ON THE DISTANCE REQUIRED TO ATOMIZE DIESEL SPRAYS INJECTED FROM ORIFICE-TYPE NOZZLES

Conductivity probe measurements, using ranges of nozzles, liquid prope rties and gas densities, have revealed more extensive and reliable inf ormation on the break-up process of diesel sprays than has been publis hed to date. The spray generated from a single-hole orifice-type nozzl e has an incompletely atomized break-up length which typically extends at least 100 hole diameters downstream. The physical structure of thi s break-up zone varies, depending on the liquid properties and both in itial and boundary conditions,from that of a central liquid column, wi th outer drops and ligaments, to, more typically, that of a chaotic 'w ire wool' structure of ligaments and drops. Time variations of the bre ak-up length are found during spray pulses and concentrations of poorl y atomized liquid are convected downstream in the form of coherent str uctures. The existence of this zone has repercussions with respect to spray-gas flow interaction, fuel vaporization and wall wetting in inte rnal combustion engines.