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Post by russellcollins on Feb 22, 2019 20:26:10 GMT -8
I've been asked several times over the last few years for the design plans to our commercial product, the Eco1 Rocket Stove. This is an all metal combustion heater with cooking options made by my company, Himalayan Rocket Stove in India for the Himalayan India market. I was not ready to release these earlier, as I wanted to be sure we could get our new company up and running before we had to face too much competition, and also to make sure it actually works as advertised. We now have made and sold around 700 units (including the larger Eco2 and Eco3 Rocket Stoves) with very positive results, so I feel confident now to say it does indeed work. Having said that, I am sure it could be improved on. Part of the idea for releasing the plans here is to invite feedback and input on improving the design, as well as to share more widely a low cost heating solution that can be replicated with CNC machines anywhere in the world. Our goal (as a social enterprise) is to reduce deforestation and pollution in the developing world, and any design improvements that help facilitate this is most welcome. The core concepts evolved out of the work of the rocket stove community online and I am happy to contribute back to this community in the spirit of joint collaboration for a better world. The Eco1 is made to be as low as possible due to the cultural context of the region where women tend to sit low to the ground whilst cooking on the top surfaces. The Eco2 and Eco3 are a better operating height generally with a taller riser being more optimal for convective draw, and more surface area to shed heat. In the Western context these are generally a better size. I will try to release the plans for these later, but at this stage I have not got around to doing up the modifications in Sketchup and nor do I have the time for that right now. You can, however, extrapolate a taller unit and adjust the various panels to suit the height you find ideal. I'm sure questions will arise and I will try to stay tuned to this thread to respond whenever I can. The link to the downloads (with some preamble and pics) is here: himalayanrocketstove.com/eco1-design-plans-now-available-for-free/Cheers, Russell Himalayan Rocket Stove |
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Post by drooster on Feb 23, 2019 6:54:55 GMT -8
 Pretty smart! |
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Post by DCish on Feb 23, 2019 14:41:08 GMT -8
Hi Russell, Indeed, a pretty build! And my respect to you for putting time and effort into a very worthy cause. I took a look through your design description, and I didn't see any insulation mentioned. One of the primary characteristics I am accustomed to seeing in rocket stove builds is highly insulated combustion areas, especially the afterburner area. Temps there are often in the 2000*F (1100*C) range, making metal (even some grades of stainless) a less than ideal material for that part of the build. One member tried a piece of triple-wall stainless steel stovepipe as a riser, and had it burn out in less than a season of heating. Another design feature I noticed that may make a difference is the off-center entrance to the afterburner (riser) area. If you look at Peter's batch box development thread ( donkey32.proboards.com/thread/511/adventures-horizontal-feed), you'll notice that the slot that enters the afterburner (riser) area is on center. This is intentional, creating a double vortex instead of a single vortex, and more aggressive mixing than if gases continue on a smooth trajectory (even if that trajectory moves from linear to circular). I would rank these tweaks in order of importance as follows: 1) Afterburner (riser) insulation -- keeping temps as high as possible here is where you would be likely to get the most gains for the least effort. Depending on how robust your materials are, though, you may have to shift from a metal riser to a refractory riser. This is easily done, however, by use of the "5 minute riser" developed by one of the folks on this forum (sorry, I did a quick search, but couldn't find who that idea belongs to right off). Basically, you would make your metal riser an inch larger in diameter, then cut a piece of half-inch ceramic fiber blanket and tuck it *inside* the metal form. It is light, easy to work with, and stiff enough to remain in place with no additional support, and risers built in this manner show no degradation even after years of use. If you are worried about ceramic fibers coming loose and being emitted as a health hazard, you could use a little rigidizer on the surface to bind the surface layer fibers in place, eliminating that concern. Generally, though, in my experience, the blanket stays well together unless it is being cut, shaped, or otherwise manipulated. 