Adhesion and Adhesive Weight Adhesion is the frictional resistance that prevents a locomotive’s driving wheels from slipping on the rail. Available adhesion depends on the conditions of both the rail and the wheel. With a clean dry wheel running on a clean dry rail the “frictional coefficient” between them may be as high as 0.35 […]
Dave Wardale defined Equivalent Evaporation as follows: Equivalent evaporation = evaporation from and at 100°C. Evaporation figures thus expressed eliminate the effects of different feedwater and superheat temperatures, and are therefore a true measure of comparison between different boilers. [Letter from Dave Wardale to Chris Newman, 5th April 2001.] Equivalent Evaporation might be more simply […]
Boiler efficiency can be defined as the amount of energy delivered from the boiler in the form of steam divided by the amount of energy delivered to the firebox in the form of fuel/chemical energy. Boiler efficiency depends on the design of the boiler and firebox, the type of fuel, and the draughting system. In […]
Drawbar efficiency can be seen as the sum of the efficiencies of a locomotive’s various components. Wardale provides examples of these in his book “The Red Devil and Other Tales from the Age of Steam” where (in Table 78, page 457) he quotes figures for standard and (proposed) modified Chinese Class QJ locomotives, and where […]
Cylinder efficiency is calculated by dividing the work done by the steam in the cylinder by the heat drop in the cylinder. In Line 84 of FDC 1.3, Wardale calculates the isentropic cylinder efficiency of the 5AT at maximum drawbar power output to be 81%. He gets this figure by dividing the actual specific work […]
The word “indicated” comes from the use of “Indicator Diagrams” that before the electronic era were mechanically plotted to indicate the variation in steam pressure inside a cylinder against the piston position as it sweeps through the piston over the length of its stroke. Separate diagrams for both ends of the cylinder were usually being […]
Drawbar Power The power output at the drawbar of a locomotive, the drawbar being the coupling between the locomotive and the train that it is hauling. Drawbar power used to be measured by attaching a “dynamometer car” between the locomotive and its train. A dynamometer car incorporates a number of measuring devices including a calibrated spring for […]
Tractive Effort “Tractive effort” (TE) is the force applied by a locomotive for moving itself and a train. Tractive effort or tractive force is measured in kilo-Newtons (kN) or pounds force (lbf) where 1 kN = 228.4 lbf. As with “power”, there are different methods of measuring tractive effort: Drawbar tractive effort – the force […]
The Front-End Limit As discussed on the Grate Limit page, the grate limit occurs when any increase in the rate of fuel delivery produces no increase in evaporation. In other words it represents the maximum rate of heat emission that a firebox can deliver beyond which point any additional fuel added to the firebox produces […]
The Grate Limit as it relates to Boiler Efficiency On page 78 of his book The Red Devil and Other Tales from the Age of Steam, Dave Wardale defines the Grate Limit for a (normal) locomotive firebox as follows: The grate limit is the point “at which even by firing more coal and supplying more […]
Specific Steam Consumption Specific Steam Consumption is defined as the steam consumed by a locomotive’s cylinders per unit output of power. It is typically measured in kg/kWh or kg/KJ. A locomotive’s Specific Steam Consumption carries important implications as may be deduced from one of Porta’s favourite equations: Thus for any given boiler output, a locomotive’s […]
Power-to-Weight Ratio The Power-to-Weight ratio of a car is a measure of its ability to accelerate. A steam locomotive’s ability to accelerate is governed by its the ratio of its “power : total train weight” ratio and by its adhesive weight and adhesion coefficient (ignoring resistance factors). The Power-to-Weight ratio of a steam locomotives is […]