Engineering Abstracts 1949

Engineering Abstracts from 1949

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

In this paper the subject of "engine wear” has been limited to

Volume XVII, No. 6, June 1954

Large Nine-cylinder Diesel Engine

A nine-cylinder engine designed to develop 11,200 b.h.p. at 115 r.p.m. under normal conditions at sea has recendy been completed by Burmeister and Wain. It has cylinders 740 mm. in diameter with a piston stroke of 1,600 mm., and is to be installed in a tanker under construction at the Nakskov Skibsvaerft for A.P. Moller, Copenhagen. It is the highest-powered marine engine constructed by Burmeister and Wain.

The new engine is equipped with three turbochargers of the Brown-Boveri VTR-630 type, these blowers being similar to those employed in the main engines of A. P. Moller’s M.S. Dorthe Maersk and the Songkhla, Samoa and Sibonga of the East Asiatic Co. The output of the 11,200 b.h.p. engine is slightly higher than that of a corresponding 12-cylinder non-turbo-charged unit, which is about 10 feet 10 inches longer and 35 per cent heavier than the nine-cylinder turbo-charged engine. Ten nine-cylinder engines of this type are being built by Burmeister and Wain and one with 10 cylinders, for a cargo ship, at Eriksbergs Mek. Verk. developing 12,500 b.h.p. In Japan an engine has been installed in the recently completed Hanmasan Maru, a cargo ship of 10,200 tons with a service speed of 17} knots. The fuel consumption of these engines, based upon the results of similar but smaller units installed in ships now in service is expected to be 0 3341b. per b.h.p. hr., the mechanical efficiency being about 88 per cent. In normal service the mean indicated pressure is approximately 1021b. per sq. in.

—The Motor Ship, March 1954; Vol. 34, p. 518.

Cas Turbine Progress

Marine auxiliary and industrial gas turbines ranging in power from 140 to 900 kW are being developed at Bedford by W. H. Allen, Sons and Co., Ltd. Of the four basic designs involved, the smallest is an all-radial-flow single-shaft unit with a rating of 200 b.h.p. (140 kW) at an air inlet temperature of 60 deg. F. (15 deg. C .); the prototype is now undergoing extensive testing and development. Designed originally at the request of the Admiralty, this small engine is intended for any duty where low fuel consumption is of less importance than such advantages as light weight, compactness, quick starting, rapid acceptance of load, and absence of cooling water. An ingenious feature is the use of a one-piece turbo-compressor rotor, with the centrifugal impeller vanes machined from one face of a forged steel disc and the centripetal turbine vanes from the other. By thus taking the familiar back-to-back arrangement of radial-flow components to its logical conclusion, the opportunity is presented of cooling the turbine by direct heat transfer across the rotor disc. The Allen designers have applied this principle so successfully that the ferritic steel disc of the prototype engine shows every sign of lasting for many thousands of running hours despite the use of inlet gas temperatures up to 800 deg. C. (1,470 deg. F.). A larger gas turbine of familiar type to the 200-b.h.p. unit has been designed, and manufacture will commence shortly. Six d.c. generator-driving versions of it have been ordered by the Alfred H olt shipping concern for auxiliary use aboard Blue Funnel liners, the rating being 350 kW at an air inlet temperature of 85 deg. F. (30 deg. C.). These sets are too large to make efficient use of a radial-flow turbine, so the single-stage centrifugal impeller is driven in each case by a two-stage axial turbine. On behalf of the Admiralty, the company is designing and constructing two interesting gas-turbo-alternators rated at 500 kW in tropical conditions. No details have yet been released for publication.

—The Oil Engine and Gas Turbine, March 1954; Vol. 21, p. 436.

Centripetal Turbine tor High Specific Outputs

In 1939 the U.S. Navy Department requested bids on

two 2,500-h.p. propulsion turbines for the Navy submarine

chaser PC-452. The author’s Company was awarded the

contract on the basis of the evaluation made by the U.S. Navy

Department, which took into consideration the weight of the

turbines, their overall dimensions, and their efficiency. The

Company’s design study resulted in the choice of a compound

turbine arrangement—this is, a high-pressure and a separate

low-pressure turbine for each of the two propelling units.

