Problem with reducing flame current only when the appliance is cold.
Problem with reducing flame current only when the appliance is cold.
(OP)
I was wondering if anyone could help me with a situation I have started experiencing.
The appliance will lit correctly, the flame current will rise almost immediately to approx. 6.0 μA.
After 20-30 seconds, the flame current will start reducing over a 30-40 second period to just above the drop-out level of 1.0 μA
After approx. 30 seconds the flame current will start to increase and continue to above 6.0 μA. These appliances will then continue to run without fault.
This behaviour will continue on these units, so every morning from a cold start, same problem.
A basic description of the appliance is as follows:
A rectangular metal fibre burner, positioned 60 mm from the underside of a flat bottomed tank which has a 2 degree draft angle to the rear.
Flue gases exit the combustion chamber at the rear into channels running around the side and rear walls of the tank before exiting through a flue.
The appliance has an ignition electrode and a seperate flame detection electrode.
The flame appears to be stable (visibly) during the reduction and recovering flame current.
The appliance will lit correctly, the flame current will rise almost immediately to approx. 6.0 μA.
After 20-30 seconds, the flame current will start reducing over a 30-40 second period to just above the drop-out level of 1.0 μA
After approx. 30 seconds the flame current will start to increase and continue to above 6.0 μA. These appliances will then continue to run without fault.
This behaviour will continue on these units, so every morning from a cold start, same problem.
A basic description of the appliance is as follows:
A rectangular metal fibre burner, positioned 60 mm from the underside of a flat bottomed tank which has a 2 degree draft angle to the rear.
Flue gases exit the combustion chamber at the rear into channels running around the side and rear walls of the tank before exiting through a flue.
The appliance has an ignition electrode and a seperate flame detection electrode.
The flame appears to be stable (visibly) during the reduction and recovering flame current.





RE: Problem with reducing flame current only when the appliance is cold.
RE: Problem with reducing flame current only when the appliance is cold.
....but I am not really sure I understand your system. I've only worked on larger systems, where heating the surrounding mass was very important.
CompPro's idea also seems reasonable.
RE: Problem with reducing flame current only when the appliance is cold.
I increased the length between the mounting face and the tip of the ceramic, 3mm of ceramic is now exposed to the combustion chamber instead of being within the insulation surrounding the chamber and 'voila' I now have a stable flame current. Sometimes you just can't see the wood for the trees!!
This is a perfect example of the worth of forums and forumites like this and how they can help people in their hour of need!!
Many thanks again.
RE: Problem with reducing flame current only when the appliance is cold.
rmw
RE: Problem with reducing flame current only when the appliance is cold.
It is galling to post an answer, only to find the original poster never even acknowleges that they found it, or that it was useful.
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Problem with reducing flame current only when the appliance is cold.