Experimental study on flame propagation through stratified crude oil vapor in a horizontal duct

Abstract

Stratified vapor–air mixtures are formed owing to evaporation after crude oil leaks in confined spaces. The concentration distribution, ignitability of the stratified vapor, flame propagation in it, and pressure buildup owing to combustion must be investigated to obtain knowledge for explosion protection and mitigation. In this study, the concentration distribution of the vapor above a 1.0-mm-thick crude oil layer in a horizontal duct was measured, and the effects of the ignition delay (tig) on the ignitability, flame behavior, and combustion overpressure were investigated. The experimental results revealed that the average concentration gradient of vapor decreased with the evaporation of the crude oil layer. The stratified vapor could be ignited from 10 to 50 min, after fuel supply, by an electric spark 150 mm above the oil surface. A two-zone flame structure including a blue premixed flame and yellow diffusion flame was observed, and the flame was farther from the oil surface as tig increased. The maximum horizontal speed of the blue flame tip and overpressure owing to combustion initially increased and then decreased as tig increased from 10 to 50 min. The yellow diffusion flame had an important function in the maximum explosion overpressure. A maximum overpressure of 530 kPa was measured at tig = 25 min, which was 80 kPa higher than that of stratified gasoline vapor obtained under nearly identical conditions in previous research.