HEAVY OIL ENGINES FOR BRITISH SUBMARINE BOATS.

The 12-cylinder engine is one that has been made in large numbers during the war by Messrs. Vickers, both at their works at Barrow-in-Furness and at Ipswich. It has also been manufactured by a number of firms working under license from Messrs. Vickers. The latter firm has latterly introduced various improvements in detail and in arrangement of controls, and as these, owing to the necessity of rapid production, were not wholly incorporated in the engines made by licensed firms, who were working to Admiralty instructions, the description we now append will include points interesting even to those who are fully conversant with the earlier engines. This 12-cylinder engine is shown in elevation in Fig. 1, while a crosssection is given in Fig. 2.

The peculiar framing construction of the engines is plainly evidenced by these drawings. First of all, it will be noticed that each main bearing is carried by a separate steel casting, and these castings are recessed into longitudinal beams, athwartship fitted bolts, not shown in the drawings, tying the two together. This construction obviously entails considerable care in chocking the engines in the boat, but with trained workmen no difficulty arises, and the required accuracy is obtained in a surprisingly short time. In adaptations of these engines when weight was relatively unimportant, a cast bedplate has been substituted, and a similar design carried out in steel is, with modern foundry methods, applicable to the light weight engines, and would probably be proposed for future work where interchangeability with previous parts, as for Admiralty work, is not important. In this respect, as in many other points in the engine, some of which will be subse quently mentioned, the designers have been handicapped by their own success, as improvements which experience has pointed out to the firm were sometimes not acceptable on account of the necessity of maintaining uniformity with the large number of engines already in commission.

The columns consist of boiler plate somewhat less than thirteen-sixteenths inch in thickness. At the top is a forged steel head into which the column plate is rabetted, three rows of rivets securing the head to the column plate. The plate is cut with lightening holes, and at the bottom is branched by a slot cut for removal of the main bearing cup. To the lower extremities of these branches are riveted four forgings, forming the feet. These are of approximately triangular elevation, and are plainly visible in the sectional view. The riveting of the heads and feet of the column is most carefully carried out, the holes being reamered and the rivets inserted alternately from opposite sides to avoid bending the column. The column is stiffened by light angles on its outer edges, these angles forming the facing for light sheet steel plates forming the sides of the crank-case. Small circular hand doors are fitted in the outboard casings to facilitate feeling the liner and lower bearings. Further stiffness is given by angles plainly shown on the elevation which support the horizontal tieplate below them. This tie-plate has a hole in it slightly larger than the cylinder jacket bottom flange, and supports the latter by means of four adjustable snugs bolted to the tie-plate. On the column head is placed a sandwich or distance-piece, which takes the weight of the liner, and to which the cover is secured by six 11⁄2-inch studs. The connecting joint consists of a cast-iron ring ground into both liner and cover. The main impulse load is transmitted from the covers to the columns by two studs and four bolts, 15%-inch diameter, for each column between adjacent cylinders, two bolts only in addition to the studs being fitted to the end columns of each of the four groups of three cylinders, into which it will be noted the engine is divided.

This framing construction permits of close determination of stresses and lends itself to a light-weight engine, but the main practical advantage is in the extreme accessibility it gives to the crankhead and main bearings, while a cylinder is rapidly replaced should occasion arise. Accessibility and facility of overhaul are, of course, of the utmost importance for marine work.

The cover, it will be seen, is a simple steel casting, the inlet and exhaust valve boxes being separate from it. These boxes seat upon coned joints in the cover, a ground metal to metal joint preventing leakage from the compression space. They are very thoroughly water-cooled, as will be seen in the elevation, the inlet valve-box even having a recess turned on its exterior into which water from the cover has access.

The water joints between the top of the cover and the valve boxes are made by indiarubber rings compressed below the flange of the latter. While no trouble is experienced on service, yet in later engines Messrs. Vickers make this joint by a pair of rubber rings in grooves on the periphery of the box, which enter into a slight recess in the cover. The advantage of this is that the joint becomes a sliding one, automatically compensating for any wear due to grinding down of the valve-box. A similar water joint is fitted between the bottom of the liner and the jacket, the two grooves being visible in the illustrations.

