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The Marchant-Stewart Electro-magnetic Injector

13th January 1933
Page 50
Page 51
Page 50, 13th January 1933 — The Marchant-Stewart Electro-magnetic Injector
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IN our recent description a the interesting Marchant-Stewart oil engine, we mentioned the fact that the injectors, or, rather, injector pumps, employed were of particularly interesting design, Owing to certain patent matters we cannot yet give illustrations of the appliance, but our Paris representative has seen the injector in operation and has obtained information from Mr. W. J. Merchant which may be of interest to readers while waiting for a complete description.

The Marchant-Stewart injector pump is an electro-magnetic device bearing no relation to any oil-injection system yet designed. One particular difficulty which all oil-engine designers have come up against is that of dribble at the end of the injection period, and this, it would stem, has been eliminated in the Marchant-Stewart arrangement. Accuracy of timing also has been aimed

• at without the need for high precision in manufacture.

The appliance, which is adaptable to practically any type of engine, comprises a small east-iron box, one for each cylinder. Within the box is a 1336

moving fuel-pump cylinder, the end of which acts as a cut-off valve for the injection orifice. The plunger within this cylinder is moved by' an electromagnet, whilst the cylinder itself lifts automatically under oil pressure. The quantity of fuel injected is controlled by the height to which the piston is allowed to rise in tire cylinder.

The instrument, whilst working at a comparatively low pressure, maintains a high velocity on the fuel, a velocity, moreover, which is increasing throughout the period of injection. Thus, as the pressure within the combustion chamber increases from the burning of the fuel, so the speed of injection increases in an endeavour to give a certain degree of penetration throughout the whole period of injection.

A further aim of the inventors has been to give a much wider range than

usual to the injection period. With the Marchant-Stewart system, the injection period can be reduced to a matter of 7 degrees or 8 degrees of crankshaft movement, or, 011 the other hand, increased to as much as 100 degrees, always maintaining the advantage of constantly increasing fuel velocity throughout the period.

It may be mentioned that the injector pump is composed of six main parts, only three being moving parts, and each of these having a perfectly straight movement without side thrust. The invention seems to have dispensed with the necessity of an extremely small injector orifice. In actual. practice it has been found that the quality of injection varies little, with a difference of from 0.2 ram, to mm.

The Merchant-Stewart injectors may be controlled with an orthodox type of distributor, such as is used in connection with sparking plugs and battery ignition in the ordinary petrol engine of to-day. It should be noted particularly that should one injector pump be put out of action for any reason, it will in no way affect the others. Further, each cylinder may be tuned separately, which is, in the opinion of the inventors, absolutely essential when dealing with compression-ignition engines of small cylinder bore, and, ipso facto, with the small quantities of fuel necessary for idling.

The inventors are of the opinion that it is the fuel-operating apparatus which, at the moment, restricts the speed of the heavy-oil engine.

It may be mentioned that the Marchant-Stewart engine, which is about to undergo bench tests, has been designed to run at something in the neighbourhood of 5,000 r.p.m., at which speed it is claimed that it will certainly not be restricted in any way by the fuel-injecting system.

It might be thought that an electro-magnetic injection s stem with distributor control would onsunte a fairly large amount of current, but as contact is made only for maximum period of about 80 degrees, or approximately 5 per cent, of the engine running time, it will be realized that current consumption is small.

An important point may be noted in connection with priming and starting.

'The movement of the injecting plunger does not depend upon the energy stored in a spring; it is positive and full jet is given at the start, even if the injectors he worked from a hand-operated push button or' switch. Another advantage of the system is that a non-firing cylinder can be traced quickly and easily by the simple method of shorting each ,auccessive injector, exactly as one shorts sparking plugs, with a screwdriver. When the offending cylinder is found, the injector can be detached, cleaned and replaced in the space of a few minutes.

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People: W. J. Merchant
Locations: Paris

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