Experimental study of thermo-chemical conditions in ethanol flames

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The essential scientific aim of the project is to examine the physico-chemical processes of chemistry-turbulence interaction in premixed flames of complex, renewable fuels. Due to its technical relevance ethanol as a more complex fuel is particularly suitable for these investigations. A novel measurement apparatus based on spontaneous Raman/Rayleigh scattering has to be developed in order to quantify the thermochemical state vector as completely as possible. The aim is the simultaneous, quantitative measurement of temperature and all major species concentrations in premixed ethanol flames. This is challenging since the number as well as the concentration of intermediate (oxygenated) hydrocarbon species (HC(O)) in the reaction zone itself is markedly increasing in comparison to more simple fuels like methane. Thus, the number of major species to be measured is increasing. Work on three central topics is required, in order to develop a technique able to measure the concentrations of the intermediate HC(O) major species as well as ethanol in flames simultaneously for the first time: (1) To evaluate the concentration data in flames, the temperature-dependent Raman response of ethanol and HC(O) species arising with higher concentrations in premixed ethanol flames must be determined. These species are at least methane, ethene as well as the aldehydes formaldehyde and acetaldehyde. Such data is not published in the literature for the required temperature range or is not available at all. Three different flow apparatus are required for that purpose, which will be set up in the course of the project: first, a novel gas heater will be developed, that will allow for heating the HC(O)-species up to very high temperatures. Second, an apparatus for the continuous generation of a defined flow of formaldehyde will be established. Third, a jet burner configuration to stabilize flames of the prevaporized fuel ethanol will be realized. (2) For the investigations, a Raman/Rayleigh spectrometer is required, which allows the most prominent HC(O) intermediates to be measured simultaneously to the other major species (CO2, O2, CO, N2, fuel, H2O and H2). For that purpose a novel spectrometer shall be developed, which is able to separate the spectrally closely spaced Raman lines of the HC(O)-intermediates and the ethanol from each other. (3) The characteristic, temperature-dependent Raman spectra of the HC(O)-intermediates and ethanol will be measured and processed into a library. Raman measurements will then be performed initially at premixed, laminar ethanol flames in order to establish the method. These form the basis for the development of an appropriate data evaluation method and also for measurements of turbulent ethanol flames in a second project period. Both a significant advancement in laser combustion diagnostics as well as an improved understanding of major species concentrations in the context of turbulence-chemistry interaction in ethanol flames are expected.