Understanding Turbulent Hydrogen Flames and Instability via Measurements and Simulations

氢是最简单的燃料，但与普通碳氢化合物相比，它具有非常不同的特性：(A)单位质量释放高能量，(B)非常高的扩散率，(C)高反应性。这三个因素导致了较高的火焰速度，峰值约为碳氢化合物的十倍，以及极宽的可燃性限制，在空气中从3%到95%。氢也有形成不稳定火焰表面的倾向，这是由于与氢分子的非常轻的性质相关的热扩散不稳定性，这形成了长的手指状的前缘和非常厚的反应区，这意味着我们描述其他碳氢化合物火焰的物理方法对氢不适用。在这个项目中，我们的目标是开发模拟和实验，以定量揭示这些不稳定性如何影响反应速度和局部物种形成，从而允许开发可用于新的无碳发动机和燃气轮机的模型。该项目将使用在大气压和温度下稳定氢火焰的直接数值模拟和实验，以确定氢/氧比和稀释度的范围。该实验数据库将首次生成重建的三维火焰表面和速度、联合二维温度、OH自由基测量和一维氢物种浓度。数值数据库将产生与实验重叠的模拟，以及将实验无法达到的条件扩展到高达5倍大气压的压力。匹配的实验数据和数值数据的结合将使直接比较成为可能，探索不稳定行为和对反应物条件的依赖，确认数值预测，并使用更完整的DNS数据从较低保真度的实验数据推断。热扩散不稳定性的特殊问题也与其他潜在的反应混合物相关，并且一些发现可能推广到其他物理情况。更直接的是，这项研究还得到了处于氢基陆地和空中推进开发前沿的工业合作伙伴的支持，拟议的研究结果将立即纳入合作设施使用的湍流燃烧模型中。

Hydrogen is the simplest fuel, yet it has very different characteristics compared to common hydrocarbons: (a) high energy release per unit mass, (b) very high diffusivity, and (c) high reactivity. These three factors result in high flame speeds, which peak at around ten times those of hydrocarbons, and extremely wide flammability limits, from 3 to 95 percent in air. Hydrogen also has a propensity to form unstable flame surfaces owing to thermo-diffusive instabilities associated with the very light nature of hydrogen molecules, which form long finger-like leading edges, and very thick reaction zones, which means that the way in which we describe the physics of flames for other hydrocarbons does not work well for hydrogen. In this project we aim to develop simulations and experiments that will unveil quantitatively how these instabilities affect the reaction rate and local species formation, allowing the development of models that can be used in new carbon-free engines and gas turbines. The project will use direct numerical simulations and experiments of a stabilised hydrogen flame at atmospheric pressure and temperature, for a range of hydrogen/oxygen ratios and dilution. The experimental database will for the first time generate reconstructed 3D flame surfaces and velocities, joint two-dimensional temperature, OH radical measurements and one-dimensional hydrogen species concentrations. The numerical database will produce simulations overlapping with the experiments, as well as an extension of conditions inaccessible to experiments to higher pressures of up to 5 times atmospheric. The combination of matched experimental and numerical data will enable direct comparison, to explore the instability behaviour and dependence on reactant conditions, confirm numerical predictions, and use more complete DNS data to extrapolate from lower-fidelity experimental data.The particular issues of thermodiffusive instabilities are also relevant to other potential reactive mixtures, and some of the findings may be generalisable to other physical situations. More immediately, the research is also supported by industrial partners at the leading edge of development of hydrogen-based land and air propulsion, and findings from the proposed research will be immediately incorporated into models for turbulent combustion used at the collaborating facilities.