Raman spectroscopic studies of the gaseous drag phase in droplet chains and sprays during the evaporation of multi-component fuels

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Alternative fuels can contribute to improve efficiency and to reduce CO2-emissions. Biogenic blended fuels, such as biodiesel or bioethanol, serve already as substitutes worldwide. It is well-known that ignition, combustion and emissions strongly depend on local mixture conditions. Therefore there is a demand for a better understanding of the evaporation of alternative multi-component fuels.Within the framework of this proposal the composition of the gaseous drag phase in droplet chains during evaporation shall be measured for different multi-component fuels. Expected interactions are studied by varying parameters such as diameter, temperature and distance of droplets as well as the ambient temperature. The data base can serve for validation o numerical models for component specific evaporation. Investigations are extended to gasoline direct injection in a spray chamber. To achieve these objectives, a Raman multipass setup is optimized for the analysis of the gaseous drag phase and extended by a fast trigger system for precise spatial and temporal resolution. Using Raman spectroscopy the gaseous drag phase of different multi-component fuel droplets with diameter less than 100 microns in a cell is examined with respect to its composition. Accompanying these measurements a high-speed schlieren technique is employed to determine the droplet velocities. Subsequently, the measurement system is transferred to a spray chamber. There, the component specific evaporation in a spray-guided direct injection by a piezoelectric injector is characterized for multi-component fuels at application relevant injection conditions. The influence of mixture formation on ignition conditions is verified, amongst others, by the determination of the air-fuel-ratio.