Vermont Castings Burn Observations

[bullittman281]

Hello everybody,
WARNING LONG!

I have some general observations that don’t quite fit in the year performance thread and I don’t want to hijack any threads so a new thread it is.

I have had a bunch of free time to browse the forums and have some observations based on my own experience and the experiences here. I have a Dauntless with out the cat. It seems most here run all the VC stoves with the cat installed, whether mandated or not in the flex burns. Most seem to run temperature monitoring well beyond the included factory “probe”. The results every body posts are wildly varying and inconsistent. First observation is the stoves are hard to run. Obviously. But I have some of my own ideas.

The design of these stoves are a secondary burn stove possibly with a catalyst for final clean up. This is unlike, say a blaze king, where there is no secondary air tubes or burning and the entire premise is the catalytic combustor does all the “burning” and the fire intentionally smolders. Somewhat of a big difference. In theory, the majority of the energy release in a VC stove should happen in the so-called refractory engine, not in the catalyst. Or at least during higher burn settings. I believe this is where the problems start. The secondary burn in these stove is temperamental at best. Its not just VC. The lopi Lyden at the time was the same or worse for this.

I have a theory that the incredible temperature spikes on the catalyst people see are because secondary combustion never lights off and the cat has to cash the entire energy check. This is fine at a low burn rate. Not so fine at higher rates when it should have some support. My stove is very easy to tell if it has good secondary combustion or not because the combustion is not silent and the smoke output is tremendous if it doesn’t light. The fix is to re-arrange the wood and fiddle with the damper and air control. Everybody running a catalyst may not notice this except for spiking catalyst temps. This brings us to the combustors.

Vermont Castings seems to run only 2 or 3 refractory engines for all four models. The part number for Intrepid and Dauntless refractory parts are the same part number and the Defiant and Encore share some ceramic pieces. The large fire box for the combustion package seems to not work as well. The Dauntless and the Defiant. No hard science, just an observation. The Defiant crowd seems to kill catalysts the best. It could be that the larger fireboxes are simply too large for the combustion package. I think of all of the stoves the Encore hits its marks the best, but even it has its issues.

For burn characteristics I know I have to follow the manual EXACTLY to get my secondary combustion to light off. The shoveling and piling of the coals are very real. It wont go if I don’t shovel the coals to the back. The wood has to be piled tight against the back of the stove for it to light. If not, no secondary combustion and prodigious smoke. The stove shop I worked with had a Defiant on display. Their Defiant had the seemingly typical sloppy front cover so it was possible to see through the gaps and see when the secondaries lit with a blue-yellow glow. That stove seemed to light MUCH better than the dauntless but their display wood is stupendously dry pine, so that may be a factor.

I guess all if this is to say that maybe the temperature problem is a secondary burn problem. For those interested in experimenting it would be interesting to see if the cat behaved better if great effort was made to ensure secondary combustion actually lit. Maybe it does and I’m just delusional. I know many smart people have many hours trying to make these things work better.

One last note on glass clarity and back puffing. For me, maintaining an air setting that keeps SOME flame present in the firebox is critical. With out that the glass gets truly annihilated and the thing is liable to back puff like crazy. A bit more air calms all of these problems right down.

If you made it this far, hopefully its worth while and can help.

 

[VRB Farm]

Nice post! I think the issue with people running the defiant is they try and run the stove to low. That stove is a power house of btu production, folks try and cut it back way to much or run smaller loads. Sizing the stove to the application seems to get missed for cosmetics and not thinking the smaller box won’t produce what they need.

 

[dmccoole]

I'm going on my 5th year with the Encore and the temperamental operation of the cat still mystifies me! I had 30 years with a Noble(non cat) stove prior. I cut most of my firewood, burn 2-3 cords per year and burn 24/7 during the winter months.

With a good base of coals, I can usually get the cat to light off quite easily. I have troubles with the wide temp swings from burn to burn with the same wood, outside temps, wind, etc. From my observations, whatever is controlling the air to the cat is not working correctly for my stove or my setup.

But you have an interesting thought on "cashing". When I add splits on a hot reload, I have seen my cat temp at ~1000 but a lot of smoke coming out the chimney. The smoke will last 15-20 minutes and then goes smokeless. I'll try to keep my eye on the smoke levels during the day and try to correlate to temp swings. I've also observed my cat running in the 800 range for extended periods on the end of a burn. Is that really burning all the smoke or is it now cashing? Keeps my engineering skills engaged for sure!

 

[arnermd]

Nice write up and interesting thoughts.... I am not sure if I agree or not, but the lack of secondary burn is a new idea I think....

 

[bullittman281]

dmccoole, this is sort of what I'm talking about. In theory, on a hot reload the secondary combustion unit is well heated and should be ready to secondary burn nearly immediately after a reload when it gets fuel to burn (smoke). If it did light off there should be zero smoke, catalyst or not. Instead, the cat goes wild because its WAY over worked. A cat that is HOT, not over whelmed, and has a good air supply should not let any appreciable amount of smoke through it. I'm guessing the mid burn temp spike people see is the secondary combustion stalling. With out a cat this is when the fire smolders out as the stack goes cold and everything gets coated in tar. With the cat the stove powers through it, at the expense of very high temps. Again, just a theory. The late stage 800* you speak of sound the most correct and normal. Temps coming out of the fire box will be the hottest with only coals and the cat cleaning up whatever is left.

For somebody that has time, good weather and adventurous, pull that cat out and run a couple of small reloads. See what the smoke level does. Its not a completely fair test as the airflow through the stove is different with and without the catalyst in place. you WILL know if it has secondary burn or not with the catalyst out. Not sure how hot the temp probe would be with direct flame impingement.

When I get a change I want to add an EGT probe to my Dauntless even though there is no cat to monitor. I'm really curious whats going on in there. I intend to use a raspberry Pi for a low buck solution. I've added a couple of random pics and video of the stack that may help people out as well. These are a sequence of loading the stove only a few minutes apart. The movie was shortened so its time stamp is wrong. Hope this helps

 

[bullittman281]

Nice write up and interesting thoughts.... I am not sure if I agree or not, but the lack of secondary burn is a new idea I think....

I welcome disagreement and discussion. Thats the intent. Other stove brand don't seem to have these problems. SOMETHING is going on. Maybe this will help find a reason and a fix.

 

[arnermd]

I welcome disagreement and discussion. Thats the intent. Other stove brand don't seem to have these problems. SOMETHING is going on. Maybe this will help find a reason and a fix.

Agreed... "Something" is going on! I have been dealing with that "something" for 13 years.... Have not found it yet.

Please do not take my comment as criticism of any kind. I 100% support the discussion here.

I am so fed up with my ceramic cat right now I may pull it this afternoon..... Will report back.

 

[skb31]

I’ve run my Encore 2040 cat-c extensively without a catalyst. You can easily achieve smokeless burns and high refractory chamber temps with secondary ignition. You seem to sacrifice longer burn times is what I have noticed.