Practically all of the basic types can be further modified by special design of their tips or orifice, thus leading to still greater variety and often to greater improvement in their spraying qual ities. These modifications of tips can be reduced to a series of classes independent of the other possible mechanical arrangements of the burners. Fig. 55 shows types of burner tips. Form 1: The design of the tip is in itself a matter of much moment, as the configuration of the tip edges has a very important physical effect on the formation of the spray, and whether the material which it is intended to spray is forced through by steam, com pressed air, or even by the effect of its own pressure supplied by a pump, the edge over which the spray last passes has a deter mining effect on the state of subdivision of the spray. In form 1 is represented an ordinary nozzle with a sharpened edge at the point of exit. If a proper angle is selected for this edge, and the edge itself is well sharpened, the outgoing stream instead of pass ing out in a straight line, as from a hose nozzle, is caused to diverge, and if divergence ensues, of course there follows an expansion in the volume of the outgoing liquid which causes a condition of more or less subdivision of the particles of the fluid. In form 2 is shown a design of orifice in which this effect is heightened by introducing a cone in the center of the conical orifice. The physical reason why this increased divergence is secured is due to the fact that the cone takes the place of any streams of oil which in the first case had the tendency to travel in the straight lines of the solid core of fluid. All the lines of fluid traveling down the cone surface meet in collision at the edge and tip of the cone and rapidly expand owing to the pressure which was behind them. In form 3 there is again indicated the same type of sharpened cone-shaped orifice, but outside of this is placed a diverging cone upon which the outgoing spray strikes and receives a greater amount of divergence than the orifice edges would alone have produced. This diverging cone is usually placed with its stem extending within the orifice, although at the right of the diagram is shown a case where the diverging cone is supported from the outside. The amount of divergence effected by this cone can be controlled to any extent by the position or shape of the diverging surface of the cone. In form 4 there is shown an orifice similar to form 1, but increased divergence of the cone of spray is obtained by circulating the fluid in a rotary manner before issuing from the sharpened orifice, the physical result of which is that as soon as the fluid leaves the orifice the effect of centrifugal action is manifested to fling the oil tangent Tally outward to some distance. In the diagram, as shown, this centrifugal effect is obtained by passing the fluid through spiral passages. Form 5 represents the original style of orifice, but the casing is so shaped as to obtain the rotational effect of the pre vious tip by admitting the fluid tangentially to the interior of the chamber. The effect on the resulting cone or spray is the same as in the previous example. Form 6: The type of nozzle is changed by inserting a ball in the outgoing current of spray, thus mechanically breaking up the action by requiring the spray to strike •the ball, this being nothing more or less than the old familiar type of the dancing ball, long made familiar in water nozzles and pneumatic nozzles as a curiosity. Its effectiveness as a spraying agent is probably no greater or as great as a well designed and proportioned orifice of form 3. Form 7 represents a class widely different from any of the preceding, which for lack of any other properly designative term might be called the "pepper-box nozzle." Its effectiveness for a certain class of burn ers may be made very great, but it always suffers under the great disadvantage of a multitude of small holes, which are exceedingly liable to become choked up by foreign matter or by the hydrocar bons formed at the tip of a burner while in action.
It is understood, of course, that in the description of types of burners just given either steam or air may be used as the atom izing agent. Steam is generally employed for stationary boilers and locomotives. When steam is used as the atomizing agent no auxiliary apparatus such as air compressors or oil pumps are re quired. Compressed air is most valuable in the case of a battery of boilers where high efficiency is essential.
Discussing the subject of atomization, W. N. Best says :a "Compressed air or steam is preferable to low pressure air be cause it requires power to thoroughly atomize liquid fuel. With low pressure or volume air, you are limited to the use of light oils, whereas with compressed .air or steam as atomizer, you can use any gravity of crude oil, fuel oil, kerosene or tar which will flow through a pipe. For stationary boilers, steam at boiler pressure is ordinarily used to atomize the fuel. In furnaces the most economical method of operation is the use of a small quan tity of compressed air or dry steam through the burner to atomize the fuel, while the balance of the air necessary for perfect com bastion is supplied independently through a volume air nozzle at from 3 to 5 oz. pressure. Every particle of moisture which enters a furnace must be counteracted by the fuel and it is there fore essential, if steam is used as atomizer, that it be as dry as possible. It is folly to attempt to use steam as atomizer on a small furnace, especially if the equipment is located some distance from the boiler room, for oil and hot water do not mix advantageously. Numerous tests have proven that with steam at 80 lbs. pressure and air at 80 lbs. pressure, by using air there is a saving of 12 percent in fuel over steam, but of this 12 percent it costs 8 percent to compress the air (this includes interest on money invested in the necessary apparatus to ,compress the air, repairs, etc.), so there is therefore a total net saving of 4 percent in favor of com pressed air." Spray burner systems are crassed as "high pressure" when the oil and steam (or air) are supplied to the burners under a pressure of over 2 lbs. per sq. in. and as "low pressure" when the pressure is less than 2 lbs.
Mr. S. D. Rickard, writing in Oil News,a says that the most essential points in an oil-burning system are : "1. That it supply oil in sufficient volume to the burner in a clean and properly heated condition, and under .a constant and automatically regu lated pressure, free from pulsations.
2. That it supply air in sufficient volume to the burners (when of that type) in a clean and fresh condition, and under a constant and automatically regulated pressure, free from pul sations.
3. That it supply steam to the burners (when of that type) in a dry, hot state, and under sufficient pressure.
4. That the air and oil supply be connected, or co-ordinated. in some way so that should the air supply fail, the oil supply will be instantly cut off.
The burning of oil is in reality the continuous feeding of two ingredients (oil and air) in proper proportion into the com bustion chamber in such a—manner that a chemical mixture will be secured and good combustion will be the result. It will be ap preciated that whenever the oil or air pressures are not constant, or pulsate, it is impossible to secure good combustion. In short. whenever the oil or air supply pulsates, it is safe to say that just 50 percent of the time good combustion is not obtained. The pressures of oil and air must also be automatically regulated ; or otherwise, whenever a burner is started up or shut down it will be necessary to adjust all of the other burners in the system. It' will also be appreciated that when wet steam is fed to a burner an excess of oil must be burned to overcome the cooling effect of this water and convert it into steam."