Numerical Investigation of a Lean Premixed Swirl-Stabilized Hydrogen Combustor and Operational Conditions Close to Flashback

Abstract

The current study presents a numerical investigation of the flow field of a swirl-stabilized burner featuring a non-swirling axial air jet on the central axis of the mixing tube. The system has been designed and optimized to burn hydrogen at the Technische Universität Berlin over the last 6 years in the context of the EU-funded projects GREENEST and AHEAD. As the burner design was based on experimental work, high-fidelity large-eddy simulations (LES) are used to provide deeper understanding on the non-reacting and reacting flow fields to elucidate the occurrence of flashback under certain operating conditions. The experimental measurements suggest that flashback is produced by a velocity deficit at the mixing tube outlet and these conditions are analyzed here using LES. The work includes code validation for non-reacting and reacting conditions by comparison to water tunnel and combustion test rig data, and aims to evaluate the accuracy of LES with a combustion model based on premixed flamelets to predict the reacting flow field under conditions close to flashback.

Numerical Characterization of a Premixed Hydrogen Flame Under Conditions Close to Flashback

“…First, a description of the flow dynamics for the inert case with comparison of the PIV data from experiments is presented. Secondly, an assessment of the perfectly premixed condition using mixing data from technically premixed simulations [20] is given with focus on the flow across the mixing tube. Note that measurements can only be taken in the combustion chamber, and numerical data in this part of the burner is of primary interest to understand the flow conditions before ignition and ultimately prevent the formation and development of flashback in this burner.…”

“…It is well known that mixing quality plays an important role in the thermochemical structure of the flames. In this burner, the fuel/air mixture enters relatively homogeneous to the chamber with a slight shift of hydrogen concentration towards the sides of the mixing tube [20]. After the jet expands in the combustion chamber, the mixture results to be slightly leaner on the sides reducing the production of OH in the outer layer.…”

Numerical assessment of mixing of humid air streams in three-way junctions and impact on volume condensation

“…Researchers in the scope of flow mixing [54,55,56] often rely on such concentration quantities to define coefficients based on squared concentration deviations, in the spirit of the intensity of segregation developed by Danckwerts [57]. A discrete version of Danckwerts' mixing index (MI) is considered in this work as a reference for mixing assessed by a passive scalar, with the following definition:…”

Influence of Axial Air Injection on the Flame Stability of a Technically Premixed Hydrogen Flame

“…Air is pre-heated at T air = 453K and hydrogen at T H2 = 320K. Burner geometry can be found in the experimental papers (Reichel et al, 2018; Reichel andPaschereit, 2017) and previous numerical work (Mira et al, 2018(Mira et al, , 2020. From this baseline condition, three computational cases were derived featuring different levels of axial air injection AI respect to the reference case AI 0 , and those are Case 1-0.9AI 0 , Case 2-0.8AI 0 and Case 3-0.75AI 0 .…”