# Impact of Oxygen Content on Wall-Temperature Phosphor Thermometry for Combustion

Tobias Guivarch, Hugo Samson, Jérôme Bonnety, Jessy Elias, Sebastien Ducruix, Clément Mirat, Christopher Betrancourt, Guilhem Dezanneau,

Ronan Vicquelin

► To cite this version:

Tobias Guivarch, Hugo Samson, Jérôme Bonnety, Jessy Elias, Sebastien Ducruix, et al. Impact of Oxygen Content on Wall-Temperature Phosphor Thermometry for Combustion. European Combustion Meeting (ECM) 2025, Apr 2025, Edimburg, United Kingdom. hal-05062170

HAL Id: hal-05062170

https://hal.science/hal-05062170v1

Submitted on 9 May 2025

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Distributed under a Creative Commons Attribution 4.0 International License
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## Context & Objectives

### Challenges of Alternative Combustion Methods

* Modified Heat Transfer to Walls or Load.

* Need for Accurate Wall-Temperature Measurements.

### Laser-Induced Phosphorescence (LIP) Thermometry

* LIP is a semi-invasive laser diagnostic based on temperature-dependent phosphorescence emission.

* Full-Spectrum Fitting (FSF) method : Uses the entire emission spectrum for improved precision [1,2].

### Termographic Phosphor YAG:Dy as a solution

* Widely used in **high-temperature** combustion applications.

* **Strong candidate** for the FSF method due to its **high spectral variability** over a wide range of temperature.

* But it is **sensitive to oxygen content** [4,5] and laser fluence.

<figure><img src="image_6.png" /><figcaption>LIP applied for an oxy-combustion combustor</figcaption></figure>

[6]

<figure><img src="image_7.png" /></figure>

### Objectives

Apply the FSF method to YAG:Dy and evaluate the impact of oxygen content and laser fluence on temperature determination.

<caption>Thermal fatigue cracks in gas turbine blade</caption>

## Full Spectrum Fitting Method

### 1 Construction of the database

<figure><img src="image_8.png" /></figure>

* Intensity ratio between 580nm and 480-500nm show little variation.

* 580nm peak compared to 460nm feature exhibits more pronounced changes.

➤ YAG:Dy is a **strong** candidate for the FSF method.

### 2 Classification problem

For a singleshot spectrum of unknown temperature $S^{\text{studied}}$

* Solve the minimization problem :

$$ \min_{T \in [T_{\text{min}}, T_{\text{max}}]} \left\{ \min_{\alpha} d(\alpha S^{\text{studied}}, S_{T}^{\text{ref}}) \right\} $$

* Associate $T_{\text{found}}$ to the single-shot.

### 3 Performance of the method

To evaluate the **reference database**, a cross-validation procedure using 5 folds is employed :

* Statistics on the temperature deviation $\Delta T = T_{\text{found}} - T_{\text{recorded}}$ are made.

* Several distances have been investigated :

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➤ Pearson $\chi^2$ is the best compromise. It achieves an **accuracy** of $\Delta T = 0.3$ K and a **precision** $\sigma_{\Delta T} = 8.4$ K on temperature determination

## Effect of Laser Fluence

<figure><img src="image_10.png" /></figure>

### Laser Fluence effects on spectrum :

* Broadband effects on normalized spectra : [440, 500] nm : at $T_{\text{min}}$ for $N_2$ and $\text{Air}$, at $T_{\text{max}}$ for $N_2$. [500, 550] nm : at $T_{\text{max}}$ for $\text{Air}$

* Increasing temperature reduces effects of laser fluence on normalized spectra.

<figure><img src="image_11.png" /><figcaption>Effect of Laser Fluence on Temperature Deviation with $F_{\text{max}} / N_2$ as reference database.</figcaption></figure>

### Laser Fluence effects on FSF method :

* At low laser fluence, increasing temperature decreases accuracy.

* 97% laser fluence extinction can lead to an error $\Delta T = 80$ K @1700K.

