Improved Measurement Techniques for Laminar Burning Velocities and Application to Alternative Fuels

For an adequate description of complex combustion phenomena, especially under premixed conditions for high-temperatures, high-quality data for laminar burning velocities serving as a key fundamental combustion property, can have significant impact. Furthermore, laminar burning velocity data are essential for the validation of complex chemical kinetic mechanisms. Data must always be obtained along with uncertainties as small as possible. Improved measurement techniques for laminar burning velocities are therefore presented in this thesis along with some applications for different fuels. Potential sources of uncertainty for the spherical chamber setup were fully characterised. The mixture preparation process itself is identified as one of the biggest reasons for uncertainties. As a result, a premixing vessel was introduced to the system for significantly improved mixture preparation. Then,the image acquisition setup was modified. The advantages of a dual-field- lens Schlieren arrangement combined with a high-power pulsed LED were highlighted with respect to increased image acquisition rate and reduced imageexposure times. This modification is very important for the investigation of fast burning fuels, e.g. hydrogen / air mixtures. Thereafter, different methodologies for the extrapolation of flame speed data to obtain unstretched propagation speed in the burnt had to be assessed. For the present setup, it is recommended to always perform measurements under slightly increased pressures, but still low enough to avoid instabilities. In general, the extrapolation routines yield the same results at increased pressures. The theory of flame propagation speed and stability of hydrogen / air flames is revisited. It was shown, that the theoretical findings for the critical radii are always considerably lower than the experiment. This is expected, because, although disturbances start growing when the flame reaches the size Rc, they do not grow as fast as the flame during the initial phase. Experimental burning velocity data for methanol, ethanol, n-propanol, and n-butanol were obtained and compared to laminar burning velocities calculated with different kinetic models available in the literature. Generally, good agreement was found for ambient pressure between the kinetic models and the experiments. However, the models tend to underpredict the experimental results for higher pressures. Experiments were also conducted for the novel biofuels 2-BTHF and 2-butanone. Newly developed kinetic models were compared against the experimental data