The Influence of Improved Mixture Quality on Engine Exhaust Em issions ana Performance

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Abstract
A large, steam-heated, fuel vaporization tank was utilized as a carburetor in multicylinder engine testing at steady-state operating conditions. In comparison to normal carburetion, the tank provided improved air-fuel mixture quality, i.e., completely vaporized fuel, thoroughly mixed with air, and at elevated temperatures. Although not a practical piece of engine hardware, the tank provided a means of determining the extent of gains to be made with improved mixture quality. Improved mixture quality produced slight reductions in rich mixture hydrocarbon and carbon monoxide concentrations but did not reduce the minimum emissions of these two exhaust contaminants. Minimum fuel consumption was similarly unaffected by improved mixture quality. The most important benefit of improved mixture quality was derived from improved geometric and cyclic fuel distribution—a substantial extension of the misfire lean limit. The significance of lean limit operation and its relationship to reduced exhaust contaminants is discussed in detail.

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