# Improved Method for Quantitative Measurement of OH Radicals Based on Absorption Spectroscopy

## TL;DR

This paper introduces a new method to measure OH radicals in flames that is more accurate by correcting for temperature changes.

## Contribution

A novel temperature-corrected model for OH radical concentration measurement using absorption spectroscopy and dual-line temperature inversion.

## Key findings

- The temperature-corrected model reduces systematic errors caused by temperature variations.
- Calibration constant C fluctuates less than ±5% across different conditions.
- Overall error decreased from 9.1% to 5.2% compared to the uncorrected model.

## Abstract

OH-PLIF quantitative measurements suffer from high temperature sensitivity and poor applicability of calibration constants, this paper combines absorption spectroscopy with dual-line temperature inversion to establish an explicitly temperature-corrected OH radical concentration inversion model. By simultaneously acquiring PLIF images and absorption spectrum data under varying hydrogen-oxygen mixture flow rates, the equivalent absorption path length is calculated and the temperature-dependent absorption cross-section σ(ν,T) is incorporated. This enables the dynamic response of the integral absorption rate to high-temperature flame environments. Results demonstrate that the established temperature-corrected model significantly reduces systematic errors caused by temperature variations, with calibration constant C fluctuating less than ±5% across different operating conditions. Further optimization via least-squares method yielded the optimal constant Copt = 0.01844. Its applicability was validated across various operating conditions, with average relative errors controlled within 4–6%. Compared to the uncorrected model, overall error decreased from 9.1% to 5.2%.