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 method for estimating air flow velocities in an engine cylinder, including assumptions and calculations.
| Identifier | ExFiles\Box 17\6\ Scan145 | |
| Date | 24th August 1933 guessed | |
| -2- The method of estimation of such velocities is as follows :- (i) The following assumptions have to be made - (a) That the law of compression of the mixture on the compression stroke is PV1.14 = C. (b) That since the induction pipe depression is constant and the pressure in the cylinder of an engine during the induction stroke is very roughly constant the pressure difference across the valve is roughly constant and the flow of air through the valve is roughly proportional to the valve opening area i.e. to the valve lift. (ii) The approximate volumetric efficiency was first obtained by measuring the compression pressure practically and calculating the volume of air taken in per stroke (induction). (iii) The mean air flow (actual) was then calculated. (for one cylinder). (iv) From assumption (b) above, the flow through one port at any given valve lift, was equal to the mean flow multiplied by the ratio of the valve lift in question to the mean valve lift. Hence the required approx. air flow through the port was determined. The air flow was measured by means of a calibrated nozzle - the pressure difference across this nozzle together with absolute pressure on one side being measured - the method of calculating the flow, together with the necessary temperature corrections made, are shown on sheet 4-7. (The volumetric efficiency calculation is also shown on this sheet.) In the case of the Bentley, it was not thought necessary to repeat the volumetric efficiency measurements - the volumetric efficiency was assumed to be approximately the same as the Phantom. | ||