Abstract
Adaptability of fuel is an essential design requirement of advanced gas turbines. Hydrogen-rich fuel gas can be obtained from a variety of sources, and its use will be an important part of the future development of gas turbines. When using gas turbine combustion technology to burn hydrogen-rich fuel, if the flame goes out, it will lead to unsafe equipment. As a result, the extinction of turbulent hydrogen-rich fuel flame is the key problem when we design gas turbine combustors.
In this study, the optimized experimental approach and numerical simulation method of counterflow flame are used to compare the extinction strain rate of two typical hydrogen-rich fuel gases under laminar and turbulent combustion conditions, and the main reasons for the difference were examined. Two typical hydrogen-rich fuel gases used in this study are called FA and FB in this paper. As far as FA is concerned, the CO component ratio of fuel is higher, the dilution ratio is lower, and the calorific value is significantly higher. FA can be considered as the typical hydrogen-rich synthetic gas obtained from entrained flow coal gasification, and FB can be regarded as the typical hydrogen-rich synthetic gas obtained from fluidized bed coal gasification, both of which have certain representative significance. The upper nozzle of the counterflow flame produces nitrogen, while the lower nozzle produces premixed fuel with varying equivalence ratios. The equivalence ratio covers a range of 0.4-1.0. The gas temperature at the nozzle outlet is 300 K. The particle image velocimetry (PIV) system is used to obtain the velocity information of the flow field at the nozzle outlet. The turbulent transport model is added to the OPPDIF code for numerical simulation.
The results demonstrated that, within the range of working conditions studied, the numerical simulation method used in this paper could well predict the extinction strain rate of laminar and turbulent flames. The difference between experimental and simulation results was less than ±10% for a laminar counterflow flame and ±40% for a turbulent counterflow flame. Due to the instability of the turbulent flow field, the measurement of the extinction strain rate fluctuated greatly during the turbulent combustion experiment, and the error bar was greater than that of the laminar combustion experiment.
Under laminar combustion conditions, hydrogen-rich fuel gas with a higher mole fraction of active radicals such as H, O, and OH in the flame front has a higher reaction rate and heat release rate of key chemical reactions, so it can resist higher flame stretching deformation. With the increase of the equivalence ratio, the extinction strain rate indicates an upward trend. Turbulence not only improves the mixing of active groups and reactants, thereby improving the reaction, which increases the rate of key chemical reactions and heat release in the reaction area, but it also improves heat transfer of the flame from inside to outside, resulting in a lower internal temperature of the flame.
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