gasoline or volatile petroleum spirit of low sp. gr., 0.65 to 0.70, liberates some of the gasoline, and the air thus saturated with vapor is equal in heating or lighting power to ordinary coal-gas. It may therefore be used as a fuel for gas-engines. Since the vapor is given off at ordinary temperatures gasoline is very explosive and dangerous, and should be kept in an underground tank out of doors. A defect in the use of carburetted air for gasengines is that the more volatile products are given off first, leaving an oily residue which is often useless. Some of the substances in the oil that are taken up by the air are apt to form troublesome deposits and incrustations when burned in the engine cylinder. The Otto Gasoline-engine. (Eng'g News, May 4, 1893.)-It is claimed that where but a small gasoline-engine is used and the gasoline bought at retail the liquid fuel will be on a par with a steam-engine using 6 lbs. of coal per horse-power per hour, and coal at $3.50 per ton, and will besides save all the handling of the solid fuel and ashes, as well as the attendance for the boilers. As very few small steam-engines consume less than 6 lbs. of coal per hour, this is an exceptional showing for economy. At 8 cts. per gallon for gasoline and 1/10 gal. required per H.P. per hour, the cost per H.P. per hour will be 0.8 cent. Gasoline-engines are coming into extensive use (1898). In these engines the gasoline is pumped from an underground tank, located at some distance outside the engine-room, and led through carefully soldered pipes to the working cylinder. In the combustion chamber the gasoline is sprayed into a current of air, by which it is vaporized. The mixture is then compressed and ignited by an electric spark. At no time does the gasoline come in con tact with the air outside of the engine, nor is there any flame or burning gases outside of the cylinder. Naphtha-engines are in use to some extent in small yachts and launches. The naphtha is vaporized in a boiler, and the vapor is used expansively in the engine-cylinder, as steam is used; it is then condensed and returned to the boiler. A portion of the naphtha vapor is used for fuel under the boiler. According to the circular of the builders, the Gas Engine and Power Co. of New York, a 2-H.P. engine requires from 3 to 4 quarts of naphtha per hour, and a 4-H.P. engine from 4 to 6 quarts. The chief advantages of the naphtha-engine and boiler for launches are the saving of weight and the quickness of operation. A 2-H.P. engine weighs 200 lbs., a 4-H.P. 300 lbs. It takes only about two minutes to get under headway. (Modern Mechanism, p. 270.) Hot-air (or Caloric) Engines.-Hot-air engines are used to some extent, but their bulk is enormous compared with their effective power. For an account of the largest hot-air engine ever built (a total failure) see Church's Life of Ericsson. For theoretical investigaton, see Rankine's Steam-engine and Rontgen's Thermodynamics. For description of constructions, see Appleton's Cyc. of Mechanics and Modern Mechanism, and Babcock on Substitutes for Steam, Trans. A. S. M. E., vii., p. 693. Test of a Hot-air Engine (Robinson).-A vertical double-cylinder (Caloric Engine Co.'s) 12 nominal H.P. engine gave 20.19 I.H.P. in the working cylinder and 11.38 I.H.P. in the pump, leaving 8.81 net I.H.P.; while the effective brake H.P. was 5.9, giving a mechanical efficiency of 67%. Consumption of coke, 3.7 lbs. per brake H.P. per hour. Mean pressure on pistons 15.37 lbs. per square inch, and in pumps 15.9 lbs., the area of working cylinders being twice that of the pumps. The hot air supplied was about 1160° F. and that rejected at end of stroke about 890° F. The Priestman Petroleum-engine. (Jour. Frank. Inst., Feb. 1893) The following is a description of the operation of the engine: Any ordinary high-test (usually 150° test) oil is forced under air-pressure to an atomizer, where the oil is met by a current of air and broken up into atoms and sprayed into a mixer, where it is mixed with the proper proportion of supplementary air and sufficiently heated by the exhaust from the cylinder passing around this chamber. The mixture is then drawn by suction into the cylinder, where it is compressed by the piston and ignited by an electric spark, a governor controlling the supply of oil and air proportionately to the work performed. The burnt products are discharged through an exhaust-valve which is actuated by a cam. Part of the air supports the combustion of the oil, and the heat generated by the combustion of the oil expands the air that remains and the products resulting from the explosion, and thus develops its power from air that it takes in while running. In other words, the engine exerts its power by inhaling air, heating that air, and expelling the products of combustion when done with. In the largest engines only the 1/250 part of a pint of oil is used at any one time, and in the smallest sizes the fuel is prepared in correct quantities varying from 1/7000 of a pint upward, according to whether the engine is running on light or full duty. The cycle of operations is the same as that of the Otto gasengine. Trials of a 5-H.P. Priestman Petroleum-engine. (Prof. W. C. Unwin, Proc. Inst. C. E. 1892.)