程数值模拟

为了研究正丁醇掺混比对燃料自身喷雾特性的影响以及探讨缸内喷雾过程随掺混比的变化规律,该文采用定容弹试验和缸内喷雾数值模拟相结合的方法,正丁醇掺混比从0增加到40%,分析了燃料的理化特性。采用定容弹试验系统对燃料的喷雾参数进行了研究,采用缸内模拟的方法分析了掺混比对喷雾过程的影响。结果表明,定容弹环境下,正丁醇掺混比增加40%,贯穿距离减小4.95%,喷雾锥角增大16.7%,喷油压力增加30 MPa,喷雾锥角增加28.43°;缸内喷雾过程中,掺混比对贯穿距离影响较小;混合气形成初始阶段,掺混比越高,燃料的SMD(sauter meandiameter)越小,最终趋于一致;随着掺混比增加,燃料喷射质量降低,蒸发质量上升;掺混比越高,喷注的速度峰值降低;在喷注下游中心区域喷雾液滴数密度最高;正丁醇有助于缸内的喷雾过程,掺混比增加,喷雾特性越好。

Spray behavior of butanol-diesel and numerical simulation of mixture formation with engine

A n-butanol/diesel spray test system was constructed to conduct common rail bench test and constant volume bomb experiments in present work to investigate the impact of different n-butanol blending ratios on spray characteristics and the spray evolution process. To be specific, the research was carried out under the n-butanol blending ratios ofwith 0, 10%, 20%and 40% respectively to study various n-butanol blending ratio effects and to analyze the variation of the physical and chemical characteristics of the fuel. Then, the fuel spray patterns data at 0.4 ms was carefully collected and analyzed to compar the effect of different n-butanol blending ratios on spray penetration and spray angle. In addition, an-butanol/diesel spray model in engine cylinder was also established, to analyze how spray penetration and SMD of blended fuel varied during spray process, , as well as the impacts of n-butanol blending ratios on evaporation characteristics of blended fuel. Furthermore the various changes in velocity field and number density field in spray processes with different blending ratios have been taken into consideration and discussed for more detailed problems. It can be observed from the research data that: in normal temperature and pressure region,as the n-butanol blending ratio increased,the spray penetration decreased and there was a moderate rise in spray angle during spray process; as blending ratios of n-butanol increased by 40%, the spray penetration slightly reduced by 4.95%while reversely the spray angle climbed by 16.7%. Also when the injection pressure ascended, there was obvious rise both in the spray penetration and spray angle, particularly, if injection pressure rose by 40 MPa , the spray angle increased by 28.43°. During the spray evolution process, the n-butanol blending ratios influenced the spray penetration slightly, while in the very initial step of fuel blending process, the higher the n-butanol blending ratio was, the smaller SMD of blended fuel became. Along with the development of the spray process, however, the ultimate spray penetrations of different blended fuel were basically the same. In the injecting duration period, with the increasing of n-butanol blending ratio, there was a substantial drop in the mass of the fuel injected into the cylinder, and the peak velocity value of the jet dropped distinctly. Moreover, as a result of the fall in the viscosity and surface tension, the volatilization of blended fuel was apparently enhanced and subsequently fuel evaporation mass was increased slightly. The n-butanol blending ratios had quite limited impact on number density of drops but obviously facilitated the spray period, that is, the larger the blend ratio was, the better the spray characteristics would be. Besides this, in the central region of the downstream jet the figure of number density reached the highest.