In the cutaway render on the left the new forced air system can be seen surrounding the nozzle.

 

Air is supplied from the bottom connection (not seen) into the central swirl air plenum, and the outer annular air is supplied from the top connection.

 

Gas is distributed into the swirling air from the nozzle above the plate, this ensures that the nozzle is in a low-pressure area so minimsing the gas supply pressure required.

 

Secondary air is entrained into the flame from the annular register surrounding the central tube, this also serves to keep the outer case and the nozzle cool.

 

Dampers on the supply ducts allow the amount of air to each register to be adjusted to get the best flame, and a further damper on the fan inlet allows the overall air to fuel ratio to be varied.

 

In practice the burner will stay alight with very little gas flow, maintaining a small blue flame at the nozzle so long as the swirl air is maintained. It will also cope with large surges in gas flow without losing flame stability and operates over a very wide range of excess air ratio.

 

At the time the design was done, we had no information on the actual gas composition and CV, and only a rough estimate of the likely maximum flow, so the performance exceeds expectations by some margin.

 

On the next page there are some pictures of the unit in actual operation.