Reflections on the Motive Power of Heat/Appendix C

 

 

APPENDIX C.

Note by the Editor.

 

All the preceding data are to-day subject to modification.

Thus a duty of 150,000,000 ft.-lbs. per 100 lbs. good coal is to-day attainable, and two thirds that figure is extremely common. With engines of large size the coal-consumption has fallen to one half, sometimes even to one fourth, the figure in the text.

Hot-air engines are superseded by the gas-engine and the oil-vapor engine; which even threaten, in the opinion of many engineers, to ultimately displace the steam-engine.

Compound and other multiple-cylinder engines, with two, three, and even four cylinders in series, are now always employed where fuel is costly. The reason of their success is, in part, that given in Note H; but in only small part. The real cause of their general adoption is the fact that the internal thermal waste by "cylinder-condensation"—which in simple engines ordinarily amounts, according to size, to from 25 to 50 per cent, or more, of all heat supplied by the boiler—is reduced nearly in proportion to the number of steam-cylinders in series.

For the applied thermodynamics of the steam-engine, following Carnot and Thomson, see the pages of Rankine and of Clausius of 1850 to 1860, and especially the treatise of Rankine on the Steam-engine. The editor has adopted the methods of these great successors of Carnot in his “Manual of the Steam-engine” (2 vols. 8vo; N. Y., J. Wiley & Sons), which may be consulted in this connection, and especially for details of the theory and the structure of this prime mover.