Investigation of sidewall height effect on the burning rate and flame tilt characteristics of pool fire in cross wind

Highlights

• Investigation of combining effect of sidewall height and cross air flow on pool fire addressed.

• The effect on burning rate, flame height and flame tilt angle of the pool fire is thoroughly investigated.

• A dimensionless parameter was proposed to analyze the burning rate, the flame height and flame tilt angle.

Abstract

In the current study the combining effect of sidewall height and cross air flow on the mass burning rate, flame height and flame tilt behavior of pool fire has been experimentally investigated. The mass burning rate increases as the cross wind velocity increases. The presence of sidewalls also influences the mass burning rate, as it is increased at lower cross wind velocities and decreased as this velocity further increases. A dimensionless parameter is introduced to illustrate the sidewall height effect on the mass burning rate. The effect of sidewall height on burning rate, flame height, and flame tilt angle of pool fire is further investigated. The flame height is an exponential function of a new dimensionless parameter $\widetilde{Fr}$. Based on the experimental results, new empirical correlations are proposed to predict flame height and flame tilt angle $\alpha$ in relation to the combining effects of sidewall height and cross wind.

Introduction

Ship fires are a real concern for the shipping industry as they may pose a great threat to the safety of ships cargo and crew. In recent years, frequent occurrence of fire events on the deck or in the engine room [1] are mainly influenced by ventilation conditions and obstacle obstructing. In order to better understand the fire evolvement of such events fundamental experimental research on cross wind conditions or the effect of sidewalls on flame characteristics of pool fire has been conducted since 1950s [2].

Previous studies have mainly focused separately on the influence of those two aspects on fire development. Concerning the effect of cross wind, recent research [[3], [4], [5], [6], [7], [8], [9]] is directed towards investigating the effect of cross wind on the fire characteristic parameters, such as burning rate, flame height, flame tilt angle. In open spaces, cross flow would entrain into the flame and the heat feedback of pool fire would change, which would result in the change of burning rate. In regard to that matter, many researchers specifically focused on the effect of cross wind conditions on mass burning rate [[10], [11], [12], [13], [14], [15]]. Blinov [10] found that the mass burning rate increased with an increase of cross wind velocity. However, experimental results operated by Welker [11] and Apte [12] revealeda different trend: mass burning rate decreasing as the velocity increased for cross wind velocity values below 1 m/s. Experimental results from Hu [13] for 5 cm to 25 cm-length rectangular pool fires in cross wind were in agreement with Welker [11] and Apte [12]. Ping [14] experimentally investigated the burning rate and flame tilt of the boilover fire under cross air flows reporting that the burning rate firstly decreased and then increased with the cross wind velocity. Zhu [15] investigated the burning rate of ethanol square pool fires affected by wall insulation and oblique airflow, and indicating an increase in the burning rate showed with increasing airflow tilt angles.

Flame characteristics, including flame height and tilt angle, under a variety of wind conditions have been extensively studied for decades [14,[16], [17], [18], [19], [20], [21]]. Thomas [16] found that wood crib flame height was associated with the burner size, mass burning rate and cross wind velocity. Many researchers improved Thomas's empirical correlation according to the experimental studies [7,17,18]. Oka [19] defined two flame tilt angles based on the experimental results of 0.1 m × 0.1 m square propane burner under the cross wind ranging from 0.5 m/s to 4 m/s. Ferrero [18] studied the flame tilt angle of wind-blown large-scale gasoline and diesel pool fires with the diameter of 1.5 m–6 m, and obtained the correlation of flame tilt angle in the different wind speed range. Ping [14] presented an empirical correlation of the flame tilt angle of pool fires in steady and boilover stage. Morehouse [20] and Atallah [21] amended the equations to evaluate the flame tilt angle of wind-blown pool fires.

Several researchers have focused on the effect of sidewalls on the pool fire behavior [[22], [23], [24], [25]]. Ji [22] conducted a series of experiments of heptane pool fires close to the sidewall of a channel and found that the burning rate firstly increased and then decreased as the distance between the pool fire and sidewall increased. Fan [23] investigated sidewall effects on the flame characteristics of heptane pool fires and concluded that the long pool rim perpendicular to the sidewall could contribute to larger burning rate due to more air entrainment. Gao's work [24] showed that flame height increased with decreasing fire-sidewall distance. Tao [25] studied the jet flame height with three sidewalls and introduced a global model to characterize the air entrainment of jet flames. However, to the best of authors knowledge the combined effect of sidewall height on the pool fire characteristics under cross wind has not yet been reported.

The goal of the present research is to experimentally investigate the combined effect of sidewall with the presence of crosswind on hydrocarbon pool fire behavior. The effect of sidewall height and cross wind velocity on the burning rate, flame height and flame tilt angle of pool fire are obtained. Furthermore, a dimensionless parameter coupling with sidewall height and cross wind velocity is proposed to analyze the pool fire characteristic parameters.