Class 5AT Advanced Technology Steam Locomotive Project. Latest Updates... 3rd February 2012

The Class 5AT Advanced Technology Steam Locomotive Project New Generation Steam -- The Ultimate 4-6-0 -- 380 mile range -- An Engineering Legacy Thermal Efficiency The "thermal efficiency" of any engine is defined as the amount of useful energy output divided by the amount of energy input . It is not a fixed quantum but varies according to the engine's load and conditions of operation. In the case of steam locomotives, thermal efficiency is defined either as "cylinder efficiency" or as "drawbar efficiency". The two definitions are subtely different: Cylinder efficiency is defined as the the amount of energy delivered by the cylinder to the piston divided by the amount of energy delivered to the cylinder in the form of steam delivered to the steamchest; Drawbar thermal efficiency is defined as the the amount of energy delivered at the locomotive's drawbar (the hook at the back of its tender) divided by the amount of energy available in the fuel placed into its firebox. Both the cylinder and drawbar efficiencies vary with speed and power output, maximum cylinder efficiency being achieved at much higher speed than maximum drawbar efficiency. This is because, as speed rises, a locomotive's rolling resistance also rises and the tractive force avalable at its drawbar falls until, at a certain speed, the drawbar force becomes zero and thus the drawbar efficiency also becomes zero. Cylinder efficiency Cylinder efficiency is governed by the shape of the Indicator Diagram and in particular by the losses that are evidenced by it - most especially expansion losses, condensation losses and leakage losses. It should be noted however, that even without these losses, cylinder efficiency is limited by Carnot's equation which states that the maximum theoretical efficiency of any heat engine is governed by the temperature difference between its heat source and its heat sink [see Thermodynamics page for further information.] Drawbar efficiency 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 (on page 501) he suggests what might be achieved from the further development to the level of "Third Generation Steam" traction. Continue reading here.....