-Cylinder, 8% × 12 in., making normally 200 revs. per min. Two oils were used, Russian and American. The more important results were given in the following table: To compare the fuel consumption with that of a steam-engine, 1 lb. of oil might be taken as equivalent to 11⁄2 lbs. of coal. Then the consumption in the oil-engine was equivalent, in Trials I., IV., and V., to 1.42 lbs., 1.48 lbs., and 1.26 lbs. of coal per brake horse-power per hour. From Trial IV. the following values of the expenditure of heat were obtained: Resistance of Trains.-Resistance due to Speed.-Various formulæ and tables for the resistance of trains at different speeds on a straight level track have been given by different writers. Among these are the following: By George R. Henderson (Proc. Engrs. Club of Phila., 1886): R0.0015(1 + va ÷ 650), in which R = resistance in lbs. per ton of 2240 lbs. and v = hour. Speed in miles per hour: 5 speed in miles per 10 15 20 25 30 35 40 45 Resistance in pounds per ton of 2000 lbs.: 3.1 3.4 4. 4.8 5.8 7.1 8.6 By D. L Barnes (Eng. Mag.), June, 1894: Speed, miles per hour. 50 55 60 10.2 12.1 14.3 16.8 19.2 Resistance, pounds per gross ton.. 70 80 90 100 12 12.4 13.5 15 17 20 50 60 By Engineering News, March 8, 1894: By Baldwin Locomotive Works: 40 45 50 60 1034 12 134 14.5 17 70 80 90 100 19.5 22 24.5 27 Resistance in lbs. per ton of 2000 lbs. = 3 + v ÷ 6. Speed....... 5 10 15 20 25 30 35 40 45 50 55 60 ΤΟ 80 90 100 Re-istance.. 3.8 4.7 5.5 6.3 7.2 8 8.8 9.7 10.5 11.3 12.2 13 14.7 16.3 18 19.7 The resistance due to speed varies with the condition of the track, the number of cars in a train, and other conditions. For tables showing that the resistance varies with the area exposed to the resistance and friction of the air per ton of loads, see Dashiell, Trans. A. S. M E, vol. xiii. p. 371. P. H Dudley (Bulletin International Ry. Congress, 1900, p. 1734) shows that the condition of the track is an important factor of train resistance which has not hitherto been taken account of. The resistance of heavy trains on the N. Y. Central R. R. at 20 miles an hour is only about 31⁄2 lbs. per ton on smooth 80-lb. 5%-in. rails. The resistance of an 80-car freight train, 60.000 lbs. per car, as given by indicator cards, at speeds between 15 and 25 miles per hour is represented by the formula R = 1+, in which R = resistance in lbs. per ton and V = miles per hour. Resistance due to Grade.--The resistance due to a grade of 1 ft. per mile is, per ton of 2000 lbs., 2000 X 0.3788 lb. per ton, or if Rg in lbs. per ton due to grade and G = ft. per mile, Rg = 0.3788G. If the grade is expressed as a percentage of the length, the resistance is 20 lbs per ton for each per cent of grade. 1 5280 resistance Resistance due to Curves.-Mr. Henderson gives the resistance due to curvature as 0.5 lb. per ton of 2000 lbs. per degree of the curve. (For definition of degrees of a railroad curve see p. 53.) If c is the number of degrees, Re the resistance in lbs. per ton, = 0.5c. The Baldwin Locomotive Works take the approximate resistance due to each degree of curvature as that due to a straight grade of 11⁄2 ft. per mile. This corresponds to Re = 0.5682c. Resistance due to Acceleration. -This may be calculated by means of the ordinary formulæ for acceleration, as follows: Let Vi = velocity in ft. per second at the beginning of a mile run. 1⁄2(V2 = V1) = average velocity during the mile. T52802(V2 — V1) = time in seconds required to run the mile. w= weight of the train in lbs. W weight in tons. = = resistance in lbs. due to acceleration 32.2 10,560 S increase of speed in miles per hour; (V2 - V1)2 = S2 × (22/15)2. Ra = resistance in lbs. per ton = .01265.S2. Total Resistance.-The total resistance in lbs. per ton of 2000 lbs. due to speed, to grade, to curves, and to acceleration is the sum of the resistances calculated above. Taking the Baldwin Locomotive Works' rules for speed and curvature, we have Rt= (3+)+0.3788G + 0.5682c + .01265S2, in which Rt is the resistance in lbs. per ton of 2000 lbs., v = speed in miles per hour, G grade in ft. per mile, c = degrees of curvature, S = rate of increase of speed in miles per hour in a run of one mile. Resistance due to Friction.