Fast Response Measurement of Combustion Air to Fuel Ratio for Stratified Two-Stroke Engines

Due to emission regulations for hand-held power tools more and more stratified-charge two-stroke engines enter into the market [Sawada et al. 1998, Zahn et al. 2000]. These engines require investigations and treatment for tuning the transient behaviour that are beyond the methods of the tuning for conventional engines. Especially the in-cylinder air-to-fuel-ratio cannot be determined from simple exhaust gas analysis any more. This paper presents an exhaust gas sampling system to enable the use of a standard lambda meter for a fast response measurement of air to fuel ratio out of the combustion chamber. The gas is sampled by means of a small restriction directly out of the combustion chamber. In case of miss-fire the hydrocarbon concentration in the sample is too high for the lambda sensor. With a dilution or a pre-converter system the hydrocarbon concentration can be adjusted to the range of the lambda sensor. Verification has been done with several tests. The air to fuel ratio in combustion is a key issue to tune the transient behaviour and to meet all customer requirements of the engine performance.