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

Abstract: 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.