ABSTRACT
In-situ burning (ISB) is an important tool to remove oil from the environment. During ISB, it is important to know the volume reduction of oil for the overall accounting of the spilled oil, as a metric for operational decisions, and to account for the ISB portion of the oil budget. The burn rate depends on the type of oil, degree of emulsification and weathering, estimated thickness, weather conditions, and size of the burn area. Furthermore, each spill has a unique physical environment and oil properties that affect burn efficiency and rate. The volume of oil consumed during ISB is typically computed using a manual, coarse, time integration of the instantaneous burn area based on visual observations and a characteristic burn rate. The area is typically estimated in the field using known boom geometry and visual inspection of the fire-water interface, and recorded manually.
We have developed methods to measure the instantaneous consumption of burning oil and thus the oil burn rate by integrating direct measurements of thickness using acoustics sensors in the water under the slick with direct measurements of the area of the burning oil using infrared and visible light images from cameras above the burning oil. Data were collected during the burning of several oils and petroleum products including ANS, rock, diesel, and hexane. The acoustic thickness measurement took into account the high temperature gradient in the oil and combined with multi camera automated burn area estimates yielded an instantaneous measurement of the volume of oil consumed while burning.
We were able to identify the buildup of the burn, the active burning phase, and in the case of confined burns the vigorous burning phase. Knowing the instantaneous thickness and surface area during burning allowed us to directly calculate the burn rate and to study the dynamics of ISB. We are working on validating the burn rate and efficiency with direct measurements of the weight of the oil and residue before, during, and after burning. The authors believe these are the first direct measurements of slick thickness using acoustics during ISB.