A numerical study on the effect of hydrogen/reformate gas addition on flame temperature and NO formation in strained methane/air diffusion flames

This paper investigates the effects of hydrogen/reformate gas addition on flame temperature and NO formation in strained methane/air diffusion flames by numerical simulation. The results reveal that flame temperature changes due to the combined effects of adiabatic temperature, fuel Lewis number and radiation heat loss, when hydrogen/reformate gas is added to the fuel of a methane/air diffusion flame. The effect of Lewis number causes the flame temperature to increase much faster than the corresponding adiabatic equilibrium temperature when hydrogen is added, and results in a qualitatively different variation from the adiabatic equilibrium temperature as reformate gas is added. At some conditions, the addition of hydrogen results in a super-adiabatic flame temperature. The addition of hydrogen/reformate gas causes NO formation to change because of the variations in flame temperature, structure and NO formation mechanism, and the effect becomes more significant with increasing strain rate. The addition of a small amount of hydrogen or reformate gas has little effect on NO formation at low strain rates, and results in an increase in NO formation at moderate or high strain rates. However, the addition of a large amount of hydrogen increases NO formation at all strain rates, except near pure hydrogen condition. Conversely, the addition of a large amount of reformate gas results in a reduction in NO formation.Dans le pr\ue9sent article, on \ue9tudie les effets de l\u2019addition d\u2019hydrog\ue8ne/reformat sur la temp\ue9rature de flamme et la formation de NO dans des flammes de diffusion m\ue9thane/air \ue9tir\ue9es, au moyen de la mod\ue9lisation num\ue9rique. Les r\ue9sultats ont montr\ue9 que la temp\ue9rature de flamme change en raison des effets combin\ue9s de la temp\ue9rature adiabatique, du nombre de Lewis du combustible et de la perte de chaleur de radiation quand l\u2019hydrog\ue8ne/reformat est ajout\ue9 au m\ue9lange combustible m\ue9thane/air de la flamme de diffusion. L\u2019effet du nombre de Lewis conduit \ue0 une augmentation de la temp\ue9rature de flamme beaucoup plus rapide que la temp\ue9rature d\u2019\ue9quilibre adiabatique correspondante quand l\u2019hydrog\ue8ne est ajout\ue9 et conduit \ue0 une variation qualitativement diff\ue9rente de la temp\ue9rature d\u2019\ue9quilibre adiabatique quand du reformat est ajout\ue9. Sous certaines conditions, l\u2019addition de l\u2019hydrog\ue8ne conduit \ue0 une temp\ue9rature de flamme superadiabatique. L\u2019addition d\u2019hydrog\ue8ne/reformat conduit \ue0 une modification de la formation de NO en raison des variations de la temp\ue9rature de flamme, de la structure et du m\ue9canisme de formation du NO. L\u2019effet devient plus important avec l\u2019accroissement de la vitesse de d\ue9formation. L\u2019addition d\u2019une petite quantit\ue9 d\u2019hydrog\ue8ne ou de reformat a peu d\u2019effet sur la formation de NO aux faibles vitesses d\u2019\ue9tirement, et conduit \ue0 une augmentation de la formation de NO aux vitesses mod\ue9r\ue9es ou \ue9lev\ue9es. Toutefois, l\u2019addition d\u2019une grande quantit\ue9 d\u2019hydrog\ue8ne m\ue8ne \ue0 une augmentation de la formation de NO, peu importe la vitesse d\u2019\ue9tirement, sauf dans des conditions proches d\u2019une flamme d\u2019hydrog\ue8ne pur. \uc0 l\u2019oppos\ue9, l\u2019addition d\u2019une grande quantit\ue9 de reformat entra\ueene une r\ue9duction de la formation de NO.Peer reviewed: YesNRC publication: Ye