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Post by 4seasons on Apr 15, 2014 9:03:55 GMT -8
After reading all about rocket stoves for a couple of months and trying to decide if I wanted one in my house I got fascinated by two different ideas. The first was my idea that fluid likes to spin in order to flow down a drain so why would flames not want to spin to go up. The second was inspired by Donkey in this thread: donkey32.proboards.com/thread/1090/turbulator-revisitedThe idea that more turbulence creates a better burn. At the end of that thread Donkey issues a challenge that I decided to take up after seeing this thread: donkey32.proboards.com/thread/850/mud-batch-boxI realized that I had enough free materials to build a mud batch box. I mixed up clay, sand, wood ash, in a 1:1:1 ratio and added in some straw to get started. I built some molds out of scraps of plywood that I had laying around. I used standard batch box dimensions from this thread: donkey32.proboards.com/thread/734/peterberg-batch-box-dimensionsI modified the placement and shape of the heat riser to see if the flames could be convinced to burn faster or hotter by changing the way they flowed up the heat riser. By the way I do not recommend using this mix for anything other than experimenting outside. It is very fragile and does not hold up long before it starts cracking and finally falls apart under its weight and the stress of rapid heating and cooling. |
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Post by 4seasons on Apr 15, 2014 9:20:34 GMT -8
First up the Single Cyclone.
For this build I offset the heat riser to the left so that as the flames came thru the port they would be forced into vortex and spiral up the riser. I made a few mistakes on this build first by getting my mix too wet and secondly by using too much to hold my internal mold together. It took a while to get everything dry and flowing as most of the mold was very wet and did not want to burn out.
In this video you can see some obstructions still in the heat riser that was slowing things down a bit:
After a tear down and clean out of the ash and parts of the mold still in the heat riser it came up to speed but was never the real rocket that I was expecting.
Shortly after this video was shot the top of the firebox collapsed due to extensive cracking. I modified the next firebox with a replaceable top to avoid having my next version fall apart before I was done testing.
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Post by 4seasons on Apr 15, 2014 9:31:33 GMT -8
Next I built the Flame Crasher.
This is an idea that I had based on Donkey's Turbulator. Rather than spinning the flames up the riser quickly, crash them back into each other to create maximum turbulence. Learning from my first build I built my mold differently. Here is the overview:
Once the mold burned out I realized that the round heat riser was causing a slow down in the system.
I needed the heat riser to match the core.
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Post by 4seasons on Apr 15, 2014 9:40:37 GMT -8
New heat riser built and burned out.
I tore it down and cleaned everything out and shot a video so you can see how I built it:
Once I got everything back together I got the nice "ram horn" effect I was looking for but never got a true smoke free burn nor did I see flames shooting from the heat riser.
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Post by 4seasons on Apr 15, 2014 9:55:24 GMT -8
After getting frustrated with the under-performing Flame Crasher I tore it down and knocked the back of the core out and repacked it to a 4 inch round heat riser. It is now a built to standard Peterberg Batch Box dimensions. I put my round heat riser back on and lit it up.
It was certainly running hotter and went smoke free almost from the beginning. I could no longer lean over the heat riser to see what the flames were doing. Even holding the camera 3 feet over the riser was uncomfortably hot on my hand. On the second reload of this version I got flames shooting from the top.
I was holding the camera 4 feet over the heat riser and was only able to hold it there for 30 seconds before it got to hot.
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Post by 4seasons on Apr 15, 2014 10:17:12 GMT -8
I am left with a few conclusions. The primary conclusion is that Peter put a lot of work and research into the dimensions that he has published and they flat out work. While other designs may work, the standard dimensions are the simplest way to ensure results.
My second conclusion is that mud is not very durable at least in the ratio that I used when exposed to the extreme heat stress of a rocket stove. While the heat risers were cracking they would probably last a long time if all they have to do is sit on the core and guide the flames. My constant tearing down and rebuilding was starting to take its toll on my mud risers and chunks were falling off. I also broke my port opening a shoving wood too far into the firebox, and had the top of the firebox collapse twice.
My third conclusion is a bit more of an intuitive leap. While the single cyclone showed promise it was far surpassed by a simple centered round riser. This would indicate that turbulence in the heat riser is a good thing, but the Flame Crasher seemed to stall, possibly from too much turbulence. So either turbulence must be used in moderation or possibly the 3 inch siamesed tubes were simply too small for proper flow. I remember reading somewhere that 4 inch is the minimum size that a rocket stove can be built before you run into diminishing returns due to flow restrictions. I am curious if a 6 inch system could actually make the Turbulator idea work using 4 inch siamesed tubes and overcome the flow restrictions.
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Post by Donkey on Apr 15, 2014 22:19:32 GMT -8
Remember that fire-clay is a variety of mud.. Your clay soils may not be up to the task.
Look around, try different soils, find a purer source (maybe a different local color or some such thing) and/or dilute it with more wood-ash/sand.
I know that I'm a lucky dog.. They made bricks around here, back in the day. My clays can handle the heat.
Keep looking, you might hit on something.
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