A Comparative Study of Different Reaction Models for Turbulent Methane/Hydrogen/Air Combustion
A Comparative Study of Different Reaction Models for Turbulent Methane/Hydrogen/Air Combustion
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DOI：
10.18186/jte.60394
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发表时间：
2015-05
影响因子：
1.1
通讯作者：
S. Muppala;B. Manickam;F. Dinkelacker
中科院分区：
文献类型：
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作者：
S. Muppala;B. Manickam;F. Dinkelacker
甲烷/氢气燃烧的反应模拟有两个重要方面。首先，这种混合物将来可能会在高效能量存储系统需求的框架内用于燃气轮机和燃气发动机等燃烧装置，其中天然气输送系统中的氢气量可能会根据可再生能源的氢气产量的变化而变化。其次，这可能是安全的一个重要方面，因为这种混合物可能会在灾难性的情况下发生，并且计算可以允许预测安全问题。由于涉及来自甲烷和氢气不同扩散率的优先扩散效应，对这种混合燃料燃烧过程的建模并非易事。在湍流火焰建模中，这个主题特别令人感兴趣，因为即使对于高度湍流的火焰，热扩散不稳定性和火焰前缘附近的局部燃烧速度的局部影响似乎也很重要。因此，这项数值工作涉及五种不同的湍流燃烧的比较研究。 1. 简介 湍流甲烷/氢气燃烧的反应模型有两个重要方面。首先，这种弹性燃料混合物将来可以广泛用于燃气轮机和燃气发动机等燃烧装置中。对于风能和太阳能等可再生能源的能源生产的强烈变化而言，这尤其适用于寻找新的大规模能源存储系统。这里，建议在阳光或风力最大的情况下，电解产生的氢气可以存储在现有的大型天然气输送和存储系统内。这种化学储能方案将允许分配广泛使用可再生能源所需的巨大能源容量。然而，这种选择需要使用天然气的常见燃烧装置（例如燃气轮机或燃气发动机）能够在不同的燃料条件下运行。为了计算此类装置，需要合适的反应模型。其次，此类燃料混合物的安全性也非常重要。如果此类燃料混合物不受控制地释放，则这适用于之前描述的能量存储场景。即使没有这一点，对于化学工业、核电站故障或者氢气输送系统的愿景是否得到落实，氢气安全仍然是一个普遍问题。虽然氢是一种潜在的能量载体，在燃烧过程中不排放二氧化碳，但由于其高扩散性、反应性和燃烧速度，不能直接用于燃烧。相反，将氢混合到碳氢化合物中可以解决这些困难。因此，安全问题不仅对于纯氢而且对于氢/甲烷燃料混合物也很重要。这里也需要相关的计算方法。另一个方面是火焰稳定性。在天然气或甲烷火焰中添加氢气可以提高极贫燃烧模式下的火焰稳定性。由于氮氧化物和烟灰的超低排放特性，这些在固定式燃气轮机等领域引起了人们的关注。因此，在当前的研究中，在雷诺平均纳维斯托克斯（RANS）模拟技术的框架下研究了氢/甲烷燃料的预混合湍流反应速率模型的扩展。众所周知，与其他碳氢化合物燃料相比，氢气具有更高的反应活性。此外，氢的高扩散率使该燃料能够更快地扩散到反应区中。这两种效应一起包含在氢气/空气火焰以及氢气/碳氢化合物/空气火焰的层流燃烧速度增加中[1]。低旋涡火焰[5]。这些火焰的运行条件范围很广，因为稳定性极限很宽。遵循两种模型方法。在第一组中，平均湍流反应速率被建模为层流火焰速度（取决于氢含量）和湍流参数的函数。将表明，这些模型都不足以计算氢含量增加的测试用例。因此，在这项工作的第二部分中，采用了一种改进的方法，考虑了分子扩散的额外影响。这里使用有效的路易斯数方法对单一燃料模型进行相当简单的修改，可以计算整组实验数据的基本特征
Reaction modelling of methane/hydrogen combustion has two important aspects. First, such mixtures may be used in future in combustion devices like gas turbines and gas engines in the frame of the demand for efficient energy storage systems, where the amount of hydrogen in natural gas delivering systems may vary according to varying hydrogen production from renewable energies. Second, this can be an important aspect for safety, as such mixtures may occur in disastrous situations and calculations may allow the prediction of safety issues. Modelling of such mixed fuel combustion processes is non-trivial due to the involved preferential diffusion effects, coming from the different diffusivities of methane and hydrogen. In turbulent flame modelling, this topic is of special interest, as also thermo-diffusive instabilities and local influence of the local burning velocity near leading edges of the flame seem to be of importance even for highly turbulent flames. This numerical work deals therefore with a comparative study of five different turbulent combustion 1. INTRODUCTION Reaction modelling of turbulent methane/hydrogen combustion has two important aspects. First, such flex-fuel mixtures may be used broadly in future in combustion devices like gas turbines and gas engines. This holds especially with respect to the search for new large scale energy storage systems with respect to strongly varying energy production from renewable energies like wind and solar energy. Here, it is proposed that on peak sun or wind situations electrolytically produced hydrogen may be stored within the existing large scale natural gas delivering and storage system. This chemical energy storage option would allow the allocation of the huge energy capacity needed for the broad use of renewable energies. However, this option would require that the common combustion devices where natural gas is used, like gas turbines or gas engines, are able to operate under varying fuel conditions. For the calculation of such devices suitable reaction models are needed. Second, also safety aspects of such fuel mixtures are of significant importance. This holds for the energy storage scenario being described before, if such fuel mixtures are released uncontrolled. Even without that, hydrogen safety is a general issue for the chemical industry, for nuclear power plant failures or if the vision of hydrogen delivering systems is followed up. Though hydrogen is a potential energy carrier offering CO2 free emission during the combustion, this cannot be directly used for combustion due to its high diffusivity, reactivity and burning velocity. Instead, blending hydrogen into hydrocarbon could solve such difficulties. With that, safety issues may be important not only for pure hydrogen but also for hydrogen/methane fuel mixtures. Also here, relevant calculation methods are needed. An additional aspect is flame stability. The addition of hydrogen to natural gas or methane flames can increase the flame stability in very lean combustion modes. These are of interest for instance in stationary gas turbines due to the ultralow emission characteristics of NOx and soot. In the current study, therefore the extension of premixed turbulent reaction rate models for hydrogen/methane fuels is investigated in the frame of Reynolds averaged Navier-Stokes (RANS) simulation techniques. It is well known that hydrogen has a higher reactivity compared to other hydrocarbon fuels. Also the high diffusivity of hydrogen allows this fuel to diffuse faster into the reaction zone. Both effects together are included in increased laminar burning velocities for hydrogen/air flames as well as for hydrogen/hydrocarbon/air flames [1]. low swirl flames [5]. These flames operate for a broad range of conditions, as the stability limit is wide. Two approaches to models are followed. In the first group the mean turbulent reaction rate is modelled as a function of the laminar flame speed (which depends on the hydrogen content) and of turbulence parameters. It will be shown, that none of these models is sufficient to calculate the test cases with enhanced hydrogen content. In the second part of this work, a modified approach is followed therefore, taking into account additional effects from molecular diffusion. Here a rather simple modification of single fuel models with an effective Lewis number approach allows to calculate essential features of the whole set of experimental data