掺氢天然气可燃极限的实验研究和机理分析

Hydrogen compressed natural gas (HCNG) is a mixture of natural gas and hydrogen that is normally produced using the excess wind and solar power. The utilization of HCNG is of practical significance as it is not only capable of digesting the excess wind and solar power but also conductive to achieving a clean combustion in combustion devices. Moreover, the study on the combustion characteristics of HCNG is of theoretical interest as hydrogen and natural gas, the two components in HCNG, are both simple and commonly seen but remarkably distinct in nature. The flammability limit of HCNG is directly related to the safe transportation, storage and utilization of HCNG. However, relevant studies are not sufficient and the accuracy of the existing experimental data does not meet the current requirement. Especially, there still lacks the in-depth understanding of the controlling mechanism of the near-limit HCNG combustion. In this project systematic experimental studies, employing advanced techniques such as the experimentation under the micro-gravity condition and the counterflow flame methodology, will be conducted to obtain accurate experimental data series and variation rules of HCNG flammability limit at various pressures over a broad range of hydrogen blending ratio. Numerical simulation and theoretical analysis will also be carried out to study the chemical kinetic characteristics and multi-species diffusion mechanisms of near-limit HCNG flames. In particular, the effects of preferential diffusion and Soret diffusion on the extinction and flammability limit of HCNG will be insightfully revealed. The results will be compared with those obtained from the studies on single-species gaseous fuels or strongly propagating HCNG flames. The conclusion of this study will establish a solid theoretical basis and shed light on the utilization of HCNG.

将风电、光伏发电的富余电力制氢气，并与天然气掺混制得掺氢天然气（HCNG）供用户使用，既可解决电力“弃风弃光”问题，也有助于燃烧设备的清洁燃烧。同时掺氢天然气由两种最为简单常见但又燃烧性能迥异的小分子燃料混合而成，对其燃烧特性研究具有重要应用价值和理论意义。掺氢天然气的可燃极限直接关系到其输送、存储和使用安全，但已有的研究比较缺乏，且实验数据准确性不足，相关机理研究不充分。本项目通过微重力实验和对冲火焰法等实验方法，获得宽掺氢比、不同压力下掺氢天然气可燃极限的准确实验数据系列和变化规律，同时通过数值模拟、理论分析等方法研究掺氢天然气近极限燃烧过程的化学动力学特性和多元分子扩散规律，揭示常压和加压条件下掺氢引发的优势扩散效应和Soret效应对熄灭极限及可燃极限的影响规律，并与单组分气体火焰和掺氢天然气强火焰进行对比，为掺氢天然气的工业应用提供理论基础。

掺氢天然气的应用既可解决电力“弃风弃光”问题，也能实现设备的清洁燃烧，具有重要意义。本项目研究了宽掺氢比、不同压力下掺氢天然气燃烧极限的变化规律，理论分析了掺氢天然气近极限燃烧中化学动力学特征，探索了掺氢天然气近极限燃烧中多组分扩散规律，并针对富氢燃料气的低氮燃烧技术进行了研发。本项目考虑喷嘴出口“二维效应”，修正了富氢气体燃料近极限火焰传播速度和熄灭极限的准确测量方法和数值模拟方法，获得了不同条件下掺氢天然气燃烧极限规律。本项目掌握了层流预混掺氢天然气/空气火焰的化学动力学特征及火焰结构特征，提出了基于化学时间尺度分析的燃烧模式相图，并得到了掺氢比变化条件下燃烧模式相图的变化规律。本项目发现了不同燃烧类型下（均质反应流、扩散火焰）氢气的优势扩散作用导致近极限着火延迟呈现出显著区别，并通过数值模拟预测了不同的化学动力学和传输耦合条件下，“热焰”和“冷焰”的转捩现象。本项目定量刻画了混合延迟作用下，掺氢天然气近极限燃烧的污染物生成特性，总结出了基于实验规律的掺氢天然气预混火焰熄灭相图，并获得了掺氢天然气临界熄灭Da数值约为0.2。本项目将临界熄灭Da数进一步推广到湍流状态，发现了在小尺度涡团引发的传热传质增强作用下，临界Da数与湍流强度呈正相关。本项目开发了富氢燃料气低氮燃烧技术，并研制了原理样机。本项目发表学术论文20篇，其中SCI期刊论文7篇，EI期刊论文5篇，国际会议论文3篇，国内会议论文4篇。获得授权专利3项，其中获得发明专利2项，实用新型专利1项。本项目为掺氢天然气的燃烧利用打下了坚实的基础，有望在未来5年内在热力供应领域实现规模化的应用。