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).
Article from 'The Motor' magazine about the design considerations for carburetor hot-spots to improve fuel vaporization.
| Identifier | ExFiles\Box 50\3\ Scan012 | |
| Date | 22th December 1920 | |
| X4305 (Filed 24-1-21) December 22, 1920. 1069 The Motor CONSIDERATIONS IN HOT-SPOT DESIGN. * Some Notes on a Very Important Subject. A Brewer type "hot-spot" in position, showing the connection to the exhaust manifold. THOSE whose motoring experience extends equally among British and American cars must have realized that in the matter of carburation American engineers are considerably in advance of our own. The reason is not far to seek, for in America the fuel used is considerably inferior to what we buy in this country, and the variations in climatic conditions absolutely demand concentrated attention being paid to obtaining proper vaporization and distribution of the fuel. which determines the proportion of fuel supplied to the air passing into the induction system and, generally speaking, needs no change of system. Vaporization to-day is the most difficult problem, and provided this can be accomplished all other carburation troubles almost disappear. Now to obtain vaporization there are three agencies available: These are heat, velocity or air, and turbulence. Heat, Turbulence and Velocity. Heat, of course, can be divided into two headings—temperature and quantity. So far as the vaporization of motor fuel is concerned the former is of prime importance. Strictly speaking, a carburetter cannot vaporize fuel completely, for the time taken for liquid to pass through the jets is too short. Turbulence, which assists vaporization, is started in some types of carburetters, but it is evident that vaporization must be carried out between the carburetter and before the mixture reaches the engine valves. Unless this is done the fuel really only vaporizes when it actually gets in the cylinders, which type of vaporization does not facilitate distribution and causes the evils of carbon deposit and crankcase dilution. Admission of hot air to the carburetter inlet certainly helps, but it does not remedy the evil, for the temperature is too low to affect any but the lightest fractions of fuel. The same remark applies to hot water jacketing. It is the heavier fractions and not the light ones which require treating, and this line of reasoning explains the reason for the “hot-spot.” A “hot-spot,” fundamentally, is a portion of the D7 The left-hand diagram gives a good idea of what happens to the globules of fuel when an ordinary form of hot-spot is used. They hit up against the flat face and rebound off into the induction pipe. The centre sketch shows how the whirling effect obtained in the Brewer system insists upon liquid particles being sluiced against the hot walls until they are properly vaporized. On the right is shown the Brewer hot-spot and vortex chamber in section. The ribs are intended to direct and collect unnecessary liquid fuel. The hot-spot manifold was originally patented by Brewer in 1913, and his design has been largely used in America, notably on the Class B. American W.D. lorries. Strictly speaking, the old-time volatile spirit is an unnecessary waste of raw material. Modern engines, properly designed, can use less volatile fuels with full efficiency of combustion, provided, of course, that these heavier grades are suitably metered, vaporized, and distributed. The modern carburetter is nothing more or less than a measuring device | ||