Earlier papers show theoretical design [2], and also including experimental results from a prototype engine [3], which describe a tuned exhaust system that can reduce both exhaust emissions and noise, and at the same time increase engine power output on two-stroke engines.
This paper shows how this design concept has been applied to the engine used for the low noise Husqvarna H356 Back pack leaf blower, which has been in production since 2005. This includes a description of the engine layout, with similarities and differences compared to a standard two-stroke engine. Experimental test results are presented for power output, fuel consumption, and exhaust emissions, which are shown to be better than previously presented for a prototype engine with this technology [3]. This makes it possible to comply with emission regulations without catalyst exhaust after-treatment.
In a second step, test results and engine layouts from two modified and further optimized engines are presented and explained, to showcase the potential for even more improvement.
The first of these engines has a minor change in the dimensions of the exhaust system, which is shown to have a profound impact on the exhaust emissions, lowering the HC emissions by 20 %. The reason for this is explained by looking at how the tuning pressure wave at the exhaust port has changed due to this modification of the exhaust system.
The second engine is a more complete redesign, with only the bore, stroke and crankcase identical with the standard engine. The cylinder port layout and exhaust pipe design are modified with a focus on increasing the power output, without at the same time deteriorate the HC emissions. The result is an engine with the same emission level as the standard engine but with a BMEP level more than 25 % higher.