Dense core response to forced acoustic fields in oxygen-hydrogen rocket flames

Oscillatory combustion representative of thermo-acoustic instability in liquid rockets is simulated by experiment and LES calculation to investigate the flame behavior in detail. In particular, we focus on how the velocity and pressure fluctuations affect the behavior of the dense oxygen jet, or ‘LOx core’. The test case investigated is a high pressure, multi-injector, oxygen-hydrogen combustor with a siren for acoustic excitation. First, the LES calculation is validated by the resonant frequencies and average flame topology. A precise frequency correction is conducted to compare experiment with LES. Then an unforced case, a pressure fluctuation case, and a velocity fluctuation case are investigated. LES can quantitatively reproduce the LOx core shortening and flattening that occurs under transverse velocity excitation as it is observed in the experiments. On the other hand, the core behavior under pressure excitation is almost equal to the unforced case, and little shortening of the core occurs. The LOx core flattening is explained by the pressure drop around an elliptical cylinder using the unsteady Bernoulli equation. Finally, it is shown that the shortening of the LOx core occurs because the flattening enhances combustion by mixing and increase of the flame surface area

Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

Electrons, photogenerated in conduction bands (CB) and trapped in electron trap defects (Tids) in titanium dioxide (TiO2), play crucial roles in characteristic reductive reactions. This review summarizes the recent progress in the research on electron transfer in photo-excited TiO2. Particularly, the reactivity of electrons accumulated in CB and trapped at Tids on TiO2 is highlighted in the reduction of molecular oxygen and molecular nitrogen, and the hydrogenation and dehalogenation of organic substrates. Finally, the prospects for developing highly active TiO2 photocatalysts are discussed

Interpretation of the response of cryogenic rocket flames to forced acoustics using large eddy simulation

Experimental measurement of flame response to acoustics under conditions relevant to industrial engines is challenging and so the scope of such measurements is often limited. High fidelity CFD can be used to model the interaction of acoustic waves with cryogenic flames, and modelling an experimental test case can not only serve as a code validation exercise but also be useful in better characterising the experimental results. This work explores this potential by extending the interpretation of high-speed imaging of representative rocket flames based on comparison with a large eddy simulation of the experiment