Nelson Evening Mail. THURSDAY, APRIL 11, 1912. THE NEW PROPULSION.

Nelson Evening Mail, Volume XLVII, Issue XLVII, 11 April 1912, Page 4

Nelson Evening Mail. THURSDAY, APRIL 11, 1912. THE NEW PROPULSION.

DEVELOPMENTS AFLOAT. INVENTION follows invention 1 wi'h sucli amazing rupidil-y.. that there seems to be no limit whatever to the hidden powers and possibilities that await discovery. Already short references have been miide in theso columns to what is termed the new propulsion by (lie utilisation of oil as fuel in large .steamships. It is interesting to go further into the! matter, and observe more of the facts connected with this new development, which prom:s<\s to be of a most • important nature so far as the propulsion of steamers is concerned. It is declared that had the development of an easily-re-versible two cycle, double-ncl ing type, kept pace with, that of the four-cycle sin gle-acting type, the oil engine to-day would probably be displacing steam just ti? ir. steam the turbine is displacing the ! reciprocating engine. Hut why piogiess 'is now being made, it is explained, is because the two-cycle type is now quite past the experimental stage.. Engines, such as the Diesel, can be reversed with mechanism no 11101 c complicated

that that of the Stevenson link, and the difficulties of double-acting cylinders, especially in regard to packing, appear to have been overcome. In eni)jieetit>n with marine work, the Diesel engine has come into much prominence during the last 12 months. The Toiler, the first vessel to be driven across the Atlanta; b,y iiltei'liai (<imbustkm power,- Was fitted with Diesel en. gines-. To-day Diesel ships, of 9COO t'onSj are" under construction, whilst the British Admiralty are experimenting with a combined steam and Diesel installation on a large cruiser. The largest Diesel ship afloat is the Selandia, which has just been built, to the order of the East Asiatic Company, of Copenhagen, for trading between Copenhagen and Bankok. The Sekindia-j the first of three motor-ships ordered by the same company, has a displacement of 7500 tons. She is driven by tWiri-screws, and her two light-cylinder engines, which are of the four-cycle type, develop 2500 horse-power. The exhaust gases, after being water-cooled, pass up the mizzen-mast, so that the Selandia. without >a funnel, presents an unusual appearance. On a trial trip she attained a speed o-f 12 knots, and her manneinM ring power was excellent-. What tin! oil consumption was is riot given, but the owners ai'e Understood to be perfectly satisfied with the ship.

An interesting description of the Working of these new engines is given in "Diesel Engines for Land and Marine Work," by A. P. Chalkley, B Sc., A.M.I.C.E. 'Mr Chalkley explains that the peculiarity of the Diesel engine lies in the very high compression us (id. The point that it is a "combustion" engine, as distinct from an "explosion" engine, which Mr Chalkley rather insists oh, also is one which will not bear pressing, too far. All that need be said is that the period of combustion is somewhat more prolonged in the Diesel engine than it is in many other types. As the heat has more time to escape, the maximum temperature is reduced, and tlr.s, tend ing, as it does, to relatively easy lubrication, is. of course, an important cons'deration. Compression is carried to about 5001b to the square inch. The temperature of the air at tlr.6 pressure is from lOOOdeg. to llOOdeg. I'alir. Oil is admitted at the commencement of the working stroke, and the quantity determined by the load variation. Practically any oil, mineral or vegetable, can be used, but in oils that have a very hign flash point, such as coal-tar, the* tem' perature would not be high enough to ensure complete combustion, and to provide against this, what may be called a detonator charge, of some oil with a low flash point, is employed to raise tho temperature. The same end might be gained by using still higher compression, but the "Zundol,"' or detonator, 's found to be be preferable. There is no less from these excessively high compressions. Much negative work is said to be done in the compression-stroke, but practically all the energy is recovered during expansion. The scavenging is positive. ■ There are the usual outlet valves for the escape of the burnt-up gaees, and, in addition to this, any 6f the products of combustion, which may have failed to escape, are forced out by , a supply of pure air, delivered by scavenge pumps.

It is necessary in conclusion to observe some of the results. Data taken from the performance of two ships, of the same tonnage (5500 tons) and ol the same power, shows that on the Diesel ship the extra cargo capacity was 280 tons, and that the saving in fuel and wages in the engine-room staff amounted to £123 a month. This '>as in a lowpowered vessel. The saving, it is explained, would be very much greater in the case of 'a- vessel like the Mauretania, which can carry practically no cargo. The coal consumption of the Mauritania is about 1200 tons per day of 24 hours. Roughly, 5000 tons would be required to steam across the Atlantic. With oilengines one-third' of the weight of fuel would suffice. Another important saving would be in the weight of machinery, and the army of stokers required on high-powered steamers —there are 180 on the Mauretania —could be dispensed with.