2) Insulate the burn box -- This is a less important place to insulate, since the main goal of this space is to begin the combustion process, not necessarily to finish it, but insulation here is still desirable. Any heat harvested before combustion is complete will contribute to lower temps and less efficient combustion overall. Even if you just insulate the sides, or the sides and bottom, you'll be a step ahead. Any insulation added in this area will make it easier to light, quicker to come up to temperature, and more forgiving of lower-quality fuel. 3) Port repositioned to center of riser -- This one is a little harder to predict. As Peterberg (Peter van den Berg) is fond of saying, even small changes in design can create significant, measurable differences in performance that are invisible to the naked eye. I would start by measuring the efficiency impact of the first two changes, then try this one to see if it adds any additional performance. Insulating is the low-hanging fruit likely to get you the greatest gains with the least amount of effort. Exploring alternate ways of introducing turbulence is a more nuanced endeavor. 4) Toroidal afterburner -- If you regularly have flame exiting your riser (perhaps not now, but when you test an insulated version of it), that would mean that you don't have enough dwell time in the afterburner for combustion to be completed (significantly more likely in your shorter stoves). If that is the case, one way you could potentially alter the afterburner to increase dwell time without increasing height would be to preserve the tangential entrance into the afterburner, but double the diameter of the bottom portion of the afterburner to the height of the entrance port. This would look like a doughnut with the final insulated riser coming out the middle of it. Centrifugal force would keep the initial flame front to the outside of the doughnut, swirling inward until it reached the center and exited up the riser. I've played with this concept to good effect in a double vortex layout, and there has been speculation that a single vortex layout could be effective as well, though I am unaware of it having been tried to date. It may reduce the amount of mixing as compared to a double vortex, but the layout may be particularly friendly to your application. And it may be that the heavier, unburned gases may be held outside by centrifugal force as compared to the lighter, more fully combusted gases, giving uncombusted gases a more time to burn, and possibly making up for the lower turbulence of the design. Again, this is a discussed, but as far as I know untested, concept. I am curious about a couple of things: 1) What is the peak temperature you are generally reaching in the afterburner? That is one relatively easily-accessible, if crude, indicator of efficiency 2) Have you used a combustion analyzer to test your flue gases? If so, could you post a chart with O2, CO, final flue temp at exit, and efficiency? There are lots of such charts posted here by Peter, Matthew, and one or two others for reference, if you would like to compare efficiencies you are reaching with the sorts of experiments being done on this site. In conclusion, thanks for sharing, it is always great to see what other folks are doing! |
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Post by russellcollins on Feb 24, 2019 18:48:07 GMT -8
Hi and thanks for the comprehensive post above (DCish)
In response...
1. Insulation: yes we do use ceramic wool wrapped around the riser tube which is made from SS 310. I forgot that that detail will not show up in the schematics. Interesting idea to use the ceramic wool inside the riser though, I hadn't thought of that and it is an interesting proposition. We have found the SS 310 to be particularly resistant to any form of noticeable degradation so far (having now had 2 winter seasons to observe this).
2. Insulated burn box: This was considered but the cultural context requires immediate radiant heat from the time of starting the fire and this is most apparent from the sides of the burn box, so at this stage we have left it non-insulated. However we have included pre-heated airflow to the primary box and this increases internal temps and improves combustion in the short riser considerably. The point about being more forgiving of lower quality fuel is noted.
3. Central Port: Original units had central ports, and my experience with them is that they work when the riser is taller. In the short form (with a 14" riser) I find the extended flame path with the single vortex to be quite effective (to the naked eye). We have yet to test the unit with a decent emissions testing gadget.
4. Toroidal afterburner: this is very interesting and something I had previous considered but not finding any evidence of this on the net, I had passed over it. I wonder if a tapered riser would be as effective as the stepped donut option you have described?
Regarding the questions...
