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).
Graph showing the thermal efficiency of a 4-stroke petrol engine against its load, with an analysis for the Phantom model.
| Identifier | ExFiles\Box 147\5\ scan0078 | |
| Date | 21th November 1925 | |
| R.R. 493A (50 M) (D.D. 21. 1?-25) L.H.D. EXPERIMENTAL REPORT. -6- Expl. No. REFHs/Rml/LG21125 GRAPH 1. THERMAL EFFICIENCY. 24% 20% 16% 12% 8% 4% 0 PERCENTAGE FULL LOAD ON ENGINE. 20% 40% 60% 80% 100% Typical curve for efficiency 4-stroke petrol engine. On the Phantom, 9.5 HP. is required to propel the car on the level at 30 m.p.h. The engine is capable of developing 60 HP. at this speed. It is therefore only working at 16% full load. Under these conditions every B.HP. developed takes as much petrol as 2 1/2 HP. generated under full load conditions. Owing to these facts every car has a speed usually about 15 m.p.h. at which it will give the greatest m.p.g. contd :- | ||