Structured illumination concepts opened up new diagnostic opportunities including (i) ultrafast videography, (ii) instantaneous 3D data acquisition, (iii) snapshot multispectral imaging, (iv) boosted spectral contrast and (v) improved temporal contrast. For example, rapidly illuminating a sample with laser beams encoded with different spatial structures, we have successfully achieved acquisition of video data on a femtosecond timescale, significantly faster than previous methods for videography. We have also demonstrated structured illumination for filtering of signals by modulation, e.g. in Raman spectroscopy and for time-resolved measurements.
Diagnostic concepts exploiting ultrashort (pico- and femtosecond) laser pulses for (i) imaging of non-fluorescing species by photofragmentation laser-induced fluorescence (PFLIF), (ii) two-photon laser-induced fluorescence (TPLIF) for imaging of species, (iii) backward lasing for single-ended detection of species, and (iv) ultrafast (fs) videography (see above). Briefly, the major achievements are: (i) specific detection of hydrogen peroxides in flames (ii) TPLIF imaging of hydrogen and oxygen atoms as well as CO in flames. The most significant achievements for TPLIF are: 1) instantaneous single-shot 2D visualization of species, e.g. for studies of turbulent flames. 2) a visualized area almost an order of magnitude larger compared to previous results. 3) simultaneous single-shot imaging of multiple species (H and O atoms). (iii) Backward lasing has been developed and demonstrated for the detection of H and O atoms.
Developed methods have been employed for detailed studies of combustion and gasification in WP3-4. For example, in investigations of ammonia combustion with a particular focus on the fuel-nitrogen conversion chemistry. Results were compared with state-of-the-art modeling including detailed chemistry and computational fluid dynamics. Studies of turbulent combustion, relevant for practical applications, were made using simultaneous imaging of multiple chemical species to clarify interactions between turbulence and combustion chemistry, in particular at high levels of turbulence with spatially distributed reactions. For biomass, the alkali-chlorine chemistry was studied with quantitative measurements of e.g. HCN, HCl, and KOH, which enabled validation of kinetic models.
WP5 aimed at investigating electric activation of combustion. The outcomes can be divided into diagnostic development and application, plasma characterization, and electric stimulation and activation of combustion. For example, electric stimulation by microwave irradiation in a large-scale swirl-stabilized turbulent flame lowered the flammability limit and increased the turbulent flame speed. A gliding-arc plasma could sustain flames under highly turbulent conditions, also at a larger scale, and stimulate a flame at elevated pressure. Nanosecond high-voltage pulse stimulation has shown promising results for the next generation of electric activation in large-scale burners.
Close connections to other projects that involved collaborations with expertise in combustion research and industrial partners ensured an immediate use of developed methods and investigations of relevant combustion phenomena. The links to industrial partners also formed a channel for disseminating results to such stakeholders, e.g. via regular meetings and program conferences for these activities. The research has been presented to the scientific community via peer-reviewed publications and substantial exposure at international research conferences. In addition, activities have been presented to the general public via articles in magazines, social media, radio and TV.
