Investigation of a multi-phase combustion system with Raman spectroscopy

We report about an experiment to investigate the influence of liquid fuel droplets on gas phase combustion. The experiment consists of a premixed turbulent natural gas / air flame; into the flame, a chain of droplets is introduced by a dedicated configurable droplet generator. We measure major species concentrations in the flame in situ by laser Raman spectroscopy. The droplet generator allows to vary the diameters, speeds and repetition rates of the injected droplets over a wide range. The influence of the injected liquid fuel onto the combustion process (notably, on the spatial structure of scalar probability density fields in the statistically stationary turbulent flame) can be investigated systematically. Results can be used to test hypotheses about droplet-gas phase interaction, and also to validate numerical models. For performing the laser-diagnostic technique in presence of droplets, the sensitive Raman signal
collection system must be protected against optical breakdowns. For this, a laser-based droplet detection system with fast camera inhibition was developed. This system allows to perform Raman measurements in the close surroundings
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of droplets, enabling collection of gas phase data in the interaction zone between droplet vapor and the surrounding
flame gases.