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).
Report page detailing engine performance regarding carburation, spark advance, and detonation.
| Identifier | ExFiles\Box 15\6\ Scan078 | |
| Date | 9th February 1929 guessed | |
| -3- In starting, the vacuum is zero and carburation is therefore full strong. As the engine idles and warms up the T.D.C. pressure increases and mixture automatically becomes leaner. As the throttle is opened the vacuum decreases and carburetter becomes as rich, as may be required for acceleration, but in a second or so the T.D.C. pressure begins to pull up and adjusts the mixture back again. A danger exists in the fact that the device cannot distinguish between slow burning due to richness or weakness, and if the mixture is allowed to become too rich it will move the control the wrong way. Mr. Stanton explained how he compensated for this, but I did not follow it except that the carburetter is set a little on the "lean" side. Cold starting conditions etc. are compensated automatically. Demonstration. As installed these two devices gave extraordinary results in lack of manual control, slow speed, pulling, steadiness of acceleration, and lack of detonation. The performance at very low speeds on steep grades was particularly noticeable, although the car is not fitted with a hot-spot. A visible spark advance indicator was fitted, and it was noticeable that as the speed increased above say 40 m.p.h., the ignition began to retard itself and would continue to do so as this speed was held, due to the increase in the internal temperature of the cylinders which made less advance necessary. Another interesting point is that "detonation" is impossible, as the very fact of the steep pressure rise after ignition causes the spark to retard itself. Power Charts. Mr. Stanton had a number of interesting power-charts on automobile and aircraft engines showing optimum spark advance obtained manually at full and partial throttles, and the degree to which this advance was reproduced by his device. In almost every case the advance curves were approximately as shown in the small chart in sketch showing that a droop in the advance is required for best results at high speeds because of the rise in internal engine temperature. Also the curve of optimum advance under road conditions was almost horizontal except for the droop at the ends. As he pointed out this advance can only be accurately obtained by allowing the engine to "read" the indicator diagram and adjust the spark to correspond. -continued- | ||