It also indicated that it was necessary to operate these turbines

at no less than 15,000 r.p.m. if the design target (with regard

to bulk, weight, and efficiency) was to be met. This high speed

ruled out the axial-flow wheel for the last stage of the low-

pressure turbine, because this type is incapable of passing the

large volume flows at such high r.p.m., without prohibitively

low efficiency. The high-specific-speed centripetal turbine

came to the rescue, and was used not only in the last stage

but also in the next-to-last stage of the low-pressure turbine,

a sectional view of which is shown in Fig. 10. This particular

application of the high-specific-speed centripetal turbine made

possible the attainment of a specific weight, for the complete

unit, of only slightly over 31b.-per-shaft horsepower, including

the double reduction gear, turning gear, and other accessories.

This specific weight is by far the lowest that has ever been

achieved for a marine propelling steam turbine. The units

fully met the efficiency guarantees, and their small dimensions made it possible to accommodate them easily in the confined

space of the slender hull. Several different sizes of turbosuperchargers

for Diesel engines have been constructed in the

past four years by the author’s Company. In the course of

the development of these units it has been clearly demonstrated

that the high-specific-speed centripetal turbine wheel is the ideal

answer for this application for the following reasons: 1. This

turbine is capable of an r.p.m. sufficiently high to bring the

compressor driven by it into a specific speed range where

maximum compressor efficiency can be obtained. An axial-

flow turbine designed for the same flow and stress conditions

would have to operate at lower r.p.m., which would result in a

correspondingly lower specific speed of the compressor, thus

preventing the attainment of maximum possible compressor

efficiency. 2. Under the particular flow and operating conditions

encountered in the service of exhaust turbines for Diesel

engines, distinctly higher turbine efficiency can be obtained

with the centripetal turbine than is possible with the axial-flow

type. 3. The efficiency of the centripetal turbine, which in

itself is high, can be further increased by the recovery of kinetic

energy in the turbine exhaust through the use of an exhaust

diffuser in the form of a simple conical duct. 4. The centripetal

turbine, owing to its low number of husky blades, is far less

delicate than the axial-flow wheel and better able to cope with

the severe service of Diesel-engine exhaust gas operation. In

addition thereto, it is cheaper to manufacture. 5. The turbine

blades and turbine rotor hub can be cooled in a simple manner,

similar to the one described for the aircraft exhaust gas turbines.

This reduces the metal temperatures even under the extreme

conditions of Diesel-engine preturbine temperature encountered

during engine overload conditions, to values which permit

designing for virtually unlimited time to rupture. 6. The

inertia of the centripetal wheel is lower than that of an equivalent

axial-flow wheel, which results in a more rapid change of

turbo-supercharger speed with a change in engine load. 7. The

stationary turbine nozzles, directing the flow into the centripetal

wheel, can be arranged between parallel radial walls,

which makes it practicable to provide for pivoting the guide

vanes to adjust the nozzle areas and angles for matching the

turbo-supercharger to the engine.

—R. Birmunn, Transactions of the A.S.M.E., February 1954; Vol. 76, pp. 173-187.

Motorships for South America

Canadian Vickers, Ltd., of Montreal is again delivering ships to The Flota Mercante Grancolombiana. First two of a series of four additional motorships, the Ciudad de Valencia and Ciudad de Cali, have been in service several months. The other two vessels, the Ciudad de Ibague and Ciudad de Cumana will be delivered in the forthcoming months. In accord with their building programme, Flota Mercante Grancolombiana, S.A., placed orders with Canadian Vickers, Ltd. for the construction of these four new vessels to augment their very fast cargo carrying service between the major ports of Venezuela, Colombia, Ecuador, New Orleans, New York and Montreal. Each ship is propelled by a single Nordberg six-cylinder Diesel engine, rated 4,275 b.h.p. at 160 r.p.m., direct connected to

the propeller shaft. The engine has a 29in. bore by a 40in. stroke and is of the two-cycle, single-acting type with port scavenging and port exhaust. The propulsion Diesel is independently scavenged by two motor-driven blowers each of 200 h.p. rating, taking air from the engine room through a Maxim silencer and each discharging 10,000 cfm. at about 2 -41b. per sq. in. discharge pressure to a common intake manifold. This method of obtaining scavenge air results in a shorter engine, and in case of failure of one of the blowers, the engine is still capable of maintaining 70 per cent ship speed with the remaining blower. The main engine control platform is at the after end of the engine on the port side and the log desk, engine telegraph, instrument panel, alarm panel, telephone booth are all disposed conveniently around the operator and are actuated by automatic controls. They have an actual air delivery of 68 cfm. at 870 r.p.m. and are of the two-stage type, water cooled and fitted with inter and after cooler. Auxiliary power on each of the vessels is supplied by three Nordberg four-cycle, eight-cylinder inter-cooled-super-charged Diesel engines. These engines are of the single-acting, trunk piston, mechanical injection type with cylinders of 9in. bore and ll^in . stroke rated 580 h.p. at 600 r.p.m. Each drives a 400 kW. 120/240 volt, 3 phase Westinghouse generator arranged for parallel operation and capable of carrying a 25 per cent out of balance current.

