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).
Resolution of petrol pump overheating and fuel vaporization by relocating the pumps, including test results.
| Identifier | ExFiles\Box 91\3\ scan0030 | |
| Date | 23th June 1936 | |
| ( 2 ) To effect a cure, we decided the pumps must be removed and mounted on a cooler part of the car. We did this, mounting them on the O.S. of the frame, directly behind the clutch and brake pedal pivot mounting. We enclose an illustration herewith. The result has been astonishing. We are now able to run the car and raise the under bonnet temperature as high as 73°c and after a stop of 15 minutes, the car will, at the first attempt, start with the throttle slightly open and continues to run as required. There is absolutely no failure of petrol supply or misfiring due to starvation under any conditions. In reply to your memo of 3.6.36, we find the outside delivery pipe is no better than the inside pipe for the conditions set out above, as the under bonnet temperature is quite uniform after a stand of 15 minutes. We do, however, point out the advantages of using the outside pipe in the following report on category (b) i.e. running conditions. In our opinion this has constituted an absolute cure, and we consider it essential that the pumps be removed from the dash-board and mounted in a cooler place, as we have no doubt that customers will encounter this trouble in hot weather. The situation of the pumps in the new position makes them comparatively accessible. We have also surrounded them with a cover so as to prevent them being affected by dirt and stones. A special mounting will be necessary as the pumps are now working upside down. We would however point out that, owing to the extra head of petrol, higher rated springs have to be fitted behind the diaphrams to maintain an adequate supply (b). We find the vapour locks we get, when running over prolonged periods at high speeds, only occur with a bonnet temperature over 60°c, with an outside air temperature of 30°c & using the outside petrol pipe, we ran the car for nearly 50 miles without stopping the engine, and not till this mileage was covered did the engine show any signs of failure. After this mileage, however, the under bonnet temperature gradually rose to 65°c, and at one point touched 68°c. After reducing speed in order to cool down, we again increased the speed but only ran about a mile or so before the engine would start to splutter, but would never fade out altogether. We again carried out this test but this time using the inside petrol pipe. The result was that owing to the heat conducted from the engine in between the blocks, the supply pipe gets heated up more quickly. Consequently, the petrol vaporises at a much earlier stage. Therefore, the only advantage we can get in using the outside petrol pipe, is that owing to the quick circulation of air, it takes a longer period to reach a sufficient heat to vaporise the petrol passing through. We are of the opinion that the petrol vaporises in the supply pipe and not in the carburetter itself. We are however, carrying out further tests to confirm this, and are trying to effect a cure, but we feel that a satisfactory cure will not be possible till the bonnet ventilation is increased, so as to reduce | ||