PETROL INJECTION—
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The Future?
Work in Britain, America and Germany Reviewed: Cost and Complication Too Great H1GH.. cost and mechanical cornplication are likely to outweigh any advantage to be derived from petrol-injection systems by way of increased power and fuel economy for several years to come. This is the broad conclusion to be reached from a symposium on petrol injection held by the Automobile Division of the Institution of Mechanical Engineers in London on Tuesday.
Papers were read by Mr. E. W. Downing, of Joseph Lucas, Ltd., Mr. Errol J. Gay, consulting engineer to the Associated Ethyl Co., Ltd., and Dr.-Ing. H. Heinrich and Dipl.-Ing. H. Stoll, of Robert Bosch G.m.b.H. Mr. Downing's paper dealt principally with Lucas developments in this field, whilst the other speakers were concerned with brief histories of petrol injection in the U.S.A. and Germany and types, at preSent employed on production units.
American Development
Mr. Downing revealed that although there was at present no production demand for petrol-injection systems in Great Britain, intensive work for the American market (including The Holley Carburetor Co.) had resulted in a developed system to deliver fuel to four, six or eight cylinders accurately and reliably at up to 6,000 r.p.m. with automatic control from cold starting and through the warm-up stages. Much of this development work •had been carried out on a 3.4-litre sports-car engine.
Experience had shown that at between 3,500 r.p.m. and 5,500 r.p.m. the same horse power could be obtained as from the carburetter, but at a specific fuel consumption about 10 per cent. lower. With a different injection setting higher torque was obtained over the same speed range.
Lucas System
The system employed by Lucas comprises an electrically driven primary pump, located close to the fuel tank, which supplies fuel at a pressure of 100 p.s.i. to an engine-driven metering distributor. The injector nozzles are in the inlet manifold, close to the inlet ports, and control of the fuel metered to the individual nozzles is in accordance with the air charge. It is regulated by the mixture-control section of the metering unit, which takes its signal from the inlet manifold depression.
Shuttle metering is employed for accurate control. This equipment consists of a rotor with two radial ports leading to a bore in the centre of the rotor. This bore contains a shuttle piston, with a control stop at one end. The engine-driven rotor fits inside a sleeve which contains appropriate fuel inlet and outlet ports.
Fuel entering an inlet port at pressure displaces the shuttle axially towards the stop at the end of the rotor and the fuel already between the shuttle and the stop is discharged at pressure through an outlet port to the appropriate nozzle.
Further rotation of the rotor brings another inlet port into line, the shuttle direction is reversed, and fuel is metered to another nozzle, and so forth. The amount of fuel injected is regulated by the position of a movable control stop in the rotor bore.
Mr. Downing concluded with the observation that petrol injection could offer the advantages of an improved torque curve or 10 per cent, fuel economy corncompared with a carburetter.
Mr. Gay saicrthat American interest in petrol injection was at its highest during 1955 and 1956. At that time it was expected that volume production in the order of 50,000 or more units per year would be seen in 1958. These predictions had not materialized for several reasons.
The main cause was the high cost of present systems (1.142 to L178), the efficiency of present carburetters, and the decision reached in 1957 by the Automobile Manufacturers Association to call a halt to the horsepower race then prevalent in the U.S.A.
Six Makes
At least six American manufacturers offered petrol-injection equipment of various types. All delivered fuel into the inlet manifold either directly under the throttle body or at a point close to the inlet valve. In Mr. Gay's opinion the latter location seemed to be preferable. There were no American systems injecting directly into the combustion chamber.
Originally it had been thought that petrol injection would be a relatively simple system, but this was soon found to be untrue, particularly when it came to obtaining the same performance as derived from modern multi-barrel carburetters. In order to approach 1.1ch efficiency, and because of the reduced demand for such equipment (16w production meaning high cost), 'most systems were far too expensive for normal road vehicles.
It was clear that if the demand for such equipment were of the order of 1,000 units per day the cost could be reduced to £12 each, hut no manufacturer has had sufficient faith in public acceptance of petrol injection to risk the estimated cost. of £1.8m. for automatic machinery and tooling. A further point retarding petrolinjection development was that the complexity of most systems demanded specialized service and that at present there are few trained personnel who could adjust and balance such a system.
On the credit side, Mr. Gay said he had seen data which showed marked improvement in fuel economy when petrol injection was combined with other engine design changes. Furthermore, petrol injection gave almost complete freedom from icing troubles associated with carburetters; freedom from stalling caused by petrol spillage on sharp turns. quick stops or stop-and-start operation on steep gradients; better distribution of petrol to each cylinder; and the possibility of incorporating fuel shut-off devices for effect when decelerating.
He believed that automotive petrolinjection systems might eventually graduate to cylinder injection, but that it would be at least five years before volume production would be seen.
German Achievements
In the third paper the Bosch representatives outlined the early work done on petrol injection in Germany, starting with the system developed between 1898 and 1901 by the Gas Engine Works, Deutz. It was pointed out, however, that even the successes achieved with petrol injection in aircraft engines between 1910 and 1920 were never so outstanding that they could not be equalled by carburetters within a short period. Much invaluable work had, however, been achieved with aero-engines, so much so that by the end of 1944 the majority of German aircraft had petrolinjection engines.
As far back as 1935 Bosch had started tests with petrol injection applied to a DKW 700 c.c. water-cooled twincylindered two-stroke engine. This unit had reverse scavenging, and a marked advance in performance was made, although it was not until 1945 that Bosch again tackled the problem of applying petrol injection to two-stroke engines.
Livelier Performance
The later experiments showed that an engine with petrol injection had much more lively performance on the road, compared with an engine with a carburetter, yet gave improved fuel economy [the remarkable economy of the Goliath Express microbus road tested by The Commercial Motor in 1955 may be recalled].
Experience showed that the inherently simple design of the two-stroke engine was not spoilt by the addition of petrol-injection equipment, as it invariably functioned satisfactorily without requiring maintenance. Direct injection into the cylinders was employed for Such engines and was considered to be the only practicable system for two-stroke units. Even in four-stroke engines, a fuel saving of at least 10 per cent. could be achieved.
Further developments would undoubtedly result in the price of the equipment being reduced to a figure competitive with that of a carburetter.