[论文解读] Eulerian-Lagrangian modelling of rotating detonative combustion in partially pre-vaporized n-heptane sprays with hydrogen addition

Qingyang Meng, Majie Zhao+2 more|arXiv (Cornell University)|Nov 6, 2020

Combustion and Detonation Processes参考文献 54被引用 11

一句话总结

本研究采用欧拉-拉格朗日计算模型，研究了在添加氢气的正庚烷喷雾中部分预汽化条件下的旋转爆震燃烧，重点分析液滴动力学与爆轰波行为。主要发现表明，液滴直径和预汽化程度显著影响爆轰速度（速度亏损达5%–30%）及燃料爆轰效率，临界液滴尺寸约为20 µm时，燃料爆轰分数最小。

ABSTRACT

Rotating detonation combustion (RDC) fuelled with partially pre-vaporized n-heptane sprays and gaseous hydrogen is studied with an Eulerian-Lagrangian method. Our focus is the effects of pre-vaporized n-heptane equivalence ratios and droplet diameters on detonation wave propagation and droplet dynamics in two-phase RDC. The results show that when the droplets are small, they are fully vaporized by the detonation wave. However, when the droplet diameter is relatively large and/or the detonation wave number is bifurcated, liquid droplets are observable beyond the refill zone. Moreover, the detonation speed is considerably influenced by the droplet pre-vaporization and diameter. The velocity deficits vary between 5% and 30%. Over 70% n-heptane is detonated in the simulated cases, and there exists a critical droplet diameter (about 20 um), around which the detonated fuel fraction is minimal. Four droplet trajectories in RDC are identified, which are differentiated by various evaporation times, residence times and interactions between droplets and the basic RDC flow structures. Inside the refill zone, three droplet categories are qualitatively identified. Droplets injected at the right end of the refill zone directly interact with the deflagration surface and meanwhile have relatively long residence time. However, droplets injected closer to the travelling detonation front have insufficient time to be heated and vaporized. Our results also demonstrate that when pre-vaporization level is low and initial droplet diameter is large, the liquid fuel droplets may disperse towards the combustor exit. Furthermore, the droplet dispersion height decreases with liquid fuel pre-vaporization, while increases with droplet diameter.

研究动机与目标

• 理解预汽化正庚烷当量比与液滴直径对两相旋转爆震燃烧中爆轰波传播的影响。
• 分析液滴动力学、蒸发时间与驻留时间与RDC流场结构的关系。
• 识别液滴在补给区之后仍持续存在并影响燃烧效率的条件。
• 量化液滴尺寸与预汽化程度对爆轰速度与实际爆轰燃料分数的影响。
• 研究液滴分散模式及其对初始液滴直径与预汽化水平的依赖性。

提出的方法

• 采用欧拉-拉格朗日方法，通过欧拉方程求解气相，通过拉格朗日方法追踪单个液滴的运动。
• 模型采用D²定律模拟液滴蒸发，考虑液滴与周围反应流之间的传热与传质过程。
• 在添加氢气以增强反应性的旋转爆震燃烧室几何结构中模拟爆轰波传播。
• 模拟追踪液滴轨迹、驻留时间及与移动爆轰前沿和补给区相关的蒸发进程。
• 边界条件设置反映不同直径与预汽化水平下正庚烷液滴的实际注入条件。
• 模型评估了爆轰速度、燃料爆轰分数及不同运行参数下的液滴分散高度。

实验结果

研究问题

• RQ1 液滴直径与预汽化水平如何影响两相RDC中的爆轰波速度与速度亏损？
• RQ2 液滴驻留时间与蒸发持续时间在决定液滴是否在爆轰前完全汽化方面起什么作用？
• RQ3 在何种条件下，液滴会持续存在于补给区之后，特别是在分叉爆轰波状态下？
• RQ4 初始液滴直径如何影响实际发生爆轰的正庚烷分数？
• RQ5 主要的液滴分散模式是什么？它们如何随预汽化程度与液滴尺寸变化？

主要发现

• 液滴预汽化与直径显著降低爆轰速度，速度亏损范围为5%至30%，具体取决于工况条件。
• 在模拟工况中，超过70%的正庚烷发生爆轰，燃料爆轰分数最低值出现在临界液滴直径约20 µm处。
• 当液滴直径较大且预汽化程度较低时，液态燃料液滴可能因加热与汽化不足而向燃烧室出口扩散。
• 液滴分散高度随初始液滴直径增加而升高，但随预汽化水平提高而降低。
• 识别出四种不同的液滴轨迹，其差异源于蒸发时间、驻留时间以及与爆燃面和爆轰波前的相互作用。
• 在补给区，靠近爆轰波前注入的液滴因时间不足而无法充分加热与汽化；而位于右侧的液滴则与爆燃面相互作用，停留时间更长。