Potential of Expansion Chamber Exhaust Pipes for Two-Stroke Powered Tools

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. With the shown possibilities to achieve different power levels from the same engine using expansion chambers, the number of engine displacements from an engine family can be reduced saving cost.