-In the above formula no account has been taken of the resistance to the friction of the working parts of the engine, nor to the friction of the engine and tender on curves due to the rigid wheel bases. No satisfactory formula can be given for these resistances. Mr. Henderson takes them as being proportional to the tractive power, so that, if the total tractive power be P, the effective tractive is uP, and the resistance (1 - u)P, the value of the coefficient u being probably about 0.8. The Baldwin Locomotive Works in their Locomotive Data" take the total resistance on a straight level track at slow speeds at from 6 to 10 lbs. per ton, and in a communication printed in the fourth edition (1898) of this Pocket-book, p. 1076, say: "We know that in some cases, for instance in mine construction, the frictional resistance has been shown to be as much as 60 lbs. per ton at slow speed. The resistance should be approximated to suit the conditions of each individual case, and the increased resistance due to speed added thereto." Holmes on the Steam-engine, p. 142, says: "The frictional resistance to uniform motion of the whole train, including the engine and tender, is usually expressed by giving the direct pull in pounds necessary in order to propel each ton's weight of the train along a level line at slow speed. The pull varies with the condition of the line, the state of the surface of the rails, the state of the rolling stock, and the speed. If M be the speed in miles per hour, and T the weight of the train in tons [2240 lbs.] exclusive of engine and tender, the resistance to uniform motion may be expressed by the formula R = [6+0.3(M — 10)T]. If T1 be the weight of the engine and tender, the corresponding resistance is which expression includes the friction of the mechanism of the engine. Holmes also says that a strong side wind by pressing the tires of the wheels against the rails may increase the frictional resistance of the train by as much as 20 per cent. Hauling Capacity due to Adhesion.-The limit of the hauling capacity of a locomotive is the adhesion due to the weight on the driving wheels. Holmes gives the adhesion, in English practice, as equal to 0.15 of the load on the driving wheels in ordinary dry weather, but only 0.07 in damp weather or when the rails are greasy. In American practice it is generally taken as from 1/4 to 1/5 of the load on the drivers. The hauling capacity at slow speed on a track of different grades may be calculated by the following formula: 1000 ÷ a R+20g Let' tons of 2000 lbs., locomotive and train, per 1000 lbs. load on drivers, a the reciprocal of the coefficient of adhesion, g = the per cent of grade, R = the frictional resistance in lbs. per ton. Then T= From this formula the following table has been calculated: Grade Per Cent, 0 0.5 1 1.5 2 2.5 3 3.5 4 5 6 7 Tons Hauling Capacity per 1000 lbs. Weight on Drivers. For a 4, R 6.. 42 15.6 9.2 6.9 5.4 4.5 3.8 3.3 2.9 2.4 2.0 1.7 a = 5, R = 8.. 25 11.1 7.2 5.3 4.2 3.4 2.9 2.6 2.3 1.9 1.6 a = 5, R = 10. 20 10. 6.7 5. 4. 3.3 2.9 2.5 2.2 1.8 1.5 Tractive Power of a Locomotive.-Single Expansion. p = average effective pressure in cylinder in lbs. per sq. in. S d = diameter of cylinders in inches. D= diameter of driving-wheels in inches. Then 1.4 1 3 The average effective pressure can be obtained from an indicator-diagram, or by calculation, when the initial pressure and ratio of expansion are known, together with the other properties of the valve-motion. The sub joined table from Auchincloss gives the proportion of mean effective pressure to boiler-pressure above atmosphere for various proportions of cut-off. These values were deduced from experiments with an English locomotive by Mr. Gooch. As diagrams vary so much from different causes. this table will only fairly represent practical cases. It is evident that the cut-off must be such that the boiler will be capable of supplying sufficient steam at the given speed. Compound Locomotives.-The Baldwin Locomotive Works give the following formulæ for compound engines of the Vauclain four-cylinder type: C2S × P c2Sx + T= D P D For a two-cylinder or cross-compound engine it is only necessary to consider the high pressure cylinder, allowing a sufficient decrease in boiler pressure to compensate for the necessary back-pressure. The formula is Efficiency of the Mechanism of a Locomotive.-Frank C. Wagner (Proc. A. A. A. S., 1900, p. 140) gives an account of some dy namometer tests which indicate that in ordinary freight service the power used to drive the locomotive and tender and to overcome the friction of the mechanism is from 10% to 35% of the total power developed in the steam-cylinder. In one test the weight of the locomotive and tender was 16% of the total weight of the train, while the power consumed in the locomotive and tender was from 30% to 33% of the indicated horse power. The Size of Locomotive Cylinders is usually taken to be such that the engine will just overcome the adhesion of its wheels to the rails under favorable circumstances. The adhesion is taken by a committee of the Am. Ry. Master Mechanics' Assn. as 0.25 of the weight on the drivers for passenger engines, 0.24 for freight, and 0.22 for switching engines; and the mean effective pressure in the cylinder, when exerting the maximum tractive force, is taken at 0.85 of the boiler-pressure. Let W weight on drivers in lbs. ; P= tractive force in lbs., say 0.25W; P1 = boiler-pressure in lbs per sq. in.; p = mean effective pressure, = 0 85p1; d = diam. of cylinder, Slength of stroke, and D = diam. of drivingwheels, all in inches. Then 4d2 × 0.85p,S D d = 0.5 VDW PS P.S 2ZD Von Borries's rule for the diameter of the low-pressure cylinder of a com pound locomotive is d2 = = ph' |