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A critical and historical review of locomotive engineering
58
.Mechanics, Physh:s, and Chemislry.
of witnessing its action. The time was approaching when Electricity would become a universal handmaiden to applied science, and mechanical men would do well to study closely its phenomena. M. Achard had, in the production of his " Embrayage Eleetrlque " - - i n substitution for the title of which an English one must be found as expressive ~demonstrated his great talent, and in Mr. Gettliffe he had found an excellent expositer.~The vote of' thanks having passed, the meeting shortly after separated.
A Critical and Ilistorlcal ]~eview of Locomotive Encjineering. By J. J. ]~)IP~OKEL. From the London Artizan, Jam~ 1864.
In our paper of January, 1863, we have shown that the total quantity of heat contained in a given weight of steam remains practically constant for all pressures, and we have therefrom drawn the conclusion that steam engines become more economical gradually as the working pressure of the steam increased, without, however, giving any numerical value to the rate of increase of economy with pressure. As this subject cannot be too forcibly impressed upon tim minds of our readers, having been enabled to supply this interesting item of information by means of the data on the density of steam furnished to us by Drs. leanMne and Fairbairn, which we have embodied into our paper of October, 1863, we now give the same in the t~ble below, and the mode of obtaining it is as tbllows : 1st. :For ,~ given volume of steam the quantity of energy created w rles directly as the pressure; 2d. The total heat contained in two equal volumes of steam of different pressures is proportiomd exactly to their respective densities; and the economic wfiue or the absolute energy contained in steam is, therefore, represented by the ratio of the rates of increase of density with pressure. With regard to the useful work obtained from steam, it may be assumed in this comparison that in non-condensing engines all steam admits of being expanded down to the pressure of the atmosphere, and that the whole of the energy contained in atmospheric steam is absorbed by the resistance of' the atmosphere ; upon these assumptions the quantity of work in foot-pounds contained in :~ pound weigh~ of steam at any pressure is expressed by the formula (1), p v ( 1 - ] - h y p , l o g @ - ) - - p t v,
(I)
where p and v st~md for the pressure per square foot, and the volume in cubic feet of a poumt of steam of any density, and p, and v, for the pressure and volume of a p u n d of steam at the atmospheric pressure; the results of this f'orrnuh~ are contained in column 5 of the table below, and the rate of increase of' efficiency or the economic value of the steam is contained in column 6.
59
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60
Mechanles, .Physics, and Chemistry.
It may not be without interest, while engaged upon this subject, to extend this comparison to condensing engines, in tile case of which it may be assumed that steam at any pressure can be expanded down to 51bs. below tbc atmosphere, ami that one-half the energy contained. in steam at the atmospheric pressure is ,~bsorbed by the air-pump and the condenser, though in practice it never reachcs that amount; the work in foot pounds contained in a pound of steatrb at any pressure, is then expressed by formula (2), p v ( l q - h y p , log.-'~z-) ---~1 p, v,
(~)
where p v and Pt v~ retain their former meaning, and % represents the volmne in cubic feet ofl~ pound of steam at 5 Ibs. below the atmospheric pressure; the results of this formuh~ ~lre contained in column 7, and the rate of economy in column 8. For the information of those who are of opinion that the eondenscr has become a useless adjunct to the steam engine, and should bc consigned to its grave alongside tile immortal Watt, its father, we have given in column 9 the relative economy of condensing engines compared with non-condensing engines, and we shall be much surprised if these figures do not cure those who labor under the above-named delusion, should they cast their eyes upon thesepages; these figures, in fact, show that at any pressure condensing engines must be more economical than non-condensing engines working at the same pressure; and from columns 7 and 5, it may be seenthat steam at 55 lbs. effective pressure in condensing engines yields as high a duty as steam at 150 gos. effective pressure in non-eondensinu engines ; and this, no doubt, does account for the fact that the locomotive engine, though working under great disadvantages, such as high velocities of piston, contracted and ditticult steam passages, cooling influence of the atmosphere, and others, works nearly as economically now as the marine engine or even tile stationary engine. It is to be r'egretted, however, that superficial observers, instead of tracing this latter fact to its real source, have drawn from it the conclusion that very high speeds of piston are not detrimental to the economic working of tile steam engine, and are advocating high piston speeds in consequence; although all observations with the indicator show, and scientific reasoning sustains the fact, that steam working under such conditions loses a great per courage of its energy through wire drawing and friction. We are fully aware that the quantities of work given in columns 5 and 7, are not actually realized, but the ratios given in columns 6 and 8 are not on that account considerably altered. We know also that steam is not cxpanded down to the limits we have assumed, but the assumption which we have worked upon only shows in a less favorable light the one fact which we have desired to impress upon the minds of our readers, viz : that tile steam engine becomes economical in proportion as high pressure steam is used.
.Mechanics, Physh:s, and Chemislry.
of witnessing its action. The time was approaching when Electricity would become a universal handmaiden to applied science, and mechanical men would do well to study closely its phenomena. M. Achard had, in the production of his " Embrayage Eleetrlque " - - i n substitution for the title of which an English one must be found as expressive ~demonstrated his great talent, and in Mr. Gettliffe he had found an excellent expositer.~The vote of' thanks having passed, the meeting shortly after separated.
