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 document detailing injection pressure and mechanical efficiency analysis.
| Identifier | ExFiles\Box 133\3\ scan0045 | |
| Date | 28th February 1939 | |
| -o- Injection Pressure. This refers to the point at which the nozzle valve lifts, and not the maximum pressure reached during injection this latter depending largely on the number and size of spray holes employed. A consideration of items involved helps towards a rough estimate of pressure required, though the actual figures can only be obtained by trial and error. The principle factors are:- (a) Spray hole dimensions. (b) Number of holes. (c) Shape of piston crown. (d) Size of cylinder bore. (e) Degree of swirl present. For a given depth of penetration, lower pressures will be required for large diameter or long holes, this latter item giving reduced divergence. This is borne out by test results as under. Injection pressure increased from 2000-5000 raised BMEP by 17.0 lbs/sq.in. Increase from 4000-5000 increased BMEP 7.2 lbs/sq.in. Mechanical Efficiency. A friction loss analysis at 2000 R.P.M. showed the following major losses. Pumping losses................... 15.00 lbs/sq.in. Piston and conn. rod............. 7.78 lbs/sq.in. Crankshaft bearings.............. 6.03 lbs/sq.in. Valve gear....................... 0.79 lbs/sq.in. Oil, water and injection pumps... 0.70 lbs/sq.in. ---------- 30.3 lbs/sq.in. To estimate the heat losses during compression when motoring, tests were carried out with a low compression piston, and the heat loss at 2000 R.P.M. was estimated to be about 2.5 lbs/sq.in. The above loss gives a mechanical efficiency of 76% at 2000 R.P.M. | ||