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).
The effects of supercharging on spark advance and exhaust gas temperatures at different compression ratios.
| Identifier | ExFiles\Box 140\1\ scan0217 | |
| Date | 28th March 1938 guessed | |
| -13- mean effective pressures occurred at slightly higher speeds for the supercharged engine than for the unsupercharged engine is problematical. Spark Advance. The effect of supercharging on maximum power spark advance is shown in Figure 22. It was necessary to retard the spark about 5 degrees at each engine speed when operating the 5.55 to 1 compression ratio engine supercharged instead of unsupercharged. Although the engine was supercharged at the lower compression ratio, the maximum power spark advance was greater than that for the standard engine unsupercharged. These curves show the trend of the spark advance over the speed range, and Figure 23 shows the spread that might be expected as a result of daily variations. Exhaust Valve And Exhaust Gas Temperatures. Exhaust valve and exhaust gas temperature for the engine when operated at various speeds with 5.55 to 1 compression ratio un-supercharged and with the 5.55 and 4.25 to 1 ratios supercharged to an intake manifold pressure of 10 inches of mercury above atmospheric are shown on Figure 24. Supercharging up to 10 inches of mercury at 5.55 to 1 compression ratio did not effect a very great change in exhaust gas temperatures. Although there was considerable variation in daily readings of exhaust gas temperatures, the variation in temperature with respect to speed remained about the same. The small increase in exhaust gas temperature with supercharging which was observed in the tests at various speeds and 5.55 to 1 compression ratio is not considered to be significant, since a slight trend in the opposite direction was observed in tests at a fixed speed over a range of intake manifold pressures. However it is considered highly probable that the temperature of the exhaust valves did increase with boost because of the corresponding increase in the amount of heat to which they were exposed per unit of time. It will be noted that both the exhaust gas and exhaust valve temperatures of the engine at 4.25 to 1 compression ratio are higher than those at the 5.55 to 1 compression ratio, which is in agreement with theoretical consideration and with other test data. | ||