Experimental study of flame spread over oil floating on water

Abstract

The phenomena and mechanism of flame spread over oil floating on water were studied using temperature measurements made by fine thermocouples and an infrared camera, schlieren images of surface convection and video recordings of flame spread. The experimental results reveal that the floating-oil depth greatly affects the average rate of flame spread and average flame pulsation wavelength. The surface tension effect is the main cause of surface convection, which controls flame spread. Momentum loss and heat loss from forward-flowing hot oil to water play an important role in retarding flame spread for oil thicknesses less than about 8 mm. With the development of the exploitation of offshore oil and marine transportation, there have been frequent fires resulting from oil spills. Because of the quick diffusion of oil leaked on water and the fast spread of flames over an oil surface, such fires usually have catastrophic consequences. Although flame spread is only a short process during a fire, it determines the direction of flame spread and the best time to put out fires. On the other hand, controlled combustion is an important way to clean up floating oil, but the precondition is that the flame can spread over the floating oil. Therefore, it is necessary to study the phenomena and mechanism of flame spread over floating oil. Flame spread over liquid fuel has been a hot topic of combustion theory and fire safety science since the 1960s and has been investigated experimentally and numerically [1][2][3][4][5][6][7][8][9]. Such researches have mainly focused on the effects of parameters such as the initial fuel temperature and tray width on the rate of flame spread and on the qualitative analysis of surface convection. However, little has been done to study flame spread over floating oil, which has the distinguishing characteristics that the floating oil is usually thin and water greatly affects the flame-spread phenomena. Mackinven et al.[10] experimented with decane floating on water and found that the average rate of flame spread increased with an increase in fuel thickness. Neil et al. [11] confirmed that fuel thickness has a large effect on the rate of flame spread. However, the researchers [10,11] obtained only qualitative results, and the reason why fuel thickness affects the phenomena of flame spread remains unclear till now. In the present study, the flame spread over different thicknesses of aviation kerosene (with a flash point of about 66C) floating on water was investigated simultaneously employing a schlieren system, an infrared camera, fine thermocouples and charge-coupled device (CCD) cameras. The paper presents the variation in the average rate of flame spread with floating oil thickness, gives reasons why the oil thickness affects the flame spread rate and presents the mechanism of flame spread.

Effect of fuel depth on flame spread over aviation kerosene

“…The momentum loss dominates in making u s decrease with fuel depth decreasing from 8 to 4 mm, and heat loss of the subsurface flow begins to play a role for fuel depth of less than about 4 mm. 5 Figure 8 also shows that the theoretical rate of the subsurface flow agrees well with experimental values, which proves that the subsurface flow is mainly driven by variation of surface tension along oil surface.…”

“…3 For 1-propanol with a depth between 2 and 10 mm, Miller and Ross 4 found that the average rate of flame increases linearly with an increase in fuel depth. In our previous study, 5 experimental results revealed that flame spread rate increases with fuel depth when the depth of aviation kerosene increases from 2 to 8 mm, and it remains nearly constant for the depth of aviation kerosene beyond 8 mm.…”

“…The effect of fuel depth on flame spread over liquid fuels has been the subject of several studies. 1–5 MacKinven and Hansel 1 investigated the phenomena of flame spread over decane with a depth ranging from 1 to 20 mm and found that the average rate of flame spread increased exponentially with an increase in the depth of decane. Neil and Michael 2 confirmed by experiments that fuel depth has large effect on the rate of flame spread.…”