极端条件下预混燃料/空气的点火机理研究

Ignition of premixed fuel/air mixture under extreme conditions frequently occurs in advanced combustion engines. For examples, it is difficult to achieve successful relight in high-altitude jet engines; and it is also difficult to maintain successful ignition in ultra-lean internal combustion engines. Motived by the key scientific problem of “Combustion under extreme conditions and combustion stability” in the major research plan, we propose a fundamental investigation on ignition of premixed fuel/air mixture under extreme conditions, either at low temperature and low pressure or near the flammability limit. Theoretical analysis, numerical simulation and experiments will be conducted. Based on models for spherical flame ignition and counter flow flame ignition, we will study the influence of low temperature and low pressure, near flammability limit, flow, and fuel droplet vaporization on the ignition process (including ignition kernel formation and development, and flame propagation) and critical ignition conditions (including minimum ignition kernel radius and minimum ignition energy). The coupling effects between extreme condition and flow on ignition will be examined. Besides, the influence of active species addition and fuel stratification on ignition promotion under the condition of low temperature and low pressure or near flammability limit will be investigated. In this proposed research, theory on ignition under extreme conditions will be extended, and the results will be helpful for understanding high-altitude relight in jet engines and ignition in ultra-lean internal combustion engines.

极端条件下预混燃料/空气的点火是先进发动机燃烧的共性问题。例如，在航空发动机中存在着高空二次点火难的问题，而在稀释燃烧内燃机中也同样存在点火难的问题。针对重大研究计划中“极端条件下燃烧及燃烧稳定性”这一核心科学问题，本项目采用理论分析、数值模拟和实验测量相结合的研究方法，系统地研究低温低压或近可燃极限这一极端条件下的点火过程。本项目将基于球形传播火焰点火模型和对冲火焰点火模型，研究低温低压、近可燃极限、流动、燃料液滴蒸发等因素对点火过程（包括点火核的形成与发展、以及后续火焰传播）和临界点火条件（包括最小点火核半径、最小点火能）的影响，研究低温低压或近可燃极限这一临界条件与流动耦合对点火过程的影响，揭示低温低压或近可燃极限条件下添加活性组分与燃料分层促进点火的规律与机理。本项目旨在发展极端条件点火理论，并为航空发动机高空二次点火和内燃机稀释燃烧点火提供理论基础和科学依据。

极端条件下预混燃料/空气的点火是先进发动机燃烧的共性问题。例如，在航空发动机中存在着高空二次点火难的问题，而在稀释燃烧内燃机中也同样存在着点火难的问题。针对重大研究计划中“极端条件下燃烧及燃烧稳定性”这一核心科学问题，本项目采用理论分析、数值模拟和实验测量相结合的研究方法，系统地研究了低温低压或近可燃极限这一极端条件下的点火过程。本项目的主要研究内容包括：（1）低温低压、近可燃极限、流动、燃料液滴蒸发等因素对点火过程（包括点火核的形成与发展、以及后续火焰传播）和临界点火条件（包括最小点火核半径、最小点火能）的影响；（2）低温低压或近可燃极限这一临界条件与流动耦合对点火过程的影响；（3）低温低压或近可燃极限条件下添加活性组分与燃料分层促进点火的规律与机理。主要研究进展包括：发展了近可燃极限预混燃气的点火与火焰传播理论，揭示了低温低压下预混点火过程中点火核的传播规律；发展了基于Livengood-Wu积分的临界点火温度定量预测方法；揭示了燃料分层对临界点火条件的影响规律；揭示了低温化学反应对热颗粒引发点火过程的影响；揭示了燃料热解促进点火的规律与机理；揭示了低温等离子体产生的活性基促进点火的机理。在国际燃烧权威期刊Combustion and Flame 和Proceedings of the Combustion Institute上发表10篇论文，项目主持人应邀担任燃烧顶级期刊Combustion and Flame副主编，并获得国际燃烧学会Hiroshi Tsuju Early Career Researcher Award。本项目揭示了低温低压或近可燃极限这一极端条件下点火核的形成与发展、以及后续火焰传播机理，揭示了添加活性组分与燃料分层促进低温低压或近可燃极限条件下点火的规律与机理，发展了极端条件点火理论，为航空发动机高空二次点火和内燃机稀释燃烧点火提供理论基础和科学依据。