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As a kind of fuel with low‐carbon emissions, hydrogen‐rich syngas has a large resource potential and is a promising alternative energy resource. A series of experiments in a constant volume combustion bomb are carried out to investigate the effects of turbulence and diffusional–thermal (DT) instability on a hydrogen‐rich syngas turbulent premixed flame. The flow field in the constant volume combustion bomb is calibrated, and the turbulent flow field's homogeneity and isotropy were investigated. The effects of different speeds of fan (1366–4273 rpm), hydrogen fractions (55%–95%), pressures (1.0–3.0 bar), and equivalence ratios (0.6–1.0) on the hydrogen‐rich syngas turbulent premixed flame are studied. According to the analyses, the flow field in the experimental device exhibits good homogeneous and isotropic characteristics. With the increase of turbulence intensity, equivalence ratio, hydrogen fraction, or pressure, the turbulent flame propagation speed increases gradually. As the hydrogen fraction increases or the equivalence ratio decreases, the effective Lewis number decreases, and the effect of DT instability on the flame increases. The research in this article is crucial for the clean and efficient utilization of hydrogen‐rich syngas and the design of related burners. [ABSTRACT FROM AUTHOR]

As a clean fuel with low carbon emissions, hydrogen-rich syngas has higher flame propagation speed and higher adiabatic flame temperature than other gaseous fuels, so its local flame propagation characteristics are also different from other fuels. In this paper, an experimental study on the hydrogen-rich syngas turbulent premixed flame was carried out at different pressures [101–303 kPa (1.0–3.0 bar)] when the hydrogen fraction was 65%, the fan speed was 3,559 revolutions/min (rpm), and the equivalence ratio was 1.0. The results show that with the propagation of the flame or the increase in pressure, the fluctuation amplitude of flame local radius and flame local pulsation radius becomes smaller. Similarly, the flame local propagation speed increases with the increase of pressure. By analyzing the correlation between the turbulent premixed flame front structure and the turbulent premixed flame propagation process in hydrogen-rich syngas, it is found that when the pressure increases, the correlation between the flame local pulsation propagation speed and the flame local pulsation radius weakens. [ABSTRACT FROM AUTHOR]

To study the effects of different diluents on the propagation characteristics of H 2 /CO/air mixture turbulent premixed flames, a series of experiments were carried out in a turbulent premixed flame experimental system. The effects of turbulence intensity (0.49–1.31 m/s), dilution gas content (10%, 20%, and 30%), hydrogen fraction (50%, 70%, and 90%), and equivalence ratio (0.6, 0.8, and 1.0) on the turbulent premixed flame were studied. The results show that with the increase in hydrogen fraction or turbulence intensity or equivalence ratio, the S T and u t increase at the same radius. Compared with N 2 dilution, CO 2 dilution showed a more obvious inhibition effect on S T. With the increase of Ka , S T;35mm /u' gradually decreased, and the extent of S T;35mm /u' decrease gradually became smaller. As the intensity of turbulence increases or the hydrogen fraction increases, the slope of S T,35mm /u' with Da/Le gradually decreases. In the turbulence intensity range of this experiment, the u t,35mm / μ l under nitrogen dilution condition has a larger floating range. The growth rate of u t,35mm / μ l at a low equivalence ratio is significantly higher than that at a high equivalence ratio. • Effect of diluent content on the turbulent flame propagation speed was studied. • Relationship between Ka and S T,35mm /u' of syngas/air mixture flame was evaluated. • Effect of u' , φ and X H2 on flame propagation characteristics were studied. • Effect of Da and Ze on the turbulent burning velocity was analyzed. [ABSTRACT FROM AUTHOR]

