DEVELOPMENTS IN OIL BURNING. 263 



grate bars, and bed of coal and clinker on the grates combine to take up 

 considerable space, there is bound to be a somewhat limited head room in the 

 furnace. For this purpose the flat spray burner is well adapted, but the flat 

 spray mechanical atomizer, as so far developed, does not at satisfactory capaci- 

 ties give as fine a spray as the round or conical spray atomizer. It is, how- 

 ever, possible, as we have found by experiment, to alter the shape of the flame 

 from the round flame burner by manipulating the air for combustion. Thus, 

 if the air be admitted through a horizontal slot, the flame will be diminished 

 in width and increased in height, and, vice versa, if the air be admitted through 

 a vertical slot the flame will be spread out sideways and decreased in height. 

 The latter effect is what is desired in the combination of coal and oil. Con- 

 sequently, while still retaining the whirling motion of the air, which we have 

 found effective, we modified the impeller plate to approach the vertical slot 

 idea, and in this way we were able to broaden out the oil flame over the coal 

 bed so as to bum .6 pounds of oil per square foot of heating surface per hour 

 in combination with a rate of combustion of 25 pounds of coal per hour per 

 square foot of grate surface. This device is shown in Fig. 12, Plate 96, and 

 Fig. 13, Plate 98. The space between the fire doors is occupied by a casting 

 designed to carry two impellers side by side, each of an oval form as indicated. 

 This casting is air-cooled and is provided with slide ways so arranged as to 

 permit of substantial cast-iron shutters being pushed up in front of the 

 impeller plates when the burners are not in operation, thus effectually shield- 

 ing the impellers and the burners themselves from the radiant heat of the 

 furnace. The burners and impellers therefore remain constantly in place 

 while burning coal, and it is only necessary to put pressure on the oil line, 

 slide the shutters down out of the way, and turn on the oil when the latter is 

 needed. Figure 14, Plate 99, shows the front of one of the boilers of the 

 United States battleship Wyoming as installed in the vessel. 



If it is desired to operate with oil fuel only, the coal fire is allowed to go 

 out, leaving the grate bars covered with ash and clinker to protect them from 

 the heat, and the oil biuners are lighted exactly as if no coal was used at all. 



Natural Draft. — In the experiments described above forced draft had 

 been available, and there is no doubt that the high velocity of the air thus 

 secured is a material assistance in securing the proper mixture with the oil 

 spray. It is often desirable, however, to run under natural draft conditions, 

 particularly when the vessel is in port. For this reason a supplementary 

 series of experiments was inaugurated for the purpose of adapting the appa- 

 ratus to the requirements of lower draft pressures. 



The principal changes found necessary were a modification of the shape 

 of the blading and an increase in size of the impeller plates. 



The results of the tests are given in Table V. 



