THE effects of introducing a portion of the fuel charge of a diesel engine into the intake manifold in the form of a fine mist are reported in this paper. Laboratory tests with swirl-chamber and open-chamber engines resulted in smoke reduction up to 80%, increase in smoke-limited power output up to 18.5%, decrease in specific fuel consumption up to 9.8%, shorter ignition lag, lower maximum rate of pressure rise, and smoother operation. In running on good-grade diesel fuel approximately 15% of the main fuel proved to be as good a manifold fuel as any. It was also found that a diesel engine could operate satisfactorily on substandard fuels down to zero cetane number when fumigation was employed.
Maximum benefits from fumigation accrued when inducting fuel in the form of a very fine mist (not over 4 microns) produced by Micro-Fog. As yet an economical method of producing this finely atomized fuel spray in large quantities has not been found. However, significantly improved performance was also obtained by the use of inexpensive pneumatic spray nozzles that require only a small amount of low-pressure air for operation.