Engineering Abstracts 1949

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Engineering Abstracts from 1949

Modern Trends in the Development of High-Powered Diesel Machinery

CARSTENSEN, H. Trans. Institute of Naval Architects, paper read 2 Sept. 1949.

Typical examples are given of high-powered marine Diesel plants of more than 16,000 b.h.p. built between 1926 and 1939. Of these, the double-acting four-stroke engine has been abandoned, and the single-acting four-stroke engine is now used very little for larger ships, though it may be preferred under particularly difficult service conditions because of its simple and robust design, moreover, tests with high-pressure supercharge have shown that its output can be increased considerably. The remaining engine types mentioned are two-stroke engines, single-acting or double-acting, having either loop scavenging or uniflow scavenging. These two-stroke engine types and the four-stroke single-acting engine have been developed into fast-running units whereby any output desired can be furnished by geared or Diesel-electric plants.

In passenger ships the arrangement of the accommodation will determine whether steam-turbine plants, fast-running Diesel engines with geared or electric transmission, or slow-running Diesel engines coupled directly to the propeller shafts will be most advantageous. The Diesel plants, particularly the direct-coupled plants, appear to be the most economical. For cargo vessels and tankers, direct-coupled Diesel plants give the greatest advantages and economies. The possibilities of higher outputs and improved economy are discussed, and the effect of the use of heavy fuel oil in Diesel engines on the relative merits of the plants is considered briefly. Some two-stroke engines of the single-acting crosshead and the double-acting types with uniflow scavenging, and examples of high-powered marine Diesel plants with these engine types for a tanker, an intermediate cargo and passenger ship, and a passenger liner are described and illustrated.

Volume XII, No. 5, June 1949

Crankshaft Damping

The author attempts to give a correct physical explanation of natural damping by torsional vibrations, and also to obtain approximate formulae for pre-calculation of the damping in any given case. The paper describes experimental work with a single-cylinder engine driven by external power, and excited to torsional vibrations by a spring- loaded cam disk. In this way the damping from the moving parts could be investigated separately, and it was found that the damping was almost entirely due to hysteresis in the crankshaft, and oil damp­ ing, due to lateral shaft movements in the main and crankpin bearings, which was directly proportional to the bearing clearance. The paper also gives a simple and practical method for the calculation of damped vibrations in arbitrary elastic systems, and the calculation of hysteresis and bearing damping in a single-cylinder engine. Formulas are given for the total damping in multi-cylinder engines, with or without heavy flywheels, and the results are compared with the measured damping in a number of oil engines in service.

—Paper P. Draminsky, read

The Modag Two-Cycle Diesel Engine

(German). Harzsa, 86 (1949), p. 1011 (15 Oct.).

Small craft used to be propelled by two-stroke hot-bulb engines, which were gradually superseded by the crankcase two-cycle Diesel. In recent years a new type has been developed in Germany, the Modag-Krupp Diesel, which is at least as simple to handle and as robust as the former two types. It is an improvement on the crankcase two-cycle Diesel, its main new feature beingthe scavenging of the cylinders by means of a rotary blower. Moreover, the engine has solid fuel injection, so that the fuel consumption is low ; it is half that of the hot-bulb engines, and considerably less than that of normal engines

with crankcase and pre-combustion chamber. The Modag Diesel is at present built with one to five cylinders, and its main structural parts are the cast-iron bed plate, the cylinder block, and the cylinder heads. Cylinder liners and pistons are made of special cast iron. The use of pressure lubrication prevents overheating of the bearings even under occasional overload. Because of its simple, robust design, this engine rapidly became popular for small German craft like coasters and trawlers. The article tabulates the main dimensions of the five engine sizes now on the market, and a diagram shows fuel consumption, engine speed, and exhaust temperature as functions of the power.

Comprehensive Oil Engine Research.

Gas and Oil Power, 44 (1949), p. 339 (Nov.).

