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).
Engine development focusing on induction systems, comparing the performance of drained pipes versus hot spot schemes.
| Identifier | ExFiles\Box 75\2\ scan0256 | |
| Date | 8th September 1921 guessed | |
| Oy3 - G 6921 Sheet #2. The condition of the cylinders is excellent after long running with the drained pipe, which has no source of heat except our ordinary low speed jet intake and water heated carburetter. No through pipe is used in the manifold with the drains. Crankcase dilution in a further test of 100 miles is 1.59% using the pilot jet several times as against 3.6% with 1" through pipe on 78-NE (high compression chassis) without using primer or pilot jet. From what we can see at present, we shall feel quite satisfied to go ahead with the drains and pilot jet, both of which schemes are undoubtedly effective and absolutely safe, until such time as we can have a really good induction system, with the carburetter on the L.H. side, short induction pipes, drains, hot spot or large hot air supply at small throttle positions, and everything which may prove necessary to make a thoroughly firstclass showing on existing fuels, giving us if possible more power at high speeds than we get now, and better acceleration. As you say, it cannot be done in a month, and it may take 12 months or more. Since seeing the effect of drains on the running of the engine, we have rather gone away from the hot spot scheme, because if we can consistently get such good results as regards dilution and the formation of carbon as we have obtained on 102-CE, there seems no need to add the complication, loss of power and tendency to detonation of a hot spot. We feel, in fact, that it would be best to put drains on at once on production and let the hot spot wait in the experimental stage for further trial with American fuel through this winter. A further effect of slopping wet heavy ends into the cylinder has been illustrated by Prof. Anderson on his Paige car, of which I have recently written you, which is fitted with his own experimental carburetter. The main feature of this is that it is a single jet horizontal throat type with a gravity feed to the jet, by means of which it is possible to get a practically constant fuel-air ratio over a wide range of speeds and throttle positions. There are a host of refinements, however. One of these is an enormous supply of hot air at all positions of the throttle up to half-open, tempered by more and more cold air as the throttle opens further, till at full throttle there is practically no hot air. His objections to the hot spot as against hot air, are that the latter can be readily instantly cut off at wide open throttle positions while the hot spot cannot. Also the dry hot air, increased in volume by heating to say 400°F.{Mr Friese} has a high velocity past the jet and great capacity for evaporating the gasoline (if the latter is sufficiently finely divided). Finally, the hot air increases the efficiency for any given power at partial throttles | ||