Abstract Combustion characteristics of hydrogen–air premixed mixture are investigated in 1 mm converging–diverging microtubes with heated wall. Numerical study performed by considering three-dimensional and transient forms of the governing equations and detailed chemical kinetics. Effects of inlet velocity, equivalence ratio and converging–diverging angle are studied on the combustion characteristics. It was founded that the flame position has decisive role in the temperature, and inlet velocity has more impact on the flame position, flame extension and luminous zone at a constant converging–diverging angle. According to the results, when the flame places in the converging–diverging section, increase of the convection heat transfer rate due to the flow velocity increasement and increase of the heat loss due to the surface to volume ratio increasement cause to decrease the flame temperature. It leads to form oscillating flames at some conditions. On the other hand, converging–diverging section plays positive role in flame stability. For cases that the flame places in the outlet section, it removes flame instability near the wall and increases upper flammability limit by increasing heat recirculation in the converging–diverging section. The results showed that converging–diverging microtubes have higher upper flammability limit than the constant cross-sectional one. Also, upper flammability limit increases with the converging–diverging angle.

中文翻译：

---

收缩-发散微管中氢气-空气燃烧的燃烧特性和振荡行为的数值研究

摘要 研究了氢气-空气预混混合物在 1 mm 带加热壁的收敛-发散微管中的燃烧特性。通过考虑控制方程的三维和瞬态形式以及详细的化学动力学进行数值研究。研究了进气速度、当量比和收敛-发散角对燃烧特性的影响。结果表明，火焰位置​​对温度有决定性作用，在恒定的收敛-发散角下，入口速度对火焰位置、火焰延伸和发光区的影响更大。结果表明，当火焰处于收敛-发散段时，由于流速增加引起的对流换热率增加和由于表面积与体积比增加引起的热损失增加导致火焰温度降低。在某些情况下会导致形成振荡火焰。另一方面，会聚-发散部分对火焰稳定性起着积极的作用。对于火焰位于出口部分的情况，它消除了靠近壁的火焰不稳定性，并通过增加会聚-发散部分的热量再循环来增加可燃性上限。结果表明，会聚-发散微管比恒定截面微管具有更高的可燃性上限。此外，可燃性上限随着会聚-发散角的增加而增加。在某些情况下会导致形成振荡火焰。另一方面，会聚-发散部分对火焰稳定性起着积极的作用。对于火焰位于出口部分的情况，它消除了靠近壁的火焰不稳定性，并通过增加会聚-发散部分的热量再循环来增加可燃性上限。结果表明，会聚-发散微管比恒定横截面的微管具有更高的可燃性上限。此外，可燃性上限随着会聚-发散角的增加而增加。在某些情况下会导致形成振荡火焰。另一方面，会聚-发散部分对火焰稳定性起着积极的作用。对于火焰位于出口部分的情况，它消除了靠近壁的火焰不稳定性，并通过增加会聚-发散部分的热量再循环来增加可燃性上限。结果表明，会聚-发散微管比恒定横截面的微管具有更高的可燃性上限。此外，可燃性上限随着会聚-发散角的增加而增加。结果表明，会聚-发散微管比恒定横截面的微管具有更高的可燃性上限。此外，可燃性上限随着会聚-发散角的增加而增加。结果表明，会聚-发散微管比恒定横截面的微管具有更高的可燃性上限。此外，可燃性上限随着会聚-发散角的增加而增加。