Study of multi-component fuel premixed combustion using direct numerical simulation
Study of multi-component fuel premixed combustion using direct numerical simulation
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DOI：
10.17863/cam.14073
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发表时间：
2014-04
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通讯作者：
Z. Nikolaou
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作者：
Z. Nikolaou
预计化石燃料储量将减少，由于大气污染日益严重，排放法规将变得更加严格。因此，工业燃气轮机发电所需的替代燃料必须能够满足上述要求。这类燃料的例子有合成气、高炉煤气和焦炉煤气。这些燃料的一个共同特点是它们是多组分燃料，其成分因其生产过程而有很大差异。这意味着它们的燃烧特性也会有很大的变化。因此，在设计阶段使用的这类燃料需要精确而又足够灵活的燃烧子模型，以确保在实际运行条件下的最佳性能。大多数燃烧子模型的开发和验证都是基于直接数值模拟（DNS）研究。然而，DNS在计算上是昂贵的。到目前为止，这限制了DNS使用单一组分燃料，如甲烷和氢。此外，迄今为止进行的大多数DNS都是在3D中使用一步化学，而骨架化学仅在2D中使用。因此，使用骨骼化学对3D DNS的需求是显而易见的。在本研究中，从骨架机理发展出适用于多组分燃料-空气燃烧的精确还原化学机理。然后利用这两种机制对自由传播的湍流预混火焰进行了三维解析，从而对这种多组分燃料火焰的火焰结构和湍流-标量相互作用有了一些了解。研究发现，与甲烷火焰相比，多组分燃料火焰在更宽的温度范围内释放热量。这是由于个别物种的反应区域并不完全重叠。简化机制的性能也使用DNS数据进行验证。结果表明，它是一个很好的骨骼机制的替代品，导致显著的时间和内存节省。在激光诊断中，常用的热释放率可视化火焰标记对于多组分燃料火焰来说是不够的，因此提出了替代标记。最后，对几种常用的平均反应速率闭包进行了多组分燃料火焰的测试。在本研究中考虑的最高湍流水平下，模型之间的性能存在显著差异。这些是由燃料的化学复杂性引起的，使用骨架化学DNS进行进一步的参数化研究将有助于模型的改进。
Fossil fuel reserves are projected to be decreasing, and emission regulations are becoming more stringent due to increasing atmospheric pollution. Alternative fuels for power generation in industrial gas turbines are thus required able to meet the above demands. Examples of such fuels are synthetic gas, blast furnace gas and coke oven gas. A common characteristic of these fuels is that they are multi-component fuels, whose composition varies greatly depending on their production process. This implies that their combustion characteristics will also vary significantly. Thus, accurate and yet flexible enough combustion sub-models are required for such fuels, which are used during the design stage, to ensure optimum performance during practical operating conditions. Most combustion sub-model development and validation is based on Direct Numerical Simulation (DNS) studies. DNS however is computationally expensive. This, has so far limited DNS to single-component fuels such as methane and hydrogen. Furthermore, the majority of DNS conducted to date used one-step chemistry in 3D, and skeletal chemistry in 2D only. The need for 3D DNS using skeletal chemistry is thus apparent. In this study, an accurate reduced chemical mechanism suitable for multi-component fuel-air combustion is developed from a skeletal mechanism. Three-dimensional DNS of a freely propagating turbulent premixed flame is then conducted using both mechanisms to shed some light into the flame structure and turbulence-scalar interaction of such multi-component fuel flames. It is found that for the multi-component fuel flame heat is released over a wider temperature range contrary to a methane flame. This, results from the presence of individual species reactions zones which do not all overlap. The performance of the reduced mechanism is also validated using the DNS data. Results suggest it to be a good substitute of the skeletal mechanism, resulting in significant time and memory savings. The flame markers commonly used to visualize heat release rate in laser diagnostics are found to be inadequate for the multi-component fuel flame, and alternative markers are proposed. Finally, some popular mean reaction rate closures are tested for the multi-component fuel flame. Significant differences are observed between the models’ performance at the highest turbulence level considered in this study. These arise from the chemical complexity of the fuel, and further parametric studies using skeletal chemistry DNS would be useful for the refinement of the models.