Pellet Burner exhaust sensor.   - Page 1
Forum section: electronics / general

author: firewalker
author_rank: Super Contributor
timestamp: March 12, 2012, 01:17:01 pm
content: Due to the high price of the heating oil a friend of mine wanted to design a pellet burner. He made everything metal related (burner, feeder auger e.t.c.) and I designed everything that has to do with the control of the unit.It is working really well for a couple of months now.An issue is the fuel-air ratio in order to have a smoke free flame. Because of the physical characteristics of the fuel (pellet), like irregular size, the amount inserted to the combustion chamber by the auger varies. As a result is the production of smoke to the exhaust.What sensor would be suitable to use in the exhaust in order to regulate the fuel feeding? A lambda sensor?Alexander.Pellet:Auger:

author: G7PSK
author_rank: Super Contributor
timestamp: March 12, 2012, 04:30:41 pm
content: A lambda sensor from a car is likely to fail quickly as there is a lot of minerals in wood which will degrade the sensor in much the same manner as leaded petrol would in a car. you need some form of particulate counting much as they have on many diesels now.

author: MarkS
author_rank: Unknown
timestamp: March 12, 2012, 04:37:36 pm
content: Wouldn't temperature be more of a factor in fuel feeding that exhaust?

author: T4P
author_rank: Super Contributor
timestamp: March 12, 2012, 07:53:12 pm
content: Indeed , EGT is one of the easiest way to control the air intake .

author: firewalker
author_rank: Super Contributor
timestamp: March 12, 2012, 08:12:34 pm
content: There is no significant temperature variation between the two states (I haven't measured the air temp though. Just the exhaust metal surface). I will measure the exhaust air temperature. Is EGT a fast responding sensor?Alexander.

author: T4P
author_rank: Super Contributor
timestamp: March 12, 2012, 09:07:20 pm
content: Quote from: firewalker on March 12, 2012, 08:12:34 pmI believe planes use EGT as a obvious sign ( At least , I )

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 13, 2012, 01:43:35 am
content: Shine an IR laser (modulated) through the exhaust and sense the reflection.

author: Dieselrunner88
author_rank: Contributor
timestamp: March 13, 2012, 01:51:57 am
content: A lamda sensor would be poisioned after a period of time but i'm not sure how long. The problem is that by the time the sensor realizes the fuel rate needs to be slowed there is already too much fuel in the furnace. More air to add oxygen to the mixture would be a faster way to control the mixture. a variable speed fan feeding the furnace?Just thoughts but an egt will only tell you if your fuel rate is too high for the amount of energy the furnace can dissipate. i.e. rise in temperature not fuel air ratio. I don't see how that would help you control particulate output. (soot).

author: kaz911
author_rank: Super Contributor
timestamp: March 13, 2012, 03:33:47 am
content: Quote from: Dave.S on March 12, 2012, 09:07:20 pmYes planes use EGT as an indicator of the "purest" burn. You trim the engine mixture until you reach peak EGT and then you add a bit of mixture to take EGT a notch down so you don't burn to lean. (Lean of PEAK EGT is a no-go according to the books). If you run the mixture to rich - then you get fouled spark plugs and fuel consumption goes up very quickly.

author: firewalker
author_rank: Super Contributor
timestamp: March 13, 2012, 08:57:36 am
content: No the air intake motor isn't variable (the ac inverter was expensive, and there "was no reason" for it since we don't monitor the exhaust).When smoke appears to the exhaust if we manually stop the pellet feed it cleans in a couple of seconds witch is ok for us.Is there an ir sensor (as NiHaoMike suggested) ready for uses.I really don't know what to search for (I know ways to implement a device that does the job, but a ready to use sensor if far better).Alexander.