Multi-Component Model of Diesel Sprays Under High Injection Pressure

The combustion efficiency of a diesel engine depends not only on spray characteristics but also on fuel-air mixing characteristics. Based on the original spray model, a new spray model is established in this paper to accurately predict the diesel spray, and then a multi-component evaporation model is added into it. The model takes the influence of component concentration gradient and species on its evaporation rate in the liquid phase into account. This paper studies the spray characteristics(spray penetration, spray angle and spray morphology) and fuel-air mixing characteristics(spray area, spray volume and air entrainment mass) using the spray model, and the results are compared with the experimental results. The comparison shows that the simulated spray penetration and spray angle are close to the experimental results with the average deviations less than 3%. Moreover, this paper studies the spray area, spray volume and air entrainment using empirical formula under different conditions. And the maximum deviations of the spray volume, spray area and air entrainment mass are less than 5% as compared with the test values. Overall, this spray model can predict the diesel spray characteristics and fuel-air mixing characteristics under high injection pressure accurately.

双层分流燃烧室结构对燃油扩散的影响

为了研究不同燃油喷射条件下的双层分流燃烧室结构对燃油扩散和燃烧室内空间利用的影响,获得该燃烧室结构优化和油气室匹配的信息,本文利用可视化实验设备测试了2种结构差异明显的双层分流燃烧室内燃油喷雾扩散过程。研究结果显示:在一定范围内设置碰撞台均能实现燃油分层流动;容积较小的浅盆形上层燃烧空间可以保证顶隙空间获得良好的利用;容积较大的浅ω形上层燃烧空间有利于燃油快速扩散,但会导致局部富油分布;底部凸起较低且容积较大的下层燃烧空间有利于燃烧室中心区域的利用。研究结果表明:提高燃油喷射压力对不同双层分流燃烧室内燃油喷雾扩散的促进作用不同;碰撞台位置对燃油喷射正时有良好的适应性,但提前燃油喷射正时降低了上层燃烧空间对顶层区域利用的影响;减小油束夹角和喷孔孔径不利于燃油的快速扩散和油气的均匀混合。

强化混合条件下乙醇柴油和柴油的喷雾混合特性

通过可视化定容燃烧弹试验台,采用纹影法研究了强化混合条件对乙醇柴油（E 20）和柴油喷雾混合特性的影响,喷油压力为50~200,MPa,燃油温度为343~423,K.试验表明：随喷油压力提高,喷雾锥角略有减小,但喷雾贯穿距和喷雾体积显著增大,喷雾的油气混合速率大幅提高;随燃油温度增加,喷雾锥角、喷雾贯穿距和喷雾体积变化不大,喷雾混合速率变化不明显.尽管乙醇的挥发性高于柴油,但添加乙醇对柴油喷雾的贯穿距和喷雾锥角影响不大.E 20喷雾贯穿距略小于柴油,喷雾锥角比柴油的约大5%,卷吸的空气体积比柴油稍大,燃空当量比小于柴油,形成稀混合气所需的时间更短.降低氧体积分数将使燃空当量比增大.提高喷油压力和掺混乙醇是加快柴油喷雾稀混合气形成速率的可行方法.

空气运动对小型直喷式柴油机着火前喷雾混合过程的影响

本文在单缸试验柴油机上，采用同步摄影技术，研究了空气运动对小型直喷式柴油机着火前喷雾混合过程的影响。试验结果表明，进气涡流对油束的吹偏作用较小；提高涡流强度使油束保持不被“撕裂”的初始段减小，碰壁前油束端部平均速度降低，油束喷雾锥角增大。提高涡流强度还使油束背风面的“撕裂”程度加剧，顺涡流方向壁面油束扩展加快。着火前燃油喷雾沿燃烧室径向分布与涡流强度和在周向气流作用下油束碰壁后的“撕裂”程度有关。

强涡流场中柴油喷雾扩散特性研究

通过可视化的快速压缩机模拟内燃机的燃烧室,研究了高压共轨柴油在40、60 MPa两种喷射压力下,柴油油束在切向、斜向和直通3种涡流场中的扩散混合特性。实验结果表明,在相同喷油压力及喷油脉宽下,切向涡流场中柴油喷雾面积与视窗面积比的峰值和谷值均为最高,直通涡流场中最低;斜向涡流场从喷油开始到喷雾完全混合整个过程用时最短,直通涡流场用时最长;喷雾油束的扩散时间与涡流的切向速度、燃油喷射压力成反比。