Wood Gas Backpacking Stove

Penny Wood Gas Backpacking Stove                                                                                                       "...a couple of test burns... you will have a very efficient stove with (little) smoke, which lets you boil 20-40 oz of water with little more than two hands full of small woodsticks." stefan "The Penny Wood is a killer stove; the Bushbuddy Ultra boils 1qt just like the Penny (~9:30) but weighs 5oz. and costs $145. The Penny is 'free' and weighs less than 3oz. What a deal!" Mike Elliott
	By Mark Jurey Originally the Penny Alcohol Stove was to work as a backup for a small ultralight 3 oz. wood backpacking stove. Since the Penny was so successful, and the wood stove development so frustrating, things soon got reversed. After years of trying to get tiny backpacking stoves to burn clean, it was the Zen Alcohol Stoves and Ray Garlington sites that finally outlined the solution and brought my design together. This is a variation of a wood gas or TLUD gasifier (Top-Lit UpDraft) stove. It uses a top down burn and hot air injectors to produce a clean efficient flame. As shown below, it was designed to fit my specific needs but many variations are possible and each shows a similar efficiency. I have heated my home with wood for over 35 years and my first home stoves were metal boxes with ways to control the air supply. Newer stoves, like the one I use today, are extremely clean burning and over 80% efficient. The Penny Wood stove has the same features found in these, including; 1- a slow controlled primary burn to release the wood gasses, 2- hot air secondary injectors to burn these gasses, 3- a double wall area to hold heat in the wood and heat the secondary air supply. I now bring the wood stove, and on some trips even leave the Penny and alcohol home. When I take both, I leave the Penny pot support (1 oz.) at home. I use the Wood stove (3 oz.) with stakes reversed as a pot support for the alcohol burner (see below). So, for 2 oz. more weight (or 2 oz. less alcohol) I have an unlimited heat source. If I'm above the tree line or want quick heat, I use the alcohol. If I have the time, or the weather turns bad, or snow is the only water source, I burn wood. The stakes are reversed to support the pot 1" above the top rim of the Penny Alcohol stove (shown are 6" titanium stakes, see below). There's nothing like a warming fire at the end of a day of hiking. Often, one night of cooking over an open fire is enough to convince the bugs to go away for the remainder of the trip. A little black on the pot is the only down side and that can be handled by packing in a plastic bag or liquid soap on the pot. The pot and stove are usually very clean at the end of a burn - little tar or soot and only a hand full of white ash. I usually wipe the stove and pot with some TP then save the TP to help start the next fire. Update - Recently I replaced the drip irrigation stakes with stock 6" titanium stakes from GossamerGear.com (shown above). They are a lighter, stronger, require no cutting, and they make better tent/tarp stakes. Because of the curved shape, the titanium stakes still support the pot 1" above the alcohol stove if the Penny's Base is not used.
Design Goals
	* Stove and shield fit inside a 2 quart Open Country or AntiGravityGear pot. * Boil one quart with one fill and no adjustments. * Additional fuel easy to add for continuous burn. * Stable base and pot support for alcohol stove. * Efficient and no smoke burn. * Leave no trace.
Specifications and Performance
	Tomato Can -(trader Joe's Marinara Sauce) 4" dia. cut to fit into the pot (3-3/4" high after tabs are bent). Three steel stakes - 6-1/2" long drip irrigation stakes with 3/4" long 45° bend on one end, or, 6" titanium stakes from GossamerGear.com Total weight - less than 3 oz. Looking into the can top you can see about 70 - 1/8" holes in bottom - large enough to let in air but small enough to hold the ash. Note the 12 - 1/4" holes just below the rim. After drilling, they were bent down using the drill bit. This helps scoop hot secondary air from the sides of the stove and shoot them onto wood gas from the primary burn. Not showing are the three 1/4" and three 1/2" side holes near the bottom. Both provide additional primary air. Don't forget the heat shield, with holes along the bottom - it's necessary to heat the wood and create a chimney effect between the stove and shield that provides hot air for the secondary jets at the top. A fuller shield will work better, this one is an aluminum dryer vent. When drilling, I suggest that you use a set or nail to mark the spot, drill slowly but keep the bit moving at a high RPM and wear gloves. Use a round file to smooth all holes and cuts. Many builders recommend you use a step drill bit!!!
	WARNING!!! The pot support stakes used for this stove could be VERY DANGEROUS when the pot is removed. Falling on the stove could cause major damage. Always remove the stakes or turn the stove on its side or upside down when not cooking.
	Performance figures - About the same as the Garlington WoodGasStove and Bushbuddy Ultra. One quart boils in less than 10 min. and holds a boil for another 5 to 10 min.. Two cups boil in about 5 min. Properly loaded, it can burn smoke free with lots of blue flame and leaves nothing but white ash.
	Notes - 1. The stakes support the pot up to 2" above the stove. This may seem high but it insures complete combustion before gasses reach the pot. This distance also supports the Penny alcohol stove 1" below the pot. If you want better efficiency in high winds, the distance can be reduced. 2. I use the Penny alcohol stove wind screen around the wood stove to preheat the air supply for added efficiency. When using the alcohol stove on top of the PennyWood, I hang the support from the pot with some thin wire. I take some foil to use if a higher wind break is necessary or to put under the stove if burning on a combustible surface. On a soft or sandy surface, I use the pot lid under the stove and foil for a lid. 3. Warning! The bent section of the original pot support stakes can sometimes spin and cause instability. If they do, file a notch in the bottom rim of the can for them to fit into.
	Filling and Lighting - Break pencil size wood 1" to 3" long, shake it down as you fill and pack it almost to the top. Dribble some alcohol or lamp oil only on the top and/or light some TP under a wood teepee on top. If necessary, feed kindling until top is fully lit. The secondary air holes will help to provide primary air to get things going. After the top wood is completely lit, put the pot on and enjoy the show. Adjust the next fill as outlined below.       Read More