Engineering Abstracts 1969
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Engineering Abstracts from 1969
Fuel Pump
Bryce Berger Ltd. have introduced the F-size fuel injection pump, which has a plunger stroke of 50 mm and which can be fitted with plunger barrels of from 36 to 50 mm bore giving a maximum output of 32 cm1 per stroke. It is designed
to operate at injection pressures in excess of 1100 kg/cm2 (15 500 lb/in2) and is suitable for engines with running speeds of 400 rev/min and over. The pump body is in two parts and these are tied, together with the heavy collar securing the delivery valve head, by four long through-studs which transfer the pumping stresses to the lower part of the housing. This construction has an additional benefit in that it is possible to provide a number of alternative configurations for the fuel inlet and control rod positions. Patented features in the plunger design are available to ensure complete control of the pumping rates at the end of injection. Forced lubrication is applied to the plunger and the tappet block, both of which are located by keys. The robust cam-follower tappet assembly is fitted with a roller which, although wide enough to remain conservatively stressed, can incorporate large edge radii for use on direct-reversing engines. This pump is suitable for the new generation of medium-speed engines now coming forward with outputs of 1000 bhp per cylinder and upwards.
—Marine Engineer and Naval Architect, May 1969, Vol. 92, p. 206.
U.S. Designed and Manufactured Diesel Engine
The purpose of this paper is to present an American designed and manufactured Diesel engine, suitable for marine propulsion. The engine described is the Model 38A20 opposed-piston engine, as produced by Fairbanks Morse Power Systems Division of Colt Industries. The 38A20 Diesel engine is a two-cycle, uniflow scavenged, opposed-piston engine with cylinders in line or a 45° vee. It has been designed with six and nine cylinders in line or 12 and 18 cylinders in vee, all rated at 1250 hp per cylinder. For marine propulsion, the engine may be direct reversing.
The cylinder block and lower base are mild steel weldments with low stress levels. A series of transverse bulkheads carry the stress between the upper and lower portions of the cylinder block. Power is transmitted to the shaft through a cast-iron cocktail shaker, oil-cooled piston, and a nodular-iron connecting rod. The large lower piston controls the air inlet parts while the small upper piston controls the exhaust parts. Since the valving action of the upper piston develops 15 per cent of the rated power, it is connected to the engine output by a rocker arm, rods, upper crankshaft, and vertical gear train.
The crankshafts are high-strength, nodular-iron castings with large corings in the mains and pins to reduce weight. Successful operations on heavy-oil fuel have been achieved on cast-iron liners with an untimed cylinder lubricating oil system. The success is attributed largely to the low metal temperatures in the engine. As marine Diesel engines must operate on the fuels available in the area in which the vessel is scheduled, the 38A20 engine has been operating on a heavy fuel which has a wide range of chemical and physical characteristics. For the purpose of this study, 3500 sec. Redwood 1 at 100°F has been used. Maintenance schedules for the engine were laid out on this premise. With proper design considerations, a 400 to 450 rev/min trunk-type, two-cycle engine without valves can operate on residual fuels successfully. As in other engines, the piston ring and ring groove wear will be slightly more rapid than on light oil. Increased maintenance on the fuel injectors may be required, depending on the fuel filtering and treatment system employed. Manoeuvrability on heavy fuel is not a problem if adequate heating of the fuel system is provided. The figure is proposed layout for twin-pinion, 18-cylinder 38A20 engines used to develop 45 000 bhp in a twin-screw ship.
—Schumacher, G. F., Maritime Reporter/Engineering News, February 15th 1969, Vol. 31, p. 14.
Maintenance of M.A.N. 52/55 Engine
It is now being shown that medium-speed engines burning residual fuel can operate for considerably longer periods between cylinder overhaul—several instances are known of 15 000-20 000 hours before cylinders have been opened up and this, coupled with the advantages of being able to drive electric generators, cargo and service pumps from either the forward end of the engines or from the gear-boxes, has contributed considerably to the growing confidence in medium- speed, geared installations.
The newly developed M.A.N. type 52/55 engine, despite having a greater number of cylinders than a slow-speed installation of equivalent power, affords genuine advantages, particularly so when it is realized that this is an engine of 1000 bhp per cylinder designed with maintenance considerations in mind. The advantages of driving generators or other auxiliary units through couplings off the engines or gear-boxes apply not only to operation at sea but also in harbour to provide sufficient electrical power for such items as cargo handling gear. Under certain conditions, such operation is also possible on heavy oil. For daily electrical power requirements in harbour, apart from when handling cargo, a single Diesel generating set is often sufficient. In view of the shorter periods during which this set is employed, it may therefore be satisfactory to use a high-speed unit of low initial and installation costs. Thus not only may costs be cut but maintenance work is also reduced.
