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This paper demonstrates the potential of optical sensors in the combustion chamber of a small two-stroke SI engine to detect conditions that hinder an optimal combustion process using emission bands and/or emission lines. The primary focus is on the spectroscopic examination of the combustion radiation emissions cycle-by-cycle. For this purpose, spark-ignition type combustion events, as well as the influence of both the air-fuel-ratio and the fuel type, are investigated on a crank angle resolved basis. Furthermore, an assessment of the radiation emissions of the OH, CH and C2 radicals is made. As a next step, the calculation of a temperature profile inside the combustion chamber is attempted by means of the line-emission-method regarding the thermally excited alkaline metals sodium and potassium. These data enable recognition of diffusion combustion and the detection of inadequate mixture quality.

The trend of higher specific power and increased volumetric efficiency leads to unwanted combustion phenomenon such as knocking, pre-ignition and self-ignition. For four-stroke engines, the literature reports that knocking depends, to a large extent, on the ignition angle, the degree of enrichment and the volumetric efficiency. In recent research, knock investigations in two-stroke engines have only been carried out to a limited extent. This paper discusses an investigation of the influence of various parameters on the knock characteristics of a small, high-speed, two-stroke SI engine. In particular, the degree of enrichment, the volumetric efficiency and the ignition timing serve as the parameters.