Dual-comb spectroscopy for the characterization of laboratory flames

TL;DR

This paper introduces a robust dual-comb spectroscopy system using electro-optical generators for precise, calibration-free flame diagnostics, capable of detecting methane concentrations and combustion instabilities.

Contribution

It presents a novel EO-based dual-comb spectroscopic system operating in the mid-infrared for advanced laboratory flame analysis.

Findings

Achieved a detection limit of 1.1 ppm for methane

Resolved spatial concentration gradients in flames

Identified dynamic combustion instabilities

Abstract

Optical spectroscopy, in particular dual-comb (DC) spectroscopy, is a critical, non-invasive tool for combustion diagnostics, offering high precision and calibration-free advantages. However, its implementation remains challenging, especially in the mid-infrared region. This work presents the development of a robust DC spectroscopic system based on electro-optical (EO) frequency comb generators and difference frequency generation (DFG), specifically designed for the characterization of laboratory flames. Operating at a center wavelength of 3427.43 nm, the system utilizes a differential detection strategy to enable precise, calibration-free measurements of unburned methane ($\mathrm{CH_{4}}$) concentrations in a McKenna burner. The experimental results demonstrate an estimated detection limit of 1.1 ppm for a 1 m path length and effectively resolve spatial concentration gradients across the combustion region. Furthermore, the system's high temporal resolution allowed for the identification of dynamic combustion instabilities, including self-sustained pulsations and fuel leakage under fuel-lean conditions. These findings validate the proposed EO architecture as a flexible and highly sensitive tool for advanced flame characterization.