EDWIX JA3fES LOVEGROVE. JOHBCLARK Ross. HESRYWARD MIDDLEXIST. AWHURJOHN SIXPSOX. HUGHRICPHERSOX MITCHELL, Stud. HEXRYEDWIN SImsoX. Inst. C.E. ERSESTALBERT STICKLAND. FRAEKFEARKE NEALL. EDWAXDRICHXOSD STOKOE, Stud. Inst. FREDERICKOSCAR OERTEL, Stud. Inst. C.E. C.E. JAYESTHOMSON. WILLIAX PARKER. HERBERTFREDERICK TOJIALIN. PETLEYLLOY.D ACGCSTCS PRICE. DAVIDTVILLIAM TRAILT‘ALENTISE. JOHXCIL4RLES RADFORD. 1 BEICESFORDVEXSCIIOYLE. Associates. VILLIAX GEORGEMAIKETTS. I CHARLESHKBBACK WATSOS. (Paper No. 2364.) ‘I The Compound Principle applied to Locomotives.” By EDGARWORTHINGTOB, B.Sc., Assoc. M. Inst. C.E. THEprimary object of the various attempts which havebeen lnade during the last thirty-six years, and more especia.lly within the lastten years,to applythe compound principleto locomotive- engines, is to expand the steam in the cylinder more than is com- monly done at present,, andthus tosave fuel. The following advantages, which mill be discussed hereafter, are claimed for com- pound locomotives :- The use of higher steam-pressures. A more powerful locomotive. Additional power at starting. Reduction of thewiredrawing action as the steam passes through the slide-valve, especially with early cut-off. Obtaining all the availablepower from the expanding steam, and thus discharging theexhaust-steam into the atmosphere at as low a pressure and temperature as possible. More even dis- tribution of strains in the moving parts, and consequently a more uniform turning effort at the crank. The realization of these advantages would no doubt be a valuable achievement, and any one, observing the violent exhaust of the modern locomotive, inay safely conclude that there is Toon1 for improvement in some, if not inall, of these directions. The ayera’ge modern locomotive burns from 3 to 5 lbs. of coal per indicated HP. per hour, conlpared with about 23 lbs. the amount consumed by a good non-condensing land engine, notwithstanding that the locomotive type of boiler is more econonlical than the Cornish cr Lanoashire type frequently used with land engines. Before considering this subject of coal consumption in com- pound engines, it may be interesting to call to mind Borneof the Downloaded by [ Purdue Univ Lib TSS] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. Procecdings.1 WORTHINGTON ox COMPOUND LOCOXOTIVEB; 3 best results obtained from the ordinary or single-expansion loco- mot.ive. Theresults brought before theInstitution by >!h. \V. Stroudley, M. Inst. C.E.,l are perhapsamong the most complete obtainable. The express engine “ Gladstone ” took a load of t\tyenty-three vehicles, weighing, with engine and tender, 335 tons 14 cwt., from London to Brighton, burning 24.87 lbs. of coal per mile. The average speed was 43 * 3 miles per hour, and the average HP., computed from a complete set of indicator diagrams taken each mile, was 528 * 63. From this it is calculated that not more than S * 04 lbs. of coal were burnt per indicated HP. per hour. Xr. Stroudley adds that about 2 per cent. of the water used was condensed exhaust-steam. Thisis a phenomenal performance seldom equalled in daily practice. It surpasses the results calcu- lated from Mr. Mallet’s and Mr. F. W. Webb‘s experiments in both simple and compound locomotives (Table 11). But conlparing it with the non-condensing compound portable engines exhibited at Sewcastlein 1887,*working with about 140 lbs. steam-pressure, the same pressure as the Gladstone locomotive, it will be found that the portable engine burnt 1 * 99 lb. per brake HP. per hour, whichis 0.05 lb. less than the locomotive’s indicated HP. per hour. This seems to suggest that in the best locomotives there is room for only S& per cent. economy of fuel by the adoption of the compound principle. From a series of tests, extending over three months, on an express engine of the Philadelphia and ReadingRailroad, about the year 1884, results were obtained showing the coal consumption per indicated HP. per hour to be 3.55 lbs. Again, the trials last year of the Stronglocomotive, on several railroads of the United States, show a consumption of 4 lbs. of coal per indicated HP. per hour with a boiler-pressure of 160 Ibs. Exact results of the work done by locomotives in England are not readily obtained, owing to the varyingweights of thetrains; but,, withoutintroducing more figures at present, it may be assumed that the usual coal consump- tion of locomotives is from 20 to 50 per cent. more than that of non-condensing land engines. In Table I1 will be found an extraordinaryinstance of the saving of a portion of this wasted fuel, namely, a comparison between Mr. Mallet’s compound engines on the Bayonne and Biarritz Railway in 1879, and some other simple engines doing similar work. Both ___ 1 Ninutes of Procecdings Inst. C.E., vol. lssxi., Tables VI1 and VIII, facing p. 106. Journal of the Roytll AgriculturalSociety of England. Sccond Scries. vol. xs!., 18Si; a180 Table V. R2 Downloaded by [ Purdue Univ Lib TSS] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. 