Triple expansion engine

“ A great advantage of multiple-expansion engines, and a cause for their adoption, is the more even turning effect and better balancing obtained. The triple-expansion engine has either three or four cylinders, more often three, arranged in successive order, H.P. (high pressure) , I. P. (intermediate pressure) , L.P. (low pressure) , each cylinder being attached by means of its piston and connecting rod to its own crank on the crank shaft, which is usually made in interchangeable sections, one for each crank. Cranks are usually set at 120° from each other to obtain even turning effect. ”

“ We have already seen that triple-expansion is just the principle of the compound engine carried one stage farther, and if the desire for attaining the high speed contemplated were to be gratified it was inevitable that this method should have been adopted. With the exception of a very few quadruple-expansion engined ships, such as the Cunard Ivernia, the White Star Baltic, and the German Kaiser Wilhelm II., most modern liners which have not been fitted with turbines are of the triple-expansion type. ”

“ But this advantage of saving room comes much more prominently forward in marine engines, especially in war ships, where every inch of room saved is valuable; and in the new type of triple-cylinder engines now coming so much into vogue in the mercantile marine, whether those engines be only the ordinary three-cylinder engines with double expansion, or the newer, triple expansion engine, expanding the steam consecutively through three cylinders—the form of marine engine which promises to come into use wherever high-class work and economy are required. ”

“ The usual practice is to make the volume of the low-pressure cylinder from 2.5 to 3 times that of the high-pressure. The total ratio of expansion in a multiple expansion engine is the product of the ratios in each cylinder. For example, if the ratio of expansion is 4 in each cylinder in a compound engine, the total ratio will be 4 × 4 = 16. The effect of a triple-expansion engine is sometimes obtained in a measure by making the volume of the low-pressure cylinder of a compound engine 6 or 7 times that of the high-pressure. ”

“ The makers claim—as the result of many tests—that with the crude rock-oil (costing in bulk about 2d. a gallon) which it uses, a horse-power can be developed for one hour by this engine for one-tenth of a penny. The daily fuel bill for a 100 h.p. engine running ten hours per day would therefore be 8s. 4d. To compete with the Diesel engine a steam installation would have to be of the very highest class of triple-expansion type, of not less than 400 h.p., and using every hour per horse-power only 1 3 / 4 lbs. of coal at 9s. ”

“ If a condenser is not used, then it is simply a compound engine.
Triple and Quadruple Expansion Engines.—Instead of using two cylinders, three, or four, are employed, each succeeding cylinder being larger than the last. As steam expands it loses its pressure, or, stated in another way, whenever it loses pressure it increases in volume. For that reason when steam enters the first cylinder at a pressure of say 250 pounds, it may exhaust therefrom into the next cylinder at a pressure of 175 pounds, with a corresponding increase in volume. ”

“ The machinery has been designed with the view of attaining the highest economy. For driving the twin screws there are two separate three-cylinder triple-expansion engines, which are to indicate together 5500 horse-power when running at the moderate piston speed of 680 ft. ”

“ Engines so arranged are termed triple and quadruple expansion engines, or multiple expansion.
The practical saving of a compound engine when its value can be utilized to the full is 10 per cent to 20 per cent. Small engines are seldom compounded, large engines nearly always. ”

“ Even the double and triple and quadruple expansion engines, by which the highest modern economy for power and steam engines has been obtained, are splendid mechanical developments of the principle of expansion, discovered and published by Watt, and used, though to a comparatively limited extent, in his own engines. ”

“ Even the finest quadruple expansion engines, with all the modern devices for super-heated steam to augment their capacity, did not utilise more than 15 per cent. We engineer workers knew that if an engine were invented to economise this waste there would be a further reduction of labor—and this device came. ”

“ To derive from this principle full advantage, it would be necessary that the varying power of the expanding steam should encounter a corresponding, or a nearly corresponding, variation in the resistance: this requisite may be attained, in engines applied to the purpose of raising water, by many obvious expedients; but when they have, as in manufactures, to encounter a nearly uniform resistance, or, in navigation and locomotion, a very irregular resistance, the due application of expansion is difficult, if indeed it be practicable. ”

“ The fact thus learned, that the benefit of expansive working has a limit which is very soon reached in ordinary practice, was not then, and has only recently become, generally known among our steam-engine builders, and for several years, during the period upon which we now enter, there continued the keenest competition between makers of rival forms of expansion-gear, and inventors were continually endeavoring to produce something which should far excel any previously-existing device. ”

“ When the steam after being utilized in the cylinder makes its exit directly to the open air, the engine is called single expansion for the reason that the action of the steam takes place in one cylinder during a single stroke, and what expansion takes place must be during one half of a revolution. ”

“ In general, it may be stated that, to secure maximum economical efficiency, steam should be worked at as high a pressure as possible, and the expansion should be fixed as nearly as possible at the point of maximum economy for that pressure. ”

“ We have seen that the mechanical effect produced by steam when the principle of expansion is not used, is always proportional to the quantity of water contained in the steam, and is likewise in the same proportion so long as a given degree of expansion is used. It is apparent, therefore, that the mechanical power which is or ought to be exerted by an (p. 291) engine is in the direct proportion of the quantity of water evaporated. ”

“ In marine practice, where economy of fuel is a much more important factor in determining the design than it is on land, the principle of compound expansion has been greatly extended by the introduction of triple and even quadruple expansion engines, in which the steam is made to expand successively in three or in four cylinders. ”

