CAREER: Influence of Unsteady Stretch on Premixed Flame Kernel Growth

事业：不稳定拉伸对预混火焰核生长的影响

• 批准号: 9702277
• 负责人: William Roberts
• 金额: $ 23万
• 依托单位: North Carolina State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-05-15 至 2001-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9702277&HistoricalAwards=false
• 关键词: CAREER; Influence; Unsteady; Stretch; Premixed

ABSTRACT CTS-9702277 This is study of the interactions of a spark-generated flame kernel at various stages of growth with a single, well-defined eddy of known velocity and length scale in order to identify the optimal hydrodynamic flowfield for the fuel-air mixture in a modern internal combustion (IC) engine. It is intended to identify which eddies are most beneficial and which are most beneficial and which a re most destructive in terms of kernel growth for various kinetics parameters such as equivalence ratio and Lewis number. It is known that at low to moderate turbulence levels there is a marked increase in the burning rate and in the flammability limits of the premixed reactants, but that this reverses as turbulence intensity increases and the length scale of the eddies become small compared to the reaction zone, since the eddies are now able to locally quench the flamefront. Advanced laser diagnostics are used to measure temperature, velocity field, and state of reaction. Hydroxyl and methylidine radicals are detected to locate the reaction zone and to indicate the state of the reaction; their absence indicates a quenched flamefront. Temperature is measured by Rayleigh scattering and by seeded nitric-oxide planar laser-induced fluorescence (PPLIF), while particle-image velocimetry (PIV) is used to measure the two-dimensional velocity field and thereby determine the local, instantaneous strain executed on the flame kernel by the local flowfield. In an internal combustion engine, the spark generates a flame kernel that may transfer its energy to the fuel-air mixture resulting in a vigorous, self-sustaining flame front, or, alternatively, may be quenched (extinguished) by a combination of hydrodynamic strain and curvature, collectively termed stretch. In the case of localized extinction, the kernel may survive but exhibit a severe degradation of ovepall combustion efficiency and in increase in pollutant emissions. Perturbation of kernel growth rate is the major cause of cycle -to-cycle variations in engines. Thus understanding of this phenomenon is the key to engines that give smooth, efficient, and clear performance.

摘要CTS-9702277 这是一个火花产生的火焰核心的相互作用，在不同的增长阶段与一个单一的，明确定义的已知速度和长度尺度的涡流，以确定最佳的流体动力学流场的燃料-空气混合物在现代内燃机（IC）发动机的研究。 它的目的是确定哪些涡是最有益的，哪些是最有益的，哪些是最具破坏性的各种动力学参数，如当量比和刘易斯数的内核增长方面。 众所周知，在低到中等湍流水平下，燃烧速率和预混合反应物的可燃性极限显著增加，但是随着湍流强度增加并且涡流的长度尺度与反应区相比变小，这种情况发生逆转，因为涡流现在能够局部淬灭火焰前锋。 先进的激光诊断用于测量温度、速度场和反应状态。 检测到羟基和亚甲基自由基以定位反应区并指示反应状态;它们的缺失指示猝灭的火焰前锋。 温度测量瑞利散射和种子一氧化氮平面激光诱导荧光（PPLIF），而粒子图像测速仪（PIV）是用来测量的二维速度场，从而确定的本地，瞬时应变执行的火焰核上的本地流场。 在内燃机中，火花产生火焰核心，该火焰核心可以将其能量传递到燃料-空气混合物，从而导致剧烈的、自持的火焰前缘，或者可替代地，可以通过流体动力学应变和曲率的组合（统称为拉伸）而熄灭（熄灭）。 在局部熄灭的情况下，内核可能会生存，但表现出严重的退化，燃烧效率和污染物排放量的增加。 核增长率的扰动是发动机循环变动的主要原因。 因此，理解这种现象是发动机提供平稳，高效和清晰性能的关键。