STEAM-ENGINE, the apparatus by means of which the stored heat-energy of fuel,'trans ferred to water and steam, is transformed into mechanical work. This transformation of thermal into dynamic energy, this thermodyna mic change, requires for its successful and economical conduct special forms of mechanism and is subject to a variety of wastes of serious aggregate amount, even with the most perfect of modern engines. The series of processes in the train between the fuel and the point of application of the useful energy with state ment of the corresponding wastes and efficien cies are as follows: it being understood that an efficiency is the quotient of useful result divided by outgo producing it, the two being 1. Combustion of fuel; ratio of heat set free to total heat latent in the fuel. This efficiency is usually not far from 90 per cent. Wastes due to incomplete combustion.
2. Heat-transfer from furnace to boiler; efficiency as a rule, about 75 per cent, as measured by heat stored in the steam supplied. Wastes occurring mainly at the chimney.
3. Heat-transfer from boiler to engine with loss by con duction and radiation, en ramie. Efficiency of operation about 90 per cent in small boilers and increasing to 95 or 98 per cent in large sizes.
4. Heat-transformation into work at the engine with wastes by defective thermodynamic change and rejection of heat at the lower limit by conduction and radiation within and without the cylinder, variable with size, with mean temperature of steam and other conditions. Efficiencies for the ideal case usually approximate 25 per cent with only thermodynamic wastes, and attain to 20 per cent with suc cessful constructions in the real case; the wastes including the thermodynamic and inevitable losses and the partly con trollable extra-thermodynamic wastes.
S. The transfer of mechanical energy from cylinder to point of application. The wastes occur by friction and usually amount to about 10 per cent, as a minimum in con densing, and to 5 per cent in non-condensing engines. Effi ciency, 90 to 95 per cent.
• The thermodynamic efficiency of the best steam-engines may be thus taken to be 25 per cent ; the thermal efficiency at the engine, involv ing other wastes than thermodynamic, about 20 per cent; the total efficiency between steam valve and fly-wheel about 18 per cent and the efficiency of engine and boiler combined not far from 14 per cent.; while the total efficiency
of engine, boiler and furnace, from coal-pile to engine-belt, may be about 12/2 per cent. In common constructions these efficiencies are much reduced and in many cases may be di vided, by from two to four, the demand for fuel of good quality ranging from about one pound or half a kilogram in the best work to several times that amount per horse-power hour, and for steam from 10 pounds, about four and a half kilograms, to a multiple of that quarttity. In some instances, as with many small boiler feed-pumps, 10 or even 20 times the minimum figure just given are reached, the wastes becoming enormous and the utilized energy of the fuel insignificant.
The "ideal case) is understood to be that purely thermodynamic operation which illus trates the conversion of thermal into dynamic energy where no other energies than thermal and dynamic are concerned, and where the change is effected in a machine which is not subject to wastes by conduction or radiation ; an apparatus composed of perfectly non-con ducting materials and perfectly constructed. In the "real case," the materials of construc tion are necessarily good conductors and good radiators of heat, and the wastes by conduc tion and radiation are often supplemented by leakage of steam as well as of heat. In the real case, the details of construction, adjust ment and operation affect very greatly the re sultant efficiency and the commercial rating of scribed a steam-turbine and several forms of steam-fountains and steam-boilers. So far as known, none of them had any useful applica tion and they were simply toys or impracticable schemes. It is unknown, in fact, whether any of them were constructed; although the draw ings appear in some cases to be those of actual constructions.