Experiments of gasoline–air mixture explosion suppression by non-premixed nitrogen in a closed tunnel

Experiments of the gasoline–air explosion suppression by non-premixed nitrogen were carried out in a closed tunnel through the visualization experimental bench, and extinction pictures of the flame front of the suppression process were acquired by a high-speed camera. Based on the analysis of the experimental data and high-speed camera photos, overpressure characteristic and flame behaviour of the suppression process were discussed. Results showed that the method of nitrogen non-premixed suppression can dramatically decrease the overpressure and overpressure rise rate of the gasoline–air explosion. When the lengths of ignition section and nitrogen non-premixed section were 45 and 226 cm, respectively, the suppression experiment would be successful if the initial gasoline vapour concentration was less than 2.12 %. Analysis of behaviour photos of the flame front showed that the whole suppression process can be divided into three periods, inertia maintenance stage, suppression attenuation stage and diffusion extinguishment stage. Energy of the high-energy radicals of the chemical reaction was taken away by the nitrogen molecule during the suppression process, resulting in that the main reaction chains were changed into termination chains. This was the dominant mechanism for the nitrogen non-premixed suppression process. The flame during the suppression attenuation stage composed of suppression attenuation zone and core zone, and the suppression attenuation zone was the main zone where the suppression attenuation took place. During the suppression attenuation stage, relationship between the flame speed and time can be summarized by a linear formula.