THE ROTARY SYSTEM OF BURNING OIL.
One of the earliest methods of atomizing em ployed by engineers in experimenting with the use of oil as a fuel was the centrifugal action of a rapidly rotating jet. French engineers, during their early trials, constructed a device that employed centrifugal action for spraying the oil, and used low pressure air as an atomizer. The oil used during these tests was similar to coal oil. It was not possible to operate the burner without the formation of large volumes of smoke ; and the evaporation of water per pound of oil was only 8Y2 lb. The mechanism was cumbersome and expensive.
During the tests conducted by the U. S. Naval Liquid Fuel Board under a Hohenstein boiler, the question of using the rotary method was given special consideration. As the possibilities of spraying oil by means of centrifugal force looked feasible, a burner was designed to utilize a ring of buckets which was formerly part of an experimental steam turbine. In this turbine there were five rings like the one used in the burner. The turbine was compounded in such a way that the outputs of power from the five rings were equal. The turbine, at a speed of 15,000 revol tions per minute, gave 20 horsepower. By the use of diverging steam nozzles the single ring, as used in the burner, should give an efficiency somewhat higher than one-fifth that of the compounded turbine. In other words, the burner turbine should, at a speed of 15,000 revolutions per minute, yield more than one horsepower on 100 lb. of steam per hour.
In designing the burner, however, the consump tion of steam was assumed at 400 lb. per h.p.-hr. This was to allow, among other things, for the un known viscous resistance of the film of oil flowing from the center of the disk to the periphery. Even with this seemingly ample allowance, only one-ninth aQ much steam should be required as in the simple jet burner. A number of tests were conducted, and many changes were made in the furnace and adjust ments. The following extracts for the report will give the reader an idea of some of the difficulties that had to be overcome : "Nov. 3, 1902.—Made a disk of sheet iron 1-16 in. thick and 10 in. in diameter, and fastened to burner in such a man ner that the oil flows over its upper surface. Assembled burner and repaired circular furnace, making it 33 in. high and 4 ft. in diameter. Tried burner at 5 p. m. It seemed to work satisfactorily in all respects. The oil was able to protect the disk from overheating during the few minutes that the experiment lasted. Speeded up turbine without ignit ing oil and caught samples of spray on blotting paper.
"Nov. 8, 1902.—Repaired brick walls. Steam at 90 lb., oh at 25 lb. Turned on steam. The burner began spinning around, and soon attained speed. Ignited some kerosene soaked waste and dropped it beside burner. Turned on oil. There was instant ignition. Stepped aside to observe the effect. More oil was being supplied to the burner than it could take and spray properly; much oil was escaping down ward from the burner. Could not shut off the oil at the valve
on account of intense heat. Ordered it shut off at the pump. Oil continued to flow on account of oil chamber on pump. Something exploded and demolished one side of the furnace. The turbine ring had broken loose. The ring was nearly driven onto the cast iron center. The heat and centrifugal force had been sufficient to expand it to the degree of mak ing it loose. When it tore off the 19 in. disk, the cast iron center continued to spin for some time. Half of the buckets were torn off the turbine ring.
"Nov. 15, 1902.—Assembled the two-jet burner and con nected pipes as before, instead of a brick wall around burner, two curved plates of boiler steel were used. The lower edges of the plates were lifted off the ground by the thickness of three bricks. The plates made an enclosure about five feet in diameter and four feet high. Turned on steam from the main boiler. Placed some oil-soaked waste on the ground within the enclosure and ignited it. Oil pump started and orders given to keep oil pressure at about 20 lb. When the oil valve was opened there was instantly an intense com bustion within the enclosure; the heat was so great that the oil supply had to be reduced. The volume of the fire was as easily controlled as a common gas jet. After about five minutes the burner went to pieces, caused by the backing out of the supporting pipe where it screws into the pipe fitting on the pedestal.
"Summary.—The steam pivot burner was a failure from the start, and it is not considered advisable to attempt to correct its faults. The solid pivot burner failed at first be cause the oil was not thrown off from its greatest diameter, and afterwards because some of the oil escaped downwards and burnt underneath, thus heating the burner and finally from the parts not being securely fastened together.
Conclusions as to Centrifugal Burners.
"First.—The oil should be thrown off from the largest diameter of the burner.
"Second.—The burner must be so arranged that the only outlet for the oil leads to the intended spraying edge. The construction of the experimental burner was such that part of the oil went wrong when the amount fed was greater than a certain maximum or less than a certain minimum.
"Third.—The oil should be introduced at the center of the spraying disk and flow over the whole of the surface exposed to the radiant heat.
"Fourth.—All parts should be secured by fastenings, which are more reliable than mere friction, however great; otherwise the very high speed of rotation will shake them loose.
"Fifth.—There is no evidence that the amount of oil flowing through the burner is not amply able to keep it at a safe temperature. In fact, the cooling power of oil, com pared to the amount of surface of the burner is many times greater than the cooling power of water compared to the heat ing surface of a boiler. The ratio is from 25 to 200 or 300 in favor of oil.