Fig. 2 illustrates the firm's sprayer for burning either hot or cold oil. The construction is similar to that of the hot type burner with the addition of a centre spindle D, and means of adjusting it. In using cold oil, this spindle is protruded through the orifice in the cap B, as shown in large scale view. The oil is fed into the whirl chamber in a similar manner to that described above, and on discharging from the orifice in the cap B, impinges on the small head formed on the end of the spindle D, and is broken up into a fine mist, in which condition it can be ignited and btirnt without smoke. When using hot oil the spindle is withdrawn into position indicated in the sectional elevation by means of the milled cap, when the sprayer operates precisely as the hot type. This burner is particularly useful for lighting up purposes when steam is not available for use in fuel heaters, being capable of burning fuels up to 900 seconds viscosity (Redwood, No. 1) at normal temperatures, cold, thereby rendering an auxiliary heater unnecessary. In both types of sprayer provision is made for quickly disconnecting, it being only necessary to unscrew U when yoke J swings down, permitting the sprayer to be withdrawn. Provision is also made for axial adjustment of the sprayers by means of the screw spindle S, whereby maximum efficiency can be obtained under all conditions of output.
The Babcock and Wilcox System. The method adopted in applying the Babcock & Wilcox mechanical system is that of pumping the oil through the burners at a considerable pressure, the stream of oil being so manipulated in the burner that it is caused to rotate rapidly, and immediately on the emission of this stream from the orifice of the burner the centrifugal force resulting from the construction of the burner breaks it up into a fine mist, which, by proper means of air mixing, can be completely burnt without smoke. This method is adopted in all cases for marine work, where the consumption of fresh water for spraying purposes is not permissible ; and the same applies to land installations, where the feed water is of bad quality, in order to avoid introducing an excessive quantity of make-up feed into the boilers. Moreover, with this pressure system, a high efficiency of combustion is obtainable.
A recent addition to the oil fuel systems is that known as the " Unolco " introduced by the United Oil & Coal Company, and fitted to a number of the Great Central Company's locomotives. In this burner fuel is fed to the main passage, which is preferably set at right angles to the middle line of the burner, into the annular chamber. Superheated steam is supplied to the nozzle by a pipe. This steam heats and liquefies the fuel in the chamber and, upon issuing from the nozzle into the cone, partly atomizes and drives it against the inner walls of the cone, carrying it forward at a high velocity to the ends of the cone. At this point the combined jet of steam and fuel is surrounded by an additional superheated steam supply issuing at a still higher velocity than that of the central jet from the annular orifice. The superheated steam is supplied by the pipe J. The annular superheated steam supply completely atomizes the jet issuing from the nozzle end and is carried forward at an increased velocity to the flattened expanding delivery nozzle.
The burner is placed below the foundation ring at the rear end of the fire-box, the ordinary ash-pan of the engine being retained. Oil passes from the tank, which has a capacity of from 800 to 1,000 gals. for a tender engine, and 450 gals. for a tank engine, through a
connecting pipe of flexible material in the case of a tender engine, to the footplate, beneath which is a pre-heater. This pre-heater consists of two pipes, one within the other, the inner pipe conveying oil and the outer one forming a steam jacket, and it serves to reduce the viscosity of the oil so that it will pass through the steam jets of the burner. After passing from the pre-heater to the burner, the oil is delivered in a spray about 6 in. above the floor of the fire-box, in which there is a layer of fire-bricks, 3 in. thick, resting on a plate at the rear end of the ash-plan.
The system provides for the atomizing and burning of pre-heated oil by means of superheated steam. Each of the three jets in the burner is a double nozzle, the inner nozzle conveying superheated steam which atomizes the oil as it issues in an ignition chamber common to the three jets, and also receiving superheated steam through a vertical port. The three nozzles are so arranged that they can be used separately or all together, thus ensuring the highest efficiency of com bustion. In practice, it has been found that one nozzle is sufficient for locomotive work.
The ease with which an oil-burning installation can be manipulated is not one of its least advantages. There is no need of skilled labour in the adjustment of the valves, once the admixture of air and oil has been properly arranged and it is a simple matter to ascertain that this has been secured. It must, however, be stated that the proportion of air let into the furnace is of the greatest importance, as on this depends the approach to perfect combustion. Any excess of air beyond that actually required for complete combustion naturally reduces the temperature and thus retards the process. From a general point of. view, that is in the employment of oil fuel for any purpose, on land or sea, the main advantages of oil over coal may be summarized. These features are classified so concisely by Engr. Lieutenant Commander F. T. Addyman in the Petroleum Year Book, that I cannot do better than reproduce from that work.
1. Ordinary oil fuel has a higher calorific value, viz., 19,500 B.T.U., as against 12,500 B.T.U. for coal, and the average engineer would often be glad to obtain 8,000 ton,000 B.T.e. !feat value of coal is, and always must be, a fluctuating quantity , it %wit-, even on one seam. Not so with oil ; ?t is of known gravity and quality, and therefore can be accepted as a constant ; hence, the bed-rock truth is that you arc bound to obtain at a minimum 80 per cent greater heat value from oil.
2. An increase in boiler efficiency, due to the clean condition in which the heating surfaces can be main tained, is another advantage ; also the completeness of combustion obtainable with a good system of firing (1 lb. of fuel averages 19,500 B.T.U., as compared with 12,500 B.T.U. for best Welsh coal) due to the high calorific value of hydrocarbon constituents and to the high purity of oils, the non-combustible matters, usually, being almost negligible.
3. A constant and equal distribution of heat in the furnaces, and, as there are no fire doors to be opened, the cooling effect of large volumes of air passing over the furnaces when firing up or cleaning fires is avoided, and its consequent losses. Complete control of air supply is maintained.
4. Superior evaporative power for weight of fuel carried, giving increased radius of action.
5. Ease of control and regulation and maintenance of proper combustion.