Effects of nitrogen addition on the combustion characteristics of hydrogen-air lean premixtures in a closed vessel

Thwe Thwe, A. ; Kadowaki, Satoshi; Katsumi, Toshiyuki

The experiments of hydrogen-air lean premixtures in a closed vessel were performed to study the effects of nitrogen addition on the combustion characteristics. The behavior of spherically propagating premixed flames was caught by high-speed Schlieren photography, and the flame radius and propagation velocity were measured. At sufficiently small flame radii, smooth flame fronts were observed. At large flame radii, on the other hand, cellular flame fronts generated by the intrinsic instability of premixed flames were observed. The flame propagation velocity increased owing to the generation of cellular fronts, and then the flame acceleration appeared. Adding nitrogen to premixtures, the cell shape of flame fronts became prominent, because of the strength of intrinsic instability. The maximum pressure in a closed vessel became lower in the case of nitrogen addition, indicating the suppression of hydrogen explosions. Moreover, the maximum pressure of experiments was lower than that of calculations under the adiabatic conditions, because of heat loss from the gases in a closed vessel to the vessel wall.