Electric Fuel Injection

A recent issue of the British aviation weekly, Flight, carried a description of a successful fuel injection system for automobiles which might be applied to aircraft engines.

Used on an Italian racing car, the Alfa-Romeo, in 1940, the system is known as the Caproni-Fuscaldo. Basic principle is an external tube containing a very small and light valve operated electrically. Apparently it may be operated in two different ways: the injection valve may be placed in the branch of the induction pipe, immediately before the inlet valve, or a small pipe can be led direct to the cylinder wall somewhere in the combustion chamber. When the injector is placed in the induction pipe, the valve opens during the induction stroke and the fuel mixes with the incoming air, being admitted through the inlet valve to the cylinder. If the direct injection system is used, the injector can be made to deliver the fuel during the compression stroke, the action then being comparable with diesel practice. The compression pressure against which the fuel is injected is, of course, a good deal lower, and spark ignition is used.

The basic advantage of the Caproni-Fuscaldo system seems to lie in the use of the small electrically operated valve of the injector. Although valve dimensions are unavailable, it is known that in the injectors used in the Alfa-Romeo racing car the valve lift was only 0.2 mm, and as the valve was very light, operating speeds were not limited by inertia forces.

Briefly described, the injector valve is housed in a small tube, with a small electromagnet above it. Electric current is passed to the magnet by way of a distributor, which can be run off the camshaft. When current passes, the valve is lifted immediately, and as soon as the current is cut off by the distributor arm leaving the segment, the valve closes under the pressure of the spring and the fuel is cut off. The timing of the injection obviously can be controlled by the distributor, and the amount of fuel admitted can be governed by controlling the amount of valve lift, either automatically or by hand. Accurate control of fuel admission, it is claimed, has been obtained down to periods as short as 1/1,000th of a second.

A more powerful pump is needed to deliver fuel to the injector valves for direct injection into the combustion space, but as the compression pressures in aircraft engines are not as high as those in diesel engines, there should be no difficulties on that account. It is possible that this electrically operated injector valve might be worth study for application in the aircraft engine field by engineers in the country.

This article was originally published in the "Aviation Engineering" column in the September, 1941, issue of Aviation magazine, vol 40, no 9, p 127.
The original includes a schematic of the Caproni-Fuscaldo system and a general-arrangement drawing of the system in an Alfa-Romeo.