Numerically-aided experimental studies are conducted on a swirl-stabilized combustor to investigate the dilution effects on flame stability, flame structure, and pollutant emissions of premixed CH4/air flames. Our goa...Numerically-aided experimental studies are conducted on a swirl-stabilized combustor to investigate the dilution effects on flame stability, flame structure, and pollutant emissions of premixed CH4/air flames. Our goal is to provide a systematic assessment on combustion characteristics in diluted regimes for its application to environmentally-friendly approaches such as biogas combustion and exhanst-gas recirculation technology. Two main diluting species, N2 and CO2, are tested at various dilution rates. The results obtained by means of optical diagnostics show that five main flame regimes can be observed for Nz-diluted flames by changing excess air and dilution rate. CO2-diluted flames follow the same pattern evolution except that all the domains are shifted to lower excess air. Both N2 and CO2 dilution affect the lean blow- out （LBO） limits negatively. This behavior can be counter-balanced by reactant preheating which is able to broaden the flammability domain of the diluted flames. Flame reactivity is degraded by increasing dilution rate. Meanwhile, flames are thickened in the presence of both diluting species. NOx emissions are significantly reduced with dilution and proved to be relevant to flame stability diagrams： slight augmentation in NOx emission profiles is related to transitional flame states where instability occurs. Although dilution results in increase in CO emissions at certain levels, optimal dilution rates can still be proposed to achieve an ideal compromise.展开更多
以某型燃烧室为研究对象,采用RANS(Reynolds average navier-stokes)和LES(large eddy simulation)两种方法进行数值模拟,并对两种数值方法的模拟结果进行了对比分析。研究结果表明,RANS的计算结果能够反应燃烧场中的主要流场特征,具有...以某型燃烧室为研究对象,采用RANS(Reynolds average navier-stokes)和LES(large eddy simulation)两种方法进行数值模拟,并对两种数值方法的模拟结果进行了对比分析。研究结果表明,RANS的计算结果能够反应燃烧场中的主要流场特征,具有一定的工程意义。LES能够复现弱轴向流动区等具体的流场细节,对剪切层位置和强度模拟较准确,还能模拟火焰动态发展过程,捕捉燃烧流场动态特性。与RANS相比,在燃烧流场数值仿真方面,LES占据更明显的优势。经计算,该工况下进动涡核由三个相对独立的螺旋涡分支组成,在燃烧室激起周期性速度脉动和压力脉动,LES捕捉到进动涡核主频率为156 Hz。展开更多
NH_(3)作为氢能载体,可实现氢能远距离输运。针对NH_(3)燃烧的反应性低、稳定性差、高燃料型NO_(x)排放问题,设计旋流燃烧器和空气分级燃烧室,实验研究功率为5~23 k W的NH_(3)、NH_(3)/CH_(4)扩散火焰NO_(x)排放特性。并采用化学反应器...NH_(3)作为氢能载体,可实现氢能远距离输运。针对NH_(3)燃烧的反应性低、稳定性差、高燃料型NO_(x)排放问题,设计旋流燃烧器和空气分级燃烧室,实验研究功率为5~23 k W的NH_(3)、NH_(3)/CH_(4)扩散火焰NO_(x)排放特性。并采用化学反应器网络(CRN)进行化学动力学模拟,分析排放变化的原因。结果表明:5 kW、Ф_(pri)=1.05的条件下,NH_(3)火焰NO_(x)测量排放最低为114.4×10^(-6)@15%O_(2);随着功率升高,NO_(x)排放增加,且导致燃烧不充分、火焰延长,此时最佳Ф_(pri)提前、燃烧范围减少、NO_(x)进一步增加;本文的CRN更适合模拟预混燃烧的NO_(x)排放,而不是扩散燃烧;功率升高不会改变反应路径,但生成NO的基元反应速率的升高幅度略大于消耗NO的基元反应速率,从而导致NO排放升高.展开更多
基金Project supported by the China Scholarship Council
文摘Numerically-aided experimental studies are conducted on a swirl-stabilized combustor to investigate the dilution effects on flame stability, flame structure, and pollutant emissions of premixed CH4/air flames. Our goal is to provide a systematic assessment on combustion characteristics in diluted regimes for its application to environmentally-friendly approaches such as biogas combustion and exhanst-gas recirculation technology. Two main diluting species, N2 and CO2, are tested at various dilution rates. The results obtained by means of optical diagnostics show that five main flame regimes can be observed for Nz-diluted flames by changing excess air and dilution rate. CO2-diluted flames follow the same pattern evolution except that all the domains are shifted to lower excess air. Both N2 and CO2 dilution affect the lean blow- out （LBO） limits negatively. This behavior can be counter-balanced by reactant preheating which is able to broaden the flammability domain of the diluted flames. Flame reactivity is degraded by increasing dilution rate. Meanwhile, flames are thickened in the presence of both diluting species. NOx emissions are significantly reduced with dilution and proved to be relevant to flame stability diagrams： slight augmentation in NOx emission profiles is related to transitional flame states where instability occurs. Although dilution results in increase in CO emissions at certain levels, optimal dilution rates can still be proposed to achieve an ideal compromise.
文摘NH_(3)作为氢能载体,可实现氢能远距离输运。针对NH_(3)燃烧的反应性低、稳定性差、高燃料型NO_(x)排放问题,设计旋流燃烧器和空气分级燃烧室,实验研究功率为5~23 k W的NH_(3)、NH_(3)/CH_(4)扩散火焰NO_(x)排放特性。并采用化学反应器网络(CRN)进行化学动力学模拟,分析排放变化的原因。结果表明:5 kW、Ф_(pri)=1.05的条件下,NH_(3)火焰NO_(x)测量排放最低为114.4×10^(-6)@15%O_(2);随着功率升高,NO_(x)排放增加,且导致燃烧不充分、火焰延长,此时最佳Ф_(pri)提前、燃烧范围减少、NO_(x)进一步增加;本文的CRN更适合模拟预混燃烧的NO_(x)排放,而不是扩散燃烧;功率升高不会改变反应路径,但生成NO的基元反应速率的升高幅度略大于消耗NO的基元反应速率,从而导致NO排放升高.
