The atomization and distribution characteristics of fuel sprays from automatic injection valves for compression-ignition engines were determined by catching the fuel drops on smoked-glass plates, and then measuring and counting the impressions made in the lampblack. The experiments were made in an air-tight chamber in which the air density was raised to values corresponding to engine conditions.
The effects of the jet velocity, chamber-air density, orifice diameter, and the orifice length-diameter ratio on the fineness and uniformity of the atomization and on the distribution of the fuel in sprays from plain cylindrical nozzles were determined. The atomization and distribution characteristics of sprays from valves having spirally grooved stems, of sprays produced by the impinging of two fuel jets, and of sprays produced by a fuel jet striking a metal lip were also measured and compared with those of sprays from the plain nozzles.
It was found that each spray is composed of several million drops whose diameters range from less than o.oo025 inch to o.oo5 inch, and sometimes to O.OLO inch. The experiments indicated that with a given fuel the fineness and uniformity of the atomization increase with an increase in the jet velocity, and with a decrease in the orifice diameter. Orifice length-diameter ratio and chamber-air density had no decided effect on the spray atomization. Centrifugaltype sprays, impinging-jet sprays, and sprays formed by a jet striking a metal lip were found to have no better atomization than sprays from plain nozzles, provided that the jet velocity was the same, but the distribution of the fuel within these sprays was found to be much better than for plain sprays.