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).
Modifying the Phantom cylinder head for improved combustion, turbulence, and spark plug placement.
| Identifier | WestWitteringFiles\O\January1926-March1926\ Scan114 | |
| Date | 6th March 1925 | |
| TO R.{Sir Henry Royce} FROM E.{Mr Elliott - Chief Engineer} Copy to - CJ. HS.{Lord Ernest Hives - Chair} ORIGINAL. E1/M6.3.25. X8050 X3867 X8770 re. PHANTOM CYL. HEAD. As we are about to make patterns for the aluminium head and block for the lighter Phantom engine we wondered if you would care to consider modifying the shape of the combustion head with a view to making it still more compact and with the sparking plugs still nearer to the centre of the charge. To this end it has been thought worth while to make rough drawings of three suggestions applied to the Phantom pro-portions of which blue prints are attached Nos. LeC. 2208. 2209., and 2210. LeC. 2208. shews a form obtained by enclosing the charge in a tightly drawn membrane embracing the valve seats and piston head. This is used in conjunction with a hollow topped piston to assist turbulence and add to the compactness of the form. With this style we are able to advance both plugs nearer the charge. LeC. 2209. & 2210. shew forms of combustion heads which, excepting the thin gas sections over the piston, give still great-er degrees of compactness, and plugs still nearer to the centre of the charge, LeC. 2210. being the most noteworthy in this respect. It appears that in America the valve in head engine was at one time regarded as a solution of the troubles due to the decline in the quality of the fuel but has proved to be somewhat of a disappointment in this respect, and there is a revulsion in favour of L. head engines using the Ricardo principle for increas-ing the turbulence of the charge. It is stated that due to turbulence L. head engines of this type will be generally superior or at least equal to valve head engines with respect to detonation, all other conditions being equal, such as compression ratio, mixture ratio, and volumetric efficiency. Furthermore, with respect to the relative spark advance necessary, in one experiment quoted the valve in head engine re-quired an advance of 64º with 4 to 1 compression ratio at 1000 RPM. as against 11º necessary on an L. head engine of the type shewn in fig. (4) of LeC. 2211. These figures of course must be accepted with a consid-erable amount of caution but it should be pointed out that in the experiment in question the intake gas velocity was the same for each engine, whereas in practice the valve in head engine usually has a smaller valve and higher intake gas velocity favourable to less spark advance. Our own experience somewhat confirms that valve in head engines require a considerable spark advance. With a rapid combustion resulting from turbulence it may be expected that the ignition need not be advanced as far as usual. It is said that this is found to be true, and the spark advance may, all other conditions being equal, be considered an excellent index to turbulence. (1) | ||