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).
Piston designs and compression ratios for F engines.
| Identifier | ExFiles\Box 42\4\ Scan067 | |
| Date | 24th June 1927 | |
| To BJ. from R.{Sir Henry Royce} c. to Wor.{Arthur Wormald - General Works Manager} RG.{Mr Rowledge} c. to Hs.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} X3867. R1/M24.6.27. RE. HIGH COMPRESSION RR+ X.4657 X.3996 F.{Mr Friese} engines. X.2428 X.3557 We think the 8 to 1 compression is somewhat dangerous even with doped fuel, so that we have now decided not to recommend this ratio of compression for any purpose until we know more about it. We have sent you today drg. LeC.2430 for two pistons suitable for the high compression cyl. taking advantage of the increased length of liner. These are 6.37 to 1 and 7 to 1 compression - (1) they are probably better for lessening detonations owing to the lower compression, better shape of the combustion chamber, and the probability of slightly more turbulence, and cooler surface of the piston due to its better section and greater length, (2) they should be cooler working pistons, avoiding gumming up, (3) greater efficiency because of less combustion chamber cooling surface (4) should save the liner and joint slightly from heat, (5) the rings are in a better position being .3" down, and (6) the increased length is at the top and the bottom compared with those in which the skirt has been removed. This increased length should give a cooler pistons, and be better for gas-tightness. The whole thing, including the reduced compression (from the 8 to 1) considerably increases the reliability. Either of these pistons and compressions would be possible for Fairey with doped fuel, and we think the 6.37 to 1 would be quite suitable for general use. As far as we know these can be made from the same Y. metal blanks as previous pistons. You may wish to modify some of the ring grooves for perfect circle rings if these are considered better. We understand that the 6.37 to 1 piston, and the high compression modified cyl. will be used in the production F.XI engine. We should go on testing the 8 to 1 compression, which can be obtained with this same piston without the hollow crown, as 8 to 1 is a quicker way of finding out whether the cyl. block, strength, cooling, and alloy are reliable. R.{Sir Henry Royce} | ||