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).
Page discussing the power output of supercharged engines, considering factors like blower power, air temperature, and air-fuel ratios.
| Identifier | ExFiles\Box 140\1\ scan0223 | |
| Date | 28th March 1938 guessed | |
| -19- It would then be necessary to calculate by equation (1) the power necessary to drive the blower, and to subtract this power from the total power previously calculated for the supercharged engine, in order to determine the expected output of the combined supercharged engine and blower. The weight of air at a given pressure which is consumed by the engine in a given time will depend of course on the air temperature, which in turn will be influenced by any cooling during passage of the air from the blower to the engine, and by heating which may result from blower inefficiency. Since this same weight of air must be supplied by the supercharger, there should be no difficulty about calculating the correct relative values of power developed and power absorbed by the engine and supercharger respectively, provided the calculations for both are based on the weight of air passing through per unit time. Probably the greatest uncertainty in this respect is introduced by the possibility of loss of fresh charge through the exhaust port due to valve overlap. It is obvious that any such loss will result in an increase in power required to drive the supercharger, with no corresponding increase in power developed by the engine. The Effect Of Supercharging On Exhaust Gas Temperature And On Maximum Power Air-Fuel Ratio. Figure 33 shows the results of exhaust gas temperature measurements at 1,000 r.p.m. and various intake manifold pressures with the 5.55 to 1 and 4.25 to 1 compression ratios. As was pointed out previously, the observed variations in exhaust gas temperature with variation in intake manifold pressure are considered to be of doubtful significance. Figures 34 and 35 show the power output of the engine at several air-fuel ratios when supercharged to various intake manifold pressures up to 30 inches of mercury above atmospheric and when unsupercharged. An interesting feature of these power curves is their flatness over such a large range of air-fuel ratios. If no trouble from valve burning should be encountered, a supercharged engine could be operated at this speed at a fairly lean air-fuel ratio without an appreciable loss in power, but with a considerable gain in economy. Unfortunately, test data indicate that the power output of the engine when supercharged was quite sensitive to air-fuel ratio variations at speeds above 1000 r.p.m. | ||