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).
Technical analysis of 'complete' and 'normal' engine scavenging cycles with associated theoretical calculations.
| Identifier | ExFiles\Box 140\1\ scan0220 | |
| Date | 28th March 1938 guessed | |
| -16- With complete scavenging (See Figure 25A) it was assumed that the overlap of exhaust and inlet valve opening was sufficient to allow the incoming fresh charge to force out all of the exhaust gas, thus leaving the combined cylinder and clearance volume, V2, filled with fresh charge at intake manifold pressure at the beginning of the compression stroke in the engine. Compression and expansion of the charge were assumed to be adiabatic, and combustion was assumed to take place at constant volume. With "normal" scavenging (See Figure 25B) it was assumed that the clearance volume was filled with residual exhaust gas at atmospheric pressure (at point 7) after the exhaust stroke had been completed and the exhaust valve had closed but before the intake valve had opened. It was then assumed that, when the intake valve opened, the fresh charge first compressed the residual exhaust gas adiabatically, as indicated by the dotted line 7-8, to the intake manifold pressure so that the exhaust gas then occupied volume V8, and the total volume of fresh charge at the end of the intake stroke was V2 - V8 at the intake manifold pressure. On this basis, the total amount of gas present (residual exhaust gas plus fresh charge) is the same for each type of cycle, but the energy available is in proportion to the fresh charge volumes V2 and (V2 - V8) for the complete and 'normal' scavenging cycles, respectively. For the 'normal' scavenging cycle, as for the complete scavenging, compression and expansion within the engine were considered to be adiabatic, and constant-volume combustion was assumed. The theoretical calculations were made according to the equations shown below, in which the numerical subscripts refer to points on the diagrams of Figures 25A and 25B and the subscripts c and in for the energy and work symbols indicate complete and 'normal' scavenging respectively. For complete scavenging: Mc = weight of charge, pounds. = 144 P2V2 ------- RT2 Qc = B.t.u. of heat added by combustion of the fuel. = 1000 B.t.u. per pound of charge. = 1000Mc | ||