Owing to the considerable increase in cylinder output of the new 52/55 engine and the reduced number of auxiliary engines required, the total number of cylinders of an installation can be reduced considerably. As a comparison between slow-speed engine installations and medium-speed plants incorporating VV40/54 engines the diagram given shows clearly the marked reduction in the total number of cylinders in the case of a layout incorporating VV52/55 engines. All three installations have approximately the same rating. Layout A shows a main engine directly coupled to a propeller with three conventional auxiliary Diesels of type G7V23, 5/33A. In this case there is a total of 27 cylinders.
Layout C shows that, with the present medium-speed engines developing 500-600 bhp per cylinder, the total number of cylinders (in this case 32) is still high and that consequently the maintenance involved is somewhat considerable.
Comparison of three propulsion and generating plants with approximately the same output showing how the total number of cylinders is reduced in scheme B by the use of a V6V 52/55 main engine and one Diesel-driven generator set— The figures on the graph represent the total number of cylinders per layout (top) and the number of main engine cylinders (bottom) In layout B, a V6V52/55 main engine with geared generator and a high-speed R8V22/30ATL auxiliary engine, giving an aggregate of 20 cylinders, the lowest total of three solutions, with correspondingly reduced maintenance work.
—Heilman, H„ The Motor Ship, May 1969, Vol. 50, “Special Survey", pp. 36^14.
Large-bore Two Stroke Dual-fuel Engines
Broadly speaking, there are two main fields of application for large-bore dual-fuel engines: (a) methane tankers, and (b) power generation. So far, and in the absence of a suitable internal combustion engine, methane tankers have been powered by steam turbines using boilers with mixed burners. Taking such a typical case as, for instance, Methane Princess with a loading capacity of 12 700 tons of gas, an operating speed of 17 knots and a total shaft horsepower of 12 500, it can easily be figured out that, besides the gas flow obtained from natural evaporation, which usually amounts to 0'3 per cent per day, about 80 per cent as much liquid fuel must be added, if we consider the thermal efficiency of the steam plant to be 25 per cent. Replacing the steam turbine by a dual-fuel engine with a total fuel consumption of 1635 kcal/bhph would mean that as little as 8 per cent of pilot fuel is required in order to provide the same output as the steam plant. Or in other words, only a negligible fraction of the total fuel must be bought, the rest being provided, so to say, free of charge. Consequently, it does not even pay to use heavy fuel oil for that purpose. Further savings are realized by the fact that only about 10 per cent of the bunkering space for the fuel oil needed in the case of the steam plant has to be provided, and that no heating and purifying equipment for fuel-processing is required. This comparison illustrates, plain enough, the enormous savings which could be achieved by replacing the steam plant with a dual-fuel engine. If future ships will be of larger tonnage, which is likely, the ratio of propulsive power to ship capacity will be reduced, provided the speed remains around 17 to 18 knots. In this case the evaporation rate required by the propulsion engine may fall as low as 0'2 per cent per day which would mean that the rest of the gas evaporated would be lost. However, it seems obvious enough and the known trends indicate that for such an expensive ship as a methane carrier, a higher speed might well prove to be more economical. This then would quickly put up the figure for the gas requirements to 0‘3 per cent per day and over as mentioned before. This goes to show that even for future methane carriers the dual-fuel engine will again be able to provide the most economical means of propulsion. A more severe problem may be presented if these carriers are to be super-tankers, requiring propulsive power above 25 000 bhp, an output which may still be provided by a Sulzer 12 RND 90 dual-fuel engine. If this case should actually materialize (up to the present the largest methane carriers require an output of 20 000 bhp) twin-screw propulsion would be the answer.
—Shipping World and Shipbuilder, August 1969, Vol. 162, pp. 1148-1150.
Research Methods for the Experimental Study of the Scavenging of Two-stroke Large Bore Diesel Engines
A description is given of the experimental equipment used and the test procedures employed at the FIAT Gas Dynamics Centre, for the study of the scavenging in two-stroke Diesel engines. The fluid-dynamic testing is based on both the static and the dynamic methods. The results obtained on the test rigs are compared with the performance of actual engines.
—Oggero, M., FIAT Technical Bulletin, 1968, Vol. 21, No. 3, pp. 86-92.
Research on Scavenging of Two-stroke Large Bore Engines
The author describes the results of recent research carried out by FIAT on the scavenging of two-stroke large bore engines. A report is also given of the results obtained both through laboratory tests at the FIAT Gas Dynamics Centre, and on the full size engines by means of which it is possible to follow the evolution of the FIAT scavenging system.
—Ciliberto, G„ FIAT Technical Bulletin, 1968, Vol. 21, No. 3, pp. 61-85.