Development of an Emission Aftertreatment System for Hand Held Powertools

This paper gives an overview of the development work for an aftertreatment system, used in hand held powertools to fulfil the corporate average US Limits.

The paper will start with a description of the annual reductions in US Limits with differences in CARB and EPA legislation and the consequences of the legislation in Europe from 2007 onwards.

There then follows a chapter describing space restrictions in the given muffler leading to a maximum size for the substrate. Tests results are shown, giving an idea of additional measures taken to avoid dangerous temperatures on the muffler surface and of the emitted exhaust gas. The exothermic temperature increase created under service conditions imposes an additional thermal load from the catalyst back towards the engine itself. Therefore, some modifications regarding gas flow and positioning of the catalyst had to be made to find an adequate solution for series production.

Durability tests were conducted, to ensure the proper durability behavior both in emissions and mechanical performance. The temperatures inside the catalyst are also discussed; these are extremely high under the harsh conditions very close to the outlet port of the two-stroke engine. Different designs of Metalit^® are investigated with respect to vibration behavior and natural frequencies in order to find a durable and cost-effective solution for series production. A shortlist of powertools that are currently in series production with the catalyst system will be given at the end of the paper.