Steam Locomotive Development

To improve cylinder performance and reduce cylinder conden sation, superheated steam is supplied to the cylinders by super heating the steam through superheater units in the boiler.

The thermal efficiency is the ratio of the work developed at the drivers to the heat value of the fuel, as fired, to produce its hauling capacity at the rear engine or tender drawbar. In the average steam locomotive the thermal efficiency, based on the fuel as fired during road service, will vary from 4 to 9% where high steam pressures and temperatures, multiple expansion, feed heating and the like are utilized.

A pound of average United States coal, as used by the railways, will run about 53,50o B.T.U. as fired, and with proper com bustion in the fire-box of a steam locomotive, will enable from so to 8o% of its heat value to flow across the boiler and the superheater heating surfaces, to the water and the steam, most of the remainder of the heat passing out of the stack in the form of cinders, escaping gases with the ash, and by radiation. The steam pressure and temperature produced, in consequence of this heat transference from the furnace gas to the water and the steam, when they reach the cylinders, transform from 8 to 9% of the total heat in the steam into mechanical energy, in the conventional single expansion cylinder locomotives, the remainder passing away through the stack with the exhaust steam. By the use of feed-heating, a certain percentage of this heat in the ex haust steam may be recovered and returned to the boiler in the form of heat in the feed-water. Likewise, the waste heat in the cinders and gases passing through the smoke-box, and out of the stack, may be partially recovered, by utilization in an econo mizer for further heating of the boiler feed.

Locomotive Design.

The problems involved in the design, material and construction of the modern locomotive are many and complex. Of first consideration is the roadway and structures over which the locomotive is to be operated, which involves the permissible truck and driving wheel loading, both static and dynamic, on the road bed and the bridges; then the width and height of clearances as established by tunnels, overhead crossings, station platforms and other limitations; the gradient and curva ture to be negotiated; the required speed; character of the local fuel and water supply; length of turn-tables and engine-houses ; engine-house and shop facilities; location and general arrangement of fuel and water supply stations; length of runs between division or intermediate terminals, and other similar factors. After the design has been prepared to conform to the foregoing require ments, then the general wheel arrangement and boiler and cylinder capacities must be determined upon to best meet the gradient.

curvature and train loading requirements for the different dis tricts over which the locomotives are to operate. In these calcula tions, the size and capacity of the boiler and superheater, with special regard for the steam pressure and temperature, grate area, fire-box volume and fire-box and boiler evaporation surfaces are important; also the locomotive bed or frame and driving or truck wheel arrangement; the kind and size of the cylinders and the valve gear, after which the auxiliary devices and appliances to make up the assembly, as a whole, must be decided upon.

With respect to the weight and clearance limitations, the European and other foreign designers have been considerably handicapped due to the restrictions which, in the United States and Canada, have been less limited, and for which reason the American practice has reached a stage, so far as size and capacity are concerned, far in advance of other countries, and which has enabled the development of heavier motive power for the handling of longer and heavier trains. However, instead of resorting to improved combustion of fuel, maximum utilization of radiant heat, high rate of heat transfer, efficient convection, higher steam pressures and temperatures and the more economical use of the heat in the steam, the general trend, particularly during the past 20 years, has been to more extravagant methods of stoking and use of fuel, lower steam pressures in boilers and cylinders and the ejection of a greater percentage of heat from the exhaust nozzle and stack. The special appliances that have been intro duced are for fuel handling, firing, combustion, superheating, boiler circulation, feed water heating and feeding, steam distri bution and utilization, lubrication, insulation, lighting, heating, safety, comfort and labour saving. Those auxiliary appliances, such as trailer and tender truck auxiliary engines, stack blowers, air brake pumps, mechanical stokers, fuel oil heaters and atom izers, power reverse gears, fire door openers, feed water pumps, injectors, grate shakers, coal pushers, ashpan slide pushers, ashpan blowers, water scoops, drifting valves, electric generators, auto matic train control devices, steam heat equipment, cab heaters, lubricators, wheel flange oilers, bell ringers, rail sanders, cylinder cocks, steam whistles, safety valves, blow-off cocks, snow flanges and like accessories all require live steam or heat from the boiler of the locomotive for their operation, which the boiler and fire box must generate, in addition to the steam which is actually used for overcoming heat losses.