The work of the British Internal Combustion Engine Research Association is described, and details are given of research work in progress and test rigs which have been developed at their laboratories. Combustion-engine roughness and knock are being studied on a Crossley BWI-17 engine, which is also used to determine the effect of different types of fuel, especially those of lower ignition quality. Investigations of torsional-vibration damping are carried out on a six-cylinder four-stroke Klockner-Humboldt-Deutz engine developing 105 b.h.p. at 1,300 r.p.m., a seismic-type of torsional vibration pick-up being attached to the front end of the crankshaft. A Petter self-induction single-cylinder two-stroke engine is used to investigate stresses in a crankweb under conditions of deliberate vertical mis-alignment of an outer bearing, and a specially designed single-cylinder engine is used for determining the cetane rating of Diesel fuels. Investigations into the cause of crankcase explosions will be carried out on a General Motors 12-cylinder two-stroke engine, in which the original crankcase door will be replaced by a special type of safety door. A prototype bearing-testing machine has been developed for investigating the performance of bearings under the type of loading experienced in a Diesel engine big-end.

An important part of the work is the study of crankshaft stresses, and two resonant bending-fatigue machines have been developed for this purpose. A number of foreign engines have recently been examined. A Paxman three-cylinder RPH engine is used for general study of pressure-charging effects, and the performance of highly rated engines on low-grade fuels is tested on two engines representative of latest practice.

New Welded Frame Engine

Cross section og a 1949 Burmeister & Wain two-stroke engine

The accompanying cross-section shows the principal details of construction of the latest type of two-stroke welded frame engine built at Copenhagen by Messrs. Burmeister and Wain. The engine in the m.s. Topeka has seven cylinders with the standard measurement of 740 mm. bore and 1,400 mm. stroke, corresponding to approximately 29 inch and 55 inch respectively. The output is 6,400 i.h.p. at 105 r.p.m., and the mechanical efficiency is in the neighbourhood of 81 per cent, giving the engine a rating of 5,200 b.h.p. which corresponds to nearly 743 b.h.p. per cylinder. The mean indicated pressure at this rating is 92Ib. per sq. in. or 6°5 kg. per sq. cm. In the case of the welded design illustrated, the bedplate, frames and scavenging air receiver are fabricated. The weight of the engine is reduced by at least 15 per cent, although the reduction may reach 25 per cent compared with cast-iron construction, depending on the type. This engine has two camshafts and there are four guides for each crosshead, and in the case of the original four-stroke B. and W. double-acting design, By using fabricated steel plates in the construction, it becomes unnecessary to carry the through-bolts which take the combustion loads down to the bottom of the bedplate. In this instance the bolts are carried from the jackets to the top of the A-frames. The exhaust takes place through a spring-loaded poppet valve centrally arranged in the cylinder cover, and scavenging air is admitted through ports uncovered by the piston at the bottom of the stroke. The air is supplied by rotary blowers, and these are driven from the crankshaft by chains and resilient couplings. It may be noted that the cylinder covers and the piston crowns are of heatresisting steel, Fresh water is used for cooling the cylinder covers and liners, the pistons being cooled by means of lubricating oil.

There is a stuffing box with tightening rings for the air and scraper rings for the crank-chamber oil. This box is located between the scavenging-air reservoir and the crank chamber. The design allows complete separation of the lower part of the engine from the scavenging-air system, while a short piston can be utilized, with a corresponding reduction in the engine height. The length of the unit is limited by placing the scavenging-air blowers at the back and a change valve is employed for the air delivery when the direction of rotation of the crankshaft is reversed. The shop trial results showed a specific fuel consumption of 0:28lb. per ih.p. hour. Reference was made to this engine on p. 78 of Engineering Abstracts, but the design shown here represents the correct representation of the engine.

—The Motor Ship, Vol. 30, August 1949, p. 193.

Werkspoor Single-acting Two-stroke Engine

(1949) Werkspoor

In Fig. 2 is illustrated a single-acting crosshead engine with multiple exhaust valves (7) in the cylinder head. The valves are Investigation of Cavitation Phenomena by Tunnel Tests moved together by a lever (8) driven from a camshaft (9). The scavengine air chamber (3) is separated from the crank chamber by a partition (20), and the lover end (25) of the liner (5) is removable, so that the piston rings may be inspected and removed without dismantling the piston, Large removable doors (27, 28) enclose the scavenging air chamber, and the bottom part (25) of the liner is lowered until it rests on the partition (20), The engine has a short piston uncovering the scavenging air ports (12). The scavenging air pump (30) is driven by levers (31) from the crosshead and is located below the level of the partition, which has an outlet (32) for the discharge of air from the pump

