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Engine Scavenging Tuning for In-Field Product Expectations of a 45cc Stratified Two-Stroke Power Head
ISSN: 1946-3936, e-ISSN: 1946-3944
Published October 15, 2013 by Society of Automotive Engineers of Japan in Japan
Citation: Bergman, M. and Sundkvist, R., "Engine Scavenging Tuning for In-Field Product Expectations of a 45cc Stratified Two-Stroke Power Head," SAE Int. J. Engines 6(4):2122-2132, 2013, https://doi.org/10.4271/2013-32-9078.
Because of todays new emissions legislation, a new 45cc Husqvarna trimmer/clearing saw power head was needed.
When reducing emissions in a conventional two-stroke engine or a stratified scavenged engine, it is important that the tuning and basic scavenging characteristics of the standard engine are maintained. A dual charge intake system is necessary for the stratified engine but it also creates air fuel delivery issues compared to a standard two stroke engine. With increasing trapping efficiency more spent gases mixes with the fresh charge, creating less favorable combustion properties and thermal loading on the engine. On top of this the sequential stratified scavenging technology introduces a spatial inhomogeneous mix problem between scavenging fresh air, new mixture and spent gases. This all add sensitivity to long term stability due to deposits of carbon both in combustion chamber and exhaust duct, resulting in a change in engine parameters due to aging.
There is of course a limit of what can be done in aspects of fuel trapping versus product performance with a simple two-stroke power head design when relying of a standard type mechanical carburettor fuel system. When optimizing the engine aspiration by tuning of intake and scavenging ducts geometry in dependens with static piston port timing.