1. Peak temps in the riser are around 850 - 900C with steady temps around 750C
2. Not yet... due to budget constraints have not managed to purchase one as yet.
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Post by peterberg on Feb 25, 2019 1:32:59 GMT -8
4. Toroidal afterburner: this is very interesting and something I had previous considered but not finding any evidence of this on the net, I had passed over it. I wonder if a tapered riser would be as effective as the stepped donut option you have described? Yes, a tapered riser is effective, provided the top end is the same cross section area as the bottom end. This is tested quite recently, see donkey32.proboards.com/thread/3379/tapered-riser-batch-core-dsr2. Although I don't know about a tapered riser that starts wide and ending narrow like a funnel shape placed with the large end down. But DCish could be right here, dwell time is very important. Starting wide costs less energy I'd say. Some observations: The port vs riser proportions are about the same as in the batchrocket design. Secondary air is fed into the sides of the port, the inside (left) of the single vortex more than the outside. Presumably because this yielded better visable results. Those secondary air "boxes" are fed through the same main air inlet under the firebox' floor, through the same holes as in the side as the port. I'd think this is a major design flaw: in my opinion the floor under the air "boxes" should be completely open. So the air jets in the port would be the one single restriction in the air path. Two restrictions in succession tend to slow down velocity quite a bit, as I found out a long time ago. In general: the higher the air velocity at this spot the better combustion achieved. This is why using a fan is so effective. Question: what is the mean exhaust temperature of this unit? I'd think it won't be as low as 80 or 100 ºC since the unit is small and this cyclone type of vortex forming takes a lot of energy so draft need to be high. I'd think it's high time to start formal testing with a gas analyser, you might be in for some surprises. |
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Post by DCish on Feb 25, 2019 7:31:02 GMT -8
1. Insulation: yes we do use ceramic wool wrapped around the riser tube which is made from SS 310. I forgot that that detail will not show up in the schematics. Interesting idea to use the ceramic wool inside the riser though, I hadn't thought of that and it is an interesting proposition. We have found the SS 310 to be particularly resistant to any form of noticeable degradation so far (having now had 2 winter seasons to observe this). I just looked up SS 310, looks like it is rated to 2100*F (1150*C). Peter has reported sustained temps in his afterburners in the 1100*C (2000*F) range, just below what your material will sustain, and your temps are well below that. Looks like you are safe with your insulation around the outside in the current configuration. Vortex has a setup now that he is working toward exploring the temperature of ( donkey32.proboards.com/thread/3418/edjumacate-me-using-glass-windows?page=4). It may be worth tracking as a reference point. It is also an example of a double-vortex afterburner that shows another way to do the afterburner layout (as yet un-tested by gas analysis equipment, but clearly producing a very high temperature burn, which is an encouraging indicator in my mind). The perfect can be the enemy of the good -- every design has its compromises. Personally, I'm partial to fire viewing, and am pursuing a design that has a piece of ceramic glass located so that the afterburner can be viewed. Everything else is well insulated, but I just love that view of the fire! I'm trying to drum up interested in a crowd-funded, shared-use flue gas analyzer. I think it is important to democratize access to test equipment so that we can accumulate some real-world-use data that allow us to empirically compare our experiments to commercial stoves tested in lab environments... and compare that to the real-world use of commercial stoves to show how big a gap there is between what is generally in use, and what we are doing. I've had a few expressions of interest, so I'm going to try to find a crowd-funding platform to set this up on, and see how it goes. If you have any interest, let me know, I'm happy to have wide participation in the project. When I was describing the toroidal idea I didn't connect it to Peter's recent tapered riser experiment -- looks like my idea isn't so far from the range of what's been tested  . As development of different afterburner shapes continues, it illuminates for me the amount of flexibility there is, within certain parameters. My guess is that if you're not getting any flame out the top of your riser, it's a moot point. Increasing afterburner volume beyond what is needed spreads the available heat across too large an area, reducing peak temperatures rather than concentrating them. [EDIT - a taller riser (longer afterburner segment) such as you have in your taller stoves wouldn't cause any negative effect, since the entire thing is system size. The negative effect I'm thinking of is if you were to use the toroidal idea without having enough flame to fill it reliably. This is the test I did that informs this comment.] |
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Post by DCish on Feb 25, 2019 9:24:54 GMT -8
Hi Russell,
I just spent some more time on your website -- looks like you've put a great deal of time and energy into the development of this! Your "Smoke pollution in the Himalayas" video makes clear how much of a contribution your current stove already is. It's hard to say how much more there is left to accomplish. What might be left to tune is in the area of CO levels, excess air, and heat harvest. If there is a lot of leftover CO, you could be able to get even more heat out of the fuel than you already are by tuning it to more completely consume the CO. If your excess air is high, you might be able to tighten things up and get more heat without excessively cooling the burn with excess air. And as Peter mentioned, if your exhaust temps are high, there could be opportunities to harvest even more of the heat that is already being produced. It looks like you are exploring extra harvest with the oven / water heater add-ons. If there is enough heat left over, an extra box that can be filled with bricks / rocks / mud that the exhaust gases flow through could serve as a thermal battery to soak up and gradually release the heat. At any rate, it looks to me like you have a fantastic build already. I hope it is popular enough to support additional development!
