The text of this article first appeared in the PiNZ Autumn 2010 Members Newsletter produced quarterly for the members of Permaculture in New Zealand As the author retains the rights to any article published it is published here for further dissemination and feedback
The principles involved in the design of rocket stoves were invented in 1982 by Dr. Larry Winiarski whilst he was Technical Director of the Aprovecho Research Centre. A link to his work: Design Principles for Wood Burning Cook Stoves, can be found at the end of this article
A rocket stove is a simple to implement and highly efficient fuel combustion and heat transfer design, utilised in the design of cooking appliances and space heaters
A typical rocket stove consists of a short chimney sitting on top of a fire chamber with a front fire box. The external design and function of rocket stoves varies considerably depending on their use as either: stoves, hot plates, ovens, space heaters, static installations, mobile devices, etc. Designs also vary considerably between manufactured and handmade stoves
My interest in rocket stove design focused around its use as a stove, primarily for base camp kitchen cooking during site work, courses, etc. My requirements differed from those of the Koanga Institute team, who have implemented a static rocket stove design in their course kitchen
Generally all stoves have similar characteristics: A firebox at the front base of the rocket stove divided into separate air (bottom) and fuel (top) intakes which allows fuel to be added above the air intake at the base of the chimney in the fire chamber. Heat in the fire chamber rises in the chimney and cause a draft at the fire box encouraging hot and efficient combustion of the fuel at high temperatures. At the top of the chimney heat is focused directly on the cooking/heating surface
Stoves designed in this way are very fuel efficient, produce very little smoke and ensure optimum heat transfer efficiency from fuel to food
My design objective was to produce a simple stove based on rocket stove design that fulfilled the following criteria:
The design can be implemented by anyone with access to the materials The design utilises actually available and affordable materials The design requires the minimum number of tools and addition inputs to implement The design is simple to construct, use and maintain The construction can be broken down and reassembled in different locations The construction can be quickly built on spec The construction is ‘safe’ The fuel must be accessible and sustainable The design works as a component of the larger design/philosophy
The first stage of my project was research. I carried out an internet study and found many interesting articles and designs and watched some inspirational Youtube videos. I also began assessing what materials I would use to build the stove, initially focussing on those used in the articles or videos of my research i.e. purchased or recycled. The more I studied the less I knew and I had begun to focus on details! At this point I moved my point of focus from the internet to a review of both my criteria and what I was attempting to achieve, the sketch pad and the physical modelling of ideas
During my review I realised that I had not included the fact that this first design implementation was only a test to see if I could make a rocket stove and assess how they worked. The design did not need to be perfect, it just had to provide the learning material to take me to the next level of design/complexity therefore the cheaper and quicker I could make the stove the better
Through this design analysis I realised that the hollow masonry/concrete block I have used in my pottage garden layout would be the ideal resource to construct the stove
My initial block stove layouts and models were large, cumbersome and obviously dysfunctional! The wonderful thing about blocks of any sort is that they can be assembled and reassembled in many different ways, and the more I handled the blocks and became familiar with their characteristics the better I utilised their features and the leaner the design sketches and models became I finally settled on a minimalistic five block model which fulfilled my design criteria and I arranged to build and test the design
I originally intended to test the stove on the beach, where I collected the fuel twigs and sticks, but unfortunately this location and several others fell under the personal revelation that you cannot just light fires anywhere you like. Testing eventually took place at home!
The blocks were easy to position and assemble on a concrete base http://picasaweb.google.com/myk.rushton/ConcreteBlockRocketStoveProposed#5443218855356920146, http://picasaweb.google.com/myk.rushton/ConcreteBlockRocketStoveProposed#5443218887154703474)
Once the blocks were in position a fire was lit in the fire chamber a fire box divider added and fuel added (http://picasaweb.google.com/myk.rushton/ConcreteBlockRocketStoveProposed#5443218947356235074)
Once the fire was set I was able to heat a tin of baked beans from opening to serving in five minutes http://picasaweb.google.com/myk.rushton/ConcreteBlockRocketStoveProposed#5443219459109196258, note scale of fuel being used) and boil 2 litres of water in the thermette in less than seven minutes (http://picasaweb.google.com/myk.rushton/ConcreteBlockRocketStoveProposed#5443219475050553810)
Following practical tests the temperature at the chimney exit was measured to be in excess of 300C
Overall, my five block rocket stove design was successful in allowing me to cook and heat water quickly with very little fuel. I have now added it unchanged to my base camp kitchen equipment, along with the thermette, a smoker and a cob oven - which will cover any cooking/kitchen requirements with fuel that I can grow myself in the form of coppice. I have no doubt that once installed in situ design modifications could increase the efficiency further
The design fulfils all of my criteria and several friends plan to implement identical designs. Further pictures and notes can be found on the following public album
Notes: To be close fitting and stable the designed stove would need to be constructed on firm level ground
Although the thermette boiled quickly and fiercely, its conical chimney shape did reduce the draft into the chimney. When the thermette was removed, flames literally jumped out of the chimney as the pressure changed
In a semi permanent installation the chimney could be clay lined and the whole stove insulated
The draft in the chimney could be improved by removing the cavity mould taper of the block to create parallel sides for the chimney
Replace the tin can sheet divider with a piece of suitable steel
A small helper to keep the fire stoked is helpful!
If the installation was static/permanent the concrete would slowly break down in the high temperatures areas near the firebox lip and the top lip of the chimney. However, the design as presented is not intended to be used as a static/permanent installation. The only solution suggested so far is to line effected areas with clay as a sacrificial surface. Clay has also been suggested as a mortar to seal the faces between the blocks in a temporary situation
The design is intended as a temporary/relocatable/emergency installation. As it is constructed from modular components all components can be rotated to different positions to spread the damage done to each block over time thus extending the lifespan of the stove as a functioning unit. As concrete blocks are ubiquitous replacement blocks will always be available
Interestingly the unique block used to make the fire chamber does not get that hot as all the heat is direct straight up the chimney. The fire chamber block can be made from a standard block by knocking out one face using a bolster chisel
I would not recommend this design for a static/permanent installation. I will however use it until a static/permanent design fitted to the required purpose is installed
Any thing could be used to line the chimney if required, but I would say that if the design needs to much modification from its original form that it is not the appropriate solution for the requirements. The world is full of solutions designed for specific purposes applied inappropriately - To me permaculture design is the appropriate application of the permaculture principles (Holmgren) and consciously designed solutions for each unique requirement
My thought was using it in an emergency/disaster situation, where there would be no shortage of "junk" lying about; and where it might have to be in service for several months if not over a year. However, when thinking about practicalities, in a system that can reach over 300 deg. C (or over 600 deg. F), any flat scrap metal might be better used as a cooking surface.
I just wanted to say thanks for posting. I put one of these together this afternoon and test fired it. It worked pretty well, but I think I need more wood and less air, so I'll redo the shelf before the next time.
Long ago I read an article on a 3 or 4 block stove. I forget exactly how it went together, but you knocked part of the middle part out of one block. One side was a vertical feed and the other was the bottom of the chimney stack. Maybe I'll try one of that type too.