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As regulations regarding exhaust gas emissions of the internal combustion engine become more stringent, new concepts are necessary. The implementation of lean operation, direct injection to increase turbulence and facilitate stratified mixtures as well as methane as fuel in combination with high compression ratios can reduce exhaust gas emissions. Conventional electrical spark ignition systems reach their limits as higher pressures lead to faster erosion of the electrodes. Laser ignition profits from rising pressures at the time of ignition and has additional advantages such as the lack of electrodes leading to less heat dissipation and the possibility of arbitrarily positioning the ignition location. In this work results of experiments carried out in a rapid compression machine using directly injected methane to facilitate a partially stratified charge are presented.

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).