混合过程对旋流预混火焰燃烧不稳定性影响的实验研究

针对预混火焰燃烧振荡问题,通过改变旋流预混燃烧器的长度和气流速度,研究了混合长度、气体流速和当量比对燃烧不稳定性的影响,检验了时间延迟模型在宽时间尺度范围内的有效性,并揭示燃烧室压力脉动与燃烧器内燃料空气混合的相互作用机制,及其对燃烧模态的影响.结果表明,燃烧室内压力脉动会向上游传播,引起预混管内当量比脉动.当混合时间尺度小于临界尺度时,时间延迟模型具有一定的可行性.预混管内当量比脉动会随气体流动传至燃烧室中,进而影响燃烧过程,导致燃烧模态随混合时间增加而出现稳定-振荡的循环变化.当混合时间尺度大于临界尺度时,压力脉动向上游的扩散和当量比脉动向下游的流动传递衰减严重,燃烧处于稳定模态.该临界尺度约为τfc=1.5.

Experimental Study on the Effects of Mixing Process on the Combustion Instability of Swirling Premixed Flame

Focusing on the problem of premixed combustion instability,the effects of mixing length,gas flow velocity and equivalence ratio on combustion instability were studied by changing the length and gas flow velocity of swirling premixed burner. The time lag model was tested over a wide time scale,and the interaction mechanism between the combustor pressure fluctuation and the mixture of fuel and air in the premixed section and its influence on combustion modes were revealed. The results show that the pressure fluctuation in the combustor will spread upstream and cause the equivalence ratio fluctuation in the premixed section. When the mixing time scale is smaller than the critical scale,the time lag model is feasible. The equivalence ratio fluctuation in the premixed section will be transmitted to the combustion chamber along with the gas flow,which will affect the combustion process,resulting in a steady-oscillation cyclic change of combustion mode with the increasing mixing time. When the mixing time scale is larger than the critical scale,the pressure fluctuation spreading upstream and equivalence ratio fluctuation spreading downstream by convection transmission will damp too much,so that the combustion is in a stable mode. The critical scale is approximately τ fc=1.5.