High Steam Pressures in Locomotive Cylinders

Abstract

In this paper the author attempts an extended survey of the efficiencies obtainable with various steam pressures, and examines the effect of the ratio of expansion on the efficiency. The Rankine cycle, it is pointed out, does not offer a satisfactory basis of comparison for the locomotive; therefore a modification is suggested, known throughout the paper as the “locomotive cycle,” and all calculations of the paper are based on this cycle. Changes in boilers to permit operation at high pressures and temperatures are discussed, and it is pointed out that such a boiler would probably require some form of water-tube firebox. Detailed compulations and comparisons of theoretical indicator diagrams are made, and the “locomotive cycle” is applied to various admission and release pressures. It is concluded that it is possible to secure a considerable increase in the thermal efficiency of the cylinders by increasing the boiler pressure. The use of three cylinders, one operating on high pressure and two low, makes compounding a very simple matter, permitting the greatest return to be received from the high pressures. For the present, however, it is not felt to be expedient to use boiler pressures much in excess of 450 lb. per sq. in. gage.