Results from Indicator Diagrams, taken from the Great Britain, Locomotive, G. W. R., in 1850. Indicated steain pressure in cylinder in ibs. per square inch. Water equivalents. Effective horse Total Admit ted for power Reserv- expend- Actually indi one ed by stroke, Com cated. ed during 1 expend ed per hour. power per hour. from diag m. water. lbs. 1984580 15 70 63.8 1.6 2.4 4.0 6-1 59.8 190 13.32 1.00 1253 89.83 817 29.5 3.69 17 88 80-3 0.6 1.9 2-5 3.0 77.5 284 15.89 082 15.07 124-53 758 27.4 3.42 21 95 86.2 1.2 3.0 4.2 4.7 82.0 372 16-71 1·09 15.62 159-45 741 26-8 3:35 14:48 168.95 760 27 5 3.44 27 70-6 1.5 2.2 3.7 5.3 66.9 389 13.89 0-91 12.98 170-37 757 27.4 3.42 31 90 79.6 1.7 3.7 5.4 6.7 74.2 497 15.62 1.13 14.49 218-35 759 27.4 3.42 31 80 73.2 2.9 2.2 6.1 6.9 €8.1 456 1476 1.00 13.76 207:35 786 28.4 3.55 9:39 223.CO 842 30-4 380 54 89 80.4 6.8 6.0 12.8 15.8 67.6 763 15.62 1.56 14-06 369-07 836 30-2 3.77 1st Notch-Means 82. 68.2 28.3 3:54 worked; and the means of the several quantities for the notches separately are as follows: As the results under each notch vary very little, the means above stated may be adopted for all practical speeds without material error. From these mean quantities the following rule is derived: RULE I.-To find the consumption of Water as Steam per horse power per hour, for a given period of admission. Multiply the part of the stroke in inches during which the steam is admitted by 22, and divide by the length of stroke in inches, and add 14 to the quotient. The sum is the required consumption in pounds. Let L-length of stroke, S-the period of admission of steam, and W=the consumption of water in pounds per horse power per hour; then W-22 S 14 L (1.) Allowing 8 lbs. of water to be evaporated by 1 lb. of coke, we have the following rule for the consumption of coke: RULE II. To find the consumption of Coke per horse power per hour, for a given period of admission. Multiply the period of admission in inches by 2.75, and divide by the length of stroke in inches, and add 1.75 to the quotient. The sum is the consumption in pounds per horse power per hour. Making C the consumption of coke, we have S (2.) These rules may be employed with safety for all periods of admission between 10 and 75 per cent. of the stroke, which are the utmost limits worth regarding in the locomotive engine. They are applicable also for maximum pressures during admission, ranging between 60 lbs. and 120 lbs., though based on results from steam of 80 lbs. to 84 lbs. maximum pressure. For extreme pressures, the results by the rule are slightly too small in the case of lower pressures, and rather greater for the higher; these divergences being due to the constant deduction of 15 lbs. for atmospheric resistance from the total pressure. It is presumed that engineers will not return to the error of low pressures in locomotives, and that high pressures will be cultivated. For pressures above 80 lbs., the rules are perfectly safe, as they err rather by excess on the safe side. The following table is worked out by Rule I., to show the efficiency of steam by expansion in the locomotive cylinder, under good conditions in actual practice. The 4th column contains the theoretical maximum relative efficiency of steam, expanding to the end of the stroke, according to the law of Boyle, with a perfect vacuum behind the piston, and without clearance, back pressure, or compression; extracted from the ordinary tables on the subject. In column 5 are given the relative amounts of work done by steam, under the admissions named in column 1, being directly as the effective mean pressures in the cylinder, which are found by a rule to be afterwards given. Efficiency of Steam by Expansion in the Cylinder of the Locomotive in Actual Practice. For Maximum Pressures during admission of 60 lbs. to 120 lbs. The periods of admission of steam to the cylinder may be varied by link-motion from 75, the greatest useful period, to 10 per cent. of the stroke. By the table, the relative efficiency varies within these limits from 1-18 to 2-22, the variation being as 1 to 2 nearly. It follows, that under the most favorable existing circumstances, the utmost possible efficiency of steam worked expansively in the locomotive by the link-motion, is about twice that of the steam when worked under full gear; that is, the same quantity of steam does twice the quantity of work. By a consideration of the effective mean pressures in the first table, it appears that the average rate at which it increases with the period of admission is expressed by the following rule: RULE III. To find the effective Mean Pressure in the Cylinder, in terms of the Maximum Pressure, for a given per centage of admission. Multiply the square root of the per centage of admission by 13.5, and subtract 28 from the product. The remainder is the effective mean pressure in per cent. of the maximum pressure of steam admitted. By this rule the following table is composed: |