ADAPTING ENGINES TO THE USE OF AVAILABLE FUELS 200017
Some of the salient facts regarding the character of the engine fuel marketed within the past few years are shown in accompanying curves. The desirability of operating present-day experimental cars with fuel that is the equivalent of fuel that will probably be generally marketed two years hence is stated and various methods of meeting the fuel problem are then examined. A dry fuel mixture is desired to prevent spark-plug fouling, to improve engine performance in cold weather and to minimize lubricating oil contamination by fuel which passes the pistons. Various methods of obtaining a dry mixture are then discussed, leading to a detailed description of the construction and operation of a device specially designed to accomplish such a result more successfully. In principle, this takes advantage of the difference in pressure existing on either side of the carbureter butterfly-valve and causes a small amount of the combustible mixture to pass through a passage parallel with the main carbureter passage. This mixture is then burned in a suitable burner and the burnt gases allowed to mix with the incoming main supply to the engine above the throttle. This gives maximum efficiency under low throttle and light load conditions. When high volumetric efficiency of the engine is desired under wide-open throttle conditions, very little mixture passes through this shunt passage and a negligible amount of heat is produced in the burner.