Combustion hazards due to impingement of pressurized releases of high-flashpoint liquid fuels

Abstract

Listen

Translate article

The hazardous scenario posed by an accidental pressurized release of high-flashpoint liquid fuel (HFF), such as diesel or kerosene, impinging upon an obstruction in the near vicinity thereby generating a flammable mixture, has been highlighted in a previous oil-industry review concerning area classification (1994). Large liquid-fuel fireballs at the recent transport sector incidents including the London Paddington (1999) train crash and the New York (September 11, 2001) aviation disaster, have focused attention on this category of combustion hazard. Secondary breakup of liquid jets due to impingement potentially exacerbates the hazard, and this study aims to benchmark the problem by indicating the relative change in spray diagnostics due to impingement in large-scale releases, assessing the relative importance of potentially influential parameters, and finally providing medium-scale demonstration studies of the hazard. Low-pressure, high-flow-rate releases disintegrating via second-wind jet breakup are considered in light of the practical scenario envisaged. Enhanced phase Doppler anemometry developed for dense spray studies and an effective mass balance methodology are shown to be appropriate diagnostic techniques for this problem. The secondary/primary mass flow ratios are surprisingly large, and the enhanced PDA measurements show an appreciable reduction in droplet sizes postimpingement both trends increase the associated combustion hazard. Strong dependence of secondary spray characteristics on release pressure, orifice size, and downstream distance to impingement is identified, the latter influenced by the length of the solid-liquid core. Only weak dependence on impingement-surface parameters such as surface roughness and angle of incidence is noted over the limited parameter ranges studied. Finally, a series of medium-scale combustion experiments consolidate the conclusions derived from isothermal studies by demonstrating the relative ease with which flammable HFF sprays may be generated from low-pressure releases postimpingement. Model development work is required to generate robust quantifiable hazard assessment methodologies for these scenarios.