Periodic Reporting for period 4 - TUCLA (Towards a deepened understanding of combustion processes using advanced laser diagnostics)
Berichtszeitraum: 2020-07-01 bis 2021-12-31
Combustion continues to account for a large part of the energy supply and utilization worldwide also in future scenarios. However, it also significantly contributes to the formation of greenhouse gases, such as CO2, and environmental pollutants, e.g. NOx and SOx. Mitigation measures include different combustion technologies and the use of renewable fuels such as CO2-neutral biomass. Hydrogen and ammonia have also gained interest in a future energy supply with a reduced carbon footprint. A future carbon-free concept is metal-particle combustion with regeneration of metal oxides using renewable energy sources, thus creating a sustainable process.
For detailed understanding of complex combustion processes to address these challenges mentioned above, crucial information can be obtained from experimental studies with non-intrusive laser-diagnostic techniques measuring key parameters such as species concentrations and temperatures. The overall objective has been to develop and apply such techniques for further understanding of combustion processes. The role of combustion in the current and future global energy supply makes the project relevant to society.
The project has been arranged in five work packages (WP1-5) for which the objectives are summarized below.
1. Structured illumination concepts to add new dimensions to present diagnostics with unprecedented temporal resolution, instantaneous 3D imaging, multi-scalar measurements and efficient suppression of background light.
2. Ultrafast femto/picosecond lasers for new diagnostic concepts based on backward lasing, non-linear optical excitation, and photodissociation.
3. Detailed flame studies under laminar and turbulent conditions and at atmospheric and elevated pressure.
4. Biomass gasification, where complex fuels require new techniques to measure nitrogen, alkali, chlorine, and sulphur compounds.
5. Combustion enhancement by electric activation, which can be introduced to handle flame oscillations and instabilities.
The majority of the project goals have been fulfilled. The research of WP1-2 has resulted in advanced laser-diagnostic methods, in many cases achieving performance beyond state-of-the-art for this type of techniques. The developed methods have been applied for phenomenological studies in WP3-5 as outlined above.
For detailed understanding of complex combustion processes to address these challenges mentioned above, crucial information can be obtained from experimental studies with non-intrusive laser-diagnostic techniques measuring key parameters such as species concentrations and temperatures. The overall objective has been to develop and apply such techniques for further understanding of combustion processes. The role of combustion in the current and future global energy supply makes the project relevant to society.
The project has been arranged in five work packages (WP1-5) for which the objectives are summarized below.
1. Structured illumination concepts to add new dimensions to present diagnostics with unprecedented temporal resolution, instantaneous 3D imaging, multi-scalar measurements and efficient suppression of background light.
2. Ultrafast femto/picosecond lasers for new diagnostic concepts based on backward lasing, non-linear optical excitation, and photodissociation.
3. Detailed flame studies under laminar and turbulent conditions and at atmospheric and elevated pressure.
4. Biomass gasification, where complex fuels require new techniques to measure nitrogen, alkali, chlorine, and sulphur compounds.
5. Combustion enhancement by electric activation, which can be introduced to handle flame oscillations and instabilities.
The majority of the project goals have been fulfilled. The research of WP1-2 has resulted in advanced laser-diagnostic methods, in many cases achieving performance beyond state-of-the-art for this type of techniques. The developed methods have been applied for phenomenological studies in WP3-5 as outlined above.
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.
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.
The method development in WP1-2 has opened up for new diagnostic possibilities, exemplified by three achievements:
• Structured illumination provides a multifaceted high-performance tool suitable for a range of laser-diagnostic applications and thus advances laser-diagnostics beyond state-of-the-art.
• Backward lasing providing increased opportunities for remote sensing has been introduced in combustion environments.
• Laser-induced photofragmentation techniques have been developed into applicable tools, e.g. in thermochemical conversion studies of biomass fuels. For example, single-shot absolute 2D concentration fields of KOH, KCl, and ammonia have been achieved for the first time using these techniques.
Achievements beyond state-of-the-art for the phenomenological studies of WP3-5 include:
• True quantitative data from experimental studies that have increased insights into the combustion processes and contributed to the development of computational models.
• New insights in combustion under highly turbulent conditions with distributed chemical reactions for which previous knowledge and understanding are limited.
• New insights on the electric activation of combustion providing improved flame stabilization and thereby extending operation to more fuel-lean conditions and further utilization of alternative fuels.
• Structured illumination provides a multifaceted high-performance tool suitable for a range of laser-diagnostic applications and thus advances laser-diagnostics beyond state-of-the-art.
• Backward lasing providing increased opportunities for remote sensing has been introduced in combustion environments.
• Laser-induced photofragmentation techniques have been developed into applicable tools, e.g. in thermochemical conversion studies of biomass fuels. For example, single-shot absolute 2D concentration fields of KOH, KCl, and ammonia have been achieved for the first time using these techniques.
Achievements beyond state-of-the-art for the phenomenological studies of WP3-5 include:
• True quantitative data from experimental studies that have increased insights into the combustion processes and contributed to the development of computational models.
• New insights in combustion under highly turbulent conditions with distributed chemical reactions for which previous knowledge and understanding are limited.
• New insights on the electric activation of combustion providing improved flame stabilization and thereby extending operation to more fuel-lean conditions and further utilization of alternative fuels.