84 COMBUSTION AND FUELS 



experiments with liquid fuel soon proved that the methods 

 adopted for solid fuel were not applicable to liquid fuel, and 

 that the latter could not be burned successfully in bulk. To 

 insure satisfactory burning of oil fuel, it must first be changed 

 to a vapor, and this is now accomplished by atomizing the oil, 

 or converting it into the form of a very minutely divided 

 spray. It is the vapor that burns, and not the liquid oil 

 itself. If a sliver of burning wood is thrust into an open pan 

 of fuel oil, the oil will not ignite, and the flame of the stick 

 will be extinguished. The reason is that insufficient oil sur- 

 face is exposed to the action of heat, and vaporization does 

 not occur rapidly enough to supply the necessary quantity of 

 inflammable gases to support combustion. By atomizing the 

 oil, each minute particle is exposed to the air, thus providing 

 for rapid evaporation and complete combustion. 



Mixture of Oil Spray and Air. Having changed the oil to 

 a spray or to a vapor, it is next necessary to mix it intimately 

 with air in the correct ratio to produce complete combustion. 

 There are different methods by which the air is admitted so 

 as to accomplish the mixing. Sometimes it is allowed to enter 

 through holes surrounding the spraying devices and some- 

 times through openings from the ash-pit into the furnace; 

 combinations of both methods may also be used. In any event, 

 the main object to be attained is the thorough mixing of the 

 spray and the air, so that each particle of oil shall be surrounded 

 by the oxygen required for its perfect combustion. 



Comparison of Steam and Air for Atomizing. In stationary- 

 boiler practice the agent most extensively used for the atomi- 

 zation of oil fuel is steam, air being used in rare or special cases. 

 There seems to be little, if any, saving of fuel by using com- 

 pressed air for atomizing, for the reason that it requires 

 about the same amount of steam to operate the air compressor 

 as to atomize the oil directly. Moreover, with the direct use 

 of steam there is less complication of apparatus than when a 

 compressor is installed, and there is a correspondingly smaller 

 risk of accidents that may interrupt the service. Also the 

 installation required for atomization by air is considerably 

 more expensive than that required for the application of 

 steam. 



