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In order to meet the new stringent emission limits for small handheld power tools technologies like methods to improve the scavenging process and after treatment devices are deployed. Additionally, professional machines such as chain saws add particular requirements to avoid mechanical failures. By precise control of the carburetion it is possible to yield the necessary reduction of the emission level yet to maintain the performance of the engine. Thus, the development of an Electronically Controlled Carburetion System to reduce the exhaust emissions of small IC engines for handheld power tools was initiated at the WHZ, Germany. Key requirements of such a system are: low cost, high reliability, low electrical power consumption, high accuracy in metering the fuel demand of the engine. First results are promising. A correlation between exhaust gas temperature and the fuel demand of the engine was confirmed for both, wide open throttle and part load operation.

Experimental methods are needed to understand unsteady three-dimensional flows. They also become an important tool where geometrical details or the complexity of the applied model would require an over-proportional numerical effort to investigate a scavenging flow. The experimental method presented in this paper applies visualization techniques to analyze the scavenging flow of small two-stroke cylinders. The principle at work is based on similarity laws, which transfer the dimensions of an actual engine into an enlarged model. The modular set-up allows fast modifications of the port geometry and detailed visualization of the flow coming out of individual transfer ports of multiple port cylinders by using different dyes. Results are presented as movies, which give a very graphic impression of the unsteady three-dimensional flow inside the cylinder.