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 test results comparing theoretical and actual engine performance with supercharging.
| Identifier | ExFiles\Box 140\1\ scan0218 | |
| Date | 28th March 1938 guessed | |
| -14- Results from Tests at 1000 r.p.m. over a range of intake manifold pressure. The percent change in power that may be expected due to a change in the compression ratio of an engine may be calculated with reasonable precision by comparison of the two theoretical engine cycles for the two compression ratios in question. It was considered desirable to determine whether a similar relationship between theoretical cycles and actual engines exists in the case of supercharging. The second portion of the dynamometer tests, conducted at an engine speed of 1000 r.p.m. with intake manifold pressures between 0 and 30 inches of mercury above atmospheric was expressly designed to indicate the effect of various supercharge pressures on power output so that the rate of increase of power with supercharging in the actual engine could be compared with the theoretical. The theoretical indicator diagram for a supercharged engine with a separately-driven air compressor is shown in Figures 25A and 25B. The work, Wp, which is represented by the area of rectangle 1-2-6-7-1 of this diagram is contributed by the air compressor since it is the work done by the entering charge on the pistons during the intake stroke. (It is assumed that the pressure of the exhaust gases during the exhaust stroke is equal to atmospheric pressure and that the work done on the gases during the exhaust stroke therefore is zero.) The work WE, which is represented by area 2-3-4-5-2 is derived from energy released by combustion of the charge, and the sum of areas 1-2-6-7-1 and 2-3-4-5-2 represents the total indicated work, WI of an ideal supercharged cycle with a separately-driven compressor. Values of indicated work based on such theoretical diagrams have been calculated for comparison with values of indicated work calculated from power observations made with the actual engine. These calculations for the actual engine are based on the following equations: WE = work derived from energy released by combustion of the charge, which corresponds to the work represented by area 2-3-4-5-2 of the theoretical diagram, ft. lbs. per minute. Wp = work done by pressure of the charge during the intake stroke, which corresponds to the work represented by area 1-2-6-7-1 of the theoretical diagram ft. lbs. per minute. | ||