# Temperature Fields of the Droplets and Gases Mixture
## 2 Experimental Set-Up and Procedure
### LIP Measurement Technique
When \(\gamma_{\rm p}\) was varied within the said range, temperature deviations did not exceed 1.5 \({}^{\circ}\)C.  
The goal of the first stage was to obtain a calibration curve (Figure 3a, on the right) - air flow temperature versus relative fluorescence of BAM:Eu particles. The procedure is similar to the one described in [17; 18]. For this purpose, a series of experiments were conducted, capturing the particle images in the air flow when increasing its temperature from 20 to 500 \({}^{\circ}\)C. The choice of the temperature range is primarily conditioned by the thermal degradation threshold of the thermographic particles used. There are several types of BAM:Eu with different threshold temperatures ranging from 600 \({}^{\circ}\)C to 800 \({}^{\circ}\)C [19]. The upper temperature threshold of the BaMgAl\({}_{10}\)O\({}_{17}\):Eu particles used in the experiments is 600 \({}^{\circ}\)C. However, as the temperature fluctuations of the combustion products (Section 3.2) often exceed 60-80 \({}^{\circ}\)C, we chose 500 \({}^{\circ}\)C as the upper limit for the experiments. At least three experiments were conducted for each point. In each experiment, an average between readings from two thermocouples installed at the input and output of the small-size observation area was taken as the flow temperature. The images obtained were processed as described previously, except the temperature field plotting (this stage was excluded). Instead, as the final stage, we used the Temperature Calibration function to plot a calibration curve from the points obtained (Figure 3a, left). At the same time, the calibration curve (Figure 3a, right), as in most 2-color methods, was plotted by comparing the emission intensitiesof the left and right sides of the spectrum (Figure 3a, left). That is, we found the emission intensity ratio of BAM:Eu (420 nm/450 nm). Then, for each ratio, we took the flow temperature measured by a Type K thermocouple in the course of video recording. The data obtained was presented as the calibration curve (Figure 3a, left). The experimental data scattering (emission intensity ratio of BAM:Eu: 420 nm/450 nm) on the calibration curve did not exceed 3% for the identical flow temperatures. The second stage involved temperature recording in a gas-vapor trace of droplet flow (Figure 3c-e). To generate a droplet flow in the observation area, we used the hardware described in Section 2.3. At least three experiments were conducted for each different water injection duration (\(t_{\text{imp}}\)). After the recording was finished, frames with the even distribution of tracer particles were selected to match the tracer distribution in the images obtained during the temperature calibration. These second-stage images were processed as described earlier. At the final stage of processing, instantaneous temperature fields of the airflow were plotted with the help of the calibration curve obtained at the earlier stage of the experiments. There is some nonuniformity of the temperature fields in Figure 3c-e, connected with an uneven concentration of BAM:Eu particles in the flow. There are regions where the concentration of phosphorescent indicator particles is small or there are none of them. This creates a noisy picture, when the results are processed. To smooth the temperature field, we used Linear Smoothing Filter, averaging the data in the region \(3\times 3\) px in size. When processing the LIP measurement data, this type of filter was used straight after finding the Ratio 420/455 nm. This allowed us to take into consideration the changes in the ratio 420/455 nm due to smoothing. Thus, the calibration curve (Figure 3b) already took into account the smoothing, and this process (\(3\times 3\) Linear Smoothing Filter) had absolutely no effect on the temperature of the resulting temperature field. In the preparation and adjustment of the experimental technique, an important issue was the influence of aerosol droplets on the reliability of temperature measurement using LIP.