...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Combustion Science and Technology >FLAME/STRETCH INTERACTIONS IN LAMINAR AND TURBULENT PREMIXED FLAMES
【24h】

FLAME/STRETCH INTERACTIONS IN LAMINAR AND TURBULENT PREMIXED FLAMES

机译：层流和湍流预混合火焰中的火焰/条纹相互作用

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The flame/stretch interactions of laminar and turbulent premixed flames are considered both experimentally and computationally. Potentially strong effects of flame/stretch interactions due to preferential-diffusion phenomena within practical turbulent premixed flames were suggested by experiments and numerical simulations of spherical outwardly propagating laminar premixed flames. These considerations were limited to conditions where ignition disturbances, pressure variations, intrinsic unsteadiness of propagating spherical flames, and radiative heat losses were small. Flame reactants consisting of H_2/O_2/N_2 and several light hydrocarbon/air mixtures were studied for various fuel-equivalence ratios and pressures of 0.5―4.0 atm at normal temperature (298 +- 3K). The measurements and predictions yielded several interesting results, as follows: Flame response to stretch was linear using a local conditions hypothesis to define characteristic flame length and time scales, yielding constant Markstein numbers for given flame conditions; effects of stretch were surprisingly strong with up to 100 percent variations of laminar burning velocities resulting from rather modest stretch rates well below extinction conditions (i.e., Karlovitz numbers less than 0.5); there was a progressive tendency for greater ranges of unstable preferential-diffusion conditions (negative Markstein numbers) as pressures were increased for all reactant mixtures studied; and several contemporary detailed treatments of multi-component transport and chemical reaction mechanisms yielded reasonably good predictions of laminar burning velocities and their sensitivity to flame stretch due to preferential-diffusion effects. The predictions suggest that the strong sensitivity of the present flames to stretch is mainly caused by preferential diffusion of light radicals and stable species relative to typical stable reaction products and heat, with increased preferential-diffusion instability at elevated pressures resulting from reduced radical concentrations in the reaction zone due to increased radical recombination rates. The potential practical importance of flame/stretch interactions was examined by considering the properties of strongly turbulent premixed flames. These measurements involved premixed H_2/O_2/N_2 and C_3H_8/air flames propagating in the thin wrinkled flamelet regime within isotropic turbulence. Test conditions included unstable, near-neutral, and stable flames with respect to effects of preferential-diffusion. The experiments yielded several interesting observations, as follows: 1) Rates of turbulent flame propagation progressively decreased as flame stability with respect to preferential-diffusion effects increased even through unstretched laminar burning velocities and turbulence properties were the same; 2) Distortion of the flame surfaces by turbulence as the flames grew caused their fractal dimensions to progressively increase from a value of 2.0, appropriate for a smooth surface, to asymptotic values in the range 2.3-2.4, irrespective of preferential-diffusion stability conditions; 3) Other parameters characterizing the extent of distortion of the flame surfaces showed no tendency to approach asymptotic values for available observation times, however, raising questions about the existence of steady turbulent flame propagation properties for the present test conditions; and 4) The extent of flame surface distortion progressively increased at a given flame diameter, but decreased at a given time Of propagation, as preferential-diffusion stability was progressively increased even though unstretched laminar burning velocities and turbulence properties were the same. These flame/stretch interactions in turbulent flames can be explained by noting that stable (unstable) preferential-diffusion conditions tend to retard (enhance) distortion of the flame surface by turbulence for outwardly propagating spherical turbulent premixed flames in much the same
机译：实验和计算都考虑了层流和湍流预混火焰的火焰/拉伸相互作用。通过球形向外传播的层状预混火焰的实验和数值模拟，表明了在实际湍流预混火焰中由于优先扩散现象而引起的火焰/拉伸相互作用的潜在强大影响。这些考虑仅限于点火干扰，压力变化，传播的球形火焰的固有不稳定性以及辐射热损失较小的情况。研究了由H_2 / O_2 / N_2和几种轻质烃/空气混合物组成的火焰反应物在常温（298±3K）下的各种燃料当量比和0.5-4.0 atm的压力。测量和预测产生了一些有趣的结果，如下所示：使用局部条件假设定义特征火焰长度和时间尺度，火焰对拉伸的响应是线性的，在给定的火焰条件下产生恒定的马克斯坦数；拉伸效果令人惊讶地很强，由于相当适度的拉伸速率远低于灭绝条件（即Karlovitz数小于0.5）导致层流燃烧速度变化高达100％;随着所研究的所有反应混合物的压力增加，不稳定的优先扩散条件（负马克斯坦数）的范围有逐渐扩大的趋势；以及当代对多组分传输和化学反应机理的详细处理，对层流燃烧速度及其由于优先扩散效应而对火焰拉伸的敏感性做出了合理的良好预测。预测表明，当前火焰对伸展的强烈敏感性主要是由于自由基和稳定物质相对于典型的稳定反应产物和热量的优先扩散所致，并且由于压力降低导致自由基在较高压力下的优先扩散不稳定性增加。反应区由于自由基重组速率的提高。通过考虑强湍流预混火焰的特性，研究了火焰/拉伸相互作用的潜在实际重要性。这些测量涉及在各向同性湍流中在薄皱纹小火焰区域中传播的预混合H_2 / O_2 / N_2和C_3H_8 /空气火焰。关于优先扩散的影响，测试条件包括不稳定，接近中性和稳定的火焰。该实验产生了一些有趣的观察结果，如下：1）即使在未拉伸的层流燃烧速度和湍流特性相同的情况下，随着优先扩散效应的火焰稳定性增加，湍流火焰传播的速率也会逐渐降低。 2）随着火焰的增长，湍流使火焰表面变形，使分形维数从适用于光滑表面的2.0逐渐增加到2.3-2.4范围内的渐近值，而与优先扩散稳定性条件无关。 3）表征火焰表面变形程度的其他参数在可用的观察时间内没有趋向于渐近值的趋势，但是，对于当前的测试条件，是否存在稳定的湍流火焰传播特性提出了疑问； 4）在给定的火焰直径下，火焰表面变形的程度逐渐增加，但在给定的传播时间减小，因为优先扩散稳定性逐渐增加，即使未拉伸的层流燃烧速度和湍流特性相同。湍流火焰中的这些火焰/拉伸相互作用可以通过以下说明来解释：稳定的（不稳定）优先扩散条件趋于通过湍流来延迟（增强）火焰表面的扭曲，从而使球形湍流预混火焰以相同的方式向外传播

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号