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).
Carburetter performance issues due to heat absorption and various attempted solutions and alterations.
| Identifier | ExFiles\Box 91\4\ scan0160 | |
| Date | 29th July 1935 | |
| ( 3 ) CARBURETTERS. We have made a big stride in getting near perfection. Our chief trouble is heat absorbed by the Carburetters while the Engine is idle, and we do not know how this is to be overcome. We have got a steady slow running of 8 MPH. acceleration good without any strong mixture. We can leave the Car for five minutes and still be O.K. with a hot Engine. Starting up first thing no trouble. Cold air to the Carburetters is, or will be difficult to obtain, and does not help at all in our trouble. The air supply is interesting and the results we have obtained, may prevent the Design Department from making useless designs. We fitted a scheme, which in an oft moment I said would be good. We have found that it is not so. We fitted two metallic pipes 2.1/2 " diameter to the inlets of the air silencer, and brought them to the front of the top sides of the Engine Bonnet, making a large loover to emit the air, the pipes being close up. We found the air temperature going into the silencer was the same as before, i.e. average 54°c with an outside air temperature of 22°c. We then fitted a scoop outside the bonnet, at each side and direct on to the pipes. We were astonished to find no improvement in the air temperature going into the silencer. We actually held a therometer at the mouth of the scoop while travelling between 70 & 80 MPH. and found that the air going into the pipes was 23°c, by the time it reached the air silencer it was 56°c. We replaced the metallic pipes with rubber pipes 2.1/2 " diameter, hoping that the insulation of the rubber would keep the air cool. Again we found that the air entering the pipes was 24°c, and at the silencer 54°c. The absorbtion of the under bonnet heat by the pipes and the silencer defeats the idea of cool air inlets. With a cool atmosphere of 18°c, the air temperature at the silencer with the above arrangement was approximately 30°c. The only method of getting atmosphere temperature in the air silencer is direct through the top of the bonnet which is impracticable. The alterations to the Carburetters we have carried on, are as follows. We have reduced the four bleed holes at the bottom of the piston to two and a half, as near as we can say. We found that from 7 to 13 miles per hour, the mixture drawn from this source was too strong. We have also reduced the resevoir at the bottom of the slow running jet by 75%. ----------------- G.W.Hancock G.{Mr Griffiths - Chief Accountant / Mr Gnapp} W. H.{Arthur M. Hanbury - Head Complaints} | ||