Regards,
Brian.
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Post by russellcollins on Feb 27, 2019 17:28:50 GMT -8
4. Toroidal afterburner: this is very interesting and something I had previous considered but not finding any evidence of this on the net, I had passed over it. I wonder if a tapered riser would be as effective as the stepped donut option you have described? I don't know about a tapered riser that starts wide and ending narrow like a funnel shape placed with the large end down. But DCish could be right here, dwell time is very important. Starting wide costs less energy I'd say.
Secondary air is fed into the sides of the port, the inside (left) of the single vortex more than the outside. Presumably because this yielded better visable results. Those secondary air "boxes" are fed through the same main air inlet under the firebox' floor, through the same holes as in the side as the port. I'd think this is a major design flaw: in my opinion the floor under the air "boxes" should be completely open. So the air jets in the port would be the one single restriction in the air path. Two restrictions in succession tend to slow down velocity quite a bit, as I found out a long time ago. In general: the higher the air velocity at this spot the better combustion achieved. This is why using a fan is so effective. Question: what is the mean exhaust temperature of this unit? I'd think it won't be as low as 80 or 100 ºC since the unit is small and this cyclone type of vortex forming takes a lot of energy so draft need to be high.
I'd think it's high time to start formal testing with a gas analyser, you might be in for some surprises. |
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Post by russellcollins on Feb 27, 2019 17:42:16 GMT -8
Hi Russell, I just spent some more time on your website -- looks like you've put a great deal of time and energy into the development of this! Your "Smoke pollution in the Himalayas" video makes clear how much of a contribution your current stove already is. It's hard to say how much more there is left to accomplish. What might be left to tune is in the area of CO levels, excess air, and heat harvest. If there is a lot of leftover CO, you could be able to get even more heat out of the fuel than you already are by tuning it to more completely consume the CO. If your excess air is high, you might be able to tighten things up and get more heat without excessively cooling the burn with excess air. And as Peter mentioned, if your exhaust temps are high, there could be opportunities to harvest even more of the heat that is already being produced. It looks like you are exploring extra harvest with the oven / water heater add-ons. If there is enough heat left over, an extra box that can be filled with bricks / rocks / mud that the exhaust gases flow through could serve as a thermal battery to soak up and gradually release the heat. At any rate, it looks to me like you have a fantastic build already. I hope it is popular enough to support additional development! Regards, Brian. Hi Brian, yes I feel that we are now in the territory of tweaking to get maximum efficiency and as Peter suggested (we've also talked about this previously) I need to get my hands on a decent gas analyser to do this properly. Hoping to do so in the next couple of months. We're on a tight budget now due to the various costs of running a production operation in India. |
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Post by russellcollins on Feb 27, 2019 18:15:15 GMT -8
When I was describing the toroidal idea I didn't connect it to Peter's recent tapered riser experiment -- looks like my idea isn't so far from the range of what's been tested . As development of different afterburner shapes continues, it illuminates for me the amount of flexibility there is, within certain parameters. My guess is that if you're not getting any flame out the top of your riser, it's a moot point. Increasing afterburner volume beyond what is needed spreads the available heat across too large an area, reducing peak temperatures rather than concentrating them. [EDIT - a taller riser (longer afterburner segment) such as you have in your taller stoves wouldn't cause any negative effect, since the entire thing is system size. The negative effect I'm thinking of is if you were to use the toroidal idea without having enough flame to fill it reliably. This is the test I did that informs this comment.] Generally flame stays within the riser, unless the fuel box is overfed, or the fuel is particularly volatile. We've optimised for general usage in this case, although it would be good to have a control system for energy dense fuels. |
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Post by DCish on Feb 27, 2019 18:35:21 GMT -8
A thought on lighting -- in one of your videos you describe a lighting procedure that is a lot like what is used in a J-tube. Have you ever tried a top-down lighting procedure such as is used in masonry heaters and which Peter recommends for his batch boxes? Basically you put your bigger wood on the bottom, medium wood in the middle, and make a nest of kindling and small sticks on the top by the port, possibly still priming the port as you currently recommend. When lit, the small stuff catches quickly and burns brightly, getting smokeless quickly, and burning down into the larger fuel more slowly, and at a rate that tends to maintain smokeless burn. Not sure if that would be value added in your stove or not.
