What question did this study set out to answer?

The aim is to simultaneously measure nitric oxide concentration and temperature for combustion diagnostics.

June 30, 2026Open Access

Simultaneous measurement of nitric oxide concentration and temperature using overlapping absorption signals in direct absorption spectroscopy at 5181.2 nm

ASAran SongYonsei University JPJiyeon ParkSungkyunkwan University DKD H KimPusan National University

Key Points

The aim is to simultaneously measure nitric oxide concentration and temperature for combustion diagnostics.
Utilized a quantum cascade laser scanning from 1929.4 to 1931.3 cm⁻1.
Developed an algorithm to analyze overlapping absorption signals and correct baseline errors.
Validated measurements against thermocouples and electrochemical sensors.
Achieved consistent measurement agreement with thermocouple data across temperatures from 603 to 653 K.
NO concentration results aligned with data from a 1.3 µm tunable diode laser absorption spectrometry (TDLAS) method.
Demonstrated reduced system complexity and enhanced reliability even in high-humidity conditions.

Abstract

Simultaneous measurement of temperature and nitric oxide (NO) concentration is essential for reliable combustion diagnostics. In this study, a single quantum cascade laser (QCL) scanning the range of 1929.4–1931.3 cm⁻ 1 was used to concurrently retrieve temperature and NO concentration, specifically addressing the spectral overlap of NO and H 2 O signals. To minimize baseline fitting errors inherent in these overlapping features, we developed an analysis algorithm incorporating a Householder reflection–based orthogonalization process. The proposed method determines temperature and NO concentration by comparing baseline-corrected measured spectra with reconstructed virtual spectra. We validated the retrieved temperature against thermocouple measurements and compared H 2 O concentration results with 1.3 µm TDLAS data. Additionally, NO measurements were evaluated against an electrochemical sensor. Experimental results demonstrated consistent agreement across the tested range (603–653 K), confirming that this single-laser approach reduces system complexity while providing enhanced diagnostic reliability in high-humidity environments.

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