—D. Shearing, Diesel Progress, December 1953; Vol. 19, pp. 42-43.

Diesel-electric Tanker

The accompanying illustration shows one of the two Diesel-electric propelling motors of 1,750 h.p. at 128 r.p.m. in the 9,300-tons Soviet tanker General Asi Aslanow. The motors are supplied with direct current at 700 volts from four 700 kW. D.C. generators, each driven by a supercharged six-cylinder four-stroke cycle Diesel engine at 900 b.h.p. at 720 r.p.m. Cylinder diameter is 308 mm. and stroke is 330 mm. The pistons are of light alloy and are not liquid cooled.

—S. Antonow, Schiffbautechnik, December 1953; Vol. 3, pp. 359-362.

Cas Turbined Coaster

The first merchant vessel to be equipped with propelling

machinery consisting of gas turbines fed by free-piston gas

generators has recently completed her sea trials. This coaster,

the Cantenac, is one of two vessels of the same type ordered

by the French M inistry of M erchant Marine on behalf of

Worms & Cie., from the Chantiers et Ateliers Augustin

Norm and at Le Havre, as war loss replacement. The Cantenac

is a vessel of 850 tons with three holds and has her propelling

machinery arranged aft. She is 185 feet in length b.p.,

30 feet 6 inches moulded breadth, 14 feet 5 inches moulded

depth to main deck, and has a mean draught of 13 feet 6 inches.

The propelling machinery consists of two Pescara-SIGMA type

GS-34 free-piston gas generators; two gas turbines connected

to a reduction gear, each fed by one gas generator; and a

double reduction gear connecting the turbines to a single shaft

and reducing the number of revolutions to 220 r.p.m. The

complete design of this vessel, both hull and engines, has been

carried out by the shipbuilders. Saving in Weight. The free-

piston gas generator operates on the two-stroke cycle and consists

of a horizontal cylinder with two opposed pistons, each of

which is directly connected to a compressor piston. The outer

part of the compressor cylinder constitutes a compensating

cushion. The mixture of exhaust gas and scavenge air forms

the gas which is used to drive the turbine. A comparison of

the weight of a gas generator installation compared with that

of a corresponding Diesel installation is in favour of the

former scheme. A typical four-stroke Diesel engine, developing

1,800 h.p. at 220 r.p.m., and with 40 per cent supercharge,,

weighs about 1261b. per h.p., whereas a gas generator installation

consisting of two GS-34 generators, one turbine and reducion

gear of the same power and speed, is about 891b. per h.p.

The saving in weight and bulk is only one advantage. There is

also flexibility of operation, avoidance of vibration, ease of

maintenance and low starting air consumption. It is claimed

that in all probability the free-piston gas generator unit will

become the engine with the highest thermal efficiency, with a

specific fuel consumption referred to the turbine shaft of less

than 0-331b. per s.h.p. per hr. At the moment it is in the

region of 0 391b. per s.h.p. per hr., a figure not far different

from the consumption of 0-331b. per b.h.p. per hr. obtained

from a supercharged two-stroke Diesel engine. Trials were

run on 19th January on fuel No. 1, which corresponds to a

Redwood viscosity of about 950 secs, at 100 deg. F. The unit

is designed to run on both distillator and light residual fuel.

The engine was run with two gas generators developing

1,200 h.p. on one trial and with one only developing 700 h.p.

on another. It is understood that the tests were highly satisfactory

and it was found possible to establish, in particular, the

ease and speed of manoeuvrability of the propelling machinery,

as well as the ease with which one fuel was substituted for

another.

—The Shipping World, 17th February 1954; Vol. 130, p. 213.

