Ignitability of sprayed liquids due to an electrostatic spark

The minimum ignition energy (MIE) is a reasonable and practical index to assess the ignition risk of flammable materials. This paper reports the results of experiments dealing with the MIE due to an electrostatic spark of a sprayed liquid under various conditions. Four kinds of liquid (kerosene, n-decane, m-xylene and styrene) were used as the materials in this study. The liquid was pneumatically conveyed to the spray gun and automatically sprayed for 7 s to measure the MIE. The spatial distribution of the MIE in the spraying liquid under various conditions was also investigated in this study. The following results were obtained. (i) In the normal temperature range (0-30 degrees C), all sprayed liquids can be ignited by a spark with a discharge energy below 10 mJ irrespective of their flash point. In particular, styrene was ignited at 4 mJ. (ii) An optimum region for ignition in a spraying liquid was observed, and it depended on the velocity, concentration and particle size of the liquid. Experimental details and a discussion are presented.