* Above a certain fluence threshold, FSF remains reliable with an accuracy of $\Delta T = -2.6$ K and a precision of $\sigma_{\Delta T} = 10.5$ K.

## Effect of Oxygen Content

<figure><img src="image_12.png" /></figure>

### Oxygen Content effects on spectrum :

* Broadband effects on normalized spectra : [440, 550] nm : at $T_{\text{max}}$ for $F_{\text{max}}$.

* No effects at $F_{\text{min}}$

* Increasing temperature and laser fluence increases effects of oxygen content on normalized spectra.

<figure><img src="image_13.png" /><figcaption>Effect of Oxygen Content on Temperature Deviation with $F_{\text{max}} / N_2$ as reference. database</figcaption></figure>

### Oxygen Content effects on FSF method :

* Impact on temperature determination is **limited**, with an accuracy $\Delta T = -9.6$ K and a precision of $\sigma_{\Delta T} = 11.1$ K.

* In the worst case, unknown oxygen content decreases accuracy at 16 K.

## Guidelines for combustion chambers

* ✓ The FSF method applied on **YAG:Dy** is a reliable thermometry technique for **harsh environments**.

* ✓ Above a certain threshold, laser fluence effects on temperature determination are negligible.

➤ Maximizing laser fluence improves SNR but increases sensitivity to oxygen content.

* ✓ Oxygen content has a **limited** effect on the accuracy of the method.

➤ With low oxygen uncertainty, a **single high-fluence database** is sufficient.

## Future work

1. Evaluate the response of YAG:Dy mixed with a **binder** to fluence and oxygen variations.

2. Evaluate the method in a **high-pressure** (60bar) and **high-temperature** (1400°C) environment.

3. Apply the method in **real combustion chambers** for industrial applications.

## References

[1] V. Lechner et al., "Full spectrum fitting method: A new approach for instantaneous phosphor thermometry in harsh environments," *Exp. Fluids*, 63(7), 110 (2022).

[2] V. Lechner et al., "Dynamic characterization of wall temperature in LOX/CH4 rocket engine operating conditions using phosphor thermometry," *Proc. Combust. Inst.*, 39(4), 5033-5041 (2023).

[3] J. Brübach et al., "Gas compositional and pressure effects on thermographic phosphor thermometry," *Meas. Sci. Technol.*, 18(3), 764 (2007).

[4] N. Ishiwada et al., "Applicability of Dy-doped YAG in phosphor thermometry at different oxygen concentrations," *J. Lumin.*, 208, 82-88 (2019).

[5] S. Nilsson et al., "High temperature thermographic phosphors YAG:Tm;Li and YAG:Dy in reduced oxygen environments," *J. Lumin.*, 256, 119645 (2023).

[6] A. Savikovskiy et al., "Numerical aspects of the J-integral estimation for thermomechanical loading," in *Adv. Ind. Math.*, pp. 157-175 (2023).

[7] A. Degenève et al., "Wall temperature and heat flux in a swirled combustor with methane-air and CO₂-diluted oxyflame," *Fuel*, 236, 1540-1547 (2019).

[8] M. Lawrence et al., "Gas phase thermometry of hot turbulent jets using laser-induced phosphorescence," *Opt. Express*, 21(10), 12260-12281 (2013).

[9] M. Poulos et al., "Lattice dynamics and thermodynamic properties of $Y_3Al_5O_{12}$ (YAG)," *J. Phys. Chem. Solids*, 162, 110512 (2022).

## Acknowledgment

This work has been conducted as part of the **HyMax** (ANR-23-CD50-0021-01) and **OXY3C** (ANR-22-PESP-0009) projects, respectively funded by the French National Research Agency and France 2030 program. It also received financial support from the **LabEx LaSIPS** (ANR-10-LABX-0032-LaSIPS), managed by the French National Research Agency under the "Investissements d'Avenir" program (ANR-11-IDEX-0003-02).