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).
Analysis of engine performance, comparing actual engine results with theoretical cycles, particularly concerning supercharging and scavenging.
| Identifier | ExFiles\Box 140\1\ scan0222 | |
| Date | 28th March 1938 guessed | |
| -18- The variations of brake horsepower, brake mean effective pressure, and air consumption with intake manifold pressure for the actual engine at 1,000 r.p.m. with both 4.25 and 5.55 to 1 compression ratios are shown in Figures 26, 27 and 28 respectively. The percentage increases in indicated power for the actual engine due to supercharging under these conditions are compared with the theoretical gains in Figures 29 and 30. The percentage increases in power with increases in intake manifold pressure are seen to be somewhat greater for the actual engine than for corresponding ideal 'normal' scavenging cycles. This suggests the possibility that during the period of valve overlap the incoming charge at boost pressures forced out at least some of the residual exhaust gas which otherwise would remain in the clearance space, thus providing space for a greater weight of charge. Figures 31 and 32 show that at the lower supercharge pressures the increase in air consumption with boost for the actual engine is greater than that for the theoretical engine cycle with "normal" scavenging and less than that for the theoretical engine cycle with complete scavenging. At the higher boost pressures, however, the increase in air consumption for the actual engine is greater than that for either theoretical engine cycle. No data are available to indicate whether at the lower boost pressures unburned charge escaped through the exhaust ports of the actual engine. However, the large increase in air consumption of the actual engine with respect to the theoretical cycles at the high boost pressures suggests that there was some such loss under these conditions. Theoretical Consideration Of Engine With Supercharger Attached. The curves of Figures 29 and 30 indicate that the percent increases in indicated power of an engine due to supercharging with a separately driven compressor are quite close to the increases which may be calculated for corresponding ideal cycles. It would appear possible, therefore, that the percent increase in net power of a given unsupercharged engine due to supercharging with a directly-driven blower could be predicted with at least fair accuracy by combining separate theoretical calculations for the engine and the blower. In such calculations the power to be developed by the supercharged engine (with no deduction for the power necessary to drive the blower) would first be determined by multiplying the power of the unsupercharged engine by the ratio of the theoretical power outputs of corresponding ideal supercharged and unsupercharged cycles. | ||