## 3 Results and Discussion
In general, the proximity of data points in the plots suggests that some parameters tend to vary collectively, with certain combinations of values occurring more frequently. In plots with more distinct clusters, this correlation is stronger, meaning that the variables involved likely exhibit some form of dependency or interaction that constrains their values to a narrower range. In contrast, the plots with more evenly distributed points indicate that the parameters in those cases do not exhibit strong correlations. Hence, the presence of clustering in certain plots can also indicate preferred operational conditions for the pre-reformer operation. These clusters may represent optimized ranges where the component performs efficiently or where specific design constraints are met. Further, main and collective effect analyses were performed to shed light on these aspects. Figure 5 gives detailed insights into the collective effects of key operational parameters on the fuel outlet temperature (Trefout). These plots, which include bar charts and 3D response surfaces, reveal the relationships between the input air flow, fuel flow, air temperature, catalyst porosity, and oxygen content parameters, highlighting their relative importance in influencing the components' thermal behavior. The bar chart given in Figure 5a quantifies the relative influence of each investigated individual parameter on the fuel outlet temperature. It shows that the air flow rate has the most significant effect on the outlet temperature, with a magnitude far surpassing all other variables. This suggests that managing the air flow rate is the most critical factor in controlling the temperature of the pre-reformer. The dominance of airflow in controlling the temperature is expected, as increased airflow promotes chemical reactions, leading to higher outlet temperatures. Its large effect size indicates that even small adjustments in airflow can result in a substantial temperature change. While the impact of air temperature is considerably less than that of the airflow, it still plays an important role in modulating the outlet temperature. This reflects the fact that higher incoming air temperatures directly contribute to higher thermal energy in the system. The catalyst porosity, oxygen, and fuel flow have a much smaller effect on the fuel outlet temperature, as indicated by the diminished bars. The relatively minor influence of the fuel flow and catalyst porosity may suggest that their impact on temperature is more secondary and indirect, influencing the efficiency of the chemical reactions rather than directly affecting the heat output. The 3D response surface plot in Figure 5b depicts the relationship between fuel flow and air flow and their combined effect on the outlet temperature. The color gradient represents temperature changes, with darker red corresponding to higher temperatures and deep blue indicating lower temperatures. Their interaction reveals that increasing both fuel and air flow results in a temperature rise, but the air flow rate appears to have a stronger influence. This confirms the finding from the main effects plot that airflow is the dominant factor in temperature control. The steep gradient in temperature as air flow increases suggests that this parameter should be carefully managed to avoid excessive heat, which could lead to overheating or inefficiency in the system. The curvature of the surface indicates a non-linear relationship between these parameters and temperature. While increasing fuel flow at lower air flows results in a moderate temperature rise, combining high air flow and fuel flow rates leads to a more significant increase in temperature, demonstrating how the interaction between these variables can compound their effects. Figure 5c shows the fuel flow and air temperature interaction effect on the outlet temperature. The surface displays similar non-linear effects, though the gradients are less steep compared to the previous air flow effect.