A rotary slurrifier of this invention comprises a pair of spinning discs, which throw a first fluid into a larger mass of second fluid in paired and flow connected impact cavities, within a counter-rotating cavity shell. The first fluid is to be largely insoluble in the second fluid. Impact of the first fluid with the larger mass of second fluid, in the impact cavities, causes atomization of the first fluid into a slurry of many small first fluid particles suspended in a continuous phase of second fluid. The final slurry flows out of the rotating cavity shell via a slowdown reaction turbine.High viscosity residual petroleum fuels and tars as first fluids can be thusly preatomized in a fuel in water slurry, and can then be cleanly and efficiently burned in small bore, high speed, diesel engines, which now require use of expensive low viscosity distillate fuels, which are in short supply.