When the ignition ports were aligned, the metal temperatures soared and bright bands were observed identical to those observed in the field.
Figure 3. CFD Predicted burner temperatures with and without aligned ports.
Figure 4. Gas velocity magnitude (m/s)
Fuel moves through the ignition port very fast and so it has a lot of momentum. When the small ignition port is aligned with the combustion air port, it flows right through it and starts to burn above the burner ring resulting in bands of high temperatures. If the ports are not aligned then fuel hits the cone wall of the burner and mixes with the fuel exiting through the main fuel ports and the problem is avoided.
"Ahhh yes this shows exactly what is on site! Perfect! I am glad we now know what is causing the hot spots." - Process Engineer
Figure 5. Observed hot spots