The exhaust and induction valves are of nickel steel, the former being water-cooled by flexible indiarubber armored hose connected to the valve head. The inlet water passes down a central tube to the bottom of the exhaust valve and escapes upwards around this tube. The practice of water-cooled exhaust valves is followed by Messrs. Vickers even in their smallest submarine engines, one advantage being that the spindle clearances may be kept fine so that on starting the leakage of gas into the boat will be negligible compared with that from uncooled valve spindles in which a comparatively large clearance has to be allowed for expansion due to heat.

The separate valve-spindle guides will be seen in the section in Fig. 2, taken at the No. 11 cylinder, this being in accordance with the desire for extreme durability of all parts. Lubrication is not now fitted to the valve spindles. The head gear calls for no particular comment beyond stating that the spring spindle has a tee-end at its lower extremity, so that if it is depressed and then turned through a right angle about its axis it can be readily removed with its spring.

The cylinder proper is very elementary in form, and consists of a plain cast-iron liner surrounded by a corrugated sheet steel jacket. This latter terminates at its lower end in a pressing forging, to which it is welded, and at the top a flange is welded to the jacket and is jointed to the underside of the sandwich plate. The liner has a number of steel bosses riveted through it, as indicated in the elevation of the eight-cylinder engine (Fig. 3). These bosses are machined to form stuffing boxes through which the piston lubrication connections pass; these connections being screwed into the liner. Eight of these feeds are fitted to each cylinder, and are supplied by a sight-feed force lubricating pump. In practice this pump is set to a low output, as very little lubrication is required for the piston.

The piston is of simple design in cast-iron. The top is concave and fitted at the center with a screwed hole for a lifting bolt. This hole at one time held a special plug designed to maintain a high temperature, and thus to facilitate combustion, but this was found unnecessary and is not now fitted. Though the hole is left open to the flame, no harm is occasioned thereby, the main impact of the injection not coming upon the center of the piston as in an air-injection engine. There are six piston rings, 0.375 inch wide at the upper part of the piston, and one wiper ring at the bottom.

The gudgeon pin is pressed hollow from special case-hardened steel, a plug being subsequently fitted to exclude the oil. The diameter is in three steps, as is usual, and is tightly driven into the pisotn, being secured at one end by a set pin and at the other by a key. A light aluminum guard is fitted over the top of the connecting rod and is secured by the gudgeon-pin set screw and by a special stud at the opposite side. The somewhat complicated lower guard originally fitted has been abandoned.

The connecting rod is of plain turned design. The top end is spherical with a non-adjustable gudgeon bearing, consisting of a bronze bush pressed into the eye of the rod and lined with white metal. This bush has a radial hole through it at the middle of its length, this hole communicating with a groove turned in the eye of the rod. By this means, if the bush should by accident or carelessness turn slightly, the oil supply from the hollow rod is not interrupted. The lower end of the rod is forged into a palm in which the crankhead brass is spigoted, provision being made for a compression plate. The crankhead brasses are of bronze, white-metal lined, with a circumferential non-staggered oil groove at their middle length. The lubrication oil passes into the top of the main bearings, thence through the crankshaft to the crank-pin, from thence up the rod to the top end. It will be noticed that this design of crankhead is somewhat heavy, and Messrs. Vickers have adopted a modified design in cast steel for crankheads of their non-Admiralty work.

The crankshaft in the 12-cylinder engine is in four three-throw sections, and was maintained at the same diameter as the solid shaft in standard six, eight and ten-cylinder engines, namely 7-inch. Nickel-chrome with hollow journals and pins was originally fitted throughout the large engine, mainly to save weight and to gain experience of this material in such shafts, the maximum stress not being materially affected by the addition of the extra cylinders. Difficulties in supply during the war led to this being, in a number of 12-cylinder engines, used only for the aft two lengths, the solid carbon steel pattern as originally used in the smaller engines being used for the forward lengths. All these shafts are oil-toughened, and the pins are trued by hand and lapped after turning.

