My team and I are creating our own backpacking stove. We are using isobutane fuel. As you can see from the image, the flame is very intense and is backflowing and exiting from the holes in the expansion valve. Our jet diameter is currently at 0.4 mm. Any ideas or recommendations to fix our camping stove so it's more of a stove than a flamethrower? Is there an ideal jet diameter we should be aiming for so the fuel-to-air ratio isn't as rich?
Welcome to CCS @BackpackingStoveTeam https://classiccampstoves.com/threads/brunton-vapor-af-37mm-jet.36380/#post-374923 I can't see your image? Use the upload a file button, suitable file types are limited so best to use JPG and select full image. Good luck with your project
@BackpackingStoveTeam There appears to be multiple problems. A lack of air in the mixture for one. The location of the jet could be blocking the holes restricting the air inlet and there should probably be 4 holes. Depending on the size and type of your burner you would see increase in over flame size and flame color going up or down depending on jet size. I've noticed the color change from light blue (lean) changing to darker blue and hints of green as it gets richer. This also depends on proper combustion. I've never been able to get the white tips or orange flames as seen with Kerosene usage while using Isobutane in a factory stove designed for its usage. This is easier seen on a silent burner as opposed to a roarer.
Do you have the fuel canister the correct way up. This stove does not look capable of liquid feed. How are the air mixing tube holes picking up the flame? Is it coming down the mixing tube on the inside or outside?
The flame is coming back down the expansion valve (on the inside) and shooting out the holes due to the intense flame and backflow
@BackpackingStoveTeam Maybe you should rethink your burner construction, it appears to be too restrictive or blocked since I see no flame coming from the burner. If your canister is inverted, then you are just flooding the stove with liquid fuel. For example, the Primus Spider has a 1 1/4" diameter burner and with a .37mm jet you get an 15" tall flame on high compared to the Gravity with 3" burner the flame is wider but only 4" on high so I don't think your .4mm jet is the problem. Omni-Fuels use a .45mm for LP gas using their terminology for isobutane/propane fuel.
I will say there's not enough information to answer the questions. If this is a secret design then that explains it.
Basic burner construction. The jet flows gas into the burner at a velocity that allows it to exit the burner holes the designed speed. The jet is placed between the air holes to act like a venturi sucking air in which makes up part of the combustion mix but more importantly speeds up the charge. The burner must be big enough to handle the fuel air mix without restricting the flow. A roarer is more tolerant of flow. A high pressure burner has more smaller holes than a low pressure burner. Why does this not work? Burner too small or too restrictive jet not placed correctly to get a venturi effect pressure wrong for set up jet wrong size for burner Try smaller first Some other restriction in the burner
We tested our burner with a commercially available expansion valve (I would have to double check but I believe it was some MSR version) and the flame was normal, acted like any other camp stove. From this, I think the problem lies with the expansion valve. So far from this thread, problems from our expansion valve could stem from: - jet placement - wrong jet size for diameter of burner The diameter of the burner is 1 inch and follows a similar design to the BSR 3000
It seems to me you need to start with a much smaller jet, 0.25 or 0.3 and see if you get a blue flame. After you have a blue flame you can fiddle with the variables (jet size, fuel, air, gaps) to get the best output.
