Efficiency of the Diesel engine, on the first development of which in France the author worked, and the possibility of using the low-priced by-products of gasoline production, led to the designing and building of several experimental engines of small size and low weight to run on fuel oil and develop the power required for average automotive work. The theoretical and commercial requirements that established the basis on which these engines were designed and built are enumerated and each type of engine is described.
The first engine, which was built in 1921 and given its first test-runs in 1922, was a four-cylinder two-cycle engine operated on the air-injection straight-Diesel principle. Scavenging air was supplied by step cylinders and the injection air was supplied at a pressure of 1200 lb. per sq. in. by a small compressor built integrally with the engine. The engine compression-pressure was 300 lb. and the fuel used was fuel oil of from 18 to 22 deg. Baumé gravity. This engine weighed 1100 lb. and was expected to develop 40 hp. at 1600 r.p.m., but in test-runs it ran at 1300 r.p.m., developed from 36 to 38 i.hp. and only 11 b.hp., and consumed nearly 2 lb. of fuel per b.hp. It was hard to start and oxidation of the fuel by the injection air caused the valves to leak. Nevertheless, it ran and was fairly flexible under load from 300 to 1300 r.p.m.
Tests of this engine made at McGill University gave results that led to the decision to build a second experimental engine, substituting solid-fuel injection for air injection to eliminate the air-compressor, the intercoolers and the oxidizing effect of air on the fuel. This also was a four-cylinder engine, made of cast iron and having a compression pressure of 405 lb. The step cylinders for scavenging were retained and it operated on the same fuel as the first engine. In preliminary runs, the engine started on the first few revolutions, attained a speed of 1600 r.p.m. and developed 18 b.hp. Scavenging pressure was found to be too high and was reduced to 14 lb. Two transfer valves were substituted for the single valve and the rotary valves of the working cylinders were changed to poppet valves. To give better scavenging, the compressors, which originally discharged directly into the working cylinders, were connected to a common reservoir in the engine jacket and each working cylinder was scavenged with air from the reservoir. After these changes, the engine developed 46 b.hp. Changes in the fuel-pump and injector adjustments increased this to 56 b.hp. at 1400 r.p.m. Fuel consumption of the engine is at the rate of 0.76 lb. per b.hp. at from 1200 to 1400 r.p.m. and 0.87 lb. per b.hp. at 600 r.p.m. The engine idles down to 120 r.p.m. and starts readily from dead cold after three to five revolutions with a 6-volt starter.
Three engines of this type were built and a car fitted with one was operated about 3000 miles in the summer of 1924 without the slightest trouble. Two-thirds of this distance was run on a dirt track at an average speed of 27 m.p.h. and the fuel consumption was at the rate of 1 gal. per 19 miles. The car, fully loaded, weighed 5100 lb.
In August, 1924, a contract was secured from the Navy Department by the Eastern Engineering Co., Ltd., of Montreal, for the building of a two-cylinder experimental engine to determine whether a light-weight heavy-oil engine suitable for airship work would stand the high compression pressures at high speed. This was built to operate on the same principle as the four-cylinder engine and designed to develop 100 hp. at 1500 r.p.m. or 125 hp. at 1750 r.p.m. and to have a weight of 3.8 lb. per b.hp. The only change in design is that the air-compressor is on the side of the engine and the pistons of the working cylinders are of standard trunk design.
The aviation engine was delivered to the engine-testing laboratory at the League Island Navy Yard in February, 1925, and after several tests and improvements on adjustments, especially on the lubricating-oil system, showed a brake-horsepower output of 85 at 1620 r.p.m. In the builder's own laboratory, however, an output of 91 b.hp. at 1525 r.p.m. has been obtained and it is foreseen that, by making some alterations that are now in progress, an additional output of from 20 to 25 b.hp. can be obtained, thereby bringing the engine up to 110 or 116 b.hp. for a total weight of 417 lb., or 3.6 lb. per b.hp. Fuel consumption is now in the neighborhood of 0.6 lb. per b.hp-hr. and it is expected that this can be reduced to 0.5 lb. per b.hp-hr. The maximum recorded speed is 2210 r.p.m.
A complete detailed description of this engine is given in the paper and the author states that tests made with it definitely establish the facts that light metal can be used in the construction of heavy-oil high-speed engines and that this type is no more difficult to build than the present type of gasoline engine. From comparative data obtained by the running of the small four-cylinder engine and the experimental two-cylinder aviation engine, the design of engines of any size and with any number of cylinders can be calculated with close approximation of the results to be expected.
Possible applications of this type of engine include trucks, motorcoaches, rail-cars, airships, tractors, pleasure craft, and tugs, at a low cost of power production that could not be dreamed of with the gasoline engine.