4 WORTHINGTONON COMPOUND LOCOMOTIVES. [Minutes of engines workingat theirmaximum power, the simple engine would burn 4.9 to 5 * 5 lbs. of coal per indicated HP. per hour, but the compound engine burnt3.3 to 3.52 lbs., showing a saving of 35 per cent. in favour of the compound locomotive. Large cylinder-capacity, withhigh boiler-pressures andearly steam cut-off, has been tried by Mr. S. W. Johnson, M. Inst. C.E., of the Midland Railway,and other locomotive engineers, as a means of obtainingthat econonly whichresults from working steam expansively. Rut such attempts seem to overtax thecapacity of the link-motion. Express locomotives at high speeds require an early release to enable the cylinders to exhaust their steam freely, or, in otherwords, to avoid what is sometimes called " smothering " the cylinders; but the Author hasoften noticed that, when simple engines are run with a very high expansion, the large ends of the connecting-rods get hot, owing, perhaps, to the great amount of friction due to the unavoidable steam-compression in the cylinder on thereturn stroke. Consequently thedriver is oldiged to lengthen the strokeof the valve, and use more steam, which causes a great drain upon the boiler. A second difficulty in the ordinary link-]notion, when working steam at high degrees of expansion, is the too early release of the steam at low speeds. Thesetwo properties of the link-motion have rightlybeen considered excellent qualities for ordinary service ; but when carried to high degrees of expansion, the distribution of steam in the cylinder is affected in such a way as to produce wiredrawing and internal strains in the machinery, also to cause the valves to jun1p from their faces. Wiredrawing is perhaps the most serious objection to the link- motion athigh speeds andhigh expansion. It occurs chiefly during the admission of steam to the cylinder, when the edge of the valve does not open the port wide enough to admit sufficient steam tofill the space behind the rapidly-advancingpiston. The use of the double-ported, or Allen slide-valve, overcomes this difficulty to some extent ; but indicator diagrams taken from locomotives at speeds above 20 miles per hour show a marked difference between the boiler and the initial cylinder-pressures, amounting in some cases to 30 lbs., part of this beingdue to the resistance of the steam- pipe, andpart to thethrottling action of the slide-valve. The irregularity of the steam-admission line clearly appears in Plate I, Figs. 1 and 6. This latter circumstance has been pointed out by Mr. D. K. Clark, M. Inst. C.E., who, in 1850, showed that it was practically impossible, with economy, to cut off steam earlier than one-third stroke, owing to wiredrawing during admission. It may, therefore, be concluded that the ordinary best-designed Downloaded by [ Purdue Univ Lib TSS] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. Proceediw.1 WORTHINGTON ON COMPOUND LOCOMOTIVES. 5 link-motion is not suitable for effecting, at highgrades of expansion in one cylinder, that distribution of steam which shallproduce the greatest possible effective pressure on the piston. Anordinary locomotive, using steam at 120 lbs. pressure per square inch, could not be run at highspeeds for any great distance with 40 per cent. of steam cut-off, without loss of boiler-pressure ; but with higher pressures and efficient early steam cut-off, the same boiler would supply steam to perform an equal amount of work with ease during any reasonable period. Severalsystems of valve-gearclaim to produce a better distribution of steam than the link-motion, but the problem of making any substantialimprovement with a single valve still remains to be solved. On the Continent double slide- valves have been employed, by Meyer in Bavaria, and Guinotte in Belgium ; also by Polonceau and others. Of late years, American locomotive engineers have endeavoured to obtain this desired high expansion in a single cylinder, by introducing improved forms of the multiple-\dve system, as follows :- Mr. W. Wilson, of the Chicago, Alton, and St. Louis Railroad, has applied a motion operating double valves to locomotive-engines, withencouraging results. Mr. Alex. Mitchell, LehighValley Railroad, and others, have Mr. Strong’s locomotives at work, which operate separate admission and release-valves by an ingenious but conlplicated motion derived from one eccentric. Mr. A. J. Stevens, of the Central Pacific Railroad, has experimented with a special motion operating a valve at each end of the cylinder. These arrangements may, however, be laid aside €or the present, as being too complicated for ordinary use, By adopting thecompound principle, the highest needful degree of expansion can be obtained without subjecting the steam to the early cut-offs and wiredrawing rendered necessary by the same degree of expansion in a single cylinder.