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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]

Hydrogen-rich syngas, produced from biomass-based feedstocks, is a promising alternative energy source. However, its combustion characteristics are completely different from those of typical hydrocarbon fuels due to the presence of hydrogen. As a result, the kinetic mechanism of hydrogen-rich syngas premixed flame (HRSPF) propagation is very complex. In this work, the propagation of HRSPF was investigated employing different fan speeds (0–4273 rpm), hydrogen fractions (55%–95%), pressures (1.0 bar–3.0 bar), and equivalence ratios (0.6–1.0). It was found that the propagation speed of turbulent HRSPF increased when the mixing process of turbulent flow was enhanced or the stretching effect of flame front was weakened. When the turbulence intensity increased, the effect of flame inherent instability on the propagation speed of HRSPF was weakened. When the relative changes of thermal diffusion and mass diffusion of flame front were considerable, the effect of diffusional-thermal instability on flame acceleration process was more significant. On the contrary, the effect of hydrodynamic instability on flame acceleration process was more significant. [Display omitted] • The stretching effect of flame front on flame propagation was studied. • Effect of both turbulence and flame inherent instabilities on the u t were evaluated. • Self-similar propagation coupled with diffusional-thermal instability was analyzed. • Effect of accelerated propagation process of the HRSPF was analyzed. [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]

For studying the effect of carbon dioxide (CO 2) on the self-accelerating properties of syngas/air mixture's turbulent premixed flame, an experimental study was carried out on 90%H 2 /10%CO/air mixture at the turbulence intensity of 1.31 m/s. The effects of various equivalence ratios (0.6, 0.8 and 1.0) and carbon dioxide contents (10%, 20% and 30%) on the flame evolution and propagation speed were studied. The effects of the CO 2 contents and equivalence ratios on the self-acceleration properties in the flame propagation transition stage were evaluated. The effects of effective Lewis number and Zel'dovich number on the fractal excess and acceleration exponent were analyzed. The results showed that, as the CO 2 contents increased, the development process of the flame slowed down, and the rate of growth of the flame's radius and the turbulent premixed flame propagation speed decreased at the same radius. The fractal excess and acceleration exponent increased with the increasing CO 2 contents and decreased with the increasing equivalence ratio. Under different equivalence ratios and CO 2 contents, the syngas/air premixed flame acceleration exponent was less than 1.5 in the transition stage. • Effect of CO 2 content on the flame evolution and propagation speed was studied. • Effect of ϕ and CO 2 content on the self-acceleration properties were evaluated. • The self-acceleration properties in the transition stage were studied. • Effect of Le eff and Ze on the acceleration exponent 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]

The self-acceleration characteristics of a syngas/air mixture turbulent premixed flame were experimentally evaluated using a 10% H 2 /90% CO/air mixture turbulent premixed flame by varying the turbulence intensity and equivalence ratio at atmospheric pressure and temperature. The propagation characteristics of the turbulent premixed flame including the variation in the flame propagation speed and turbulent burning velocity of the syngas/air mixture turbulent premixed flame were evaluated. In addition, the effect of the self-acceleration characteristics of the turbulent premixed flame was also evaluated. The results show that turbulence gradually changes the radius of the premixed flame from linear growth to nonlinear growth. With the increase of turbulence intensity, the formation of a cellular structure of the flame front accelerated, increasing the flame propagation speed and burning speed. In the transition stage, the acceleration exponent and fractal excess of the turbulent premixed flame decreased with increasing equivalence ratio and increased with increasing turbulence intensity at an equivalence ratio of 0.6. The acceleration exponent was always greater than 1.5. • Effect of turbulence intensity on turbulent burning velocity was studied. • Nonlinear propagation characteristics of turbulent premixed flame were evaluated. • Fractal and acceleration characteristics in the transition stage were studied. [ABSTRACT FROM AUTHOR]

To investigate the effect of equivalence ratio and turbulence intensity on the combustion characteristics of syngas/air mixtures, experiments involving premixed combustion of 70% H 2 /30% CO/air mixtures at various equivalence ratios and turbulence intensities were conducted in a turbulent combustion bomb at atmospheric temperature and pressure. The turbulent burning velocity and flame curvature were used to study turbulent combustion characteristics. The results show that the turbulent burning velocity grew nonlinearly as the equivalence ratio increased, while the normalized turbulent burning velocity tended to decrease. When the equivalence ratio was relatively low, the turbulence intensity was a greater determinant of the burning velocity. The normalized turbulent burning velocity increased as the turbulence intensity increased. Re and Da were found to be directly and inversely proportional to u' / u L , respectively. A linear relationship was observed between u T / u L and ln Re. As the turbulence intensity increased or equivalence ratio decreased, the wrinkle degree of the flame front increased, and the maximum and minimum values of flame front curvature increased and decreased, respectively. Meanwhile, the range of the flame front curvature increased gradually. The proportion of components with smaller absolute value of flame front curvature gradually decreases. • Effect of equivalence ratios on the turbulent burning velocity were studied. • Effect of turbulence on the burning velocity were studied. • Turbulent premixed flame curvature was studied. [ABSTRACT FROM AUTHOR]

An experimental study was conducted using outwardly propagating flame to evaluate the laminar burning velocity and flame intrinsic instability of diluted H 2 /CO/air mixtures. The laminar burning velocity of H 2 /CO/air mixtures diluted with CO 2 and N 2 was measured at lean equivalence ratios with different dilution fractions and hydrogen fractions at 0.1 MPa; two fitting formulas are proposed to express the laminar burning velocity in our experimental scope. The flame instability was evaluated for diluted H 2 /CO/air mixtures under different hydrogen fractions at 0.3 MPa and room temperature. As the H 2 fraction in H 2 /CO mixtures was more than 50%, the flame became more unstable with the decrease in equivalence ratio; however, the flame became more stable with the decrease in equivalence ratio when the hydrogen fraction was low. The flame instability of 70%H 2 /30%CO premixed flames hardly changed with increasing dilution fraction. However, the flames became more stable with increasing dilution fraction for 30%H 2 /70%CO premixed flames. The variation in cellular instability was analyzed, and the effects of hydrogen fraction, equivalence ratio, and dilution fraction on diffusive-thermal and hydrodynamic instabilities were discussed. [ABSTRACT FROM AUTHOR]

In this study, the influence of turbulence intensity on flame local structural and local propagation characteristics was studied. In order to achieve this, 50% H2/50% CO with equivalence ratio of 0.8 were conducted under different turbulence intensities ranging from 0 to 1.31 m/s at atmospheric pressure and temperature. The distribution of the flame local radius and flame local propagation speed and the correlation between the two were investigated. The results show that the turbulence can increase the disturbance in the flame front, and enhance the fluctuation of the flame local radius, resulting in an increase in the fluctuation of the flame local propagation speed. With the development of flame, the distribution of the flame local propagation speed tended to become uniform, while the intersection zone of the flame local propagation speed and the flame local radius distribution gradually decreased. When the turbulence intensity ranged between 0.49 m/s to 0.74 m/s and between 1.08 m/s to 1.31 m/s, the sensitivity of the flame local propagation speed to its local characteristics reduced with the increase of the turbulence intensity. [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]