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).
Comparison of the chief characteristics of the Lorraine engine with the 20 HP engine.
| Identifier | WestWitteringFiles\Q\February1927-March1927\ 114 | |
| Date | 25th January 1926 | |
| 2162 contd : -10- Some of the chief characteristics of the Lorraine compared with the 20 HP. are as follows :- (1) Maintains a good B.M.E.P. at high speeds. The B.M.E.P. increases with the speed up to its maximum value at 2200 r.p.m. (2) High compression ratio - 5.9 to 1 - and only detonates slightly at low speeds on ordinary low grade fuel. (3) Small amount of ignition advance required. Dual ignition requires appreciably less advance than single. (4) Two carburettors with no balancing pipe which give a very low induction pipe depression. (5) Low gas velocity past inlet valves which open and close rapidly and have long duration of opening. The inlet valve is still 73% of its maximum lift when piston is at bottom centre. The 20 HP. inlet valve is only 53% open at bottom centre. The Lorraine exposes a considerable opening area after bottom centre. (6) The power to rotate the engine is greater than the 20 HP. after 2000 r.p.m. and increases rapidly. (7) The 'master period' of the crankshaft occurs at a high speed - 3900 r.p.m. - which is well outside the working speed range. It seems probable that such factors as compression ratio, gas velocity, induction pipe depression and valve duration may explain the major part of the difference which exists between the Lorraine and the 20 HP. In view of this we are at the moment carrying out some experiments on the 20 HP. using a cyl. contd :- | ||