Ultrafast-laser-absorption spectroscopy in the mid-infrared for single-shot, calibration-free temperature and species measurements in low- and high-pressure combustion gases

TL;DR

This paper introduces an ultrafast mid-infrared laser absorption spectroscopy technique capable of single-shot, calibration-free temperature and CO measurements at 5 kHz in combustion gases across a range of pressures, enabling detailed analysis of high-pressure combustion processes.

Contribution

It presents a novel ULAS diagnostic method with a detailed spectral-fitting routine, validated for high accuracy in harsh, high-pressure combustion environments, advancing real-time combustion diagnostics.

Findings

Validated at 1000 K and 40 bar in a heated-gas cell.

Applied to characterize temperature and CO in propellant flames at 1-40 bar.

Demonstrated sub-nanosecond time resolution in high-pressure combustion environments.

Abstract

This manuscript presents an ultrafast-laser-absorption-spectroscopy (ULAS) diagnostic capable of providing calibration-free, single-shot measurements of temperature and CO at 5 kHz in combustion gases at low and high pressures. A detailed description of the spectral-fitting routine, data-processing procedures, determination of the instrument response function, and practical considerations for imaging ultrashort pulses in the mid-infrared are presented. The accuracy of the diagnostic was validated at 1000 K and pressures up to 40 bar in a heated-gas cell before being applied to characterize the spatiotemporal evolution of temperature and CO in AP-HTPB and AP-HTPB-aluminum propellant flames at pressures between 1 and 40 bar. The results presented here demonstrate that ULAS in the mid-IR can provide high-fidelity, calibration-free measurements of gas properties with sub-nanosecond time resolution in harsh, high-pressure combustion environments representative of rocket motors.