To investigate self-acceleration propagation characteristics of a laminar premixed flame, an experimental study of H 2 /CO/air mixtures with various hydrogen fractions and equivalence ratios was conducted. The acceleration exponent and fractal excess were defined to quantitatively investigated flame self-acceleration in the transition and saturation stages. Also, the influence of flame inherent instabilities on the acceleration exponent in the transition stage were investigated. The results indicate that with an increase in the hydrogen fraction, the first and second critical radius decreased, the proportion of the transition (saturation) stage in the whole flame propagation process decreased (increased), and the acceleration exponent and fractal excess of the transition and saturation stages increased. Because of the limits of flame radius and different degrees of pulsation in the saturation stage, the acceleration exponent and fractal excess at the saturation stage measured do not show obvious regularity; the values are less than 1.5 and 0.33, respectively. When the hydrogen fraction in syngas is changed, the acceleration exponent in the transition stage showed a nonlinear decreasing trend with an increase in the effective Le number. The hydrodynamic instability usually increased with a decrease in flame thickness, and the acceleration exponent in the transition stage increased. • Effect of hydrogen fraction on flame inherent instabilities was studied. • Effect of hydrogen fraction on self-acceleration propagation was studied. • Correlation between acceleration exponent and Le number was studied. • Correlation between acceleration exponent and flame thickness was studied. [ABSTRACT FROM AUTHOR]

To investigate the effect of flame inherent instabilities on the flame structural characteristics of H 2 /CO/air mixtures, experiments were conducted in a constant combustion bomb at various hydrogen fraction and equivalence ratio at room pressure and temperature. Wavelet transform was adopted to decompose the disturbances with different scales in the flame front. To study quantitatively the flame geometric structure characteristics, the maximum and minimum fluctuation radius growth rate, fluctuation range growth rate and energy of decomposition component were defined. The results indicated that with the flame development the disturbances at different scales all get greatly promotion. The higher the scale of the decomposition, the greater the amplitude and the energy of the disturbances. The disturbances at lower decomposition scales are the dominant component of the flame geometric structure characteristics; the ones at higher decomposition scales have a significance influence on the flame local geometric structure characteristics. When the flame development approached to a certain degree, the fluctuation range growth rate increased with the flame development. With the decrease of the equivalence ratio or the increase of hydrogen fraction, the thermal-diffusive instability enhances, leading to an increase of the fluctuation range growth rate and the relative energy of the approximate component at decomposition scale nine. [ABSTRACT FROM AUTHOR]

• Turbulent combustion experimental studies of hydrogen-rich syngas were conducted in a fan-stirred turbulent combustion chamber. • The power-law correlations between S T /S L and Re T,flame were obtained under different conditions. • The acceleration exponent was extracted to quantitatively investigate the flame self-acceleration propagation in the transition stage. • The relationships between acceleration exponent and u' , Kz , L T , δ , ρ u / ρ b , Le eff were analyzed. In order to investigate the flame self-similar propagation and flame acceleration characteristics of hydrogen-rich syngas turbulent expanding flames, the turbulent combustion experimental studies of H 2 /CO/air mixtures with X H2 = 55%-95%, φ = 0.6–1.0, P = 1 bar-3 bar, u' =0.809–2.533 were conducted in a fan-stirred turbulent combustion chamber with an inner diameter of 380 mm. Results show that the normalized flame propagation speed S T /S L and turbulent flame Reynolds number Re T,flame could be represented by power-law correlations. With the increase of hydrogen fraction from 55% to 95%, the power exponent decreases from 0.413 to 0.301. The increase of hydrogen fraction makes the flame acceleration weaker because that the enhancing of laminar flame speed is more obvious than the differential-diffusion effect by decreasing Le. With the decrease of equivalence ratio from 1.0 to 0.6, the power exponent increases from 0.304 to 0.411 in this study. The relative high power exponent under low equivalence ratio is due to the coupling between differential-diffusion and the flame stretch on the local wrinkled flame structures. In addition, the influence of turbulence and flame intrinsic instabilities on flame acceleration propagation process of hydrogen-enriched syngas were studied. The acceleration exponent was extracted to quantitatively investigate the flame self-acceleration propagation in the transition stage, and the relationships between acceleration exponent and turbulence intensity (u'), Kovasznay number (Kz), turbulence integral length scale (L T), flame thickness (δ), thermal expansion ratio (ρ u / ρ b), effective Lewis number (Le eff) were analyzed [ABSTRACT FROM AUTHOR]