—Brit, Pat, No. 616,893, issued to N.V. Werkspoor, Amsterdam. The Motor Ship, Vol. 30, September 1949, p. 244,

Controlled Injection in High Speed Diesels

(1949) Nozzle

In a paper read by Mr. Garton of the Shell Petroleum Co,, Ltd., in Stockholm some time ago, reference is made to the knock in high speed Diesel engines with fuels of low ignition quality. This is due to the fact that these fuels give rise to a relatively long ignition lag; hence a considerable amount of fuel has been injected into the cylinder by the time ignition starts, and it is the rapid, uncontrolled inflammation of this fuel which causes knock, One method of overcoming this difficulty, and permitting smooth operation with low cetane number fuels, is by arranging to inject only a small quantity of fuel during the earlier part of the injection period, and to increase the rate after ignition has occurred. In the Atlas system this is accomplished by the use of a two-stage cam in the fuel pump, and_a specially designed injection valve. A particular case of controlled injection is pilot injection, in which a small amount of fuel is injected before the main charge. It has already been mentioned that separate chamber engines are less sensitive to fuel ignition quality than open chamber types. The former are, however, somewhat more difficult to start at low temperatures. One method of overcoming this difficulty, without the use of heater plugs, is the Pintaux nozzle patented jointly by Messrs, C.A.V. and Messrs. Ricardo (Fig. 1) Recent experimental work has shown that the hottest zone of the separate chamber on starting is outside the normal spray path. The Pintaux nozzle is so designed that on starting (ie, at slow speeds) partial lifting of the needle valve permits a side spray of fuel into the hottest zone of the chamber (Fig. 2), thus facilitating starting. As the speed increases, the full lift of the needle valve results in most of the fuel spraying through the normal nozzle, though some delivery through the auxiliary nozzle acts as ilot charge, thus reducing combustion noise to some extent,

—The Motor Ship, Vol. 30, August 1949, p. 201.

A New 4,500 B.H.P. Engine

Successful tests have been carried out by Messrs. John G. Kincaid of the first two-stroke, single-acting, crosshead design of the eccentric-type, opposed-piston, propelling engine which is being installed in the motor vessel Braeside.

An illustrated description is given of the engine which has six cylinders 24.4 in. in diameter, the main piston stroke being 55.1 in and that of the exhaust pistons 18.5 in. Maximum continuous rating is 4,500 b.h.p. at 115 r.p.m., the mean indicated pressure being 92.4 lb/sq. in. The engine has ample width of bedplate when compared with the overall height. On account of the head-room available, the pistons and rods can be completely withdrawn vertically. The crankshaft is of the fully-built type, the webs being of cast steel.

Integrally cast with each crankweb is an eccentric for operating the exhaust-piston gear. Each pair of eccentrics is coupled by eccentric straps and rods and four steel side rods to the cast-steel yoke of the exhaust piston. The exhaust pistons are therefore driven by, and, in turn, transmit power through the eccentrics on the crankshaft.

The cylinders are of vanadium cast iron, cast in one piece, and are water-jacketed above the flanges by which they are bolted to the scavenge belt. The scavenge air has a clear blow-through, ensuring a fresh charge of air for each compression stroke. The scavenge air is supplied by two positive rotary blowers each driven by Renold triplex chains from the crankshaft. The fuel pumps are independent units operated by a camshaft driven by chain from the crankshaft. The main and exhaust pistons are oil-cooled and the engine is force-lubricated throughout.

The overhauling arrangements are very complete, and the gear supplied enables maintenance work in port to be cut down to a minimum. The engine runs smoothly and quietly.

Opposed Piston Diesel Engine

The first Fairbanks Morse opposed piston Diesel engines were built in 1934. The first engines built attracted the attention of the U.S. Navy, and approximately three million horsepower was installed in various types of Naval vessels. As currently constructed, the engine is built in 8£ inch bore and 10 inch stroke on each piston. The engine has been built in 5, 6, 7, 8, 9 and 10 cylinder assemblies, and the makers are now beginning on a 12 cylinder engine. The most common engine is the ten cylinder size, which the U.S. Navy rated up to 2,000 h.p. at 850 r.p.m. In commercial service engines of six cylinders are rated 960 h.p., eight cylinders 1,250 h.p., ten cylinders 1,600 h.p.

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