Free Piston Cas Generators

The Baldwin-Lima-Hamilton free piston generator development was conducted under a (U.S.) Navy Department contract to obtain a unit suitable for naval-combatant requirements. Consequently, it was designed with a view toward high specific output, reasonably low weight, and compactness, and to provide high thermal efficiency and reliability. In other words, to fulfil its purpose, it had to compete favourably with the thermal efficiency of modern Diesel engines and give the added advantages of simplicity, low initial cost, and smooth vibrationless

operation. 'I'he power plant constructed was a twin unit with

two gas generators supplying gas to a single turbine and reduction

gear. It is outward-compression with both direct-bounce

and reverse-bounce cylinders for control. The two gas generators

are synchronized to reduce pulsations of the gas to the

turbine and they can be operated together or singly, as the load

requirements necessitate. The principal specifications are given

as follows: —-

Table 2.—B-L-H Model B Gas Generator Specifications

Power-cylinder bore, inches ... ... 8 1/4

Compressor-cylinder bore, inches ... 23

Direct-bounce-cylinder bore, inches ... 8 1/4

Reverse-bounce-cylinder bore, inches... 23

Piston stroke (full load), inches ... 11

Cyclic frequency (maximum), cycles per min. ... ... ... ... 1,035

Exhaust pressure to turbine, lb. per sq. in. gauge ... ... ... ... 90

Exhaust temperature to turbine, deg. F. 1,295

Gas horsepower (maximum) ... ... 885

The complete power plant, after completion of its acceptance trials at the builders’ plant, was sent to the U.S. Naval Engineering

Experiment Station at Annapolis, Md., in 1950, for further test and evaluation. The principal data obtained during 700 hours of test operation are presented. Fig. 11 shows the gas-generator output, based on adiabatic expansion of the gas. The output pressure to the turbine was carried to 901b. per sq. in. gauge as contrasted with 501b. per sq. in. gauge for the French SIGM A Model GS-34. Of course, the relation of horsepower output to exhaust pressure is mainly a function of the size and characteristics of the turbine used in these tests. The curve shows outputs up to 1,770 gas-horsepower with the 901b. per sq. in. gauge maximum pressure to the turbine. On later accelerated tests to determine piston-ring and cylinder-liner suitability, where more severe operating conditions were imposed without a turbine, the same output was reached with only 701b. per sq. in. gauge exhaust pressure and the same exhaust temperature. This was a result of increasing the effective orifice area because the turbine used has a smaller equivalent orifice. The gas-horsepower curve in Fig. 11 shows that the output is increasing without any decrease in rate up to the limiting exhaust temperature and pressure set by this particular design. The shaft-horsepower curve in Fig. 11 is based on the desired 85 per cent efficiency for turbine and reduction gear, as it was in the SIGMA data. T hat efficiency

was not reached with the turbine used on the actual tests. However, turbines are available with peak efficiency of 85 per cent or higher. The shaft-horsepower curve is corrected for the power requirement of the auxiliary equipment which cannot be driven directly from the turbine. Thus about 1,420 s.h.p. is available from an installation with a weight and space no greater than that of current Diesel installations and less than that of other types of power plants having comparable thermal efficiency. The model now under development at B-L-H is much smaller and lighter. Fig. 12 shows the measured fuel consumption on a gas-horsepower basis and those calculated for a possible turbine efficiency of 85 per cent. The maximum thermal efficiency of 40 3 per cent at the gasifier discharge is very satisfactory and compares favourably with the SIGMA maximum of 3 8 2 per cent. This increase in thermal efficiency

is to be expected in view of higher operating conditions. The correction to a shaft-horsepower basis shows a greater reduction than was made for the SIGM A design because exact information was available on the B-L-H power plant and deduction was made for all losses, including supply of auxiliary control air, cooling-water pumping, and similar power expenditures.

The only deduction made for the SIGM A unit was based on turbine efficiency of 85 per cent. It is not known if the previously published data include corrections for power to auxiliary equipment. After making these corrections to a minimum shaft-horsepower basis, the thermal efficiency is still 32’3 per cent. The turbine was rated at a maximum inlet temperature of 1,350 deg. F. However, the peak pressure of 901b. per sq. in. gauge was reached with less than 1,300 deg. F. As stated before, without the turbine and with a variation in the gas pressure-to-orifice relationship, the same temperature gave as much load with only 701b. per sq. in. gauge exhaust-gas pressure.

—J. J. McMullen and W. G. Payne, Transactions of the A.S.M.E., January 1954; Vol. 76, pp. 1-14.