

FUEL 509 



In connection with the consideration of the values of Fuel, as producers of mechani- 

 cal power, the Economists Fran$ais has published an article in which it examines the 

 improvements that may be introduced into motive machines by the application of the 

 science of the mechanical theory of heat. The writer thinks that the science itself is 

 sufficiently advanced to afford important practical results, and, in support of that 

 view, names the recent work of M. Leon Pochet, La^Nouvdle Mecanique Industrielle. 



Every thermal machine, which has for its object the conversion of heat into 

 mechanical power, approaches perfection exactly in relation to tho amount of heat 

 which it transforms ; this transformation has a maximum limit which cannot possibly 

 bo passed, but the machines at present in use are far from attaining the degree of 

 perfection indicated by the theoretical limit. By calculating the heat necessary for 

 converting water into steam at the proper temperature, in a supposed perfect machine, 

 the consumption of fuel amounts to 0*17 kilogramme (of 2'204 avoirdupois Ibs. of 

 7,000 grains) per horse-power per hour (see HOESB POWEB); while the consumption of 

 engines in industrial use is as follows : The most perfect engines of large power, one 

 kilogramme ; those of moderate power, two ; and small machines, four to six kilo- 

 grammes. This statement shows that many improvements are still to be looked for in 

 our motive engines : and we may enquire in what direction and with what results the 

 endeavour towards such amelioration has been pursued of late, with a special view to 

 the economy of combustion. 



The power of a boiler is measured by the weight of steam produced per hour for a 

 given amount of heating surface, and its working power by the weight of steam pro- 

 duced by a given weight of fuel, for a boiler may give a large quantity of steam per 

 unit of surface and by time, and yet utilise but a small portion of the heat emitted by 

 the fuel. Thus, engineers are occupied at the present time with the question of the 

 disposition of steam generators ; the types employed in industry vary infinitely in their 

 details, but they may all be referred to one or other of the seven heads following : 

 1. Waggon-head boilers ; 2. Cylindrical boilers with exterior furnaces; 3. Cylindrical 

 boilers with interior furnaces ; 4. Boilers with hot-water tubes ; 5. Tubular boilers ; 

 6. Boilers with circulating arrangement ; 7. Marine boilers. 



According to the results of a considerable number of experiments made with various 

 forms of apparatus, the weight of steam produced by a kilogramme of fuel oscillates 

 between 4'30 (boiler with two lateral hot-water tubes, experimented on by M. Chaves 

 on the Northern Eailway of France) and 10'84 to 11-30 (cylindrical boiler, with a Wye- 

 Williams' superheater), the exceptional limit yet arrived at. These figures, which 

 indicate the economic value of each system, depend upon a great number of conditions, 

 amongst which it must be remembered that the experience and care of the stokers are 

 not the least important. From the economical point of view, little or no progress has 

 taken place in boilers since the time of Watt. The old Cornish and London boilers 

 gave about eight kilogrammes of steam for one kilogramme of fuel : modern apparatus 

 only attain this result exceptionally. This arose in great part from the care with 

 which the first boilers were constructed ; precautions were taken in them to avoid loss 

 of heat, which have unfortunately been neglected of late. The necessity for econo- 

 mising space aggravated the effects of this negligence. In diminishing the length of 

 the boilers that of the flues was also lessened, and consequently the gases were 

 allowed to escape at a higher temperature than befere. What was gained in space 

 was thus lost in economy. 



In the present state of the art of construction, the maximum result to be looked 

 for, under ordinary circumstances, from a good boiler, is that of seven kilogrammes 

 of steam per kilogramme of coal of average quality, producing ten per cent, of 

 cinders. In fixing at 8,000 units the heat disengaged by the combustion of a kilo- 

 gramme of pure coal, we recognise the fact that the utilisation of boilers corre- 

 sponds with a fraction equal to about fifty-seven per cent. More than a third of 

 the heat is lost in our best steam generators. The care of a good stoker may easily 

 augment the result by ten per cent. 



Although this portion of our steam apparatus seems susceptible of notable 

 improvements, still if we consider the stationary conditions of caloric effect since 

 Watt s time, it would seem that these improvements are exceedingly difficult to bring 

 about. _ The Siemens' furnaces appear to be the only apparatus introduced with 

 the object of economising fuel, which deserve special notice; but their application is 

 necessarily restricted to fixed engines. 



Steam once produced, the next thing is to turn it to account, and in this case we 

 can scarcely look for improvement in future but from amelioration in the details of 

 the apparatus and industry has almost arrived at perfection in this respect steam- 

 engines which consume a kilogramme of coal per horse-power effective and per hour, 

 are not far removed from it. 



It has been sought to replace steam in thermal engines by other vapours or by gas. 



