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Aviation History
1940
1940 - 0388.PDF
120 FEBRUARY 8, 1940 AIRCRAFT POWER PLANTS (CONTINUED) are apparently anxious to adopt fuel injection. Fuel injection may utilise any of the following methods: Direct-injection into each cylinder, using a high valve overlap; injection into the induction branch of each cylinder, either close to, or remote from, the inlet valve ; or injection into the eye of the blower. A British Experiment The greatest progress with petrol injection has been made in Germany; certainly that country is employing the system to a much greater extent than any other. Although it was not until January 18, when Flight pub- lished the first full description of the Junkers direct- injection system, that the world was initiated into German secrets, it must not be forgotten that for very many years aero-engine designers have been experi- menting with this principle. Particularly we would mention the Draco engine made by the Bristol Company Two examples of extension shafts : (above) on the big twenty - four - cyl - inder Hispano- Suiza H engine and (below) on a beautifully cowled Pratt and Whit- ney Double Wasp. Little has lately been heard of " flat " engines as exem- plified by this Potez. for the Air Ministry in 10.32. Essentially the Draco was a modified medium - super- charged Pegasus. Two Bosch fuel pumps were used, fuel being injected into the inlet elbow of each cylinder and against the air flow. Extremely promising results were obtained, but tests were discontinued in 1935 for the following reasons: There was no mea- surable reduction in fuel consumption ; the rated alti- tude of the Draco was slightly less than for the standard Pegasus (due to the reduced density of the air in the supercharger owing to the absence of petrol); and the distribution of radial engines was, in any case, excellent and could not be improved by petrol injection. Icing Eliminated One indisputable advantage of direct-injection is the elimination of carburetter icing; this, in conjunction with the promise of better distribution for certain types of engine and possible improvement in fuel consump- tion, may lead to its increased adoption. For the time being it seems that heavy oil, or diesel, engines will remain in the background due to the pre- occupation of designers with problems attaching to the high-performance petrol engine for military use. The design of current aircraft diesels is quite as varied as that of contemporary petrol units. Mr. Ricardo, who has made a deep study of diesel problems, states that there are three |[ main avenues of approach: The high-com- pression, four-cycle, lightly supercharged engine ; the high-compression, two-cycle unit; and the relatively low-compression, highly supercharged four-cycle type. Current ex- perimental units include radial adaptations.
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