Suppression of CO2 and H2O on the cellular instability of premixed methane/air flame

Due to the cellular instability, the premixed methane/air flame will generate self-acceleration which can increase the explosion intensity. This work explored the suppression of CO2 or/and H2O on the cellular instability to mitigate the explosion intensity. The cellular instability was analyzed qualitatively and quantitatively in the viewpoint of the flame schlieren images and cellular instability parameters. The inhibition mechanism of CO2 or/and H2O on the cellular instability was also analyzed by numerical simulation. One important result is that CO2 can decrease the number of cellular structures obviously while H2O can increase the size of cellular structures, indicating that CO2 or/and H2O can inhibit the destabilization of cellular instability to spherical flame significantly. Meanwhile, CO2 enhances the intensity of diffusional-thermal instability while H2O decreases the intensity of diffusional-thermal instability. However, the intensity of hydrodynamic instability is inhibited by CO2 or/and H2O significantly due to an increase of flame thickness and a decrease of thermal expansion ratio. The inhibition mechanism analysis show that the key free radicals and adiabatic flame temperature are important to cellular instability. Both the peak ROP of H/O/OH and the mole fraction of H/O/OH can be decreased noticeably by CO2 or/and H2O. The adiabatic flame temperature decreases monotonously with increasing CO2 or/and H2O volume fraction. The most elementary reaction of enhancing adiabatic flame temperature is R38 while the first inhibiting reaction is R52.