湍流部分裂解氨/空气预混合球形火焰

S. Zitouni, P. Bréquigny, C. Mounaïm-Rousselle
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引用次数: 0

摘要

对于大多数能量转换系统而言,氨的燃烧需要氢气等燃烧促进剂,以保证启动、稳定性和燃烧效率。与纯氨相比,部分裂解氨(PCA)可以提供足够浓度的氢气来提高燃烧速度。然而,在相关湍流条件下使用 PCA 混合物的研究却很少。为此,我们采用了向外传播的球形火焰构型,以确定 PCA(NH3/(H2+N2))和相应的二元(NH3/H2)混合物在各种湍流燃烧条件下的层流和湍流火焰传播特性。首先,在不同的湍流强度下,PCA 和氨氢混合物的火焰传播速度相似,甚至在层流情况下也是如此。在最贫油的条件下,湍流燃烧速度最高,而层流火焰在高于化学计量的条件下火焰速度最高。在富氢条件下,无论氢含量多少,都没有测得湍流导致的火焰大幅增强。湍流条件下火焰没有增强的原因是优先扩散的影响,这与测量的马克斯坦数的趋势非常吻合。归一化的湍流火焰速度主要是由于氢的存在提高了分子扩散率,最高可达 15%,而在贫氢和化学计量条件下,进一步添加氢后,湍流火焰速度会降低。这种 "弯曲 "现象可能是多种因素共同作用的结果,其中包括:与低达姆克勒数(Da)和火焰增粗相关的燃烧状态之间的转换;由于氨的存在而导致的小火焰合并,从而增强了皱纹;以及层流燃烧速度和优先扩散行为的综合变化。此外,湍流火焰速度与包含湍流伸展(Ka)和非液体扩散(Le)影响的相关性也有很好的一致性,一致性随着化学与湍流时间尺度比(Da <<1)的降低而降低。
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Turbulent partially cracked ammonia/air premixed spherical flames

The combustion of ammonia requires, for most energy conversion systems, a combustion promoter such as hydrogen to guarantee the start-up, stability and combustion efficiency. Partially cracked ammonia (PCA) can provide sufficient hydrogen concentrations to enhance the burning velocity in comparison with pure ammonia. However, little work exists on the use of PCA blends operating under relevant turbulent conditions. To that end the outwardly propagating spherical flame configuration was employed to determine the laminar and turbulent flame propagation characteristics of PCA (NH3/(H2+N2)) and corresponding binary (NH3/H2) mixtures across various turbulent combustion regimes. First, PCA and ammonia-hydrogen blends exhibit similar flame propagation rates under various turbulent intensities, even for the laminar case. The highest turbulent burning velocity was observed at leanest conditions, as opposed to laminar flames which exhibited highest flame speed at conditions above stoichiometry. Under rich conditions, no substantial flame enhancement due to turbulence was measured irrespective of the hydrogen content. This lack of flame enhancement under turbulent conditions is attributed to the effect of preferential diffusion with good agreement observed with trends in measured Markstein numbers. The normalized turbulent flame speed is dominated by the enhanced molecular diffusivity afforded by the presence of hydrogen up to 15 % enrichment, prior to decreasing upon further hydrogen addition under lean and stoichiometric conditions. This ‘bending’ phenomenon may be the contribution of several factors including; the transitioning between combustion regimes associated with low Damköhler numbers (Da) and flame thickening; merging of flamelets due to the presence of ammonia enhancing wrinkling; and combined changes in laminar burning velocity and preferential diffusional behavior. Furthermore, good agreement for turbulent flame speed is observed with a correlation that includes the influence of turbulent stretch (Ka) and non-equidiffusion (Le), with the agreement reducing with decreasing chemical to turbulent time scale ratios (Da << 1).

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Effects of difference in heating sources on ammonia reactivity: Possibility for photolysis-assisted ammonia combustion Investigations on conical lean turbulent premixed hydrogenated natural gas flames Diversity in the acceptance of sustainable aviation fuels: Uncovering varying motivational patterns Flame stabilization and pollutant emissions of turbulent ammonia and blended ammonia flames: A review of the recent experimental and numerical advances Turbulent partially cracked ammonia/air premixed spherical flames
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