Measurement of Steam Rate and Indicated Horsepower of Locomotives

Abstract

Abstract It has been the customary procedure to determine the steam rate and indicated horsepower of locomotives and other reciprocating steam engines from indicator cards. This paper points out that particularly at high locomotive speeds, the obtainment of indicator cards is subject to gross errors, and that the expense of rigging up for such tests is hardly warranted by the results that can be expected. The paper discusses in detail another method of determining the steam rate and indicated horsepower of a locomotive, which other writers have referred to as the “heat-drop method”. The paper proves both the simplicity of the method as well as its relative accuracy. The method is applicable to such locomotives only in which the exhaust steam is at least dry, and only in the absence of moisture, the Btu contents per pound of both admitted and exhausted steam can be accurately determined through pressure and temperature measurement. The paper contains detailed suggestions for successfully applying the method on the locomotive. Thus it contains data on the construction and location of the thermocouples, and the manner in which these thermocouples are applied and wired up to the instrument with which the pyroelectric force is determined. The results of the tests carried out with this method on two different locomotives, are presented in the paper and, in general, it is shown what advantages this simple method has for the test and analysis of all those design factors or devices which are liable to affect the steam rate of a locomotive. Toward the conclusion of the paper, reference is made to a suggestion by L. K. Botteron, which appeared in the Railway Mechanical Engineer of July, 1930, to the effect that the exhaust nozzle of a locomotive could be considered a flowmeter nozzle for the determination of the quantity of steam that the locomotive exhausts. The paper proceeds to show how the specific volume and velocity of the steam, while passing through the mouth of the locomotive exhaust tip (which quantities are essential for the Botteron method), are derived from the exhaust-steam temperature and pressure measurements that are incidental to the carrying out of the heat-drop determination.