To provide more insight into the laminar burning velocity reduction of diluted syngas premixed flames, the laminar burning velocities of diluted syngas premixed (H 2 /CO/N 2 /air and H 2 /CO/CO 2 /air) laminar spherical flames were systematically and thoroughly investigated experimentally via Schlieren technology. In the present investigation, the volume fraction of H 2 was varied from 30% to 70%, the volume fraction of CO was varied from 30% to 70%, the volume fraction of CO 2 was varied from 0% to 60%, and the equivalence ratio was varied from 0.7 to 1.0. In the present investigation, the effects of equivalence ratio, hydrogen fraction, and dilution fraction on the laminar burning velocities were studied. Compared to N 2 dilution, the laminar burning velocity reduction with CO 2 dilution was analysed through the thermal, transport, and chemical effects. In addition, the contributions of third-body and direction effects were also studied. [ABSTRACT FROM AUTHOR]

The laminar burning characteristics of syngas-premixed (H 2 /CO/CO 2 /air) laminar spherical flames have been systematically investigated through an experiment using Schlieren system. In the experiment, the volume fraction of H 2 in the H 2 /CO part of the H 2 /CO/CO 2 /air mixtures was varied from 30% to 100%, the volume fraction of CO 2 in the H 2 /CO/CO 2 mixtures was varied from 0% to 60%, and the equivalence ratio was varied from 0.4 to 1.0. The effects of hydrogen fraction, carbon dioxide fraction and equivalence ratio on flame propagation, Markstein length, and laminar burning velocities have been studied. The obtained laminar burning velocities were compared with existing data from the literature and excellent agreement was obtained. The flames become more unstable by decreasing the equivalence ratio and increasing dilution fraction. The value of laminar burning velocity decreases apparently with the increase of carbon dioxide dilution fraction due to combined effect of decrease in adiabatic temperature, thermal diffusivity and the CO 2 participation in the chemical reaction of CO + OH ↔ CO 2 + H. With the increase of hydrogen fraction, the laminar burning velocity increases significantly due to the chemical effect and diffusion effect rather than thermal effect. [ABSTRACT FROM AUTHOR]

An experimental study was performed in a constant volume vessel by using the Schlieren system to investigate the laminar burning velocities and Markstein lengths ( L b ) of H 2 /CO lean and stoichiometric ( φ = 0.4 to φ = 1.0) premixed flames under various hydrogen fractions (from 0% to 100%) at atmospheric and elevated pressures and room temperature. The unstretched laminar burning velocities ( S u 0 ) are compared with data from previous literature. Results indicate that excellent agreements are obtained. At 0.1 MPa and room temperature, the stretch behaviour is governed by both the hydrogen and carbon monoxide with hydrogen fraction of less than 50%. However, the hydrogen governs the stretch behaviour with hydrogen fractions of more than 50% because Markstein lengths are essentially the same as for H 2 /air flames. Furthermore, L b generally increases with increasing equivalence ratios for most hydrogen fractions; an opposite trend is observed when the hydrogen fraction is 0%, i.e., in pure carbon monoxide. The unstretched burning velocities of lean and stoichiometric synthesis gas (syngas) premixed flames increase with increasing hydrogen fraction and/or equivalence ratio. The value of unstretched burning velocities decreases with increasing initial pressure with a specific equivalence ratio and hydrogen fraction. [ABSTRACT FROM AUTHOR]

Syngas, a promising renewable alternative fuel, shows different combustion characteristics depending on its exact composition. In this study, the effect of different diluents on the laminar premixed flame of hydrogen-rich syngas was experimentally investigated using a 90% H 2 /10% CO/air mixture in a constant-volume combustion bomb. In particular, this investigation revealed the effects of varying the equivalence ratio (0.6, 0.8, and 1.0) and dilution content (10%, 20%, and 30%) on the flame propagation and explosion characteristics of syngas/air mixture. The results showed that for a given dilution gas content, the flame propagation speed under CO 2 dilution is less than that under N 2 dilution; however, the flame acceleration effect of CO 2 dilution is significantly higher than that of N 2. As the dilution increases, the rate of pressure rise and the maximum combustion explosion pressure gradually decrease. For a given equivalence ratio, the maximum rate of pressure rise and the deflagration index of the flame mixed with N 2 were higher than those for CO 2. • Effect of diluent gas on the flame evolution and propagation speed was studied. • Effect of φ and diluent gas on the self-acceleration properties were evaluated. • The explosion characteristics under various diluent gas were studied. • Effect of dilution fraction on the deflagration index was analyzed. [ABSTRACT FROM AUTHOR]