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 theoretical possibilities and limitations of fuel economy for the Phantom model.
| Identifier | WestWitteringFiles\N\2October1925-December1925\ Scan158 | |
| Date | 12th June 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. -4- Expl. No. REF: Hs{Lord Ernest Hives - Chair}/Ru/LG211125 FUEL ECONOMY POSSIBILITIES - PHANTOM. The figures given on this blue print (No.4) may seem somewhat contradictory. It is obvious that if an engine having no internal friction were fitted to a chassis having no rolling resistance and no oil churning losses, there would be no work to be done and hence the m.p.g. would be infinite! If, however, a frictionless engine were fitted to a chassis having a rolling resistance of 100 lbs/ton, and the m.p.g. taken, and the rolling resistance were then halved, the petrol consumption would not be halved. This is because the indicated thermal efficiency of an engine decreases with reduced load. When a very small charge is drawn into the cylinder, a disproportionately large amount of heat is lost to the cylinder walls during combustion. In the limit, if a minute charge only were admitted it would be capable of doing no useful work, all its heat being dissipated in the cylinder, and the indicated thermal efficiency of the engine would be infinitely poor. As long as an internal combustion engine is working as such, therefore, it must have a very definite petrol consumption even though it be assumed to be frictionless. The significance of this is that in striving for petrol economy, if we eliminate 50% of the total friction losses, no matter whether internal (piston friction etc.) or external (rolling resistance), we shall not improve the petrol consumption by 50%. This is because owing to a reduced charge being drawn into the cyl. to cope with the diminished quantity of work to be done, the thermal losses will be very substantially increased per I.H.P. produced. contd :- | ||