Page:Science vol. 5.djvu/393

 M-vr 1, 1885. 1

��Slid unusually detailed diaciisBlon. Mr. Mail- lifts been one of the earlleat atid most earnest adrDcntes of this «f*lem ot 'independent engine-tests,' and liiu fol' towed closely upon the sleps of Mei sra. Farej- it Don- kin, and of Sir Frederick Braniwcll, In carrying out this undoubtedly correct method.

By this system, the power of the engine, and the ilistrlbutiou and Tarialiocia of weight of swani in the steam-ey Under, are determined by the iudicntor in the usual way; while, at the same time, the discharge of heat into the condenser of the engine is raeasuretl by introducing a weir at tha discharge from the hot- well, and, by the use of property disposed thermome- ters, calculating from Lbe readings so obtained the number of thermal units of be:it-energy thus carried away from the engine. The sum of the quantities of lieat carried off, the heat converted into power and utiliied as mechanical energy, and the heat wasted in various ways in its passage through the niacliine, should evidently Iw equal lo the heat re< celved from the boiler. The latter quantity Is usually capable of easy determination ; and th? power of the engine as shown by the indicator, and the losses in the condensing water, are the other important qiiau- titles, and these are also readily ascertainable. The coraparisDu thus made is that of the heat produced at the generator, with the power derived from it; and, this comparison being effected. It becomes easy to calculate, from the data thus obtained, what is the actual efficiency of the engine; what are the wastes, and In what direction they occur; and. Anally, in what direction improvement may be iooited for. and lo what extent it is possible.

Mr. Mair's trials were made and Iq some cases with the sai ing conditions. Of the engii single^ylinder beam-engine, oi engine,' and the others were Woolf arrangements of the compound engine. With the first ot IhPse eu- gines, steam was carried at from 5A to BD pounds' pressure, measured from vacuum. The speed of pis- ton was from 222 to 240 feet per minute, and the ratio iif cKpausion varied from 2 to 4.33. The steam used was praotically ilry, coiitaining, by observation, but one per cent of water. The amount passing lliruugb Ihe jacket was from 4.4% to i.0%, except on one oc- casion, when the JocIiet'Steam was entirely shut off. The power of the engine was from 120 lo 125 horse- power, OS shown by indicator.

The proportion of water condensed in the cylinder, up to the point of cut-off, varied from l&% to 30%, OS the ratio ot expansion increased from 2 U> 4.33, and was brought up to 37% at the ratio 3.S4 by shot- ting off the jacket. The heal supplied to the engine, measured in British thermal units, varied from 416 to um per horse-power per minute; the best work being done, and most economy exhibited, at a ratio of expansion of 3.1(1. When the jacket-steam was shut oS, the consumption of beat amounted lo GIO units per minnte. Tbe consumption of steam amounted to from 21 to 2S.5 pounds per horse-power per hour. The iheoreiical efficiency was from 25% to 27%, while the aci iial efflcleiicy was from H % to 10 %, or from .3:! % tu

��ivitb several engines,

e engine under vary-

is tested, one was a

IS a ' Bull-Cornish

��37% of that estimated on the assumplioD of perfect freedom from wastes other tlian the necesiary Ihemc^ dynamic waste of the perfect engine.

Comparing these figures, it will be seen that Ihe cylinder waste amounts, in this engine, to about ten or twelve hundredths the ratio of espanslim. In per- centage of the total heat or steam supplied In the caacs of trial of the jacketed cylinder. Throwing off the jackets brings up the waste to a percentage equal to nearly flfteeu-hundredihs the ratio of expansion.

The > Bull-Cornish engine' Is a pumplng-englne In which (he steam- distribution is effected as in the or- dinary Cornish engnie; but the beam is dispensed wltb, and the cylinder Is Inverted and set directly over the shaft and pump-rod. It is thus impossible lo use safely as large a ratio of expansion as in the common form of Cornish engine, the distribution of weights being less capable of a wide range of adjusts ment. In this ca<e, the engine was worked with 5-'i pounds' absolute sleam-pressure, at a piston-speed of 244 feet per minute, using dry steam at a ratio of expansion of 1.75. In this case, the amount of con- densation at cut-off was 17%; the power was 175 horse-power; the heat useil was about 624 thermal units per minute, and the sl«am ^'J pounds per horse-power per hour; the theoretical efficiency was i 23%, the actual 7%, and the latter was 3li% ot the former. The 'Bull-Cornlsh engine' is (bus seen to | be substantially equal to the single-cylinder, jacketed beam-engine tu waste by condensation, but, on tha whole, lo be inferior to the latter in Its consumption of heat and of steam under sulntanlially equivalent.

The Wooir compound eh gines were worked with steam varying from 67 to 78 pounds' pressure, absolute, with piston-speeds from 2(M to ;1B8 feet per minute, and at ratios of expansion varying between 10 and 10..'). Their power ranged from 133 to Hi liorse- ])ower, and the amount of beat supplied ranged from i 2D6 to 3'24 thermal units per horse-power per hour. ' The cylinder-condensation ranged from 24% to 31%, or atHDUt eight times the square root of llie ratio of expansion, in per cent, of steam supplied. The engines used from 15.12 to ld.6 pounds |>er horse- power and per hour. The efflclencies, theoretical and actual, were from 25% to S0%, and from 13% lo 14%; the latter quantity being nearly one-half the former. The consumption of steam, ou these trials, is cxtraor- diiLarily low, — the lowest on record, probably, — and should be checked by repeated experiment.

On the whole, these reports present the class of data that the engineer greatly needs, both for the purpose of determining the direction and the limttft- tlons of fiulher improvement of the steam-engine, and tar the purpose of securing a more practically applicable theory of the real, as disUnenished from [be ideal heat-engine. R. H. Thubstom.

��AfBTEOROLOGICAL NOTES.

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