Computational analysis of end-of-injection transients and combustion recession
Computational analysis of end-of-injection transients and combustion recession
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DOI：
10.1177/1468087417701280
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发表时间：
2016-11
影响因子：
2.5
通讯作者：
D. Jarrahbashi;Sayop Kim;Benjamin Knox;C. Genzale
中科院分区：
文献类型：
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作者：
D. Jarrahbashi;Sayop Kim;Benjamin Knox;C. Genzale
发动机燃烧网络的混合和燃烧使用高分辨率多维数值模拟来模拟喷射结束后的喷雾A，以探索最近的燃烧衰退实验观察的物理基础。反应喷雾模拟使用传统的拉格朗日-欧拉耦合制定的两相混合物传输与雷诺平均的Navier-Stokes方法使用开源计算流体动力学代码OpenFOAM。Cai等人和Yao等人的正十二烷化学动力学模型被用于评估机理制定和低温化学对燃烧衰退行为预测的影响。Cai机制的模拟表明，在标准喷雾A条件下，喷射结束瞬态在喷嘴附近的不同区域诱导第二阶段点火，这些区域最初在空间上与提升的扩散火焰分离，但随后迅速与火焰合并。相比之下，姚机制未能预测足够的低温化学混合物上游的扩散火焰在结束的注射瞬态和不预测燃烧衰退相同的条件。喷射结束瞬态的形状和持续时间对喷嘴附近的卷吸波的影响，燃烧衰退的可能性，以及近喷嘴混合物中的混合和化学的时空发展也进行了研究。对于更快速的斜降喷射曲线（斜降持续时间< 400 µs），在斜降开始后较早发生较弱的燃烧衰退。对于极快的斜降（斜降持续时间= 0），卷吸流量在喷嘴附近迅速变化，混合物的过度倾斜完全抑制燃烧衰退。对于相对于标准喷雾A条件的较慢的斜降轮廓，观察到朝向喷嘴的完全燃烧衰退，并且燃烧衰退在稍后时间发生。模拟定性同意与过去的实验和建模观察到的燃烧衰退与不同的结束喷射瞬态。
Mixing and combustion of engine combustion network Spray A after end of injection are modeled using highly resolved multidimensional numerical simulations to explore the physics underlying recent experimental observations of combustion recession. Reacting spray simulations are performed using a traditional Lagrangian–Eulerian coupled formulation for two-phase mixture transport with a Reynolds-averaged Navier–Stokes approach using the open-source computational fluid dynamics code OpenFOAM. Chemical kinetics models for n-dodecane by Cai et al. and Yao et al. are deployed to evaluate the impact of mechanism formulation and low-temperature chemistry on predictions of combustion recession behavior. Simulations with the Cai mechanism show that under standard Spray A conditions, the end-of-injection transient induces second-stage ignition in distinct regions near the nozzle that are initially spatially separated from the lifted diffusion flame, but then rapidly merge with flame. By contrast, the Yao mechanism fails to predict sufficient low-temperature chemistry in mixtures upstream of the diffusion flame during the end-of-injection transient and does not predict combustion recession for the same conditions. The effects of the shape and duration of the end-of-injection transient on the entrainment wave near the nozzle, the likelihood of combustion recession, and the spatiotemporal development of mixing and chemistry in near-nozzle mixtures are also investigated. With a more rapid ramp-down injection profile (ramp-down duration < 400 µs), a weaker combustion recession occurs earlier in time after the start of ramp-down. For extremely fast ramp-down (ramp-down duration = 0), the entrainment flux varies rapidly near the nozzle and over-leaning of the mixture completely suppresses combustion recession. For a slower ramp-down profile with respect to the standard Spray A condition, complete combustion recession back toward the nozzle is observed and combustion recession occurred later in time. Simulations qualitatively agreed with the past experimental and modeling observations of combustion recession with different end-of-injection transients.