A Critical and Ilistorlcal ]~eview of Locomotive Encjineering. By J. J. ]~)IP~OKEL. From the London Artizan, Jam~ 1864.
In our paper of January, 1863, we have shown that the total quantity of heat contained in a given weight of steam remains practically constant for all pressures, and we have therefrom drawn the conclusion that steam engines become more economical gradually as the working pressure of the steam increased, without, however, giving any numerical value to the rate of increase of economy with pressure. As this subject cannot be too forcibly impressed upon tim minds of our readers, having been enabled to supply this interesting item of information by means of the data on the density of steam furnished to us by Drs. leanMne and Fairbairn, which we have embodied into our paper of October, 1863, we now give the same in the t~ble below, and the mode of obtaining it is as tbllows : 1st. :For ,~ given volume of steam the quantity of energy created w rles directly as the pressure; 2d. The total heat contained in two equal volumes of steam of different pressures is proportiomd exactly to their respective densities; and the economic wfiue or the absolute energy contained in steam is, therefore, represented by the ratio of the rates of increase of density with pressure. With regard to the useful work obtained from steam, it may be assumed in this comparison that in non-condensing engines all steam admits of being expanded down to the pressure of the atmosphere, and that the whole of the energy contained in atmospheric steam is absorbed by the resistance of' the atmosphere ; upon these assumptions the quantity of work in foot-pounds contained in :~ pound weigh~ of steam at any pressure is expressed by the formula (1), p v ( 1 - ] - h y p , l o g @ - ) - - p t v,
(I)
where p and v st~md for the pressure per square foot, and the volume in cubic feet of a poumt of steam of any density, and p, and v, for the pressure and volume of a p u n d of steam at the atmospheric pressure; the results of this f'orrnuh~ are contained in column 5 of the table below, and the rate of increase of' efficiency or the economic value of the steam is contained in column 6.
59
~..~C-lOO~.~',~
oo+
"
*
"
•
•
~ '
°
.~ +
o~
+ +,D ~ I 0
"~ "~ 0
"-~ '+"~
P
++++
F~
<
P~
<
E~
U'I
+m
<
A
h©
II 0
~
~
~
0
-~
~-~
<~
~
° Cmm~
*~ ~
, ~ C, 0 ,~+ C , , ~ , ~ , ~
0
~+ C,~<~ < ~ i ~ i ~ ! ; ~#~
•
[
60
Mechanles, .Physics, and Chemistry.
It may not be without interest, while engaged upon this subject, to extend this comparison to condensing engines, in tile case of which it may be assumed that steam at any pressure can be expanded down to 51bs. below tbc atmosphere, ami that one-half the energy contained. in steam at the atmospheric pressure is ,~bsorbed by the air-pump and the condenser, though in practice it never reachcs that amount; the work in foot pounds contained in a pound of steatrb at any pressure, is then expressed by formula (2), p v ( l q - h y p , log.-'~z-) ---~1 p, v,
(~)
where p v and Pt v~ retain their former meaning, and % represents the volmne in cubic feet ofl~ pound of steam at 5 Ibs. below the atmospheric pressure; the results of this formuh~ ~lre contained in column 7, and the rate of economy in column 8. For the information of those who are of opinion that the eondenscr has become a useless adjunct to the steam engine, and should bc consigned to its grave alongside tile immortal Watt, its father, we have given in column 9 the relative economy of condensing engines compared with non-condensing engines, and we shall be much surprised if these figures do not cure those who labor under the above-named delusion, should they cast their eyes upon thesepages; these figures, in fact, show that at any pressure condensing engines must be more economical than non-condensing engines working at the same pressure; and from columns 7 and 5, it may be seenthat steam at 55 lbs. effective pressure in condensing engines yields as high a duty as steam at 150 gos. effective pressure in non-eondensinu engines ; and this, no doubt, does account for the fact that the locomotive engine, though working under great disadvantages, such as high velocities of piston, contracted and ditticult steam passages, cooling influence of the atmosphere, and others, works nearly as economically now as the marine engine or even tile stationary engine. It is to be r'egretted, however, that superficial observers, instead of tracing this latter fact to its real source, have drawn from it the conclusion that very high speeds of piston are not detrimental to the economic working of tile steam engine, and are advocating high piston speeds in consequence; although all observations with the indicator show, and scientific reasoning sustains the fact, that steam working under such conditions loses a great per courage of its energy through wire drawing and friction. We are fully aware that the quantities of work given in columns 5 and 7, are not actually realized, but the ratios given in columns 6 and 8 are not on that account considerably altered. We know also that steam is not cxpanded down to the limits we have assumed, but the assumption which we have worked upon only shows in a less favorable light the one fact which we have desired to impress upon the minds of our readers, viz : that tile steam engine becomes economical in proportion as high pressure steam is used.