Puff Backs Hotblast 1557M

Post by **franco b** » Sun. Oct. 09, 2016 11:08 pm

An alternative to banking that may work well is to take a poker and drill down in several places in the fresh coal bed to provide an open path to hot coal. Emory from the Stove Hospital suggested that and I find it quickens the appearance of and supports blue flame.

Sunny Boy · Post by **Sunny Boy** » Sun. Oct. 09, 2016 11:54 pm

lsayre wrote:Yes, and on top of that air is only 20.9% oxygen. Yet, when I searched on the internet for an explanation for what I was observing, the chimney draw back theory comes up at several sites. Guess that should teach me not to believe everything I see on the internet.

Are you certain the wood stove is closed down completely when that happens ? Could there be air leaking in somewhere ?

Paul

lsayre · Post by **lsayre** » Mon. Oct. 10, 2016 7:35 am

Sunny Boy wrote:Are you certain the wood stove is closed down completely when that happens ? Could there be air leaking in somewhere ?

Paul

I hope I wasn't implying 100% closed down. There must be air leakage at some level. I would assume that to be built in.

Post by **coaledsweat** » Mon. Oct. 10, 2016 7:41 am

It isn't air leaking in. It is the explosive gases backing up until they get to the fire... then boom!

lsayre · Post by **lsayre** » Mon. Oct. 10, 2016 7:50 am

coaledsweat wrote:It isn't air leaking in. It is the explosive gases backing up until they get to the fire... then boom!

Gases building up in the chimney or the firebox?

Post by **Rob R.** » Mon. Oct. 10, 2016 9:52 am

Is there plenty of combustion air available to the stove?

lsayre · Post by **lsayre** » Mon. Oct. 10, 2016 9:59 am

Rob R. wrote:Is there plenty of combustion air available to the stove?

Apparently not for the case when I completely damp it down.

Sunny Boy · Post by **Sunny Boy** » Mon. Oct. 10, 2016 10:12 am

My thought was that,.... as with any volatile gases, It takes a certain ratio of air to volatile gas to get it to ignite. The wood fire will constantly produce volatile gas (fuel and ignition source).

By shutting the dampers, but not 100% stopping air intrusion, what you have created is basically an internal combustion engine with an intake and exhaust system, and a glow plug igniter.

Get too much gas to air (too rich), or too much air to gas (too lean) and you don't get gas ignition. Same thing happens with gasoline and diesel fuel. Too much, or too little air and no boom.

If there was some small amount of air intrusion, then each time the stove "puffed" it used up all of that air that mixed in the right proportions with the volatile gases inside the stove.

The puff also creates enough sudden back pressure within the stove to temporarily halt the air intrusion and make it too lean for the constant gas being produced by the still burning wood to stay ignited.

Once that temporary back pressure is gone, then the chimney draft takes back over and starts to pull more air in. When the air/fuel ration reaches the correct ratio again, Puff !

And the cycle repeats itself until the conditions are changed such as allowing more air in for a constant burn rather than intermittent burn.

If you could somehow mount a piston in the stove you could drive your wood splitter !

Paul

lsayre · Post by **lsayre** » Mon. Oct. 10, 2016 10:18 am

Sunny Boy wrote:My thought was that,.... as with any volatile gases, It takes a certain ratio of air to volatile gas to get it to ignite. The wood fire will constantly produce volatile gas (fuel and ignition source).

By shutting the dampers, but not 100% stopping air intrusion, what you have created is basically an internal combustion engine with an intake and exhaust system, and a glow plug igniter.

Get too much gas to air (too rich), or too much air to gas (too lean) and you don't get gas ignition. Same thing happens with gasoline and diesel fuel. Too much, or too little air and no boom.

If there was some small amount of air intrusion, then each time the stove "puffed" it used up all of that air that mixed in the right proportions with the volatile gases inside the stove.

The puff also creates enough sudden back pressure within the stove to temporarily halt the air intrusion and make it too lean for the constant gas being produced by the still burning wood to stay ignited.

Once that temporary back pressure is gone, then the chimney draft takes back over and starts to pull more air in. When the air/fuel ration reaches the correct ratio again, Puff !

And the cycle repeats itself until the conditions are changed such as allowing more air in for a constant burn rather than intermittent burn.

If you could somehow mount a piston in the stove you could drive your wood splitter !

Paul

This explanation nails it on the head! Nice work Paul!!!

Isn't there something like a 'pulse jet engine' that essentially works on this principle?

Sunny Boy · Post by **Sunny Boy** » Mon. Oct. 10, 2016 10:23 am

lsayre wrote:
Sunny Boy wrote:My thought was that,.... as with any volatile gases, It takes a certain ratio of air to volatile gas to get it to ignite. The wood fire will constantly produce volatile gas (fuel and ignition source).

By shutting the dampers, but not 100% stopping air intrusion, what you have created is basically an internal combustion engine with an intake and exhaust system, and a glow plug igniter.

Get too much gas to air (too rich), or too much air to gas (too lean) and you don't get gas ignition. Same thing happens with gasoline and diesel fuel. Too much, or too little air and no boom.

If there was some small amount of air intrusion, then each time the stove "puffed" it used up all of that air that mixed in the right proportions with the volatile gases inside the stove.

The puff also creates enough sudden back pressure within the stove to temporarily halt the air intrusion and make it too lean for the constant gas being produced by the still burning wood to stay ignited.

Once that temporary back pressure is gone, then the chimney draft takes back over and starts to pull more air in. When the air/fuel ration reaches the correct ratio again, Puff !

And the cycle repeats itself until the conditions are changed such as allowing more air in for a constant burn rather than intermittent burn.

If you could somehow mount a piston in the stove you could drive your wood splitter !

Paul
This explanation nails it on the head! Nice work Paul!!!

Isn't there something like a 'pulse jet engine' that essentially works on this principle?

Possibly. I've never looked at the technology to know enough about how a pulse, or ram jet engine works.

But if your stove takes flight then we can assume it's very much the same.

Paul

lsayre · Post by **lsayre** » Mon. Oct. 10, 2016 11:30 am

Sunny Boy wrote:Possibly. I've never looked at the technology to know enough about how a pulse, or ram jet engine works.

But if your stove takes flight then we can assume it's very much the same.

Paul

Hopefully I'll never damp it down that much again, so I'll never see it take flight.

McGiever · Post by **McGiever** » Mon. Oct. 10, 2016 12:01 pm

See now Larry why your AHS coal gun stoker boiler has the built in puffback protection?

You know...
At the start of the firing cycle with the draft fan starting up the over fire air then gets sealed off due to the negative fan pressure pulling the sight tube flapper shut.
Then later at the end of the firing cycle that flapper gets released again to it's natural open position due to the combustion fan coming to a stop again?
That over fire air is now being again allowed through that sight tube flapper for the idle cycle. And, at same time it also happens to be greatly reducing the bottom induced draft air with the fan now being off and flapper above opened. This is what plays a large part in keeping the fuel mix not to be able to reach the critical ratio to produce a puffback.

That's the theory, but as many AA/AHS owners know, there are some other variables that may or may not needing tweaked also that might come into play.