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 comparison of various engine head designs to optimize gas turbulence.
| Identifier | WestWitteringFiles\O\January1926-March1926\ Scan115 | |
| Date | 6th March 1925 guessed | |
| (2) Turbulence caused by the initial intake gas velocity is said to give in the common overhead valve cyl. a general flow as shewn in fig(1) Lec.2211., and to result in the contending currents when compressed largely dying away. The usual L. head engine is thought to make better use of its intake velocity in creating one large general current. The small eddy currents represent loss of turbulence. Ricardo developed a type for making the best use of this flow shewn in fig. (2) Lec. 2211. for which he claims very good results. Figs. (3) & (4) shew the well known Ricardo device for producing turbulence by means of the piston. A general movement of the gases occurs immediately before and during ignition. Fig.(4) is the Tyler type. This design was developed it is said by Ricardo after he had observed the effective way in which fig (5) operated with paraffin on his tank engine with relatively high compression without knocking. Ricardo stated that it was almost impossible to make the engine knock on paraffin at compression ratios of 4.75 to 1. Fig.(5) is used by Duesenberg and also on the Bugatti aero engine. Fig.(6) is a type with which we are familiar, having a venturi between the piston and the combustion head. Within our own experience we know that the Hispano engine, though apparently a straight-forward overhead valve type, requires comparatively smaller spark advance on either 2 plugs or 1., and leads one to the conclusion that in some way an appreciable degree of turbulence has been achieved. The Exp. Dept. at Derby suggest this is possibly due to the shape of their cams which have a very rapid cut off from full lift to shut. We could try experimentally a similar effect with a flat topped cam and using a masked valve. Our standard valve gear has reached the limit of maximum deceleration owing to the question of grinding the cam. Another method of accomplishing the same object would be to remove the rollers from the ends of the tappets and shape these ends to a curve equivalent to a very large dia. roller. We suspect the Hispano may have a high intake gas velocity which combined with their cam form may give good turbulence without reducing volumetric efficiency. Lec.2208. is hoped would possibly possess a higher degree of turbulence than a flat head with a cone topped piston apart from being more compact and with closer plugs. Lec.2209 approximates to Ricardo tank engine head shewn in fig.(5) Lec.2211., while Lec.2210. employs the principle of of | ||