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Abstract:In this study, the effect of flame intrinsic instability on the flame structural characteristics of hydrogen/air mixtures premixed at various equivalence ratios were experimentally investigated from the macroscopic and microscopic perspectives, respectively. The correlation degree and the relative deformation degree were defined to quantitatively study the global flame structural characteristics. Peak detection was used to capture the characteristic length of the flame and fast Fourier transform was adopted to study the components of the fluctuation of the flame front. The results show that with the development of flames, the wrinkles in the flame front increase and the correlation degree of the flame decreases. The relative deformation degree of the flame first decreases and then increases. When the equivalence ratio is 0.6, the average characteristic length initially exhibits an increasing trend, followed by a decreasing trend. The average characteristic length scale gradually increases, and the growth rate gradually decreases when the equivalence ratio ranges from 0.70 to 0.99. With the increase in the wavenumber, the amplitude of the corresponding disturbance exhibited an increasing trend followed by a decreasing one. With the development of the flame, the maximum amplitude of the disturbance shows a reverse trend, i.e., first decreasing and then increasing. The disturbances with smaller wavelengths could be further developed.

To investigate the effect of the flame inherent instabilities and turbulence on the flame structural characteristics, premixed combustion experiments of 50% H2/50% CO at a equivalence ratio of 0.6 were conducted in a turbulent combustion bomb in atmospheric temperature and pressure. The correlation degree was defined to study the correlation relation between flame structural characteristics at different moments, and the wavelet transform was used to investigate the detail components at different scales. The results indicate that, with the development of the flame, the cellular structure was enhanced and the correlation degree gradually decreased. The fluctuations of the detail components at the larger scale were stronger and included more energy, which corresponded to the main factor causing the flame front complex. With the turbulence intensity increase, the root mean square amplitude and energy of the detail components increased, leading to the increase of the interaction of different disturbances, while the correlation degree of the flame decreased. The correlation degree of the detail components presented a staggered distribution of higher and lower values, which indicated the complex changes of the disturbances at different scales.

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