The exhaust main is not shown on the drawing, but it consists of a pair of water-jacketed headers, one for each six cylinders, built up in lengths with independent outlets to atmosphere. The Admiralty engines are fitted with cast-iron mains, but for ordinary purposes welded sheet steel has proved quite satisfactory. The order of firing of cylinders is 1, 7, 3, 9, 2, 8, 6, 12, 4, 10, 5, 11, and deflecting diaphragms are fitted in the mains to prevent interference between the cylinder exhausts.

The flywheel is of cast-iron fitted with teeth on the outside to engage with a three horsepower electric or hand-turning gear of Vickers' patent, specially designed for instant operation, and to meet the limited space available. The center eye of the wheel is separate from the rim to which it is bolted by a series of bolts shown in Fig. 3, and it is divided along its diameter to facilitate machinery overhaul in the boat.

The 12-cylinder engine illustrated is of the latest class, in which the unit system of fuel pumps originally favored by the submarine service is fitted. In this the inlet and exhaust valve cams are fitted on a shaft running in ring-oiled bearings, at about the middle height of the engine. The lower end of each of the long push rods carries the case-hardened steel roller, and on either side of it is a guide block sliding upon specially prepared guides in the cam casing. A loosely fitted cover surrounds the push rod, and excludes dirt from the casing. A lead from the bearing oil supply is led to each cam roller and guide, the oil entering at the back and squirting into the hollow interior of the roller block, as shown in Fig. 2. The cam casings drain back to the crank-case, the only oil remaining in them being

that in the small troughs under each cam into which the latter dip. The cams are wide, and are made of case-hardened steel pressed to a hollow section. The cam-cases-which were originally of aluminum alloy, but owing to other demands for that material have during recent years been made in cast iron-are bolted to the camshaft brackets, and are provided with a footstep to facilitate access to the top gear. The lower camshaft is driven by spur gearing in the middle bay of the engine, while the upper camshaft receives its motion through a bevel-driven vertical shaft visible in the middle of Fig. 1. The timing gear on the vertical shaft is also shown on this illustration. On rotating the horizontal wheel it is moved vertically upon the thread shown, and thereby advances or retards the upper shaft relative to the crankshaft owing to the upper bevel wheel being driven through a number of spiral keys on a coupling moved vertically by the hand wheel and sliding on straight keys on the vertical shaft. As the upper shaft carries the fuel admission cams, this effect is analogous to that of moving the “spark" in a petrol engine. It is a refinement not usually applied to Diesel engines, but intelligently used it enables the best setting for any condition of working to be obtained.

For ordinary running the spray valve, when at full power, is due to be opened at about 16 degrees, measured on the crankshaft, before the top dead center of its piston, and the controls, which will be presently described, have been re-designed so that as the duration of the spray valve opening is reduced for lower powers; the point of injection is simultaneously adjusted to that suitable for ordinary surface conditions. With these conditions it is unnecessary to adjust the timing gear when varying the power, but in the event of a heavy "charge" being put upon the main motors of the boat, thus considerably increasing the load on the engine, it is possible to retard the injection a few degrees or with a light condition of the boat or a following wind the timing may be advanced slightly. Adjustments of fuel valve settings to suit variations of fuel are also very conveniently carried out in similar manner.

