Abstract
Boundary layer flashback from the combustion chamber into the premixing section is a threat associated with the premixed combustion of hydrogen-containing fuels in gas turbines. In this study, the effect of pressure on the confined flashback behaviour of hydrogen-air flames was investigated numerically. This was done by means of large eddy simulations with finite rate chemistry as well as detailed chemical kinetics and diffusion models at pressures between 0 . 5 and 3 . It was found that the flashback propensity increases with increasing pressure. The separation zone size and the turbulent flame speed at flashback conditions decrease with increasing pressure, which decreases flashback propensity. At the same time the quenching distance decreases with increasing pressure, which increases flashback propensity. It is not possible to predict the occurrence of boundary layer flashback based on the turbulent flame speed or the ratio of separation zone size to quenching distance alone. Instead the interaction of all effects has to be accounted for when modelling boundary layer flashback. It was further found that the pressure rise ahead of the flame cannot be approximated by one-dimensional analyses and that the assumptions of the boundary layer theory are not satisfied during confined boundary layer flashback.
Highlights
The combustion of hydrogen-rich fuels instead of pure hydrocarbon fuels in gas turbines is one possible measure to reduce anthropogenic CO2 emissions in power production
The kinematic viscosity was fixed to ν = 1.8 × 10−5 m2 s−1. This numerical setup resulted in accurate average velocity profiles and turbulent kinetic energy profiles compared to literature DNS results [15]
At atmospheric pressure, confined boundary layer flashback is modeled at bulk velocitites of 10 m s−1, 20 m s−1 and 30 m s−1
Summary
The combustion of hydrogen-rich fuels instead of pure hydrocarbon fuels in gas turbines is one possible measure to reduce anthropogenic CO2 emissions in power production. Endres and Sattelmayer [15] recently presented first simulations that accurately reproduced confined flashback limits of turbulent hydrogen-air flames at atmospheric pressure. They applied large eddy simulations (LES) with finite rate chemistry and a detailed species diffusion model. Comparing the results at different pressure levels allows for the investigation of the influence of average quantities, such as the maximum turbulent flame speed and the average flow deflection, on the flashback limits This is followed by an analysis of the influence of local quantities, such as the local quenching distance and the local separation zone size, on the flashback process. The results are used to investigate the applicability of the one-dimensional pressure estimation (2) and the Stratford separation criterion (1) for BLF prediction
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