Study on the Flame Propagation Limit and Its Control by Turbulence

高负荷燃烧是近年来设计高效燃烧设备的热点之一。湍流混合和火焰传播的控制是在有限的燃烧空间内实现大比例燃烧的必要条件。本项目旨在阐明湍流对预混湍流火焰传播极限和精细结构的影响，并将其应用于高负荷燃烧的控制。得到以下结论：1）随着湍流强度的增加，湍流火焰的精细结构将其自身从化学控制的层流小火焰改变为混合控制的分布式反应区。随着火焰混合强度的降低，层流火焰结构在贫燃火焰传播极限处消失; 2）分布反应区火焰可定义为接近熄灭的火焰或失去自传播能力的火焰; 3）来流中的初始湍流增强了燃烧室内的混合和火焰传播。初始强湍流对高负荷燃烧是有效的; 4）在可燃极限附近，初始强湍流对贫油燃烧的促进作用不大。过度的湍流会产生分布反应区结构，从而导致火焰的局部熄灭。

The high-load combustion is one of the recent interest in combustion technology in designing effective combustion facilities. The control of turbulent mixing and flame propagation are essencial to burn a large rate of fuel in a limited combustion space.In the present project, we planned to elucidate the effects of turbulence on the propagation limit and the fine structure of premixed turbulent flames, and to apply the results to the control of the high-load combustion.The following conclusions have been obtained.1) With the increase in turbulence intensity, the fine structure of a turbulent flame changes itself from a chemistry-controlled laminar flamelet to a mixing-controlled distributed reaction zone. The structure of laminar flamelet disappear at the lean flame propagation limit when the mixture strength of the flame is decreased.2) The flame of distributed reaction zone can be defined as a flame near extinction or a flame which lost the ability of self-propagation.3) Initial turbulence in an approaching flow enhances the mixing and flame spread in a combustor. Initial intense turbulence is effective for the high-load combustion.4) The initial turbulence does not contribute to the enhancement of combustion in a lean mixture near flammability limit. The excessive turbulence produces the structure of distributed reaction zone, hence the local extinction of flames.