Possibilities of the Rotary Valve
Page 31
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Mr. F. M. Aspin, M.S.A.E., M.Inst.B.E., explains the Salient Features of his Unit and Answers Some Interesting Questions Bear
ing on its Running
T"type of engine you may expect on the road after the war, in the 10 h.p.'elass; will be' capable of develop
ing 50 at 4,500 r.p.m. . . . with -a fuel consumption of at least 45 m.p.g. when driven hard.". So said Mr. F. M. Aspin, M.S:A.E., M.Inst.B.E„ in a lecture recently. given under the auspices of the North-West Region of the I.M.T. Mr. 'Aspin, as may be knovyn, is the inventor, of the rotary-Valve engine bearing his name, a type of unit which holds out inatnense possibilities. In .the course of his address, the lecturer said that the lubrication of rotary valves is, perhaps, one of the greatest difficulties which beset the designer. One of the reasons why increased power could•be obtained from an engine of this type was that it was possible to employ a much higher compression ratio than with the normal type of poppet-valve unit.
Mr. Aspin recalled the satisfaction he felt over the first engine he made, " because it ran." The second one produced also ran quite well but, because of the cylinder head splitting, all the information that it was hoped to secure could not be obtained. However, as alterations were made so . the design progressed. Oil consumption was low and the unit was quiet running. Then came the time to produce a fourcylindered-type engine embodying, of course, the-same form of valve opethtion, as in. the experimental singlecylindered unit.
The use of a cast-iron rotor in a castiron head had to be abandoned, and the compression ratio altered—about 10 to 1 being found most satisfactory. After experimenting with various bearing metals an engine was produced that would run for hours without any symptom of seizing, 'The 8 h.p. model which was evolved, had a rotor of mild steel. • The next step was to produce a more powerful engine for heavier duty, and this unit, which gave good results, had a bore of 4k ins, and a stroke of 5 ins.
Question time produced some interesting replies from Mr, Aspin. Regard.: ing the need for a means for advancing and retarding the ignition, the lecturer said that such was not absolutely necessary. At maximum engine torque a fixed setting was used.
In answer to the question, " Are special plugs necessary? " Mr. Aspin replied that, normally, they: are not. On ordinary straight fuels the type of plug -employed was the Lodge CB 14.
Since the advent of leaded petrol, trouble had been experienced with the heating-up of the combustion space.
In an answer to another question, the speaker said that, in certain models of the engine, the bore was greater than the stroke dimension. For instance, it might be that the bore would be 3 ins. and the stroke 2 ins. This, he said, reduced rubbing friction, and the . results, generally, were better. " Whatever a poppet-valve engine can do on good fuels," he added, " we can do. better."
Another questioner asked, ." How do manufacturing •c o st s compare' as between the Aspin and poppet-valve types? " " We consider," was the reply, " that our simplest form of engine is cheaper to maim; it has a smaller number of pieces than poppetvalve types."