The 12 x 18 inch automatic engine was a new machine and had not been used; it had only been in operation at the shop long enough to determine the set of its valves and the correctness of its construction. Its internal friction was naturally high, but it is presumed that the variation, if any, would follow the same law as when the engine has attained a smoother condition by long service. The brake arm was 7 feet long, suspended with a counterpoise which removed all its weight from the brake wheel and engine bearings. A continuous stream of water kept its temperature down. The steam supply was not equal to that required by the engine at full power, and it could not, for that reason, be worked at its rated capacity. Its details had the fol lowing dimensions: Rod 24 in. diameter, main shaft 5 in.; main pulley 6 ft.; weight 1,700 pounds; weight of shaft and crank 900 pounds. The log is given below, and the results of the trial indicate the usual condition: nearly constant friction loss, independent, in even its minute variations, of the load on the engine. No sensible change of friction was found, for the changes of speed observed, due to the shortness of steam supply. This engine was also finally taken apart and tested for distribution of internal friction, as elsewhere described, a transmission dynamometer being substituted for the brake used in these trials, the engine driven by an external source of power, and part after part taken off to give the friction of each of its important elements. The tandem compound engine of the same builders was 28 inches stroke of piston, and the two cylinders 14 and 21 inches in diameter, both secured on one rod and driving the same crank. The exhaust steam from the high-pressure cylinder is conveyed to the low-pressure engine through a pipe, which is also a sleeve for the valve-stem of the former. This valve stem passes also through a hollow stem driving the valve of the low-pressure engine. The latter is driven by a fixed eccentric, while the highpressure valve is actuated by a loose eccentric, which latter is adjusted momentarily by an automatic system of governing. The regular speed is 200 revolutions per minute, the engine non-condensing. The machine was tested in the erecting shop, like the preceding, and in substantially the same manner. It was new, Brake H. P. Friction H. P. and its friction waste therefore abnormally high. The same brake was used as before, and it worked admirably and gave, probably, thoroughly reliable data. The friction was 28 H. P., and very constant through the whole series of trials. Three light cards, the engine being entirely unloaded, give an average of 28.85 H. P., and nineteen cards at various loads give an average of 27.33 H. P. The steam pressure was very evenly held at 85 pounds by gauge; but a contracted supply pipe caused some fall of pressure en route to the engine at heavy loads. This produced some falling off of speed. The method of operation was, in these tests, usually, to first apply the brake load, then to allow the engine to fully reach the speed desired, and then, when at constant speed, to take indicator diagrams, record of steam pressure, speed and the brake load as nearly simultaneously as possible. Cards were taken earlier by driving the engine with low-pressure cylinder alone, thus securing a measure of its friction as a single cylinder engine; two sets of cards thus taken, light, gave a friction of 32.6 and 34.6 H. P. respectively. Eight cards, the entire engine loaded, gave 20.2 H. P. at 150 revolutions, and 31.6, H. P. at 175 revolutions. The trial on which the conclusions of this paper were based was made later, after several days' operation, and the valves readjusted to give a better distribution of work. The last card obtained was taken two or three weeks later while at regular work. The variation of speed noticed was unaccompanied by any observable variation of internal friction. The following is the log: Still another most interesting and important investigation was made upon a compound condensing engine, built by the same works, as a part of an electric lighting plant. Several such engines have been constructed, each consisting of independent engines in pairs, the small engine exhausting high-pressure steam into the other cylinder steam chest, and the exhaust of the larger passing over into a condenser. The main shafts are connected by a coupling in such manner that they may be at any moment separated and worked independently, should accident to either make it necessary, or should but a small amount of power be needed at any time. The two engines are placed about 25 feet apart, and connected by a 4-inch pipe. During these trials the brake was attached to the small engine flywheel, and the tests were conducted as nearly possible in the way already described, the same brake being used as when making trial of the automatic engine last referred to. The high-pressure engine, in this case, had an automatic governor, and the low-pressure cylinder had an eccentric fixed to cut off at stroke. The two engines were first operated independently, and then together. The engine friction was unquestionably independent of the amount of power produced by either or by both engines. The log of these last trials is given below. TABLE IX. FRICTION WITH CHANGE OF LOAD. Lansing Iron Works. Compound Condensing Engine. Low-Pressure Cylinder, 22" × 18" High-Press. Cylinder, 21" × 20′′. M. E. P. I. H. P. I. H.P 1187 2190 1.00 3 190 1.00 4196 0.05 0.3 10 208 4.00 4.2 11208 2.00 2.1 8.208 4.15 4.6515.10 16.78 31.88 7:20 8.50 3.5 12.72 12.48 25.20 0.85 3.42 2.61 6.03 1.15 3.42 3.62 7.04 3.0 4.5 3.50 5.03 8.53 15.57 0. 1.72 1.03 2.75 6.8 9.5 5.196 0.05 0.3 1.72 1.03 2.75 6.1 10.4 6.196 0.05 1.72 0.3 1.03 2.75 7.2 8.9 29.1 36.0 35.5 39.7 26.3 31.2 34.1 38.0 20.0 20.3 22.5 28.9 28.4 37.5 11.3 12.3 12.3 11.3 0. 0. 15.92 Crank. Total. I.H.P. for both Cyls. |