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In the last decades the operational requirements to control the gas exchange of an internal combustion engine increased immensely. The gas exchange is mainly controlled by the valve train system affecting the combustion behavior and power output of the engine. The necessary valve lift curve must be ensured within the whole operation range of the engine. Moreover, a minimum friction has to be achieved. On the one hand engine speeds and loads of the valve train components have increased and the weights of the components have decreased, on the other hand the demands regarding durability increased as well. The engine development department has tried to find out optimization potentials of valve train dynamics to get along with these challenges. During an engine development process analysis tools together with measurements of the dynamic valve train behavior on motored cylinder heads using Laser Doppler Vibrometry are applied.

Due to reduced emission limits for handheld gasoline powered tools worldwide, hydrocarbon emissions of two-stroke engines used for those applications need to be reduced drastically. In this paper, the potential of expansion chamber exhaust pipes to reduce hydrocarbon emissions generated by scavenging losses of the two-stroke engine is investigated. On a series production backpack blower engine, a box silencer is compared to a baseline expansion chamber and a modified expansion chamber. Also, as this is a very cost-sensitive market, possibilities to achieve different power levels from the same engine using expansion chambers of different stages of tune are investigated. The results show that using expansion chambers, power of the series production engine can be raised by 40 percent while still offering an advantage in emissions of 34 percent. Tuning an expansion chamber for the same peak horsepower as the box silencer gives an advantage in emissions by 62 percent.