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The usage of alternative fuels inside internal combustion engines (ICE), is one promising approach to meet the higher requirements concerning the efficiency and emission of modern combustion systems. The injection and mixture formation of such fuels has a major impact on the subsequent combustion as well as the formation of pollutants. To rate the influence and to gain a better understanding of those new alternatives a basic understanding of these dominant processes is mandatory. The principle of laser-induced fluorescence (LIF) is a well-known method to display and evaluate fuel distributions inside combustion chambers. A suiting online calibration routine allows the visualization of air-fuel equivalence ratio (λ) two-dimensionally during different operation modes. As cyclic variations can become a more critical issue while using alternative fuels, cycle- resolved test series become more and more important.

Gaining detailed knowledge about the injection and mixture formation inside engines and combustion chambers during different operation modes is of major importance for improving conventional systems as well as developing new, innovative concepts. To reduce pollutants while maintaining high performance and efficiency an advanced understanding of these mechanisms is necessary. Additional challenges arise when it comes to analyzing transient engine operation and cyclic fluctuations as well as rating their contribution to the formation of emissions. This study contains the evaluations of the injection and mixture formation inside a rapid compression machine (RCM) with directly injected methane. A newly developed highly repetitive optical measurement system based on laser-induced fluorescence (LIF) is used for the quantitative visualizations of the air-fuel equivalence ratio (λ).