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Enhanced Burning of Difficult to Ignite/Burn Fuels Including Heavy Oils.


pdf icon Enhanced Burning of Difficult to Ignite/Burn Fuels Including Heavy Oils. (15045 K)
Wu, N.; Torero, J. L.

NIST GCR 98-750; 259 p. June 1998.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service
Order number: PB98-148190

Keywords:

crude oil; flame spread; heat flux; ignition; in situ combustion; lateral ignition; liquid fuels; oil spills; weather effects; flash point

Abstract:

An experimental technique has been developed to systematically study the ignition, flame spread and mass burning characteristics of liquid fuels spilled on a water bed. The final objective of this work is to provide a tool that will serve to assess a fuels ease to ignite, to spread and to sustain a flame, thus helping to better define the combustion parameters that affect in-situ burning of oil spills. A systematic study of the different parameters that affect ignition, flame spread and mass burning has been conducted in an attempt to develop a bench scale procedure to evaluate the burning efficiency of liquid fuels in conditions typical of oil spill scenarios. To study ignition and flame spread, the Lateral Ignition and Flame Spread (LIFT) standard test method (ASTM E-1321) has been modified to allow the use of liquid fuels and a water bed. Characteristic parameters such as the critical heat flux for ignition, ignition delay time and flame spread velocity as a function of the external heat flux have been obtained. A series of "fire properties" corresponding to the fuel can be extrapolated from these tests and used to assess the tendency of a fuel to ignite and to sustain flame spread. The ignition and flame spread data is complemented by means of the Flash Point Temperature as obtained from the ASTM D56 Tag Closed Cup flash point tester. Mass burning has been studied by determining the burning efficiency of different fuels under conditions where a simple one-dimensional heat conduction model describes the surface regression rate. The methodology was validated using SAE 30W oil and different crude oils in their natural state and under different levels of weathering. The present results show that flame spread velocity is controlled by the thermal properties of the heavier fractions of the fuel and the flash point temperature. Weathering has therefore no effect on the thermal properties but significantly affects the flame spread rate and the minimum external heat flux necessary to sustain spread. The thermal properties determining the ignition delay time are, again, determined by the fractions but the critical heat flux necessary for ignition is a strong function of the weathering level. A relative evaluation of the efficiency of the mass burning process can be obtained experimentally under controlled bench scale conditions and used to evaluate the efficiency of the burning process under more realistic scenarios.