Net Zero: Flame Instability of Ammonia Aerosol Combustion

在寻找可再生和无碳燃料的过程中，氨的使用被认为是发动机和燃气涡轮机应用的有吸引力的解决方案。与氢等其他无碳燃料相比，它具有显著的优势。它不仅易于从可再生的氮和氢来源生产，而且储存和运输更安全，并且具有更高的能量含量。此外，它可以在不改变工业已经部署的基础设施的情况下生产，运输和分销。然而，为了成功地将氨用作燃料，需要克服与其燃烧相关的一个主要挑战：其低反应性需要高点火能量、窄可燃范围和低燃烧速度。这使得燃烧火焰的稳定变得复杂，从而不可避免地导致不可靠的点火和不稳定的燃烧。燃料液滴云（或气溶胶云）的燃烧在燃气轮机、柴油和火花点火发动机、熔炉和危险环境中具有实际重要性。有实验证据表明，与预期相反，在某些情况下，气溶胶云中的火焰传播高于完全汽化的均匀混合物中的火焰传播（可能高达3倍）。此外，燃料液滴的存在会增强火焰起皱不稳定性的产生。在更丰富的混合物和更大的液滴的情况下，液滴有可能进入反应区，并通过产生进一步的火焰燃烧来进一步增强现有的气相不稳定性。因此，火焰经历周期性的减速和加速，这些振荡在100 ms内持续几个周期。当然，当在燃气涡轮机中燃烧氨时，燃烧速度的提高可能有利于提供更快速的燃烧。由于氨气溶胶燃烧尚未得到广泛研究，有必要弄清楚氨气溶胶火焰在多大程度上继承了这种振荡行为，因为这种火焰振荡将与热声振荡耦合并损坏涡轮机叶片。虽然一些理论研究已经研究了气溶胶云中的火焰传播，但控制火焰振荡的过程仍然不清楚，特别是对于氨。我们将使用利兹大学为STFC资助的天体物理研究开发的数值技术和流体力学代码，以增加我们对这种现象的理解，并将氨作为无碳燃料。

In the search for renewable and carbon-free fuels, the use of ammonia is considered an attractive solution for engine and gas turbine applications. When compared to other carbon-free fuels, such as hydrogen, it has significant advantages. Not only is it easy to produce from renewable sources of nitrogen and hydrogen, it is safer to store and transport and has a higher energy content. Furthermore, it can be produced, transported and distributed without changing the infrastructure already deployed by industries. However, for the successful application of ammonia as a fuel, one main challenge related to its combustion needs to be overcome: its low reactivity requires a high ignition energy, a narrow flammability range and low burning velocity. This complicates the stabilisation of the combustion flame and thus inevitably causes unreliable ignition and unstable combustion.The combustion of clouds of fuel droplets (or aerosol clouds) is of practical importance in gas turbines, diesel and spark ignition engines, furnaces and hazardous environments. There is experimental evidence that, contrary to expectations, flame propagation in aerosol clouds, under certain circumstances, is higher than that in a fully vaporised homogeneous mixture (possibly by up to a factor of 3). Also, the presence of fuel droplets is shown to enhance the generation of flame wrinkling instabilities. With richer mixtures and larger droplets, it is possible for droplets to enter the reaction zone and further enhance existing gaseous phase instabilities through the creation of yet further flame wrinkling. Therefore, the flame experiences periodic deceleration and acceleration with these oscillations lasting for several cycles within 100ms. Surely, the burning velocity enhancement may be advantageous in giving more rapid burning when burning ammonia in a gas turbine. As ammonia aerosol combustion has not been extensively studied yet, it is necessary to make clear to what extent ammonia aerosol flames inherit this oscillating behaviour as this oscillation of the flame will couple with thermo-acoustic oscillations and damage the turbine blades.While some theoretical research has studied flame propagation in aerosol clouds, the processes governing flame oscillations are still unclear, especially for ammonia. We will use the numerical techniques and hydrodynamics codes developed at the University of Leeds for STFC-funded astrophysical research to increase our comprehension of this phenomenon and advance ammonia as a carbon-free fuel.