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Numerical Investigations of a Hydrogen Jet Flame in a Vitiated Coflow.

机译：通风气流中氢射流火焰的数值研究。

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摘要

An ever increasing demand for energy coupled with a need to mitigate climate change necessitates technology (and lifestyle) changes globally. An aspect of the needed change is a decrease in the amount of anthropogenically generated CO2 emitted to the atmosphere. The decrease needed cannot be expected to be achieved through only one source of change or technology, but rather a portfolio of solutions are needed. One possible technology is Carbon Capture and Storage (CCS), which is likely to play some role due to its combination of mature and promising emerging technologies, such as the burning of hydrogen in gas turbines created by pre-combustion CCS separation processes. Thus research on effective methods of burning turbulent hydrogen jet flames (mimicking gas turbine environments) are needed, both in terms of experimental investigation and model development. The challenge in burning (and modeling the burning of) hydrogen lies in its wide range of flammable conditions, its high diffusivity (often requiring a diluent such as nitrogen to produce a lifted turbulent jet flame), and its behavior under a wide range of pressures. In this work, numerical models are used to simulate the environment of a gas turbine combustion chamber. Concurrent experimental investigations are separately conducted using a vitiated coflow burner (which mimics the gas turbine environment) to guide the numerical work in this dissertation. A variety of models are used to simulate, and occasionally guide, the experiment.;On the fundamental side, mixing and chemistry interactions motivated by a H2/N2 jet flame in a vitiated coflow are investigated using a 1-D numerical model for laminar flows and the Linear Eddy Model for turbulent flows. A radial profile of the jet in coflow can be modeled as fuel and oxidizer separated by an initial mixing width. The effects of species diffusion model, pressure, coflow composition, and turbulent mixing on the predicted autoignition delay times and mixture composition at ignition are considered. We find that in laminar simulations the differential diffusion model allows the mixture to autoignite sooner and at a fuel-richer mixture than the equal diffusion model. The effect of turbulence on autoignition is classified in two regimes, which are dependent on a reference laminar autoignition delay and turbulence time scale. For a turbulence timescale larger than the reference laminar autoignition time, turbulence has little influence on autoignition or the mixture at ignition. However, for a turbulence timescale smaller than the reference laminar timescale, the influence of turbulence on autoignition depends on the diffusion model. Differential diffusion simulations show an increase in autoignition delay time and a subsequent change in mixture composition at ignition with increasing turbulence. Equal diffusion simulations suggest the effect of increasing turbulence on autoignition delay time and the mixture fraction at ignition is minimal.;More practically, the stabilizing mechanism of a lifted jet flame is thought to be controlled by either autoignition, flame propagation, or a combination of the two. Experimental data for a turbulent hydrogen diluted with nitrogen jet flame in a vitiated coflow at atmospheric pressure, demonstrates distinct stability regimes where the jet flame is either attached, lifted, lifted-unsteady, or blown out. A 1-D parabolic RANS model is used, where turbulence-chemistry interactions are modeled with the joint scalar-PDF approach, and mixing is modeled with the Linear Eddy Model. The model only accounts for autoignition as a flame stabilization mechanism. However, by comparing the local turbulent flame speed to the local turbulent mean velocity, maps of regions where the flame speed is greater than the flow speed are created, which allow an estimate of lift-off heights based on flame propagation. Model results for the attached, lifted, and lifted-unsteady regimes show that the correct trend is captured. Additionally, at lower coflow equivalence ratios flame propagation appears dominant, while at higher coflow equivalence ratios autoignition appears dominant.
机译：不断增长的能源需求以及减轻气候变化的需求，使得全球范围内的技术（和生活方式）发生了变化。所需改变的一个方面是减少了人为排放到大气中的二氧化碳排放量。不能期望仅通过一种变更或技术来实现所需的减少，而是需要一系列解决方案。碳捕集与封存（CCS）是一种可能的技术，由于它结合了成熟和有前途的新兴技术，例如在燃烧前的CCS分离过程所产生的燃气轮机中燃烧氢气，可能会发挥一定的作用。因此，无论是在实验研究还是模型开发方面，都需要研究有效的燃烧湍流的氢喷射火焰（模仿燃气轮机环境）的方法。燃烧氢（和模拟燃烧）的挑战在于其广泛的易燃条件，高扩散性（通常需要诸如氮气等稀释剂以产生升起的湍流射流火焰）以及其在各种压力下的性能。在这项工作中，数值模型用于模拟燃气轮机燃烧室的环境。并行的实验研究是使用通风的同流燃烧器（模仿燃气轮机环境）进行的，以指导本文的数值工作。使用各种模型来模拟实验，并偶尔进行实验指导。在基本方面，使用层流的一维数值模型研究了H2 / N2射流火焰在带风同流中的混合和化学相互作用。和线性涡流模型。共流中射流的径向轮廓可以建模为燃料和氧化剂之间的初始混合宽度分开。考虑了物质扩散模型，压力，同流成分和湍流混合对预测的自燃延迟时间和点火时混合物成分的影响。我们发现，在层流模拟中，微分扩散模型比等扩散模型允许混合物更快地自燃，并且燃料更富燃料。湍流对自燃的影响分为两种情况，这取决于参考层流自燃延迟和湍流时间尺度。对于大于参考层流自燃时间的湍流时间尺度，湍流对自燃或点火时的混合物几乎没有影响。但是，对于小于参考层流时标的湍流时标，湍流对自燃的影响取决于扩散模型。差分扩散模拟显示，自燃延迟时间增加，并且随着湍流的增加，点火时混合物成分随之变化。均等扩散模拟表明湍流增加对自燃延迟时间的影响，并且点燃时的混合比最小。;更实际地，举起的火焰的稳定机制被认为是通过自燃，火焰传播或以下两种方式的组合来控制的：他们俩。在大气压下，在流通的气流中，用氮气喷射火焰稀释的湍流氢的实验数据表明，喷射火焰附着，举升，举升不稳定或吹出时具有独特的稳定性。使用一维抛物线RANS模型，其中湍流-化学相互作用通过联合标量PDF方法建模，而混合则通过线性涡流模型建模。该模型仅将自燃作为火焰稳定机制。但是，通过将局部湍流火焰速度与局部湍流平均速度进行比较，可以创建火焰速度大于流速的区域图，从而可以根据火焰传播来估算起升高度。附加，解除和解除不稳定状态的模型结果表明，可以捕获正确的趋势。另外，在较低的同流当量比下，火焰传播占主导地位，而在较高的同流当量比下，自燃占据主导地位。

著录项

  • 作者

    Frederick, Donald Jerome.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Engineering Mechanical.;Energy.;Engineering Environmental.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 63 p.
  • 总页数 63
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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