分层比对分开分层旋流预混火焰结构的影响

摘要

To understand the characteristics of the separated stratified premixed swirl methane/air flame,effects of the Stratification Ratio (SR) on the structure of the separated stratified premixed swirl flame are experimentally investigated.Methane is used as the fuel in the experiment,and the change of the mean flame configurations—or the macrostructures—characterized by flame CH* chemiluminescence,including flame stabilization,flame front and flashback,etc.are measured by varying the SR at normal temperature and pressure.We observe the changes in the method of flame stabilization and the main heat release zone.Under the combined influence of the corner recirculation zone,lip recirculation zone and principal recirculation zone,flame stabilization points appear at four locations,including the downstream of the central body,the rims of the lip and the edge of the main tube exit,as the SR varies.Hence,6 new modes of the separated stratified premixed swirl flame are first proposed:Y mode,V mode,symmetric D mode,wrinkled mode,narrow W mode and wide W mode,which are different from the modes of the stratified premixed swirl flame in other research.The results show that the SR has an important impact on the flame macrostructure and flame self-excitation,which can be explained by rich burn,lean burn and flammable limit of methane.%为了充分认识分开分层旋流预混火焰的特性,实验研究了分层比(SR)对分开分层旋流预混火焰宏观结构的影响.实验以甲烷为燃料在常温常压下展开,通过改变分层比研究了用CH*化学发光信号表征的火焰宏观结构的变化,包括稳火方式、焰锋、主释热区等.观察到火焰的稳火方式以及主释热区的位置发生了变化.在角涡回流区、台阶回流区和中心回流区的共同作用下,随着分层比的变化,分别在中心体下游、台阶内外沿和主燃级通道出口外沿存在稳火点,并依此首次提出和以往研究中分层旋流预混火焰相比不同的6种类型分开分层旋流预混火焰模式:Y型、V型、对称D型、多褶型、窄W型和宽W型.结果表明,火焰宏观结构受分层比影响而发生变化,可以用甲烷的富燃、贫燃和可燃极限来解释分层比对火焰宏观结构以及自激振荡的影响.