FORCED FUEL FEEDING.

Press, Volume LX, Issue 18233, 18 November 1924, Page 12

FORCED FUEL FEEDING.

European racing recently lias revived interest in the subject of supercharging, or forced fuel feeding to the cylinders, for touring cars. Briefly, the object of a supercharger is . completely to fill the cylinders with explosive mixture at high crankshaft speeds; for on a normal engine, where the gases are aspired into the cylinders by the descent of the pistons therein, it is a difficult matter to ensure that the cylinders shall be completely filled at such speeds. It is largely, owing to this difficulty that high-effi-oiency engines, both for automobile and aviation work, have been developed with a multiplicity of overhead; valves and complex carburation systems employing several carburettors. The supercharger is another method of obtaining the desired result, since a blower is utilised to force air through the carburettor, and so to deliver mixture under pressure to the cylinders. This does not imply an effort to get some sort of quart, or eve» a drop more than a pint, into a pint pot. It is obvious thai,the immediate result of thus starting a' compression stroke with a volume of gas not only comparatively filling the cylinder, but several pounds above normal initial pressure must, "at the end of the compression Btroke, involve a total compression far above the designed ratio, thus inducing pinking—if not actual preignition—at an earlier r.p.m., fatal to the hope of getting a higher power output. The whole trouble is that the high-speed engine never does fill the cylinders more than two-thirds of their designed content. Whilst at the moment the supercharger appears to be a racing device pure and simple it seema not improbable that it may be developed for touring cars, so that a comparatively small-powered engine by rating may be capable of developing all the power required for a large car. The prospect opens up possibilities in the way of fresh developments in design which, in such event, will again demonstrate that the shortcut to automobile evolution is still via the racing test, the value of which has lately been questioned by a number of English manufacturers.