Brake. A simple rope brake passed once completely round the flywheel, and to one end was attached a spring balance and to the other a dead load. The flywheel has an effective circumference of 17.458 feet. Gas Meter.-The gas was measured by a standard meter made by Messrs. Alexander Wright & Co. for the Society of Arts motor trials. It now belongs to my laboratory and can be accurately read to of a cubic foot. The ignition gas was measured through a smaller meter, which can be estimated to Too of a cubic foot. Sampling. The gas was sampled by Mr. Huntley over water through a bye-pass close to the meter, a continuous sample being taken for the whole period of trial. For the exhaust a continuous stream was sucked through a small pipe by a vacuum pump, the sample being taken at right angles to the floor of the main stream. The whole arrangement was devised by Mr. Huntley, and a very perfect average sample of gas and exhaust could thus be obtained. Water. The jacket water was run to waste over a syphon pipe, and was measured in calibrated tanks before it entered the jackets. The inlet and outlet temperatures were taken on standardised thermometers. Counters. Both revolutions and explosions were recorded by mechanical counters. Power Developed.-The mean pressure from the nine diagrams is 60-3 lbs. per square inch, and the explosions being 84.7 per minute, the gross I.H.P. works out to 13.2. The mean pressure during the pumping stroke is 1.6 lb. per square inch, which should be subtracted from the 60.3 lbs. above to give the true effective mean pressure. The net effective H.P. would then be 12.8. With a net load of 126 lbs. and 172.1 revolutions per minute the brake H.P. = 11·47. Mechanical Efficiency.—The mechanical efficiency will then be 89.6 per cent. reckoned on the net I.H.P., and 86.8 per cent. reckoned on the gross I.H.P. Air used. The air consumed was not directly measured, but its amount can be very closely calculated by the following indirect method. The gas per explosion was '0592 cubic foot, and the temperature of the meter being 51° Fahr. and the pressure of gas 14.75 lbs. per square inch, its specific volume would n × (51 + 461) The value of n obtained from the analysis be 14.75 x 144 ·0592 of the gas is 128-1, and the specific volume therefore would equal 30.95 cubic feet per lb. The weight of gas used per explosion is therefore = .00191 lb. On entering the cylinder this gas would be raised in temperature to a point which may be assumed to be midway between the outlet temperature of the jacket water and the meter temperature; here 60° to 89° Fahr., or 550° Fahr. above absolute zero. The pressure at the end of the suction stroke measured upon the pumping cards is 13-1 lbs. per square inch. The specific volume of the gas on entering the cylinder is therefore 128.1 x 550 = 37.35 cubic feet per lb., and the volume occupied 13.1 x 144 by the gas ·00191 × 37·35 = 07145 cubic foot. The total volume (cylinder + clearance) being ⚫8377 cubic foot, there remains 837707145 cubic foot to be occupied by air and exhaust products from the last explosion. The exhaust products will amount approximately to the volume of the clearance = 2467 cubic foot, and their specific volume being (from the value of n obtained from the exhaust analysis, 556 × 550 = 16.21 cubic feet per lb.; their weight 13.1 x 144 viz. 556) The air will therefore occupy 8377-(07145 + 2467) =5196 cubic foot. Its specific volume will be 53.2 × 550 13.1 x 144 = 15.51 cubic feet per lb., and its weight, The total weight of the charge will therefore be (00191 015203349) 05061 lb. Temperatures (figs. 203 and 204).-The constants required for the calculation of the temperatures at the different points of the stroke will be as follows. From the analysis of the gas, its specific heat at constant volume (K) and at constant pressure (K) are (in foot lbs.) For the mixture, air, gas, and exhaust products before explosion, in which 66.15 per cent. is air, 3.8 per cent. gas, and 30-05 per cent. exhaust products, by weight, the values should be= 6615 × 1848 +038 × 5324 + 3005 × 205·8 = 203.9 = ·6615 × 131·6 + ·038 × 404·3 + ·3005 × 150·2 = 147·5 Difference K – K1 = N = 56·4 As a check upon this last value N may be found from the known conditions of temperature, pressure, and volume at com mencement of the stroke, namely, N = = 56.7. 13.1 x 144 x 8377 550 x 05061 The two values are here practically identical, showing that no serious error has been introduced by the above assumptions. The expansion curve on the mean diagrams and the com pression curve may be expressed by an equation of the form P Vn a constant. For the expansion curve the value of 'N' is 1.31, and the compression 1:37. For adiabatic expansion the corresponding value would be 1-37, and for compression 1.39. The compression is therefore very nearly adiabatic, while during expansion a considerable amount of heat must have been added. For the purposes of calculation the curves have been drawn with these indices and the theoretical card marked A B C D E assumed. Its area is equivalent to 5,307 foot lbs., while the area of the actual mean card is equal to 5,140 foot lbs. The temperature at A has, as already stated, been assumed equal to 550° above absolute zero Fahr. At B on the theoretical card the temperature will be-taking the value of N for this 69.9 x 2467 × 144 part of the cycle as 56·4 above, 56.4 × 05061 = 869° abso REVOLUTIONS PER MIN HORSE 60 EXPLOSIONS 00 6 BRAKE 20 BRAKE 89-98 BO LOAD ON SCALE FOR 20 REVOLUTION 40 10 MEAN PRESSURE 30 AND 20 + AND 8 INDICATED 40 |