两次喷射柴油喷雾特性的定量研究

Quantitative Study on Diesel Spray Characteristics of Twice Fuel Injection

利用复合激光诱导荧光技术,在定容燃烧弹内,对单次喷射和两次喷射时柴油喷雾发展过程及喷雾特性进行研究,结果表明,喷雾发展伴随液滴蒸发和气体卷吸的相互竞争.喷雾发展初期气液相同时形成,液滴蒸发速率较小,气相大部分位于Φ<2区间.喷雾发展中期蒸发速率逐渐升高,喷雾内部形成Φ>2的过浓区.喷雾充分发展后气体卷吸占主导,过浓区减小.两次喷射时,停喷间隙可促进油气混合,降低过浓混合气的质量分数,从而改善碳烟排放;另一方面,两次喷射影响油气空间分布,减小喷雾前锋油气堆积,使过浓混合气与稀混合气燃烧区相分离,有效抑制碳烟的生成.

Spray development of single-pulse injection and twice-pulse injection was quantitatively studied by using planar laser induced exciplex fluorescence （PLIEF）technique in a constant volume vessel. The experiments showed that the development of diesel spray accompanied the competition between evaporation and gas entrainment. At the early stage of spray development, the evaporation rate is low, and the vapor phase spray is mainly in ~〈2. At the middle stage of spray development, the evaporation rate increases and a vapor rich core is formed in the inner part of spray with φ〉2. At the fully developed stage of spray, the gas entrainment occupies a leading position so the vapor rich core with ~〉2 decreases. In the twice fuel injection, the dwell between injection pulses enhances fuel-air mixing, thus the mass fraction of rich mixture with φ 〉2 decreases and soot formation is significantly reduced, In addition, the twice fuel injection has effect on mixture distribution. The rich mixture region at spray tip is not replenished, which reduces soot formation and accumulation.