The columns are of cast iron, and span the main bearings. Vickers have made oil engines varying in design from the enclosed type, where the cylinders are supported on cast crank cases, to the open class sup ported on cast columns, turned pillars, or built-up boiler plate transverse frames. Of these the transverse frame has been found to give such accessibility to the engine that this type has been adopted for the commercial design, castings being used in this case in order to secure the exceptional rigidity so necessary for durability.
The guide is a single one, spanning the columns on the ahead side (generally inboard), the slipper and cross head details being in accordance with the best steam engine practice.
The cylinders consist of massive conical iron castings, spread at the lower extremity to form a continuous entablature to which the columns and stays are attached. The liner is dropped into the cylinder and held in place by the cylinder cover, being free to expand at the lower end.
The cover is an iron casting of the usual pattern, providing special allowance for difference of expansion. A novel arrangement is followed for thoroughly cooling the lower face and the top of the liner, and preventing deposits on parts subject to the higher temperature. Cleaning doors of ample dimensions are fitted to the water spaces.
Both inlet and exhaust valves are of special steel, the latter being water-cooled. The motion is developed from the designs followed by Vickers in their high duty reversing engines, and comprises very few parts.
The power reversing is applied as directly as possible, thus saving air and making the engine manageable at low air pre-x.ures. Hand gear is fitted for use in emergencies.
Forced lubrication is fitted throughout the principal bearings of the engine. The crank-case is totally enclosed, except for ventilation pipes, by readily portable casings, thus ensuring a clean engine room and preventing contamination of the lubricating oil by dirty oil from the pistons or by water from the glands of the piston cooling pipes.
The fuel injection pumps are in front of the engines, in view of the engineer, and acliver into a main from which the individual cylinders arc supplied through their spray or measuring valves. These valves can be con
trolled collectively by a hand lever, while in case of necessity an individual cylinder can be immediately cut out of action.
The air starting compressors will, in the larger installa tions, be separately driven, though in the smaller ships it mad• be preferred to drive pumps by means of a clutch from the engine shaft, thus following the lines of many shore installations of gas or large semi-Diesel engines.
A point of departure from other Diesels is in the adop tion of a fuel injection system in which the air com pressor is entirely eliminated. With this system consumptions by the hour down to 0-378 lbs. b.h.p. have been obtained.
In addition to these another variation has been invented, namely, that known as the Still engine, the chief feature of which is that it embodies the Diesel and the steam cycles, each reacting upon the other. This is effected by utilizing a considerable portion of the heat in the cooling water and exhaust gases, whereby the efficiency is increased by 20 per cent. The cylinder jacket forms part of a high-pressure steam circuit, a temperature of about F. being maintained by the heat from the exhaust gases. In addition to maintaining the temperature from these sources of heat, steam is also produced and utilized on the under side of the piston in a similar manner to that adopted in a reciprocating engine. The upper end of the cylinder is operated as a two-stroke Diesel engine. Connected with the steam circuit is a boiler in which steam is generated for starting the engine, and the circuit is effected by steam on the under side of the piston.
Owing to the high temperature of the cylinder walls, the outsides of which are jacketed with water at a tem perature of 350°, a compression pressure of about 280 lbs. the square inch is sufficient to cause ignition, instead of the usual compression pressure in Diesel engines of 450 lbs. the square inch. Moreover, greater horse-power can be obtained from a given size of cylinder and, if an increase of horse-power is demanded, it can be met by maintaining the boiler, fired with liquid fuel, in commission. The low consumption of 53 lbs. per b.h.p. per hour has been obtained with one of these engines.