氩气氛围下氢氧射流混合及燃烧基础问题研究

For piston engines, a closed-loop cycle with direct-inject H2 into hot compressed Argon (Ar) in the cylinder, in which containing ~10% O2; in this way, Argon as the working fluid in a power cycle with oxygen/ H2 combustion, leads to the highest possible thermal efficiency and zero emissions. Meanwhile, exhausted Argon is re-circulated back into the engine intake and water produced from combustion is removed with a condenser. Hydrogen can be produced from fossil fuels or by electrolysis (>75% efficiency) using surplus electricity from emerging renewable electric power, such as wind power or from natural gas. In the latter case, the H2 becomes stored renewable energy that can be converted back to electricity, at any time, at >75% efficiency using an Argon power cycle. Recognizing challenges of H2 direct injection in a large bore engine, we propose research activities aimed at improving our predictive capability of injection of H2 (low density, high diffusivity) into hot Argon; and informing the choice of direct injection strategies for use in an Argon engine. High-speed imaging of experiments in a vitiated co-flow burner and in a high pressure constant volume device in the applicant’s group at Tongji University will be performed in fundamental investigations for injection strategies using H2; H2+Ar into Ar+O2; or O2 into Ar+H2; and associated computational investigations will also be accomplished. The characteristics of mixing and combustion of H2/O2/Ar co-axial injection under reaction and non-reaction condition will be revealed. New knowledge on turbulent H2 jets into Argon will be generated, and form the basis for selecting optimal fuel injection strategies leading to continued worldwide development of the Argon engine.

在活塞式发动机中采用封闭式循环，将氢气直喷至10％氧含量的高压氩气氛围中燃烧，利用氩气作为工作介质，可实现最高的热效率和零排放。废气中的氩气将重新循环至发动机的进气，循环中产生的水由冷凝器除去。氢可能来源于化石燃料，也可使用可再生电力如风电或从天然气发电的剩余电力进行电解水制氢（效率> 75％）。H2作为可再生能源的存储源，并能在任何时间利用以氩气作为工质的燃烧循环高效地转换回电能。基于对大缸径直喷氢气发动机的研究，本项目旨在提升对氢气（低密度，高扩散性）喷入热的氩氛围的预测能力，从而优化氩气发动机的直喷策略。基于高温高背压定容燃烧弹和活化热氛围燃烧器，结合高速摄影，研究氢气喷射策略、氢氩喷入氩氧氛围及氧气喷入氩氢氛围的混合及燃烧特性，揭示反应及非反应状态下氢氧氩协同喷射射流特征及影响因素，获得关于氩气氛围下氢气湍流射流的新理论，为未来氩气发动机研发与可持续发展提供优化的燃料喷射策略。

氩气动力循环是实现内燃机的高效、低排放运行的最有潜力的技术之一，其本质是一种热力循环，以Ar为循环工质，利用Ar的高比热比实现高效运行，通过Ar对N2的替代消除NOx排放，初步的台架实验表明氩氧氛围下天然气发动机指示效率可达47.8%。围绕氩气动力循环发动机基础问题，项目开展了喷射/协同喷射特性与燃烧特性研究。.设计加工了高温高背压定容燃烧弹，最高耐压可达30MPa。研究了小分子量气体在高密度环境下的喷射：喷入Ar环境时，O2射流贯穿距相比H2射流贯穿距仅略微低约0~6%，前者卷吸率是后者的2.4~3.0倍；H2射流在空气中的贯穿距比在Ar/O2混合气中的贯穿距增大11%，而锥角相对减小3%；设计了协同喷射方案并开展了试验研究，发现内H2外O2的喷射特性与内O2外H2射流接近；与单一气体射流相比，协同射流的贯穿距离增大，但相应的Ar卷吸量降低。研究表明射流气体分子量大小，以及环境气体密度大小对射流的影响可以忽略，为氢气缸内直接喷射的应用提供了支撑。.基于定容燃烧弹研究了H2层流预混火焰的点火与燃烧特性。与空气环境相比，O2/Ar混合气中H2最小点火能量和火焰发展期显著减小；且随着Ar比例的提高，最小点火能量显著提高，火焰发展期延长；随着混合气的过量氧气系数的提高，火焰发展期延长；随着混合气中Ar比例从70%提升至79%，层流火焰速度降低72.6%；可通过控制过量氧气系数实现氩气循环发动机燃烧优化和爆震的控制。.基于活化热氛围燃烧器，研究了H2射流在热Ar/O2氛围中的燃烧特性。相比于N2/O2氛围，Ar/O2氛围促进了H2射流的燃烧，火焰起升高度降低，火焰长度延长，火焰更明亮，且出现部分黄色火焰；随着Ar比例的提高，火焰起升高度升高，且此现象在低温区域更加显著。内H2外O2射流火焰的高温燃烧区位于火焰中心，而外H2内O2射流火焰在H2/O2裹挟接触面外侧形成高温燃烧区，外H2内O2的火焰起升高度更低。内H2外O2射流火焰长度整体上小于外H2内O2，前者在过量氧气系数为1时取得最大值，而后者在过量氧气系数为2时达到峰值。.研究结果丰富了基础研究数据，为氩气循环发动机样机开发提供技术和策略支撑。