PRINCIPLES OF NAVAL ENGINEERING 



In a straight-through-flow atomizer, all oil 

 pumped to the atomizer is burned in the boiler 

 furnace. The fuel oil is forced through the 

 atomizer barrel at a pressure between 125 and 

 300 psi. With this type of atomizer, the firing 

 rate is controlled by changing the number of 

 burners in use, the fuel oil pressure, and the 

 size of the sprayer plates. 



A straight-through-flow atomizer assembly 

 consists of a goose neck, a burner barrel (also 

 called an atomizer barrel), a nozzle, a sprayer 

 plate, and a tip. These parts are shown in 

 figure 10-12. The fuel oil goes through the 

 nozzle, which directs the oil to the grooves 

 of the sprayer plate. These grooves are shaped 

 so as to give the oil a high rotational velocity 

 as it discharges into a small cylindrical whirl- 

 ing chamber in the center of the sprayer plate. 

 The whirling chamber is coned out at the end 

 and has an orifice at the apex of the cone. As 

 the oil leaves the chamber by way of the ori- 

 fice, it is broken up into very fine particles 

 which form a cone-shaped foglike spray. A 

 strong blast of air, which has been given a 

 whirling motion in its passage through the 

 burner register, catches the oil fog and mixes 

 with it. The mixture of air and oil enters the 

 furnace and combustion takes place. 



I GOOSE NECK | 



iTOMIZER 

 SSEMBLY 



Figure 10-11. — Fuel oil burners 

 boiler front. 



38.70 

 installed on 



I NOZZLE I 

 SPRAYER PLATE 1^^ 



38.71 

 Figure 10-12.— Parts of a straight-through- 

 flow atomizer assembly. 



The sprayer plates most commonly used 

 are called standard sprayer plates. Two types 

 of standard sprayer plates are shown in figure 

 10-13. Standard sprayer plates may be either 

 flat-faced or dished and rounded, and they may 

 have four, six, or eight oil grooves. Standard 

 sprayer plates with four grooves are most 

 common. 



Now that the Defense Department has au- 

 thorized the conversion to a new distillate fuel 

 (NSDF), sprayer plates for burning this type of 

 fuel will be of the 6, 4, and 3 slot type. Sizes 

 will also be changed as the viscosity of the 

 new fuel is less than that of Navy Special fuel 

 oil (NSFO). Therefore, each class of ship will 

 need the correct size sprayer plates to permit 

 them to burn the correct amount of fuel for full 

 power and overload conditions. 



In a return-flow (also called a variable- 

 capacity) atomizer, part of the oil supplied to 

 the atomizer is burned in the boiler furnace and 

 part is returned. Several types of return-flow 

 atomizers are in use. One type (Todd) is de- 

 signed to operate with a constant fuel oil supply 

 pressure of 300 psig and a minimum return 

 pressure of 25 psig. Another return-flow ato- 

 mizer (Babcock & Wilcox) operates with a 

 variable fuel oil supply pressure (up to 1000 

 psi) and a variable return pressure, StLIl an- 

 other type (also Babcock & Wilcox) operates with 

 a constant supply pressure of 1000 psi and a 

 variable return pressure. 



The return-flow atomizer shown in figure 

 10-14 operates with a constant fuel oil supply 



242 