“ The reduction of coal-bunker capacity is largely compensated by the increase of economy secured by superheating, by increased expansion, elevation of piston-speed, and the introduction of surface-condensation.
A good marine steam-engine of the form which was considered standard 15 or 20 years ago, having low-pressure boilers carrying steam at 20 or 25 pounds pressure as a maximum, expanding twice or three times, and having a jet-condenser, would require about 30 or 35 pounds of feed-water per horse-power per hour ”

“ Superheating especially promises to yield substantial results as compared with the practice with ordinary engines, but the margin of saving in steam over the best quadruple expansion engine cannot be great. Lord Kelvin however expects it to be the final contribution of science to the highest possible economy in the steam engine. ”

“ The governor is usually attached to a throttle-valve in the steam-pipe, an arrangement which is not the best possible under variable loads, but which produces no serious loss of efficiency when the engine is driven, as at competitive trials, under the very uniform load of a Prony strap-brake and at very nearly the maximum capacity of the machine. The most successful engines have had steam-jacketed cylinders—always an essential to maximum economy—with high steam and a considerable expansion. ”

“ The engines are usually very carefully designed. The cylinders are nicely proportioned to their work, and their pistons travel at high speed. Their valve-gear consists usually of a plain slide-valve, supplemented by a separate expansion-slide, driven by an independent eccentric, and capable of considerable variation in the point of cut-off. This form of expansion-gear is very effective—almost as much so as a drop cut-off—at the usual grade of expansion, which is not far from four times. ”

“ A new type of engine can, if at all, probably only supersede the common form when engineers can employ steam of very high pressure, and adopt much greater range of expansion than is now usual. Great velocity of piston and high speed of rotation are also essential in the attempt to make any revolution in steam-engine construction a success. ”

“ With triple expansion, initial pressures of 180 pounds or more may be used to advantage. The gain from compounding may amount to about 15 per cent over simple condensing engines, taking steam at the same initial pressure. When compound condensing engines are compared with simple non-condensing engines, the gain in economy may run from 30 to 40 per cent. ”

“ Each engine performed a duty of ten millions, both of them were called expansive, while in fact neither of them were so, for the pressure of the steam in the boiler did not admit of it. As Lean says, "As the steam used was raised but little above the pressure of the atmosphere, it was found that the power gained did not compensate for the inconvenience of a more complicated and more expensive machine." Or, as Watt said to Robert Hart, "We resolved to give up the expansion of the steam until we could get men that could work it," as he found it more costly than profitable. ”

“ It appears to be indispensable to the realization of any large amount of benefit by expansion, that the cylinder should be enclosed in a steam jacket, or should in some other way be effectually protected from refrigeration. In some engines not so protected, it has been found experimentally that less benefit was obtained from the fuel by working expansively than by working without expansion--the whole benefit due to expansion being more than counteracted by the increased refrigeration due to the larger surface of the cylinder required to develop the power. ”

“ It must not be forgotten that, especially at full load, explosion-engines are most efficient, and that, under these conditions, it will generally be advisable to subordinate the utility of having a reserve power to the economy which follows from the employment of a motor running at a load close to its maximum capacity. On the other hand, the gas-engine user is unwilling to believe that the stipulated horse-power of the motor which is sold to him is the greatest that it is capable of developing under industrial conditions. ”

“ The reciprocating marine engine, however, had been steadily improved, until it was a marvel in efficiency. Quadruple expansion engines driving twin-screws of a size and shape known to develop the greatest efficiency, for several years offered invincible competition to the new type of engine. ”

“ In it he contended that a perfect engine would be one in which all the heat applied to the steam was used up in its expansion behind a working piston, leaving none to be sent into a condenser or the atmosphere, and that the best results in any actual engine would be attained by carrying expansion to the furthest possible limit, or, in practice, by the application of a regenerator. Anxious to realise his theories further, he constructed a twenty horse-power engine on the regenerative plan, and exhibited it at the Paris Universal Exhibition of 1855 ”

“ If a steam-engine is still needed to drive the generator that furnishes the electric current to drive the motors, where does the economy come in? Why not use small steam-engines, and get rid of all intervening electric appliances? The answer, as every engineer knows, lies in the much higher efficiency of large steam-engines than of small ones. A single steam-engine of 1,000 horse-power will use many times less steam and coal than a thousand little steam-engines of one horse-power each, particularly if each little steam-engine required its own little boiler. ”

“ Trevithick's high-pressure condensing whim-engines had been for some years at work in Cornwall, but mine adventurers had not dared to risk the application of high-pressure steam to the large pumping engines, fearing its great power would prove unmanageable, and its rapid movement cause breakage of the pump-rods and valves.
Two distinct inventions or improvements, each of which was actually followed up in different mines, show themselves in this engine: one being the form of boiler to give with economy and safety high-pressure expansive steam for large engines ”

“ From the foregoing it follows that from 15 to 20 up to 500 horse-power the engine driven by producer-gas has considerably the advantage over the steam-engine in first cost and maintenance. For the development of horse-powers greater than 500, the employment of compound condensing-engines and engines driven by superheated steam considerably reduces the consumption, and the difference in the cost of running a steam- and gas-engine is not so marked. ”

“ Flight Program - The first recovery vehicles will probably be ballistic, but the control and safety advantages of lifting re-entry vehicles warrant their development. [2] A million-pound-plus booster can be achieved about three years sooner by clustering engines than by developing a new single-barrel engine, but the cluster would not have the growth potential of the larger engine. Further growth potential requires the development of the single-barrel engine. ”