Session: Student Poster Competition

Submission Number: 187032

Effect of Hydrogen Enrichment on Flame Structure and Thermoacoustic Instability in a Single Nozzle Combustor 

Hydrogen enrichment in gas turbine combustors is a promising approach for reducing carbon emissions. However, its high reactivity significantly alters flame structures and thermoacoustic characteristics, posing challenges for stable operation. This study investigates the effect of hydrogen enrichment on flame structure and thermoacoustic instability characteristics in a swirl-stabilized single nozzle combustor featuring separate main and pilot fuel passages.

Experiments were conducted at a fixed thermal power with natural gas and hydrogen mixtures at hydrogen volume fractions of 0%, 30%, 40%, and 50%. OH* chemiluminescence imaging was employed to capture flame structure, while dynamic pressure measurements characterized the instability behavior. Steady-state RANS CFD simulations were performed to analyze the flame structure, and a 1D thermoacoustic model based on a closed-loop framework of acoustic and flame transfer functions was developed to predict instability frequencies and growth rates.

The experimental results revealed a distinct transition in flame structure with increasing hydrogen content. At lower hydrogen fractions, a single-anchored flame was observed with the reaction zone located downstream of the pilot nozzle exit. As hydrogen enrichment increased beyond 40%, the flame transitioned to a dual-anchored configuration, where an additional reaction zone appeared near the pilot nozzle tip. The overall flame length also decreased significantly with increasing hydrogen content. Thermoacoustic instability at approximately 260 Hz was observed under these high hydrogen conditions, which was suppressed by increasing the pilot ratio.

CFD simulations successfully reproduced the experimentally observed flame structures, including the transition from single-anchored to dual-anchored flames with increasing hydrogen content. The simulations also showed that increasing pilot ratio mitigates the flame length reduction caused by hydrogen enrichment. The 1D thermoacoustic model, incorporating a flame transfer function modeling suitable for technically-premixed flames, demonstrated that the reduction in flame length leads to an increased growth rate of the 260 Hz mode. These results suggest that hydrogen-induced flame shortening is the primary driver of instability, and that pilot ratio control suppresses instability by mitigating this flame length reduction.

This study experimentally characterizes the flame structure in a dual-passage nozzle under hydrogen-enriched conditions, and combines CFD and 1D thermoacoustic modeling to identify flame length as the primary driver of thermoacoustic instability in the present system. The results further indicate that pilot ratio serves as an effective parameter for controlling flame length and, consequently, thermoacoustic stability.

Presenting Author: Junwoo Jung Gangneung-Wonju National University

Presenting Author Biography: Junwoo Jung is a Ph.D. candidate in the Energy and Power System Lab at Gangneung-Wonju National University, South Korea, under the supervision of Prof. Daesik Kim. His research focuses on gas turbine combustion instability modeling.

Authors:

Daesik Kim Gangneung-Wonju National University
Junwoo Jung Gangneung-Wonju National University
Jaewoo Jang Gangneung-Wonju National University
Min Kuk Kim Korea Institute of Machinery and Materials
Jeongjae Hwang Korean Institute of Machinery and Materials
Won June Lee Korean Institute of Machinery and Materials