A Two-Stroke Chain Saw Engine to Fulfil Current Tier II Emission Levels

Two-stroke engines are widely used in handheld power tools due to the demand in high power-weight-ratio and reliability. Particularly, two-stroke engines remain to be the ultimate power source for handheld chain saws and continuous efforts resulted in an improved engine design with increased power output and reduced weight. Besides these continuing efforts engine manufactures must make their products compatible to exhaust emission standards, which have been implemented in most of the important markets worldwide [1], [2].

One particular area of interest is the scavenging process of naturally aspirated two-stroke engines, which affects power and emission output, both. Advanced scavenging methods offer the possibility to design two-stroke engines which achieve the lowest present emission levels i.e. hydrocarbons plus nitrogen-oxides: 50 g/kWh without compromising the power output at given engine parameters such as displacement or rated speed. The paper presents a chain saw engine, which fulfils the requirements described above. Only a full and detailed understanding of the scavenging flow enabled the development engineer to design a clean and powerful engine.