# Experimental Study of Flame Dynamics in a Triple-Injector Swirling Nonpremixed Combustor Under Different Thermoacoustic Self-Excited Instability Modes

## TL;DR

This study explores how flame behavior changes under different types of combustion instability in a specialized engine setup, aiming to improve engine design.

## Contribution

The study reveals nonlinear flame dynamics and distinct heat release patterns under various thermoacoustic instability modes in a triple-nozzle combustor.

## Key findings

- Lower frequency instability modes are driven by fluctuations in flame length.
- High-frequency modes are dominated by flame surface wrinkles and convective processes.
- Higher frequencies show simultaneous patterns of flame length and surface fluctuations.

## Abstract

Combustion instability is one of the prominent and unavoidable problems in the design of high-performance propulsion systems. This study investigates the heat release rate (HRR) responses in a triple-nozzle swirling nonpremixed combustor under various thermoacoustic self-excited instability modes. Dynamic pressure sensors and high-speed imaging were employed to capture the pressure oscillations within the combustion chamber and the characteristics of flame dynamics, respectively. The results reveal nonlinear bifurcations in the self-excited thermoacoustic instabilities at different equivalence ratios. Significant differences in flame dynamics were observed across the instability modes. In lower frequency modes, the fluctuations in flame length contribute to the driving force of thermoacoustic instability. In relatively high-frequency modes, HRR fluctuations are dominated by the rolling up and convective processes of wrinkles on the flame surface. Alternating regions of gain and damping are observed on the flame surface. At even higher frequencies, both aforementioned HRR fluctuation patterns are simultaneously observed. These findings provide a deeper understanding of the complex interactions between flame dynamics and thermoacoustic instabilities, offering new insights into the design and optimization of nonpremixed combustion systems. The study underscores the importance of considering the spatial and temporal variations in flame behavior to effectively predict and control thermoacoustic instabilities.