摘要:
利用非接触的激光PLIF技术测量了在湍流贫燃预混燃烧中的OH自由基分布。以典型煤制合成气真实组分为基础进行工况设计,分为H2含量变化、CO/(CO+CH4)相对比例变化、雷诺数变化和中低热值对比4部分进行实验。通过OH-PLIF信号分析,探讨了H2含量、CO/(CO+CH4)相对比例和雷诺数对燃烧的影响。实验结果表明,雷诺数、H2含量和CO/(CO+CH4)相对比例的变化对合成气燃烧过程都有显著的影响。其中雷诺数的增大和H2含量的增加都加强了OH-PLIF信号强度,即有利于火焰中OH自由基的生成。而CO/(CO+CH4)相对比例的上升,因同时减少了CH4含量,导致OH自由基浓度下降。H2含量的升高和CO/(CO+CH4)相对比例的上升(转折点前)对于火焰行程都有缩短的作用,强化了燃烧。转折点之后CO/(CO+CH4)相对比例的继续上升不利于燃烧。后文对裂解气火焰瞬时图像和火焰面密度的分析印证了上述规律。
Abstract:
The application of simultaneous single-shot imaging of OH radicals using the non-intrusive planar laser-induced fluorescence (PLIF)method to investigate lean premixed turbulent jet flame was reported.13 working conditions were designed according to real component of typi-cal air gasification coal syngas.Effect of H2 content,CO/(CO+CH4 )relative ratio and Reynolds number on flame structure were studied based on the acquired OH-planar laser-induced fluores-cence (OH-PLIF)images.And then,this method was applied to typical premixed turbulent py-rolysis syngas flame.Pyrolysis syngas contained over 80 percent combustible component,which led to a much higher calorific efficiency.Results indicated that,each of H2 content,CO/(CO+CH4 )relative ratio and Reynolds number played an important role in the formation of OH radical during combustion,therefore had an effect on combustion structure.H2 content increase and Reynolds number increase can enhance OH-PLIF signal in measuring range,which means they promote the formation of OH radicals.While the increase of CO/(CO+CH4 )relative ratio have an obviously decrease effect on OH signal.With the increase of Reynolds number from 4000 to 12000,the flame surface became wrinkled,the pulsation intensity of syngas flame became larger, and the unburnt area lengthened due to the increase of total amount of syngas.In general,Reyn-olds number strengthened the combustion progress.When the H2 ratio raised from 0 to 25% by 5% per step,the results showed that both length and width of the unburnt area reduced,and OH-PLIF signal became much stronger at upstream of the flame.In one word,the increase of H2 ratio can accelerate turbulent syngas combustion.As the CO/(CO+CH4 )relative ratio was investigated as a variable,the measurement results became complex.CO/(CO+CH4 )relative ratio was enhanced from 0 to 100% by 20% per step,and a turning point appeared during the procedure.In the first 4 working conditions,in which the CO/(CO+CH4 )relative ratio was 0 to 80%,the unburnt area was slowly reduced both in height and width dimensions.After that, with the CO/(CO+CH4 )relative ratio continue increasing to 100%,the unburnt area suddenly enlarged to a very high scale.Another undeniable fact need to be pointed out was that,OH-PLIF signals in these measurements series continued decreasing along with CO/(CO+CH4 )relative ratio increase.That’s because,CO/(CO+CH4 )relative ratio increase led to the decrease of CH4 ,which was the only one hydrogen supply to form OH radicals.Before the turning point, OH radical density could still satisfy the demand of reaction,so it strengthened combustion pro-gress;after the turning point,combustion was obstructed since the short of OH radicals.This OH-PLIF image analysis system was applied in premixed turbulent pyrolysis syngas flame,and the results showed an agreement with what discussed above.
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