Study on the Flame Propagation Limit and Its Control by Turbulence

高负荷燃烧是近年来燃烧技术在设计高效燃烧设施方面的研究热点之一。湍流混合和火焰传播的控制对于在有限的燃烧空间中进行大比例燃烧是必不可少的。在本课题中，我们计划阐明湍流对预混湍流火焰的传播极限和精细结构的影响，并将研究结果应用于高负荷燃烧的控制。1)随着湍流强度的增加，湍流火焰的精细结构从化学控制的层流火焰转变为混合控制的分布反应区。当火焰的混合强度降低时，在稀薄火焰传播极限时，层流火焰的结构消失。2)分布反应区的火焰可以定义为接近熄灭的火焰或失去自传播能力的火焰。3)接近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)初始湍流对接近可燃极限的稀薄混合气的燃烧没有促进作用。过大的湍流形成了分布反应区的结构，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.