In order to improve understanding of the ignitability of liquid, this current paper deals with the Minimum Ignition Energy (MIE) due to an electrostatic spark of a sprayed liquid relative to the percentage of nitrogen (N2), including the compression in an air cylinder and the charge amount at the nozzle while spraying. The electrostatic sparks occurred in spray region were also observed while spraying. Two types of hand-held spray guns and a supply air pressure in the range of 0.1 to 1 MPa were used in this study. As the materials, kerosene was selected for ignition tests while spraying and water including some sodium chloride was used to investigate the charge amount of the sprayed liquid. The following interesting results were obtained: (1) the ignitability of sprayed liquid was drastically controlled by atomizing with N2 instead of pressurized pure air. The increasing efficiency of MIE increased with increasing a supply air pressure in the tests. (2) The charge to mass ratio, -1.72 to -2.62 micro C/kg, was obtained using spray gun A (-0.82 to -3.75 micro C/kg with spray gun B). These values obtained in this paper are far from safe in painting industry. (3) Several electrostatic sparks in spraying region were observed while spraying. Therefore, a spray must be carefully managed since it is always possible that electrostatic spark energy could exceed the values established for safety in the spraying process when not all of the equipment is grounded.

Extended Abstract Status: File Uploaded