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oe MARINE REVIEW. ee | a Marine Engine Design. Written for the Marine Review by W. F. Durand, Principal of graduate school of marine engineering and naval archt- tecture, Sibley College, Cornell University. We have next to derive the value of m.e. p. from the boiler pressure and expansions assumed. A gauge pressure of 160 ths. equals 174.7 lbs. absolute pressure. The final pressure in the L. P. cylinder should be about 12 tbs. absolute. This cor- responds to 14.56 expansions. If this be taken as the value of 7 in the common formula: mean forward pressure--=p (1-;-hyp. log. 7) yy. we should have m. f. p.=174.7 X 3.68 14.56 As a matter of fact, however, the m. f. p. realized in any given engine would fall far short of this amount. This loss is due to two causes. 'The effect of clearance, and the loss in pres- sure due to the resistance of the passages and pipes, and the consequent drop in pressure between the boilér and engine, and between the successive cylinders of the latter, as previously re- ferred to. The loss due to both causes, even in well designed engines, may aggregate about 25 per cent., so that instead of 44.1 m. f. p. we should not expect to realize more than about three-quarters of this or say 33 Ibs. The mean back pressure will be about 3 lbs. leaving 30 Ibs. as the value of the m. e. p. In connection with the estimation of the probable m. e. p., having given the boiler pressure, the following table will be use- ful. It is computed for a final pressure in all cases of 12 lhbs., and assumes a loss of one-quarter, with 3 tbs. back pressure as explained above: Gauge Absolute = 44.1 Probable mean Probable mean Pressure. Pressure. Forward Pressure. Effective Pressure. 140 ane 31.9 28.9 145 159.7 32.3 29.3 150 164.7 32.5 29.5 155 169.7 32.8 29.8 160 174.7 oe BX, 165 179.7 Poe 30.3 170 184.7 Solos 30.5 175 189.7 33.8 30.8 180 194.7 34.1 ould 185 199.7 34.3 31.3 190 - 204.7 34.5 31.5 195 209.7 34.7 ail eeeyh 200 214.7 34.9 31.9 Inserting the various values into the I. H. P. formula and solving for A we have 33,000 X 1,500 -- 2X30X3.5XI00 . The corresponding diameter is 53.6 inches for L. P. cylin- der. We may next find the suitable diameter of H. P. cylinder. To this end we fix upon the desired number of expansions in this cylinder, which in its present case we may take as 2. It follows that the number of expansions between the high, and end of the low pressure cylinders is 7.28, and hence the area of the H. P. will be 2357+ 7.28324. 'The corresponding diameter is 20.3 inches. For the determination of the diameter of I. P. cylinder we shall assume the 7.28 expansions noted above to be divided into two equal steps. The ratio between the areas of the I. P. and I. P. will therefore be as V7 28 tO 10%, as 2.7 to vr. ° Therefore area of I. P. cylinder=2,357--> 2.7=873. The corresponding diameter is 33.3-inches. . We have therefore as the general dimensions of the engine 53.6", 33.3. and 20.3" diameter by 42" stroke. After reaching such values we have to take the nearest practical shop dimen- sions. 'These may be taken to the nearest quarter or half inch. We may also note that no allowance has been made for the reduction in the area of the piston rod. If therefore we take say the nearest half above, the error will lie in the opposite direction and the requireinents will be practically fulfilled. We take then 54" 33%" and 20%" as the diameters of the cylinders. = 2,357 square inches. EQUALIZATION OF WORK AMONG THE CYLINDERS. Equality of work means in general equality of turning moment on the three cranks, and a just division of the total stress between the three portions of the engine as a whole. It is also true in general that the arrangement for best thermo- dynamic efficiency is usually one which will give a nearly equal sub-division of.the work. The problem of adjusting the amount of work among the various cylinders, in the case of a new design requires the laying down of the probable indicator cards, and the adjustment of the I. P. and L. P. cut-offs to effect the equalization desired. It must be remembered that the positions of these cut- offs have but slight influence on the power of the engine as a whole. The H. P. cut-off determines the amount of steam which enters per stroke, while the other cut-offs only effect the way in which it is utilized. In general an earlier