Conceptual Design Study for a Catalytic Muffler Chainsaw Application to Fulfill Emission Standards and Thermal Demands

The new stringent regulations for pollutant emissions of handheld power tools such as chainsaws require new solutions to reduce significantly the hydrocarbon emissions. This paper gives an overview of the development work for an exhaust gas aftertreatment system that has to be integrated into a professional chainsaw. The exothermal HC oxidation causes a heat flux of about 1.4 kW for a 50 cm³ chainsaw and therefore the exhaust gas temperature increases from 550°C to 1.000°C after the catalyst within the muffler. On the external side of the engine this additional heat flux is not allowed by the SAE regulation J335 [8] to increase the exhaust gas temperature at the outside surface of the chainsaw above 246°C. This temperature level is nearly reached also without a catalyst, therefore the exhaust gas temperature must be reduced over 750 K, using the same engine design and without changing the outlet direction of the exhaust gas. In addition, any measure has to be considered to avoid any thermal or fire impact to the environment.

This paper describes the principle idea of how to cool down the exhaust gas, the way to find the best fitting concept under the working conditions of a chainsaw, and the following virtual design process. The assessment of the prototypes shows that all targets concerning the thermal demands and the safety aspects can be achieved.