高空极端条件燃烧室等离子体燃油裂解与点火机理研究

Improving the reignition altitude of aero-engines is a complicated scientific problem with significant military requirement. For the reignition at high altitudes, the chemical reaction rate drops remarkably due to the low pressure and low temperature, which needs to be solved with new techniques. In this project, a new method, in which nanosecond pulsed plasma is used to realize the fuel pyrolysis, fast heating and active particles production, is proposed. With this method, the chemical reaction chain in ignition can be changed and the chemical reaction rate is increased, which is expected to improve the reignition altitude notably. Aimed at the scientific problem of nanosecond pulsed plasma pyrolysis and ignition in oil-gas mixture at low-pressure low-temperature environment, a succession of comparative experiments will be conducted under the conditions of ambient pressure/ low pressure + room temperature/ low temperature, conventional atomization/ plasma pyrolysis + conventional ignition/ plasma ignition, and different electrical parameters. Diagnostic parameters, including the discharge energy, rotational and vibrational temperature, electron temperature and density, components of the pyrolysis products, burning nucleus evolution process and so on, will be measured comprehensively. Combining the measurements with the theoretical analysis together, the fundamental data and the laws of the influence of nanosecond pulsed plasma fuel pyrolysis and ignition on reignition boundary, will be obtained. Meanwhile, this research can also reveal the mechanism of nanosecond pulsed plasma pyrolysis in fuel-air mixture, and the mechanism of multichannel nanosecond pulsed plasma ignition with pyrolysis products involved. The achievements of this project will provide a firm support for the breakthrough of the scientific problem in research plan “Controllable combustion mechanism in extreme conditions”, and also for the innovation of aero-engine combustors.

提升航空发动机的高空二次点火高度具有重要的军事需求和复杂的科学问题。高空二次点火面临低气压低温的极端条件，化学反应速率显著降低，亟待发展新的技术途径。本项目提出采用纳秒脉冲等离子体裂解燃油、快速加热和产生活性粒子，改变点火的化学反应链并提高化学反应速率的新思路，有望显著提升二次点火高度。针对低气压低温油气混合物纳秒脉冲等离子体裂解与点火机理的关键科学问题，通过常压/低压+常温/低温、常规雾化/等离子体裂解+常规点火/等离子体点火、不同放电参数的对比实验，放电能量、转动与振动温度、电子温度与密度、裂解组分、火核演化过程等综合测试与理论分析，获得纳秒脉冲等离子体燃油裂解与点火影响点火边界的基础数据与参数变化规律，揭示油气混合物纳秒脉冲等离子体裂解机理、裂解产物参与下的多路纳秒脉冲等离子体点火机理。项目成果将为重大研究计划“极端条件下可控燃烧机制”科学问题的突破和航空发动机燃烧室的创新提供支撑。

高空低压低温等极端条件下，煤油雾化蒸发和化学反应速率显著降低，点火边界显著变窄甚至难以成功点火。高推重比航空发动机高温升燃烧室、涡轮-冲压组合动力宽域模态转换，对先进点火技术有重要需求。本项目针对航空发动机燃烧室高空低压低温极端条件下二次点火高度不足的难题，提出了多通道等离子体点火和滑动弧等离子体燃油裂解的创新思路。通过层流点火研究，揭示低气压条件下点火性能下降的主要制约因素，获得等离子体与最小点火能以及临界火核半径之间的影响规律。针对传统点火器放电能量小、火核尺寸小的突出问题，实验发现了等离子体电阻这一限制放电效率和能量的瓶颈。突破了新型多通道放电等离子体点火器技术，显著增大等离子体电阻。突破了半导体表面放电等离子体阻抗调控、电极布局优化、点火器集成等技术，研制了多通道等离子体点火器，将放电效率从传统点火器的20%提升到50%，火核体积增大150%，火核高度增大55%，分别在旋流基础燃烧室、三旋流高温升燃烧室和超燃冲压燃烧室上进行了实验验证，旋流燃烧室低温点火边界拓宽13%，高温升燃烧室点火进口速度边界拓宽15%，超燃冲压燃烧室点火时间缩短50%~60%，揭示了多通道等离子体点火的高能量、大火核、强穿透机理。针对低温低压极端条件下煤油雾化特性显著恶化、难以与点火火核接触的突出问题，提出了旋流空气驱动的交流滑动弧等离子体燃油裂解方法，获得了旋流滑动弧等离子体的工作特性和温度、电场强度等关键参数，在简单旋流火焰、基础旋流燃烧室和双头部模型燃烧室上验证了等离子体燃油裂解技术，液滴尺寸从约150μm减小到约30μm，裂解产生甲烷、乙烯、乙烷为代表的小分子烃，揭示了滑动弧等离子体强化燃烧的雾化蒸发改善与油气裂解重整机理。实现了低温低压条件下点火边界拓宽30-48%、点/熄火边界基本一致的显著效果，成功将高空10 km贫油熄火边界拓宽30%。