Messrs. Vickers have carried out extensive trials in various conditions to investigate the effect of the timing gear and the result is to show that within the limits of practical working the brake horsepower and maximum cylinder pressure are both increased by advancing the injection, the curve of increase on a base representing the angle of injection being a straight line. Indicator cards varying in character from the flat-topped card representative of the normal air injection engine to the sharplypeaked card of the explosion engine, can be obtained at will, and the whole forms a most interesting study. In ordinary trials the firm limits the maximum pressure to a more reasonable figure, but on occasions on service where extra speed has been required the engines have been run with timing gear adjusted to give cylinder pressures of 700 pounds per square inch and over without any ill-effect. The control of the spray valves is effected by the left-hand vertical hand wheel seen in Fig. 1. This, by gearing, partially rotates the spray valve control shaft, the lowest of the three shafts running along the top of the engine. At each cylinder this shaft has a notched lever keyed to it. Alongside this lever is a similar lever with a spring clutch handle, the second lever being fixed to a short sleeve riding on the spray valve control shaft. When this sleeve is rotated by the handle the eccentric fulcrum mounting of the spray valve lever is partially turned by means of the two levers and the connecting rod, plainly seen in Fig. 2. The eccentricity of this mounting and the link proportions are so designed that a close approximation to the required point of fuel admission to suit any reduced duration of admission is obtained. Ordinarily the clutch handles are pushed forward to engage with the levers on the control shaft, in which case all spray

valves are controlled by the hand wheel, and over a wide range of power a movement of this wheel is all that is required to regulate the power. Should it be desired to cut out any cylinder the handle is drawn down, disengaging the sleeve lever from the one alongside it, and on bringing the handle forward to a notch in the fixed quadrant, as shown dotted in Fig. 2, the spray valve is put out of operation, a small cam on the sleeve lifting the suction valve of the fuel pump and putting it also out of action as the spray valve ceases to operate.

The whole is particularly simple, though the repetition of the units for each cylinder gives a first impression of complication, but it is plain that experience was necessary to enable the required somewhat complicated co-relation of functions of timing and duration to be obtained by such an elementary form of apparatus.

The fuel pumps at each cylinder are eccentric operated and consist of bronze castings supported in a steel casting secured to the cylinder cover. This casting carries the upper camshaft bearing, on the cap of which is mounted a separate small bearing in which the top-most shaft slides. This shaft is actuated by the right-hand wheel in the center of the engine, and by means of a downwardly-projecting stirrup slides a spiral scroll cam at each pump to the position required for the correct fuel output. This output is varied as the cam does not allow the suction valve of the pump to close till the desired point in the downward stroke of the latter. The high-pressure pump is marked on No. 12 cylinder in Fig. 1, and the spring returning the tappet for the suction valve can be detected in the drawing. The bore of the pump is 1⁄2 inch and its stroke 1 inch, special soft packing being used in the gland. Ordinary webbed cone-seated valves are usually fitted, but ball valves have been found equally efficient, and are now finding favor in the service. The whole of the bracket, pump and details have been redesigned in Vickers' later models with advantages as regards ease of manufacture, weight and efficiency, but in so doing, interchangeability has been maintained to a considerable degree of detail.

The fuel from the pump passes through the pipe shown on the right of it to a strainer, and thence into an accumulator tube shown vertically just to the left of the right-hand column on No. 12 cylinder. It then passes to the spray valve. The strainer at one time consisted of a plate with fine holes drilled in it, but the later type, which is much cheaper and affords greater filtering area, consists of a series of perforated discs, each with a shallow circular projection on one face close to the edge. This projecting annulus is knurled, and a number of these discs strung on a central bolt form a cartridge with circumferential rows of tiny triangular holes on its surface, through which the fuel passes to the center and thence through the end plate to the outlet pipe. A vent valve is fitted to the spray valve body, this valve, for convenience, being fitted on the head of the pulsator, which casting also forms the strainer body. The pulsator is a slightly flattened steel tube, and its function is to receive the fuel charge from the pump, when this is supplying only its own cylinder, pending the opening of the spray valve. A pressure gage is mounted on the discharge pipe so that the pumping plant for each cylinder is complete in itself, as originally specified. At the bottom of the pulsator a valve is now fitted, and through this valve each pulsator can be connected to a main, originally fitted for priming purposes. The common practice is now to run with the pulsators coupled to this main, in which case the pumps are, of course, not measuring the fuel to each cylinder, the spray valves performing this function. This is opposed to the ordinary idea, but consideration will show that the valve is more likely to be accurate than the pump. The system thus run becomes a pressure