cut-off in the I. Ee or L. P. cylinders results in more work trom such cylinder, and a later cut-off, vzce versa. Te In order to lay down the probable indicator cards, we should require a knowledge of the clearance and receiver volumes, the angular relations of the cranks, and combined with all an element which can only be derived from experience. Every theoretical card is more ore less modified in the engine itself due to friction through passages,condensation,.re-evaporation etc.,in a way whichis simply beyond the reach of any exact analysis. Nevertheless by a careful estimate of the influences at work, cards may be laid down which shall not be far wrong, and from which the equalization of power may be effected with all neces- : sary accuracy.. The operation itself is, however, long and tedious, and is beyond the limits of our available space. If the I. P. and I. P. cylinders are provided with variable expansion valves, the work may be equalized approximately for any given set of conditions. Ifthe link is the only expansion apparatus, the adjustment may usually be effected, but it may require such excessive linking up as to result ina sacrifice in the smooth running of the engine. Under such conditions, it is better to run smoothly, even at a sacrifice of the equalization of the work. In the case of the design at present before us, the points of cut off in I. P. and Ll. P. cylinders must remain undetermined so far as they depend on the laying down of the cards of three cylin- ders--at least for the present. A valve of from % to 4 with appropriate values of the clearance and receiver volumes, would be found, however, to-give a fair equalization of the work among the cylinders. From this point on, the design of a marine engine is con- cerned with the various details, their sizes, forms, ratios, etc., each one of which must be settled in the light of various op- posing considerations. 'The points bearing on some of the more important of these, may be made the subject of an article ata tuture time. CHICAGO LAKE INTERESTS. WESTERN OFFICE, MARINE REVIEW, t No. 13 Western Union Building, CH1cAGo, II1., Dec. 8. The Chicago underwriters who are attending the Detroit meeting this week, went there with the finest lot of chaotic plans fur the reorganization of Inland Lloyds, that could have been gathered. In fact, they did not know what to do, and if the deliberations result in something definite and practic- . able, the Chicago insurance men will come back well satisfied. It is possible that an attempt will be made to remove Inland Lloyd's to this city. The - reasons which will be urged for this movement will be that Buffalo is not the best place for the Lloyds, because of the predominance of one general insur- ance agency there. The objection against Cleveland will be that ship builders and vessel owners have too much direct influence. It will be urged in behalf of Chicago that insurance business here is so divided between general agencies that out of the conflicting interests might come absolute impartiality. Still it -- may be that the reorganized vessel inspection will have its headquarters in Detroit, on account of that city being the half-way place. Detroit is certainly preferable to Buffalo, looking at the question from the standpoint of Chicago. The war on smoking Chicago tugs has broken out again, and a large num- ber of suits have been instituted against tugs on account of making smoke. There has been plenty of bark in this warfare, but no one has yet been bitten. In other words, none of the monumental fines imposed on smoking tugs have ever been collected. Kingston Notes. Special Correspondence to the MARINE REVIEW. Kineston, Ont., Dec. 8.--The steamers Tilley and Rosedale had a race down from Fort William, and notwithstanding that the former had a barge in tow she arrived here two hours before the latter. The Tilley has made the trip mentioned in seven and a half days and from Duluth here in eight and a half. . Already this year W. W. Ogilvie of Montreal has received 1,354,000 bu- shels of the Manitoba wheat crop of 1892. This is the largest portion of any one crop received by any one firm in Montreal. Next week Capt. John Gaskin leaves for Ireland to make arrangements for the construction of the Montreal Transportation Company's new steel steamer, mln . . . . . . The steamer Algonquin will receive a new iron stern here this winter.