Effects and mechanisms of steam-diluent on the H2-O2 coaxial diffusion flames characteristics

Abstract

The wet hydrogen-oxygen combustion technology with steam dilution is considered one of the most promising hydrogen utilization in the future. Steam dilution significantly influences the flame's physical yield by affecting diffusion. This study's diffusion mechanisms of steam dilution hydrogen-oxygen coaxial diffusion flame are experimentally and numerically investigated on the macroscopic and microscopic scale. The results indicate that steam dilution has a suppressive effect on combustion. At the macroscopic scale, there is a reduction in flame brightness, height, and width across a wideband wavelength spectrum as the content of steam increases. Steam dilution reduces the concentration and the space distribution of OH* in the main reaction zone. Moreover, there appears to be a threshold value for steam content at approximately 30 %∼40 %. Significant changes are observed in flame characteristics at high steam content and contrast at low steam content. The increased jet momentum flux ratio and the weakening of the heat release effect are critical factors for steam diluent to effectively reduce flame stoichiometric mixing lengths. At the microscopic scale, the H₂ effective diffusion coefficient is analyzed to achieve a molecular-level analysis of the mechanism of steam dilution. The impact of turbulence on the H₂ effective diffusion coefficient gradually intensifies as the jet distance increases. The steam addition concurrently alters the multi-physical characteristics, including velocity field, temperature field, and kinematic viscosity. The synergistic effects of these characteristics slightly modify the H₂ effective diffusion coefficient's peak while delaying its appearance in the physical field. This study provides theoretical foundations and data support for advancing wet hydrogen-oxygen combustion technology.