# Flame Evolution Characteristics for Hydrogen/LPG Co-Combustion in a Counter-Burmer
## 4 Results and Discussion  
### Experimental Results  
Figure 12 represents images of flame behavior that were obtained practically using a high-resolution digital camera. These images cover the combustion cases and their transition stages from lean to rich modes as well as the increase rates. The MATLAB program was used to convert these images into binary images. These binary images were used to calculate the flame propagation velocity and flame front diameter as well as to study the color change resulting from the addition of hydrogen. The flame behavior of LPG was studied when it was mixed with increasing percentages of hydrogen (5%, 10%, 15%, and 20%) to determine how these percentages affected some flame properties such as the flame color and flame front diameter. The flame color depended mainly on the generated temperature and the type of combustible materials. When LPG was mixed with hydrogen, noticeable changes in the flame color occurred due to the combustion properties of hydrogen, as shown in Figure 12. In the case of poverty (equivalence ratio of less than one), the ratio of LPG + H\({}_{2}\) to oxygen was low, i.e., oxygen was available in more quantities  
Figure 11: Comparison of numerical and experimental results of flame temperature and flame burning velocity at equivalence ratio equal to one. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Min. for Recorded Value** & **Max. for Recorded Value** & **Min. and Max. (Uncertainty) \% Error** \\ \hline Air flow rate (L/min) & 8.5 & 10.5 & \(\pm\)(0.34–0.17) \% \\ LPG flow rate (L/min) & 0.26 \(\times\) 10\({}^{-3}\) & 0.9 \(\times\) 10\({}^{-3}\) & \(\pm\)(0.13–0.089) \% \\ H\({}_{2}\) (hydrogen) (L/min) & 0.25 \(\times\) 10\({}^{-4}\) & 1.04 \(\times\) 10\({}^{-4}\) & \(\pm\)(0.11–0.061) \% \\ Flame temperature (\({}^{\circ}\)C) & 673 & 1292 & \(\pm\)(1.9–1.3) \% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Uncertainties of the measured parameters. compared to the fuel, which led to the complete combustion of the mixture. As can be seen in the pictures, the flame color was clear-blue and was characterized by clarity and transparency and did not produce soot or unburned particles. The blue color in the poor flame was evidence of good and effective combustion, and the flame was usually stable and more efficient in generating heat. In the case of an ideal flame, where the ratio of LPG + H\({}_{2}\) to oxygen was balanced (equivalence ratio = 1.008), the complete combustion of the gas occurred, which is known as ideal combustion. The picture shows the flame in a brighter blue color compared to the poor flame, which may contain shades of light blue in some areas. This flame is characterized by high temperatures and is usually used in applications that require a clean and highly efficient flame. In the case of the rich flame (equivalence ratio higher than one), there was a lack of sufficient oxygen to complete the combustion process. The flame here appeared in a blue-yellow color, and sometimes there was a spectrum of red due to the presence of unburned carbon particles that glowed and produced an orange or yellow color when burning. The rich flame was less energy efficient and was accompanied by the emission of smoke and soot, which makes it unsuitable for applications that require clean combustion. The change in the degree of the blue color of the flame helped in distinguishing between the poor and effective full flame and rich flame. More so, by mixing liquefied gas with hydrogen, noticeable changes occurred in the color of the flame due to the combustion properties of hydrogen. It is clear from the above that adding hydrogen to the liquefied gas affected both the flame color and the flame front diameter, as the flame became bluer as the ratio increased, while the flame front diameter decreased and became thinner as a result of the increased combustion rate. Figure 12: Flame behavior of PLG with 5%, 10%, 15%, and 20% hydrogen at different equivalent ratios.