入口温度对微型凹腔燃烧器中H_2/air燃烧效率的影响

Effect of Inlet Mixture Temperature on Combustion Efficiency Of Lean H_2/air Flames in a Micro Cavity-Combustor

通过数值模拟研究了入口温度对贫燃H2/air混合气燃烧效率的影响。结果表明：当量比为0.5时,即使入口温度为300 K也能获得很高的燃烧效率,而当量比为0.3和0.4时,由于火焰尖端发生分裂,导致燃料泄漏和燃烧效率下降。入口温度上升50100 K时,火焰尖端分裂得到显著改善。分析表明：一方面,依据Arrhenius定律,提高混合气温度可以直接增加燃烧反应速率;另一方面,提高入口温度在一定程度上可以增加混合气的有效Lewis数;此外,提高入口温度可使火焰高度变小,削弱火焰拉伸效应的影响。总之,对于贫燃H2/air火焰来说,小幅提高混合气的初始温度就能明显增加火焰尖端的燃烧强度,抑制火焰尖端分裂现象的发生,提高燃烧效率。

In the present work,the effect of inlet temperature on tip opening of very lean H2/air flames（φ= 0.3,0.4,0.5） in a micro-channel with wall cavities was numerically investigated.It is demonstrated that for φ=0.5,flame tip opening does not occur even at Tin=300 K,while forφ=0.3 and 0.4,this phenomenon becomes serious.As a result,a great amount of fuel leaks and the combustion efficiency drops sharply.Nevertheless,if the inlet temperature is increased by around50100 K,the flame tip opening phenomenon can be notably improved.On the one hand,according to the Arrhenius law,the reaction rate can be directly enhanced by raising the mixture temperature.On the other hand,the effective Lewis number is increased.Moreover,the flame height and thus the stretch rate are reduced with an increasing inlet temperature,which can intensify the combustion reaction at the flame tip.In conclusion,the flame tip opening phenomenon in the micro-channel with wall cavities can be effectively remedied by appropriately preheating the incoming cold mixture.