I built a 6" batch rocket based on Peter"s designs on batchrocket.eu The fire box and heat riser are insulated with 3" of rockwool. I have an infrared temperature gauge that goes up to 960 degrees F. Sometimes parts of the inside of the fire box and heat riser will max out the reader so I might be hitting 1000 degrees occasionally but not the target temperatures of 1200-1800 degrees. The exhaust is clear with no wood smoke smell. But the exhaust does smell dirty, sort of like a diesel engine.
Can I clean the exhaust up more?
How do I raise the temperature inside my stove?
With this smell what chemicals are likely to be still un-burnt? ( I see that odorless Carbon Monoxide burns at 1128 degrees)
Glad you have taken the plunge and built yourself a Peterberg Dragon.
A few questions for you:
1) What is your firebox made from? Hard firebrick, soft insulated firebrick, ceramic fiber board...other?
Dense firebrick takes a bit of time to get up to high enough temperatures to produce a clean burn and ceramic fiber board has a curing phase that burns out the binders. Both of which may produce the smell your experiencing.
2) What is your heat riser made from? Even if you have a liner, rock wool is not rated high enough for the temperatures a heat riser will get to. Perhaps the rock wool is burning up and producing a smell?
3) What type of wood are you burning? Is is clean dry wood? Painted or preservatives of any kind?
4) Are you choking the fire down at all or running it wide open? I've experimented with mine choking it down partially about 10 minutes into the burn and I get this real awful chemically smelling exhaust.
5) I'm assuming your secondary and primary air dimensions are all to spec as well?
6) Are you running it outside without a barrel over the heat riser or naked?
Hi Gary, thanks for responding to my post.
1: The entire core is made from hard fire brick recycled from an incinerator. 4.5" by 9" I have noticed it takes 30 minutes for the fire brick to get warm on the out side. I will measure
the temp on my next burn. I have also noticed that the burns are getting more rocketty with each burn. Maybe the result of the core drying out.
2: I did wonder if some of the smell is coming from the Rockwool. I know lots of products off gas and it does have some small odor when being installed in a house. According to their
website it is good to temps of 1000 c and I didn't think the outside of the core would ever get that hot. Inside yes hopefully.
3: I have been burning Black walnut. Several years old and seasoned in a completely dry wood shed. I did notice that my last burn where I used split wood instead of 2-3" diameter
sticks burned hotter and faster. I have read that tree bark is fire resistant compared to the interior wood. No painted, preserved or wet wood.
4: I am using a primary air opening of 2" by 4". Slightly bigger than the recommended 2 6/16 by 2 6/16, but it seems to run better that way. I haven't made a door yet so I am
blocking the rest of the opening with bricks. I have noticed that chemically smell when using my vertical coal/wood stove in the past. Getting rid of that smell is part of my interest in
5: I made the P channel 2 1/4 wide by 5/8 high. I always run with both wide open.
6: I am building it in a garage with a 6" stove pipe collecting the exhaust and running it into the chimney. The chimney is only 8' high and made of brick so long term I intend to build it
higher and line it with more 6" stove pipe then insulate it with a clay perlite mixture to maintain exit temperature. Since the heat riser is the "engine" of a rocket I'm not sure that's
necessary but it can only help right? I am still in the process of building the bell.
1: I need to a better way to measure temperatures and exhaust quality. Any recommendations? Where in the rocket are you measuring temp for the 1200-1800 F goals? Interior fire
2: Advice on raising the temperature in the rocket for complete combustion?
Thanks again for your time and help, Lesleigh
I am currently using rock wool wrapped around my core also (made with firebrick splits) but with a 5 minute riser (ceramic fiber blanket wrapped inside a sheet metal outer casing).
The rock wool has been there approximately 1 season now and will be very curious to see how its held up over time. Its the heat riser though where temperatures get real hot and wonder if rock wool will last.
I think I might do a 6 minute riser (riser extends all the way to the floor) with rock wool and see how that fares. Will get back to you on that.
I don' have any experience burning black walnut so I'm not sure how it smells. If you can switch to another type just to experiment that would help eliminate that possibility (seeing as you were getting the same smell from your other wood stove). I know for me when I burn Douglas Fir bark, it can produce a chemically smell if not burned hot.
Insulating your exhaust pipe is only necessary when it exits the building so condensation doesn't form. Keeping a warm exhaust is important as it also contributes to good draft.
Although it has been stated that the riser pushes the gasses along, some feel very strongly that its the pull that makes draft occur. Either way, a warm chimney is your friend.
Peter has since switched over to the floor channel as a way to deliver secondary air to the port (also on his website) but the P channel you are currently using would not be a problem if you continued to use it.
Makes it much easier to replace when the time comes, is in the direct flame path which preheats the secondary air better and acts as an 'end iron' to helps keep wood from blocking the port.
I got a thermo-couple and I got consistent temps of 1450 F on my last burn all through the middle phase. I closed a leak that was hurting my draft and the new thermometer goes up to 2400 F so I can get better ideas of whats going on. No smell to speak of once it got going. Still using the black walnut as that's what I've got seasoned right now. I cast the bell lid yesterday and will install it once the it fully sets. Will post again after testing to see how it affects exhaust quality.
I will look into the floor channel. Ease of replacement is a good thing.
thanks again, sorry about divulging your code name. Lesleigh
Rock wool experiment:
The other day I popped the barrels off and inspected the condition of everything. I didn't feel like removing the 6 minute heat riser (which was in great condition) so I decided to just put a piece of rock wool at the base of the riser right in the blast zone where the flames come out the port. After one batch of wood I did another inspection. The rock wool survived but went from a grey to tan coloured and was powdery. I would say that it lost about 1/4 of its thickness. I took it out and came to the conclusion that it wouldn't be much longer before it disintegrated.
It dawned on me that I remember seeing another fellow who had done a rock wool heat riser years ago. Web4deb. His was disintegrated at the bottom and looking to be in rough shape for the rest of it.