FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1932
1932 - 1258.PDF
FLIGHT, DECEMBER 8, 1932 One Hundred Horsepower per Litre ! Further details are given this week of the very promising two-stroke engine which we illustrated and described briefly in our issue of November 10. An aircraft engine of about 340 h.p. is now being considered as the next step from the existing experimental single cylinder unit. KNOWN as the E.J.J, engine, the experimental single-cylinder unit which has been built at Wallington has caused, perhaps more comment than any other new engine of recent years. Even in its admittedly experimental state, the results so far obtained have been little short of phenomenal, and are certainly such as to warrant very keen interest being taken in the further development of the type. Messrs. F. Edwards, F. Jearum and J. Jameson have, from the first, taken simplicity of design as their main aim. In doing so they naturally turned to the two-stroke cycle in order to avoid the complication of valves. The adop tion of this principle has enabled the general design so to be laid out, that manufacture should be both cheap and easy. Our drawing shows a section of the existing cylinder, and from this it can be seen that the use of a piston valve in the cylinder head, together with cylinder wall ports for both inlet and exhaust, result in a casting which is both straightforward and sym metrical. In the drawing, (A) is the main piston. This is quite ordinary with a hemispherical head, two compression rings above the gudgeon pin and one scraper ring near the bottom of the skirt. This piston is of light alloy and has massive internal ribbing under the head. (B) is the piston valve which controls the admission of the mixture. The small extension of this carries two compression rings and has a concave head conforming to the shape of the combustion chamber (C). The upper part of the piston valve is of larger diameter, giving clearance for a short crank (F), from a layshaft, to rotate within-it. This layshaft is driven at engine speed by a chain, and operates the piston valve by means of a short connecting rod. The lower end of the A view of the experimental unit on the Heenan-Froude test brake. (FLIGHT Photo.) cylinder in which the piston valve works has around its circumference a series of inlet ports (E), and these are uncovered as the valve rises. The design of these ports, in conjunction with the spherical combustion chamber, ensures that the mixture is in an exceptionally turbulent state when it is fired by the sparking plug (D). The mixture is supplied to the inlet ports under a pressure of approxi mately 8 lb,/sq. in. by a blower of the rotor and vane type, which has, after repeated failures of other types, been developed for this engine by the designers. On leaving the combustion chamber the gases reach the main cylinder through a comparatively narrow orifice, giving a venturi effect, which further enhances the turbulence already achieved, ensuring complete and rapid combustion and preventing detonation. It may also have the effect of speeding up the gases on their downward expansion path, thus assist ing not only the downward travel of the piston, but also achieving an un usually high degree of scavenge through the exhaust ports (G). The cylinder capacity of this unit is only 411 c.c, yet the Heenan- Froude brake upon which it has been running shows a b.h.p. of 54 at 5,000 r.p.m. ; and this power can be obtained steadily at any time. The high efficiency of the engine may be judged from the fact that the power curve is said to be perfectly straight up to these revolutions; giving 10 h.p. for every 1,000 r.p.m., while the peak of the "curve has not so far been reached, although 5,400 r.p.m. have been attained upon occasions. The compression ratio is 7:1 and the B.M.E.P. 156.4. We recently had the opportunity of seeing this unit stripped down after it had done some 600 hr. running. Nowhere was there any sign of abnormal wear. An in teresting point was the little end of the connecting rod. This bearing around the gudgeon pin gave trouble for a long time until the designers hit upon the idea of replac ing the bearing with a unique one formed by having a shallow recess turned on the pin to contain a complete row of needles, where rollers would normally be used. These needles were then covered with a single sleeve, or outer race as it were, which fitted inside the end of the connecting rod. Since fitting this bearing no trouble has been experienced at all. A study of the accompanying valve-timing diagram shows that the timing which has been finally decided upon as giving the most efficient results, allows the inlet ports to open about 30 deg. before bottom dead centre and to remain open until 90 deg. after bottom dead centre. The piston valve, which, as already described, controls these ports, is so arranged that its most rapid travel occurs at the actual moments of opening or closing, this being a feature which contributes largely to the efficiency of the engine. Even though not a normally aspirated engine, the time taken to open the inlet ports is still waste time in so far as the efficiency of the cycle of operations is concerned. The valve, it will be seen, is also arranged so that its operating mechanism will be on bottom dead centre at the moment when the pressure in the cylinder is greatest, and will therefore give the valve the most sup port it can against that pressure. 1172 A cross-section of the " E.J.J." en gine drawn diagrammatically :—(A) piston ; (B) piston valve ; (C) com bustion chamber ; (D) sparking plug ; <E> inlet ports ; (F> layshaft and crank ; (G) exhaust ports ; (H) connecting rod : (I) water space.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
