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M. S. AMERIKA—TOP OF MAIN ENGINE—NEW TWO-CYCLE DOUBLE-ACTING DIESEL with self-expanding Perlit piston rings, and arranged for oil cooling inter- nally. The piston valve for the bot- tom is also of the plain piston type provided in the center with a large hole for the piston rod and fitted in- ternally as well as externally with self-expanding piston rings. The hollow space is oil cooled in the same way as the top piston valve, the oil being taken from the forced lubrication system and admitted by means of telescopic pipes. Usual Design of Pistons The pistons are of a similar de- sign to that of the pistons of Bur- meister & Wain’s double acting four stroke engines, but longer, like all pistons for the two-stroke types, viz., the length of stroke minus the height of the scavenging port. They are, nevertheless, shorter than for the most of the types of double acting two stroke engines, owing to the adop- tion of only one row of scavenging ports and the elimination of exhaust ports. The piston halves of Perlit are bolt- ed around the piston rod flange; the bottom half is extended forming a cyl- indrical liner surrounding the piston rod for its whole length. The pistons are oil cooled, and the oil admitted by means of telescopic pipes to the annular space between the piston rod and the liner, being led away through the central hole bored in the piston rod. The effective scavenging and the fact that the parts most exposed to the hot combustion gases are reduced to about one-half the size of the cylinder is the great advantage of this system. Further, the stroke of the piston valve passing the ports is only BOAT DECK OF M. S. AMERIKA—HIGH CHOCKED LIFEBOATS 30 MARINE REVIEW—March, 1930 about one-third of the piston stroke with a correspondingly smaller speed, The top and bottom exhaust piston valves are rigidly connected by means of crossheads and links. They have no moving parts requiring lubrication outside the crankcase. All the moy- ing parts are inside the crankcase, They consist of balancing levers and connecting rods driven from a smaller crankshaft arranged in the bed plate parallel to the crankshaft and con- nected to this by means of a chain drive. The whole mode of procedure in con- trolling the exhaust resembles that of the ordinary piston valve gear for steam engines, but with one important difference. While the steam piston valve renders a certain resistance, owing to friction, thus reducing the mechanical efficiency of the engine, the exhaust piston valve of this double acting two stroke engine is de- veloping useful work. On account of having a suitable angle of lead for the exhaust piston valve gearing, the mean pressure acting on the valve will be high. The piston valve gear will increase the horsepower of the engine to about 10 per cent above that developed by the main piston. Airless injection is used on exactly the same principle as fitted for the four-stroke _ type. Automatic fuel valves are fitted in each cylinder end diametrically opposite to each other. Each cylinder end is thus provided with two spraying nozzles. Each nozzle injects the fuel in a fan- shaped spray extending over a hori- zontal plane. In order to clear the piston rod and the cylinder wall the directional axis of the sprays is set to form an angle of approximately 45 degrees with the connecting diam- eter of the two nozzles. The path of the sprays of atomized fuel are slightly curved, carrying the fuel along through the combustion space, on ac- count of a moderate whirling motion of the body of the combustion air due to the tangentially disposed scaveng- ing ports. Diesel Auxiliaries Are Fitted There are three auxiliary six cylin- der Burmeister & Wain diesel engines of single acting trunk piston two stroke cycle type with direct driven rotating scavenging pump and airless injection. They are constructed for an output of 600 shaft horsepower each at 300 revolutions per minute, and are direct coupled to 220-volt dynamos, having a capacity of 365 kilowatts. Of these one or two will be needed at sea according to Cit- cumstances. Consequently a total of about 1100 kilowatts is available for (Continued on Page 64)