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Aviation History
1956
1956 - 1630.PDF
790 / ;;••; •.:..,..:'..;' '"'-'-• '""-- -•"•'••••*• FLIGHT, 16 November 1956 CENTAURUS 373 Direct-injection Engines for the Beverley FOR nearly 40 years "Flight" has periodically published articles record-ing the progress of new Bristol reciprocating aero engines. What follows may, perhaps, be the lastS INCE the 1920s the engine division of the Bristol AeroplaneCompany (now Bristol Aero-Engines, Ltd.) have been steadily developing air-cooled radials incorporating a valvesystem using a single sleeve of the basic Burt-McCollum type. The last and greatest of these engines is the Centaurus, whichwas coming into production at the end of World War 2 with a rating of 2,000 to 2,200 h.p.Owing to the exigencies of the war, early production engines employed the American Bendix carburettor. However, all thepost-war series of engines used the Hobson/R.A.E. pattern, which meters the fuel according to the demands of the engine andinjects it through orifices in the intake manifold. This system is employed in all Centaurus engines currently in use. Neverthe-less, advantages can be gained by employing direct injection of fuel into the cylinder heads, and Bristol began to study a direct-injection Centaurus as long ago as 1945. Between that year and 1952 over 1,300 bench-hours were run at powers up to 3,400 b.h.p.on modified Centaurus 57s fitted for injection into the cylinders from nozzles in the induction pipes. Such an engine was first runin 1947 and a pair were flown in a Brigand test bed in 1949. By 1952 the D.P.I, (direct petrol-injection) Centaurus hadceased to be an active project, but events elsewhere were taking place which have now re-activated the programme. Thesedevelopments concerned the Blackburn Beverley heavy military transport. The original General Aircraft G.A.L. 60 design (forerunner ofthat aircraft) was based on four Bristol Hercules 261s driving propellers of 14ft diameter. By the time that Blackburn andGeneral Aircraft, Ltd., was established as a single firm in 1949 it was appreciated that the design could be greatly improved byemploying Centaurus engines and larger propellers. Unfor- tunately, money was tight at that time and development was ableto proceed only by using an engine very similar to the Centaurus 661 of the B.E.A. Elizabethan class. This necessitated somecompromise, but Blackburn and Bristol were able to evolve the Centaurus 160 series with a single-speed supercharger andmethanol/water injection to give a maximum take-off rating of 2,850 h.p. Centaurus 165s were fitted to the second prototype,although retention of the original wing prohibited any increase in propeller diameter. After flying for many months, the aircraftwas fitted with a completely new wing and re-spaced engines of the type now standard on the production Beverley. This per-mitted installation of the slightly modified Centaurus 173 driving de Havilland hollow-steel-blade propellers of 16ft 6in diameter,the largest used in Britain. Nevertheless, it could still be shown that the Beverley would befurther improved by even more powerful engines. Blackburn wanted to be sure that power would be available to keep pace withthe maximum possible development of the aircraft, and lengthy talks took place with a view to determining how further increasesin power could best be provided. In the early part of 1954 the Bristol Aeroplane Company put forward a proposal for twofurther stages of development of the basic Centaurus 173: a D.P.I. Centaurus rated at 3,150 b.h.p. and a Turbo Centaurus of3,600 b.h.p. After discussions with the Ministry of Supply it was decided to proceed with the first stage of this programme, and theD.P.I. Centaurus project accordingly became active once more. It was expected that the lengthy background of direct-injectionexperience already gained at Bristol would hasten development, and this has proved to be the case. The first Centaurus 373 wasrun on the test bed in July last year; considerable development time has now been recorded and flight trials are about to begin. During the first programme of D.P.I, development, fuel wassupplied to the induction belt around each cylinder and injected through ports in the sleeves. Such an arrangement overcame thedifficulty of accommodating the injection nozzle in the already fairly crowded cylinder-head. In the 373, however, it was decidedthat cylinder-head injection was well worth while and this has, in fact, been achieved. Such an arrangement removes restric-tions on spray angle and also permits an even radial spray over the entire combustion space. It also makes the injection systemindependent of valve timing, and the latter has been adjusted to provide greater overlap. To a considerable degree the injection pumps resemble thefamiliar pattern long used on London buses and other commercial vehicles, the supplier being the same firm, C.A.V., Ltd., ofLondon, W.3. The Centaurus 373 has two such pumps mounted one at each side of the supercharger casing. Each pump has nineplungers and feeds nine cylinders, the fuel delivery being regulated by a Hobson control unit. Generally similar to the present Developed jointly by Hobson, C.A.V. and Bristol, these units are the chief additions to the Series 373 engine. The control unit is the largest item; the injection pump is on the left and a single injection nozzle is also visible.
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