- Author
-
Bennett, J. M.
- Title
- Literature Review of Mechanisms of Droplet/Spray Ignition by Hot Surfaces.
- Coporate
- Dayton Univ., OH
- Report
-
UDR-TR-98-00158
March 27, 1998
90 p.
- Keywords
-
hot surfaces
|
droplets
|
sprays
|
ignition
|
literature reviews
|
fire safety
|
machinery
|
ignition temperature
|
vaporization
|
experiments
|
evaporation
- Abstract
- A frequent source of fire safety concerns in applications involving operating machinery is the presence of heated surfaces (due to equipment operation or other means) that could come into contact with leaking or spraying flammable fluids (such as fuels or oils) due to equipment malfunctions. A particular example of such a scenario is the occurrence of fires in the engine nacelles of aircraft, due to leaking fuel, oil or hydraulic fluid lines spraying or leaking fluid onto hot engine case or accessory surfaces. The U.S. Air Force alone has been estimated to have over 100 engine fires per year, and they are also a common occurrence in commercial aircraft. On-board extinguishing systems do not consistently mitigate such types of fires, due to their severity and intensity, location in obstructed areas and stability, and potential to re-ignite after initial extinguishment. Studies of this phenomenon have been limited, and typically only address certain scenarios, or have observed complex behavior that is difficult to model and predict. Large-scale experiments intended to replicate the aircraft nacelle environment have identified strong sensitivities in minimum surface ignition temperatures to a myriad of operating parameters. Most of these parameters (such as spray behavior and air flow fields) are difficult to control sufficiently in large scale to analyze and understand the mechanisms. Small scale experiments and analyses by the academic community have produced a better understanding of some of the fundamental mechanisms and phenomena present, but such data is by no means comprehensive, and not always consistent in its findings. A primary interest of this community is the design of more efficient combustors, in which the desired behavior and operating conditions are not consistent with fire safety objectives. For example, combustor designers desire ignition at lower surface temperatures, and can tailor fuel introduction conditions (such as droplet shape) to achieve these goals, which is also convenient for experimentation and modeling but less relevant to fire safety issues. Fluid introduction scenarios more common to fire events, such as fluid streams or films on heated surfaces (of uncontrolled flow rate) are correspondingly not as present in the literature. As a result, caution and some discernment must be applied in consideration of such data, although invaluable findings and analyses are present in the academic journal literature that can be useful in the understanding of the mechanisms of this fire scenario. This document is a discussion and summary of a recent limited review of the literature available, both from academic journals and government reports, which relates and provides some insight into ignition by hot surfaces. The information was analyzed by reviewing separately the affect of various parameters on minimum ignition temperature, fluid vaporization and droplet lifetime, as reported by several authors, to observe consistencies or inconsistencies.