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 […]
Locomotive Power Power is defined as “the rate of doing work”. Common units of power in the metric system are Watts (W), kilowatts (kW), Megawatts (MW) and Gigawatts (GW), where 1 Watt = 1 Joule per second = 1 Newton-metre per second. Alternative units of measurement are calories per second and kilo-calories per hour (1 […]
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, the term thermal efficiency may refer to […]
There are six interrelated properties that define the state of steam: Temperature Pressure Dryness Fraction (within the saturated zone) Enthalpy Internal energy Entropy Fixing the value of any two properties defines the value of all the others. Thus fixing the values of Enthalpy and Entropy is sufficient to define Temperature, Pressure and Internal Energy of […]
Steam Tables Steam tables used to be (and may still be) published in the form of a small booklet listing values of steam temperature, pressure, specific volume (i.e. the volume of 1kg of steam at a given temperature and pressure), specific entropy, specific enthalpy against various input values, separate sets of tables being provided for […]
Anomalies in Thermodynamics Draft Text Only – Readers’ suggestions and inputs are welcome Thermodynamics is not an easy subject to master and there are many instances where it defies intuitive judgement. The following examples are offered by way of enlightenment and perhaps education: Steam viscosity increases with temperature Whilst it is intuitive that liquids become […]
Enthalpy is a “term of convenience” that is useful in the interpretation and application of Thermodynamics. Enthalpy is basically a measure of energy, but its main function is in the calculation and measurement of “flow energy” or gaseous energy (e.g. steam energy). [Note (borrowed from mathpages.com): Enthalpy is not a specific form of energy. It […]