The Optimization of a 26.2 cc, OHV, 4-Cycle Engine Aspiration System to Achieve 1999 CARB Emissions Standards 961737

This paper reviews the emissions reduction program that was pursued during the development of the small 26.2 cc, OHV, 4-cycle engine recently introduced by the Ryobi Group of Companies. This new engine's packaging and power density is designed to compete directly with pervasive, hand held, two-stroke power plants. The 4-cycle OHV design produces substantially less HC and CO emissions relative to the existing two stroke state-of-the-art hand held power plant. The challenge of minimizing NOx emission however is complicated by the practical limitations of low cost, diaphragm carburetor fuel metering systems. The levels of NOx emitted by the production engine are controlled by a careful manipulation of combustion chamber design, compression ratio, spark ignition timing, and internal and external exhaust gas recirculation. The results of experimental evaluations used to achieve a 1999 CARB standard capable design are discussed.


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