Abstract
The effect of wall thickness on the combustion characteristics of nonpremixed hydrogen micro-jet flames was studied by two-dimensional numerical computation with a detailed reaction kinetics for the development of hydrogen micro-burner. The hydrogen jet diffusion flames achieved by micro-tubes with the same inner diameter and length but different wall thicknesses were investigated. The heat exchange between solid tube and gases were included in the numerical computation. The distributions of flame temperature, OH radicals, details of thermal interaction, and combustion efficiency were analyzed for comparison. It was found that the temperature distribution, flame shape, and heat recirculation are changed with the fuel flow velocity, and they are affected by wall thickness. The mechanism of wall thickness on the combustion characteristics of hydrogen jet diffusion flame was clarified. Finally, an interesting numerical experiment was conducted to give a further explanation of the effect of heat recirculation and to provide guidance of the thermal management of the micro-burner.
Highlights
With the increasing consumption of fossil fuels and the worsening of the environmental issues, the interests on alternative fuels have been significantly increased in the last decade (Alazemi and Andrews, 2015)
The hydrogen micro-jet flames achieved by micro-tubes with inner diameters (4) of 0.28 and 0.71 mm and wall thickness (δ) of 0.1 and 0.17 mm were measured by using planar laser-induced fluorescence technique for OH radical (OHPLIF)
The results reveal that reducing the thermal conductive wall thickness can improve the heat recirculation at fuel velocities of 1 and 2.5 m/s, while all the micro-tubes play a negative role on the hydrogen flame at the fuel velocity of 0.4 m/s because the heat is transferred from the gas to the inner surfaces
Summary
With the increasing consumption of fossil fuels and the worsening of the environmental issues, the interests on alternative fuels have been significantly increased in the last decade (Alazemi and Andrews, 2015). Hydrogen can be produced from flexible renewable energy sources, such as wind and solar power generation. The application of hydrogen combustion has advantages in emissions, since it has no CO2 and soot generations (Sharma and Ghoshal, 2015; Dimitriou and Tsujimura, 2017). These advantages make it as one of the promising candidates for future energy system. Extensive work has been conducted to study the combustion characteristics of hydrogen or hydrogen blend fuels in various power systems. The combustion characteristics of jet-A and hydrogen flames in a turbojet engine have been compared based on numerical computation (Kahraman et al, 2018). It was found that the power output and thermal efficiency
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