Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Abstract

This numerical study investigates the combustion modes in the second stage of a sequential combustor at atmospheric and high pressure. The sequential burner (SB) features a mixing section with fuel injection into a hot vitiated crossflow. Depending on the dominant combustion mode, a recirculation zone assists flame anchoring in the combustion chamber. The flame is located sufficiently downstream of the injector resulting in partially premixed conditions. First, combustion regime maps are obtained from 0-D and 1-D simulations showing the co-existence of three combustion modes: autoignition, flame propagation and flame propagation assisted by autoignition. These regime maps can be used to understand the combustion modes at play in turbulent sequential combustors, as shown with 3-D large eddy simulations (LES) with semi-detailed chemistry. In addition to the simulation of steady-state combustion at three different operating conditions, transient simulations are performed: (i) ignition of the combustor with autoignition as the dominant mode, (ii) ignition that is initiated by autoignition and that is followed by a transition to a propagation stabilized flame, and (iii) a transient change of the inlet temperature (decrease by 150 K) resulting into a change of the combustion regime. These results show the importance of the recirculation zone for the ignition and the anchoring of a propagating type flame. On the contrary, the autoignition flame stabilizes due to continuous self-ignition of the mixture and the recirculation zone does not play an important role for the flame anchoring.

Effect of Mixing on the Anchoring and Combustion Regimes of Pure Hydrogen Flames in Sequential Combustors

“…This findings were confirmed experimentally [13], and numerically [12]. Three combustion regimes were observed while investigating numerically the steady-state and transient operation of the same sequential burner [14], namely propagation, propagation assisted by autoignition, and autoignition. Habisreuther et al [15] showed numerically that consumption speed of flames increases for increasing mixture temperatures above the autoignition value, also changing the flame structure.…”

“…Several studies analyzed flame stabilization mechanisms in second stage flames featuring a jet-in-crossflow configuration [10,11] where [10] used H 2 -rich fuels. In sequential combustion configuration [12][13][14][15][16][17][18][19] used natural gas/air mixtures. It was demonstrated using LES that flame stabilization is governed by autoignition and propagation combustion regimes [12].…”

Numerical study of ignition and combustion of hydrogen-enriched methane in a sequential combustor

“…tion zone (Z2) is located in the CC and strengthens the flame stabilization. Hot combustion products and radicals are trapped in this recirculation zone and support flame anchoring at the burner outlet, thereby inhibiting sudden flame blow-off when the ignition delay becomes significantly longer than the residence time in the SB [39,5].…”

Autoignition flame transfer matrix: Analytical model versus large eddy simulations

“…Research at Ansaldo Energia of Bothien and co-workers focuses on flame transfer functions and matrices. [8][9][10][11] Schulz and Noiray 12,13 as well as Aditya et al 14 and Gruber et al 15 investigate the occurrence of propagation and autoignition stabilized regimes of reheat flames. In contrast to propagation stabilized flames, only a few studies on analytical modelling approaches for autoignition flame acoustics exist.…”