From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter from Ethyl Export Corporation discussing compression ratios and octane numbers of C.F.R. engines.
| Identifier | ExFiles\Box 150\1\ scan0072 | |
| Date | 11th November 1935 | |
| CABLEGRAMS: ETHYLPORT, LONDON. Curve in Tuning TELEGRAMS: ETHYLPORT, SOWEST. ETHYL EXPORT CORPORATION Incorporated in the State of Delaware, U. S. A.{Mr Adams} with limited liability. THAMES HOUSE, MILLBANK LONDON, S.W.1 Telephone: VICTORIA 5520 Head Office: 135 EAST 42ND STREET NEW YORK, U.S.A 11th November, 1935. W. A.{Mr Adams} Robotham, Esq., Experimental Department, Rolls-Royce Ltd., Nightingale Road, DERBY. Your ref: Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}19/KW. Dear Mr. Robotham, Many thanks for your letter of the 8th November, and as requested I am sending you herewith a curve showing the relation between compression ratio and octane number for the C.F.R. engine. As you probably know, the C.F.R. motor is of a relatively low duty type, and no special attempt was made in the design to obtain any high power output. The cylinder is 3¼" bore, having a plain pot head integral with it, the valves being totally enclosed within the cylinder circle. The sparking plug is placed between the valves on one side of the combustion chamber and the bouncing pin diametrically opposite; the piston is of cast iron. There is no "squish" whatsoever, although a certain amount of turbulence is induced by a shrouded inlet valve. The B.M.E.P. at 6 to 1 compression ratio and at 900 r.p.m., is only slightly in excess of 90 lbs. per square inch. In the circumstances I think you will agree that it is not possible to apply absolute figures from this engine to more highly efficient designs, although the principles may be compared. I have also shown two curves obtained off an experimental single cylinder engine in our laboratory, with side valve heads rather typical of American car practice; you will note the variations. I think the interesting fact which is shown up is what I mentioned in my previous letter, namely, that a greater advantage is obtained of a given octane number increase at the high end of the scale than a similar increase lower down. Thus, an increase from 76 to 80 octane gives an improvement of 0.15 of a ratio per octane number, whereas for the same head an increase from 60 to 64 octane the figure is 0.06 of a ratio per octane number. I have pencilled in, as pure guess work, the probable response to, say, your Bentley engine with the aluminium head. I would be interested if you have, say, just a couple of isolated points which you could put on these curves for any of your engines, as I am interested in the octane requirements of the high efficient English types. | ||