GENERATION, CHARACTERIZATION AND IGNITION OF LUBE OIL MISTS

In this work, the generation conditions of lube oil mists by spray, their droplet size distributions and their flammability characteristics were studied. At first, tests were carried out on brand new lube oil having a viscosity of 32 mm(2).s(-1) at 40 degrees C (ISO VG32) and a flashpoint higher than 200 degrees C. Experiments were performed in a vertical semi-open tube with a 0.07 m-square cross section connected to ignition systems supplying energies ranging from 1 mJ to 5 kJ. The average droplet diameter, determined using a laser diffraction sensor, ranged from 4 to 60 mu m depending on operating parameters. In the case of brand new mineral oil mists, the probability of ignition by a spark discharge can be considered as low, the minimum ignition energy (MIE) being 2 kJ for 5 mu m droplets. The minimum explosive concentration is fairly high, in the order of 250 g.m(-3). For mists with droplet diameters around 60 mu m, MIE slightly increases to reach 2.5 kJ. The flammability of oil mists generated in case of maloperation (accidental fuel/lube mixing) was also studied. The ignition properties of used lube oil were not notably modified with regard to the brand new oil. However, the addition of organic volatiles compounds leads to a modification of mists flammability, nevertheless it is only perceptible for fuel contents greater than 20%v.