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Chemiluminescence information is of great significance for characterization of flame structure and combustion characteristics. An atmospheric low swirl burner was developed to investigate the chemiluminescence characteristics of OH* and CH* in low swirl flames, with the equivalence ratio varying from 0.8 to 1.2 and the swirl number from 0.2 to 0.6. The chemiluminescence images were captured via ICCD cameras coupled with narrow-bandpass filters, and an Abel inversion method was introduced to transform the line-of-sight-integrated image into two-dimensional radial distributions. The results show that the distribution of CH* is smaller than that of OH* and concentrated more upstream of the flame near the burner. The equivalence ratio has a relatively more direct influence on chemical reactions, while the swirl number has a more evident effect on the flame structure. As the equivalence ratio increases, the peak value of OH* and CH* increases and the peak position moves downstream of the flame, suggesting that the chemical reactions become more intense. In contrast, the height and width of chemiluminescence distribution increase linearly with increasing swirl number. Moreover, it is found that the equivalence ratio and swirl number can be feasibly estimated based on chemiluminescence measurement results, using the correlation between them derived from this study. [ABSTRACT FROM AUTHOR]

Numerical and experimental studies on 1-D, steady premixed methane-air flames were performed to investigate the quantitative measurement of heat release rate (HRR) using chemiluminescence. A detailed reaction mechanism, incorporating sub-reaction models for excited state radicals (CH* and OH*) was employed in the numerical study. The numerical work utilized the CHEMKIN-PRO package to investigate the distribution rule of excited state radicals and HRR. The heat release characteristic of elementary reactions and the relationship between net reaction rate and HRR were analyzed as well. According to the result of numerical study, experimental work was conducted to measure the HRR and chemiluminescence of OH* and CH* in the flat flames. The distributions of HRR and chemiluminescent intensity were measured by high-accuracy coated Pt/13%-Rh-Pt thermocouple and ICCD camera, respectively. The results shows that OH* and CH* are located in the narrow area where severe chemical reactions occur with much heat release. Compared to CH*, OH* is more effective in marking the spatial distribution of HRR and the correlation between chemiluminescent intensity and HRR possesses characteristic of linearity. Thus, the HRR quantitative measurement method using chemiluminescence has been acquired. • OH* is more effective in marking the spatial distribution of HRR than CH*. • HRR can be measured quantitatively by OH* and CH* chemiluminescence. • There is a strong linear correlation between chemiluminescent intensity and HRR. • The proportionality coefficient decreases with increasing equivalence ratio. [ABSTRACT FROM AUTHOR]

Abstract As single component chemiluminescence cannot accurately measure the distribution of heat release rate, this paper put forward the idea of employing OH* and CH* chemiluminescence for the measurement. However, it is difficult to characterize the relationship between chemiluminescence and heat release rate, so the method of deep learning was applied to process numerical simulation results of methane-air steady premixed flames and a deep neural network model was developed to determine the distribution of heat release rate with OH* and CH* chemiluminescence. The evaluation indexes of the model performed satisfactorily: root mean square error of the normalized heat release rate is less than 0.13, mean relative error of peak and opening distance is below 3%, and mean error of peak position less than 0.01 mm. The validation results showed that OH* and CH* chemiluminescence could properly measure the distribution of heat release rate: relative error of peak ranges from −6% to 6%; on test dataset, correlation coefficient between predictive results and simulation results is above 0.99 in terms of heat release rate peak, peak positions and opening distance. Highlights • Deep learning was applied to process numerical simulation results. • HRR can be characterized by OH* and CH* chemiluminescence. • The deep neural network has good generalization ability and average performance. • OH* and CH* chemiluminescence can properly measure the distribution of HRR. [ABSTRACT FROM AUTHOR]

Computed tomography of chemiluminescence (CTC) is a promising technique for combustion diagnostics, providing instantaneous 3D information of flame structures, especially in harsh circumstance. This work focuses on assessing the feasibility of CTC and investigating structures of hydrogen-air premixed laminar flames using CTC. A numerical phantom study was performed to assess the accuracy of the reconstruction algorithm. A well-designed burner was used to generate stable hydrogen-air premixed laminar flames. The OH⁎ chemiluminescence intensity field reconstructed from 37 views using CTC was compared to the OH⁎ chemiluminescence distributions recorded directly by a single ICCD camera from the side view. The flame structures in different flow velocities and equivalence ratios were analyzed using the reconstructions. The results show that the CTC technique can effectively indicate real distributions of the flame chemiluminescence. The height of the flame becomes larger with increasing flow velocities, whereas it decreases with increasing equivalence ratios (no larger than 1). The increasing flow velocities gradually lift the flame reaction zones. A critical cone angle of 4.76 degrees is obtained to avoid blow-off. These results set up a foundation for next studies and the methods can be further developed to reconstruct 3D structures of flames. [ABSTRACT FROM AUTHOR]

• A heat-resisting quartz tube is designed to confine a supersonic jet flame. • The characteristics of confined jet flames are comprehensively studied. • Three representative combustion modes of the confined jet flames are concluded. • The distributions of CH* and OH* of the confined flames are presented. This work studied the combustion characteristics of a highly-turbulent premixed jet flame influenced by a confined space. A piloted premixed jet burner is used to generate a supersonic methane-air fuel-rich flow and a heat-resisting quartz tube is located coaxially above the jet flame which acts as the confined space. Flame luminosity, OH* and CH* chemiluminescence were captured at different distances between the tube and the burner (H). Jet flame characteristics have been comprehensively investigated from flame extinction to combustion enhancement with the increasing of H. A critical value of H has been identified, below which the flames will be extinguished by the ejection effect of the confined space and the central jet. For the self-sustained confined jet flames, it can be concluded that there are three representative flame structures with the increasing of H , namely the V-shaped flame, converging flame and fully developed flame. The ignition failure of the central region in the fuel jet is found to be the immediate cause for the presence of the V-shaped flame. In the converging flame, a region where strong combustion occurs (the first intense combustion region, FICR) can be observed around the entrance of the confined space, which is mainly formed by the chemical reactions of CH* and OH*. For the fully developed flame, besides FICR , a second intense combustion region (SICR) that mainly related to OH* reaction pathways will emerge in the confined space. [ABSTRACT FROM AUTHOR]