Effects of ignition position on the ignitability and flame behavior of stratified gasoline vapor

Abstract

Stratified vapor–air mixtures are formed owing to evaporation after a leakage of gasoline in confined spaces. In this study, the effects of ignition position and ignition delay (tig), defined as the time interval between ignition and the moment of fuel spill, on the ignitability and flame behavior of the stratified vapor above a 0.8-mm-thick gasoline layer were experimentally investigated in a horizontal duct. Experimental results revealed that the ignitability of the stratified gasoline vapor depended on both ignition position and tig. The closer the ignition source was to the oil surface, the earlier the local stratified gasoline vapor became ignitable and thereafter lost flammability. A two-zone flame structure, including a blue premixed flame and a following yellow diffusion flame, was observed, and the blue flame propagated along only a certain layer of the gasoline vapor. The depth of the leading blue flame first increased and thereafter decreased with an increase in tig. The heat release owing to the yellow diffusion flame played an important role in the maximum explosion overpressure (Pmax), which closely related to both ignition position and tig. For a certain tig, Pmax was nearly independent of ignition position. The relationship between Pmax and tig varied with ignition position. The highest value of Pmax was obtained when ignition source was around the center of the duct, and the lowest value of 66 kPa appeared when ignition source was close to the duct roof.