含氢中、低热值燃气在分层燃烧模式下燃烧稳定性的实验及LES研究

Hydrogen containing fuel gases with medium and low heat value (MLHV), such as biomass gas and syngas (heat value is around 5-20MJ/Nm3), are important alternative fuels for industry gas turbines. However, how to combust them stably in the dry low NOx (DLN) gas turbine is still an open challenge because of their lower heat values and much different combustion characteristics compared with nature gas. In stratified combustion mode, if the richer branch premixed flame (equivalence ratio smaller than unit) propagate towards lower equivalence ratios, an enhanced flame propagation and extended flammability limit can be achieved and therefore combustion stability is improved. This stratified combustion concept provides a feasible means of burning hydrogen containing fuel gases with MLHV stably. In the present project, a series of experimental studies on a novel visual turbulent combustor, with a confinement and a double-swirling-flow passage (manufactured by advanced 3D printing technology), are conducted to determine the combustion stability of fuel gases with different levels of hydrogen content and heat value in various conditions. For doing so, several measurement apparatuses are employed, including PIV (particle image velocimetry) and PLIF (planar laser induced fluorescence) methods. At the same time, large eddy simulations (LES) of the measured flames are performed systematically by using two different sub-grid scale combustion models. After a reliable validating of the accuracy of the used combustion models, detailed experimental data and highly accurate LES results are analyzed together for obtaining a deep insight of the interaction mechanism between turbulent swirling flow and stratified flame, for grasping the influencing law of various combustion state parameters on combustion stability, and for gaining a better understanding of the similarities and differences between the combustions of nature gas and hydrogen containing fuel gases with MLHV. The present project can hence provide a theoretical guidance in design uniform DLN gas turbine combustor, which is suitable for burning either nature gas or hydrogen containing fuel gases with MLHV.

生物质气、合成气等含氢燃气是燃气轮机的重要替代燃料，由于其热值及燃烧特性与天然气差异较大，如何实现它们在干式低NOx燃气轮机中的稳定燃烧是一个挑战；而分层燃烧模式下如果浓混气火焰向稀混气传播，则能扩大可燃界限，提高燃烧稳定性。本项目以含氢燃气的分层燃烧为研究对象，利用PIV、PLIF等多种测量方法对受限的带有双旋流入流通道的新型可视化分层燃烧装置开展一系列的燃烧实验，确定不同含氢量不同热值的燃气在各种条件下的燃烧稳定性；同时利用两种亚网格燃烧模型对测量的火焰开展系统性的大涡模拟计算。在可靠校核模型性能的基础上，对比分析计算结果与实验数据，深入研究受限空间内旋转湍流与分层火焰相互作用的内在机理，掌握各种燃烧状态参数对燃烧稳定性的影响规律，充分了解分层燃烧模式下含氢中、低热值燃气与天然气燃烧特性的异同，为设计既可燃烧天然气又可燃烧含氢中、低热值燃气的干式低NOx燃气轮机燃烧室提供理论指导。

含氢中、低热值燃气其热值及燃烧特性与天然气差异较大，如何实现它们的稳定燃烧是一个挑战。本项目采用大涡模拟和实验方法对含氢燃气的部分预混火焰进行研究，以了解含氢燃气与天然气燃烧特性的异同。研究内容包括：（1）开发适用于部分预混燃烧的亚网格燃烧模型；(2)利用新燃烧模型计算非均匀入流射流火焰，比较掺氢燃气与甲烷燃烧特性及吹熄极限的差异；（3）设计新型可视化燃烧装置并采用多手段进行联合测量。.在数值计算方面，将REDIM化学表格法与概率密度函数方法相结合，构造新的燃烧模型：REDIM-PFDF，随后用于非均匀入流部分预混火焰的计算，计算结果与实验结果吻合良好。将此燃烧器中的燃气由甲烷替换成低热值的掺氢燃气（热值为甲烷的35%），发现掺氢燃气的射流火焰吹熄极限与甲烷燃气的差别很大：掺氢燃气在FA、FJ两种布局下的火焰吹熄极限速度分别为90m/s和109m/s，而对应的甲烷的火焰吹熄极限速度分别为74m/s和128m/s。这种吹熄速度上的差异，与不同布局下燃气与空气混合不均匀程度相关，可以通过改变或优化燃气与空气的混合过程来提升中低热值燃气的稳定性。此外，还开展了H2:CH4体积比为1:1时中热值燃气射流火焰的计算研究。.在实验研究方面自主设计了一个包含一个3D打印的双通道旋流喷嘴。采用LabVIEW软件同步采集和处理高速摄像机拍的火焰图像及压力传感器采集的压力数据，将火焰形态与热声振荡导致的压力脉动综合分析。通过高速摄像机的拍摄，发现在该燃烧器中出现了两类形状截然不同的M型火焰和V型火焰。通过系列性的实验发现这两类火焰可以通过状态参数的改变来进行转换，且这种转换在大涡模拟计算中也得到了很好的再现。通过对压力脉动信号的功率谱特性分析和相空间重构分析，发现此双旋流燃烧室内存在400Hz和256Hz的两个不稳定频率。