Aerodynamics and Kinetics Effects on the Dynamics of Steady/Unsteady Laminar, Stretched Flames

实际情况下的火焰行为受化学反应的详细动力学、热量和质量的扩散以及拉伸、湍流和大尺度流动不均匀的空气动力学过程控制。在这个项目中，层流预混火焰对拉伸和不稳定的响应将在降压和升压环境下在逆流燃烧器结构中进行实验确定，并使用详细的火焰和动力学代码进行数值模拟。重点将放在控制稳定拉伸火焰熄灭的过程，不稳定对火焰熄灭、位置和详细结构的影响，实施基于非侵入性激光的诊断以绘制速度分布图，以及确定复杂的动力学机制。在定常和非定常两种情况下，还将研究气动拉伸对层流扩散火焰熄灭的影响；在这种情况下，实验构型将包括空气层流射流与来自相反方向的层流燃料射流的碰撞。通过实验结果和数值结果的比较，将评估现有提出的动力学机制的有效性，并在灭绝点测试先前开发的灭绝动力学标准。不稳定对扩散火焰熄灭的影响将被量化，并获得与该问题相关的各种时间尺度的相对重要性的洞察。实际上，所有真实火焰都受到空气动力拉伸，表现为流动不均匀、火焰曲率或火焰/流动不稳定。在预混火焰中，由于传输和反应过程之间的内在相互依赖，这种影响是很强的。因此，了解拉伸预混火焰的性质不仅具有重要的实际意义，而且具有重要的意义。例如，火焰稳定化和通过拉伸层流火焰的概念对湍流火焰进行建模。扩散火焰也会受到拉伸的影响。扩散火焰对流场不均匀的响应很大程度上取决于反应物泄漏，而泄漏会导致反应不完全和熄灭。此外，扩散火焰更容易熄灭，因为在逆流结构中，扩散火焰的两侧都在“失去”热量，而预混火焰的一侧是绝热的。

Flame behavior in realistic situations is governed by the detailed kinetics of chemical reactions, the diffusion of heat and mass, and the aerodynamic processes of stretching, turbulence, and large-scale flow nonuniformity. In this program, the response of laminar premixed flames to stretching and unsteadiness will be experimentally determined in a counterflow burner configuration in both reduced and elevated pressure environments and numerically simulated using detailed flame and kinetics codes. Emphasis will be placed on processes governing extinction of steady stretched flames, the effects of unsteadiness on flame extinction, location, and detailed structure, the implementation of non-intrusive laser- based diagnostics to map velocity profiles, and the determination of complex kinetic mechanisms. The effects of aerodynamic stretching on laminar diffusion flame extinction will also be studied for both steady and unsteady flowfields; in this case, the experimental configuration will consist of an air laminar jet impinging on a laminar fuel jet coming from the opposite direction. From comparisons between experimental and numerical results the validity of existing proposed kinetic mechanisms will be assessed, and, at the extinction point, previously developed kinetic criteria of extinction will be tested. The influence of unsteadiness on diffusion flame extinction will be quantified and insight obtained on the relative significance of various time scales associated with the problem. Practically all realistic flames are subjected to aerodynamic stretching, manifested through flow nonuniformity, flame curvature, or flame/flow unsteadiness. In premixed flames, this influence is strong due to the inherent interdependence between the transport and reaction processes. Thus, understanding the properties of stretched premixed flames is of substantial practical importance as well as of fundamental interest. Examples include flame stabilization and the modeling of turbulent flames via the concept of stretched laminar flamelets. Diffusion flames can also be affected by the presence of stretch. The response of a diffusion flame to flowfield nonuniformities depends critically on reactant leakage which can lead to incomplete reaction and extinction. Furthermore, diffusion flames are more susceptible to extinction in that they are "losing" heat on both sides in a counterflow configuration whereas premixed flames are adiabatic on one side.