Optical Evaluation of Directly Injected Methane Using a Newly Developed Highly Repetitive Laser Diagnostics System

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). Various operation conditions, such as different compression ratios, variations of the start of injection, variations of charge pressure as well as different injection pressures allow to evaluate influences on the mixture formation. Interpretations of the recorded images deliver a better understanding of direct injection and mixture processes under engine-like conditions as charge motion and λ-distributions are displayed during the compression cycle with a high recording frequency. Regarding different injection and charge pressures the comparison with results from preliminary experiments using a constant volume combustion chamber (CC) lead to a more profound impression of the ongoing processes. Thus, the influences on the penetration length of the spray as well as on the characteristic of the injector can be shown.