Emissions and Performance Potential of a Small Stratified Charge 2-Stroke Engine Using Reed Valves

Stratified concepts offer a reduction of the scavenging losses of 2-stroke engines. STIHL has developed a stratified reed valve engine to comply with Phase2 emissions, introduced into the market in the new STIHL Cutquik™ TS 700. The engine with a displacement of 98,5 cm₃ offers performance and product specifications that exceed its conventional predecessor. The results of the engine optimization process including flow simulation, concept evaluation and combustion process development are presented. The paper focuses on the design specifications of the air head carburetor and the specific layout of the reed valve scavenging process. Further, a cyclone type air filter system is presented.

The engine today meets the FEL 72 g/kWh limit. The concept offers further potential to improve trapping and volumetric efficiency, enabling a power and torque increase as well as emission control for the future.