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Post by russellcollins on Feb 28, 2019 18:13:30 GMT -8
A thought on lighting -- in one of your videos you describe a lighting procedure that is a lot like what is used in a J-tube. Have you ever tried a top-down lighting procedure such as is used in masonry heaters and which Peter recommends for his batch boxes? Basically you put your bigger wood on the bottom, medium wood in the middle, and make a nest of kindling and small sticks on the top by the port, possibly still priming the port as you currently recommend. When lit, the small stuff catches quickly and burns brightly, getting smokeless quickly, and burning down into the larger fuel more slowly, and at a rate that tends to maintain smokeless burn. Not sure if that would be value added in your stove or not. That's a good idea... worth testing to see if it works with our setup for sure. I'll try it and see how it goes and report back. |
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Post by russellcollins on Jul 22, 2019 23:07:25 GMT -8
I've had a test report done on the Eco1 Rocket Stove by a lab in India. Unfortunately I was not able to be there, so I don't know exactly how they did the tests, as they were set up to test improved cook stoves rather than combustion heaters. I'm interested in any feedback on the CO, CO2 and PM2.5 numbers here.
The ratio of CO to CO2 comes out at 3.5% which seems ok.
Anyone got any thoughts on this, happy to hear them.
(NOTE: tried to upload a screenshot of the data, but it won't load so I'll write the numbers in here, which are from an average of 3 burns)
Fuel Burn Rate: 1.8kg / hr
Moisture in Fuel: 7.66%
Exhaust Flow Volume: 548 m3
CO: 133PPM
CO2: 3788PPM
PM2.5: 6.33 mg.m3
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graham
Junior Member
Posts: 74
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Post by graham on Jul 25, 2019 22:45:21 GMT -8
www.ncbi.nlm.nih.gov/pmc/articles/PMC4344692/Since the stove test environment differs from actual use, it seems most work is done at looking at the room PM2.5 and CO when actually cooking. This stove comparison shows that forced air stoves did generally better than natural draft stoves. Measuring PM 2.5 is difficult so people use CO instead as a proxy. But that only work when the CO parallels the PM 2.5 which is not always true. Anyway, you need a chimney to take the gases and particulates away from the house as I believe you're doing. BTW, my commercial ULEB wood fire is rated as 0.2 mg/m3 when it's in gasification mode which is 30 times more efficient.
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Post by russellcollins on Jul 27, 2019 20:44:42 GMT -8
BTW, my commercial ULEB wood fire is rated as 0.2 mg/m3 when it's in gasification mode which is 30 times more efficient. Thanks for the comment and link... regarding the PM 2.5 reading from the external flue exhaust, that number (of 6.33) is an average of a 3 x 1 hour test burns, including the heat up and cool down periods, during which time there is smoke in the exhaust. I don't have a reading from the best part of the burn cycle, but for sure it will be far better than the overall average. |
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. As development of different afterburner shapes continues, it illuminates for me the amount of flexibility there is, within certain parameters. My guess is that if you're not getting any flame out the top of your riser, it's a moot point. Increasing afterburner volume beyond what is needed spreads the available heat across too large an area, reducing peak temperatures rather than concentrating them. [EDIT - a taller riser (longer afterburner segment) such as you have in your taller stoves wouldn't cause any negative effect, since the entire thing is system size. The negative effect I'm thinking of is if you were to use the toroidal idea without having enough flame to fill it reliably. 