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Aviation History
1934
1934 - 0512.PDF
FLIGHT, MAY 24, 1934 A 1,200 H.P. DIESEL ENGINE Designed by a Belgian Engineer, M. D. J. Deschamps, and now, we understand, being built by the Lambert Engine and Machine Company, of Moline, Illinois, U.S.A., the new engine is claimed to be designed for a power output of 1,200 b.h.p. and a total weight of 2,400 Ib. IESEL engines are to the fore just now. The world's altitude record recently established has called attention to the British " Phoenix " compression- ignition heavy-oil engine, and now comes news from America of a large inverted Vee 12-cylinder design, water cooled, which claims to be the world's most powerful Diesel aero unit. The design owes its origin to M. D. J. Deschamps, a Belgian engineer who was formerly associated with the Minerva Company, for whom he designed a sleeve-valve type of aero engine. The engine is an inverted 12-cylinder V type, working on the two-stroke cycle, of 6 in. bore and 9 in. stroke, making the displacement 3,052 cub. in. The two banks of cylinders make an angle of 30 deg. with each other, which gives a compact power plant with minimum frontal area. In fact, the front elevation can be enclosed in a rect- angle 261 in. wide by 49-,% in. high. Mr. P. M. Heldt, writing in Automotive Industries, Philadelphia, of May 5th, 1934, states that complete with all accessories, including starter, air compressor, double fuel strainer, fuel booster pumps, fuel lines, superchargers, torsional vibration damper, safety clutch for the accessories drive and over- running clutches for the supercharger drive, the engine weighs about 2,400 lb., or 2 lb. per h.p. It works with a compression ratio of 16 to 1. Starting is by compressed air, and means are provided for relieving the compression of either bank of cylinders. With the object of increasing the general safety factor, all important accessories are provided in duplicate, and great care has been taken to minimise trouble with the " plumbing " of the fuel and cooling systems. In fact, each bank of cylinders has an independent cooling, fuel, lubricating and scavenging system, so that the power plant virtually consists of two engines with only the crankcase and the crankshaft common to both. If necessary, one bank of cylinders could be shut off and the plane landed on the remaining bank. Each cylinder has two injection valves, supplied by individual fuel pumps, so trouble with the injection system is pretty well guarded against. The experimental engine was designed to be reversible, so as to meet the requirements for use on airships. On aero- planes the reversing feature is not necessary, but M. Deschamps considers it valuable there, too, since it would make it possible to brake by means of the propeller in the event of an emergency landing. From tests of a two-cylinder experimental engine of the same cylinder dimensions it is expected that this 12-cylinder engine will develop 1,200 h.p. at about 1,600 r.p.m. A normal continuous output of 900-1,000 h.p. is figured on. Cylinder blocks and crankcase are in a single casting of magnesium alloy. The crankcase is substantially ribbed for increased stiffness, and the bearings are supported by box girder-type partition walls. Cylinder liners are made of nitralloy steel and hardened on thei inside to 900-1,000 Brinell. It will be noticed that the exhaust collector, which sur- rounds the cylinder, is supported in such a way as to allow it the maximum freedom of expression. The cylinder heads are cast in an aluminium alloy, in a single unit for each bank of cylinders. Scavenging air is supplied by two General Electric centri- fugal compressors, one for each bank of cylinders. These are driven at 13J times crankshaft speed, and at normal engine speed they deliver 25 per cent, more air than the displacement of the engine. Scavenging air is normally delivered at a pressure of 12 lb. per sq. in. gauge. Tests with the two-cylinder experimental engine showed that a pressure of 8 lb. gauge is required to effect proper scaveng- ing at 1,600 r.p.m., so 4 lb. per sq. in. is available for supercharging. A butterfly valve on the air intake of the compressors enables the pilot to adjust their output. Air from the superchargers enters the cylinders through two valves in the head, which open and close in unison. Two valves are used instead of a single one to reduce the inertia and to .enable the valves to open and close very quickly without excessive strain. A compression-relief mechanism enables the pilot to shift the camshaft axially, thereby bringing a special cam in line with the valves, which keeps them open during the compression stroke. An automatic locking device secures the camshaft in either of its two working positions. Exhaust gas leaves the cylinder through twelve ports at the bottom of the stroke. A special feature embodied in the piston design is in- tended to prevent a trouble often experienced with two- stroke engines—that of top rings sticking, due to carbon formed by the combustion of oil on top of the piston being carried to them by the exhaust gases. To prevent this from happening, the top ring is located sufficiently low down so that it is completely covered by the cylinder walls before the exhaust ports open. Special pains were taken to assure adequate cooling of the bridges between exhaust ports, to prevent distortion of the liner and assure long life of rings. The top and bottom edges of the ports are rounded, to prevent the rings from catching on them. Pistons are of Y alloy and are provided with deep radial cooling ribs. One of the features of the engine, on which a patent is pending, is a method of locking the inner race of the thrust bearing without cutting a screw thread on the shaft adja- cent thereto (which is always a source of weakness). A two-piece threaded sleeve is located between the inner race and a shoulder on the shaft, and the customary lock nut screws over that sleeve. When the nut is tightened 512
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