Design and Characterization of a Hot-Surface Ignition (HSI) Experiment
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abstract
The ignition of flammable liquids on hot surfaces is both a safety concern to industry and an important phenomenon for IC engines and some liquid propellant igniters. Hot-surface ignition is a function of fluid properties and environmental parameters, chiefly surface temperature. A new laboratory-scale experiment was constructed to determine the hot-surface ignition characteristics of flammable liquids without the presence of a spark. A stainless-steel block is heated using embedded electrical resistance heaters, and 20.5-L drops of liquid fuel are dispensed onto removable test surfaces. Several experiment iterations with design improvements were implemented to minimize the negative effects of surface oxidation of the metal plate, droplet movement along the surface, and surface temperature non-uniformities. The final experimental apparatus is well-characterized, provides a uniform surface temperature within the range of 25-750 C, and was utilized to characterize the hot-surface ignition of several flammable liquids. Ten drops were tested at each surface temperature condition with a single test surface, which was replaced prior to testing alternative surface temperatures. This procedure was repeated at least once at each surface temperature, and the resultant datasets were reported as ignition probability (e.g., the percentage of ignition events per total number of drops at each temperature). These data were utilized to create ignition probability curves over a range of surface temperatures for all liquid fuels evaluated herein. The ignition probability data were also correlated with logistic regression curve fits. Furthermore, high-speed video analysis was completed to observe the fundamental phenomenon linked to hot-surface ignition. The experiment developed herein proved to be a useful tool for evaluating fundamental parameters that drive the hot-surface ignition behavior of various liquid fuels of interest.
