AbstractsAstronomy & Space Science

Advanced Laser-based Multi-scalar Imaging for Flame Structure Visualization towards a Deepened Understanding of Premixed Turbulent Combustion

by Bo Zhou

Institution: University of Lund
Year: 2015
Keywords: Combustion Regimes; Mild Combustion.; Distributed Reaction Zone; HCO/CH Radicals; Multi-scalar Instantaneous Visualization; High Spatial Resolution; PLIF; Laser Diagnostics; Turbulence/Flame Interaction; Turbulent Premixed Combustion; Technology and Engineering; Physics and Astronomy; Chemistry
Record ID: 1371337
Full text PDF: http://lup.lub.lu.se/record/4933891



The work presented in the thesis concerns the developments of laser-based diagnostics and its application to the study of turbulent premixed combustion. The diagnostic developments, mainly concerned with planar laser-induced fluorescence (PLIF), are intended to provide instantaneous visualization of the key species originating from the combustion processes involved in the burning of hydrocarbons and nitrogen-containing fuels under turbulent conditions. For the burning of hydrocarbons, these species include HCO, hot O2 etc. and for the burning of nitrogen-containing fuels, these include NH3, NH and CN. In connection with this, the potential for instantaneous temperature mapping using two-line atomic LIF (TLIF) with a novel seeding system are also demonstrated. The study of turbulent premixed combustion involves simultaneous imaging of such scalars as HCO, CH, CH2O and OH as well as temperature. Laboratory-scale premixed CH4/air flames stabilized on the Lund University Pilot Jet burner (LUPJ) and the Low-Swirl Burner (LSB) were investigated over a wide operational range and various combustion regimes. The results from both the LUPJ and the LSB flames provide the first experimental evidences for its being possible to appreciably broaden the reaction zone of premixed flames can be significantly broadened through rapid turbulence mixing, the results being verified by observations of broadened/distributed short-lived radicals, HCO and/or CH. The observations obtained for the two clearly different burner configurations suggest that distributed reactions can be a common combustion mode. For the LUPJ flames, the dependence of the reaction zone broadening on the jet speed and the equivalent ratio was investigated systematically. Spatial correlations between the scalars that were measured were investigated, and the detailed local flame structures with and without the presence of distributed reactions were analyzed and compared. It was found that having a temperature above ~ 1000 K is important for sustaining the distributed reactions. The build-up of radical pools through rapid turbulence transport in regions containing (intermediate) reactants was found to be responsible for the distributed reactions occurring. In addition, a study of Mild combustion that has similarities with the distributed reaction concept was performed using optical diagnostics. Certain insights concerning the reaction zone structure of Mild combustion are discussed. Nowadays, the majority of energy production comes from combustion which is universally linked to daily human activities. Public awakening of the environmental effects of combustion pollution evokes extensive research activities in improving combustion efficiency and reducing pollutant production. Development of combustion processes also includes the use of renewable biomass-derived fuels has emerged to replace the foreseeable limited energy supply from fossil fuels. However, in spite of the long history over which man has tried to control combustion, our knowledge of combustion…