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).
Experiment comparing the fuel economy of a standard 25/30 HP engine with one modified with vacuum controlled ignition advance.
| Identifier | ExFiles\Box 147\5\ scan0119 | |
| Date | 12th January 1937 | |
| To Rm.{William Robotham - Chief Engineer} 25/30 H.P. ECONOMY. 12.1.37. An experiment has been carried out on a 25/30 engine, to determine what advantage could be gained by applying vacuum controlled ignition advance (as for example used on the Chevrolet). This extra adjustment (over and above the standard mechanical ignition governor) applies only to part throttle conditions, and for this reason the results are most interesting, when it is remembered that about 90% of the running of a normal car is carried out under these part throttle conditions. Considering the attached graph No.S.12, Curve No. (1) shows the normal B.M.E.P. produced by the 25/30 at full throttle full load. Curve No (1a) shows the required ignition advance to produce curve No.(1). Curve No. (2) is produced by throttling back at corresponding speeds to produce (approx.) half the load of (1). Curve No. (2B) shows the effect on the specific consumption over (1B) by throttling back in this way. Curve No. (3) shows the gain in B.M.E.P. by advancing the ignition to (3A), and also the curve (3B) shows how the specific consumption is affected by this move. The gains shown are brought about by adjusting the ignition only. The throttle openings and R.P.M. are maintained constant, while the adjustment is made every 500 R.P.M. throughout the speed range. ROAD TEST. This apparatus was then transferred complete to a standard 25/30 H.P. car, and set to do exactly the same thing as done on the test bed. RESULT. Two identical runs were done of 70 miles, both at the same average speed of 46 m.p.h. (1) STANDARD CAR. Petrol consumption 13.9 m.p.g. (2) WITH VACUUM IGNITION CONTROL. Petrol consumption 15.4 mpg. Rm{William Robotham - Chief Engineer}/C, T, Salt. | ||