In this study, a two-stage Lagrangian (TSL) model is used to investigate the ignition process of a fuel spray under engine-like conditions. The existing two-reactor TSL model developed for quasi-steady flames is improved to simulate the ignition process of a fuel spray at engine-like conditions, by inserting a well-validated entrainment model for the liquid fuel spray. The ignition delays of n-dodecane and n-heptane sprays predicted by the improved TSL model are validated with Engine Combustion Network Spray A and Spray H data over a wide range of ambient temperatures and oxygen concentrations. The results show that the two-reactor TSL model is capable of capturing the complex interaction between turbulent mixing and chemistry at the spray core and periphery regions during ignition. A 4-step ignition process at intermediate temperatures is observed. First, 1-stage ignition appears at the fuel-lean spray periphery when the local residence time reaches a critical value. Then, the transport prompts the 1-stage ignition in the core region. After a kinetic-dominated 2-stage ignition in the fuel-rich core region, the flame propagates into the whole equivalence ratio space. At ambient temperatures that are considered relatively high for internal combustion engines, the 1-stage and 2-stage ignition in the fuel-rich core region is so short that the 1-stage ignition does not occur at the spray periphery, resulting in a 3-step ignition process. The high equivalence ratio in core region restricts the local temperature rise, and the 2-stage ignition finally appears at the spray periphery with an increasing local residence time and the transport from the core region. The effectiveness of the two-reactor TSL model also demonstrates the dominant role of transport in the multiple-step ignition process of a high-pressure liquid fuel spray.

中文翻译：

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使用两阶段拉格朗日模型评估燃油喷雾点火延迟行为

在这项研究中，使用两级拉格朗日（TSL）模型来研究类似发动机条件下燃油喷雾的点火过程。通过插入经过充分验证的液体燃料喷雾夹带模型，改进了为准稳态火焰开发的现有双反应器 TSL 模型，以模拟类似发动机条件下的燃料喷雾的点火过程。通过改进的 TSL 模型预测的正十二烷和正庚烷喷雾的点火延迟在各种环境温度和氧气浓度下通过发动机燃烧网络喷雾 A 和喷雾 H 数据进行了验证。结果表明，双反应器 TSL 模型能够捕获点火过程中喷射核心和外围区域的湍流混合与化学之间的复杂相互作用。观察到中间温度下的 4 步点火过程。首先，当局部停留时间达到临界值时，在贫燃料喷雾外围出现一级点火。然后，传输促使核心区域进行一级点火。在富燃料核心区域进行动力学主导的两级点火后，火焰传播到整个当量比空间。在内燃机相对较高的环境温度下，富燃料核心区域的 1 级和 2 级点火时间非常短，以至于喷雾外围不会发生 1 级点火，从而导致 3 级点火。步点火过程。核心区的高当量比限制了局部温升，最终在喷雾外围出现二级点火，局部停留时间增加，并从核心区转移。双反应器 TSL 模型的有效性还证明了输运在高压液体燃料喷雾的多步点火过程中的主导作用。