Saturday, February 27, 2010

Knock on Wood

The observant amongst you will notice that most of my posts are named after song titles. This one is no exception. I have just returned from a week long odyssey to All Power Labs in Berkeley in Northern California to learn all about running engines on wood.

All Power Labs is based at "The Shipyard", a kind of creative artists community workspace, based in a couple of industrial units at the south end of Berkeley. They have a well equipped metal machining workshop with big machine tools and a metal fabrication shop. The artists share the facilities and develop great mechanical art projects such as the "Neverwas Haul" (pictured above) which attend festivals such as "Burning Man". Anyway the Shipyard is a very cool place - and I was lucky enough to hang out there for a week, and sofa surf.

Wood can be converted to a flammable gas, by a process known as wood gasification. The woodgas is then used to fuel a converted internal combustion engine. The technology to do this has been around for over 100 years and it was extensively used for running vehicles during WW2 - as documented in the recent book "Wartime Woodburners".

The aim of my trip was to learn how to make the technology work - so I could then set up a similar system in my Energy Shed and derive most of my household heat and electricity from waste woodchips.

So I flew out to San Francisco and crossed the bay to Berkeley - home of All Power Labs (APL) and the GEK gasifier. GEK is shorthand for Gasifier Experimenter's Kit.

APL is the brainchild of Jim Mason, a self taught gasification guru. When the city of Berkeley authorities tried to evict the artists from the Shipyard, they cut the power supply. Jim and his colleagues took the Shipyard offgrid with solar and diesel power and so they could remain operational.

Looking for an alternative to expensive diesel powered generation, Jim and his team re-discovered old studies on wood gasification and so the GEK was developed.

Over the weekend of 19th to 21st February I attended the Gasification Workshop, with 60 other delegates from all over the world. The workshop was hands on experience in working with the GEK gasifier, and other system components.

The fuel for wood gasification is just chipped wood. This drum load was made in a few minutes by running some old pallet planks through a wood-chipper. This sort of material can be obtained from tree surgeons who make so much they can't get rid of it quick enough.

During the course of the weekend we converted a Lister type diesel engine to spark ignition so that it could be run directly on woodgas. The conversion consisted of fitting a long reach spark plug in place of the diesel injector and devising a spark ignition circuit. A new pair of copper head gaskets were made using the CNC plasma cutter, and these were used to lower the compression ratio down to about 13:1.

The ignition circuit was made from an Arduino and a car ignition coil. A Hall effect sensor was used to detect a magnet on the flywheel, placed a few degrees before top dead centre. The Arduino was used to create the correct timing delay and fire off a darlington power transistor with a multi-burst spark.

A friend in Michigan had made a special wood-gas carburettor, which allows the air and the wood-gas to be mixed in the correct ratio. This fitted right on to the air-intake of the Lister engine.

By the Sunday evening we had the Lister running - in fact amazingly it ran first time without major adjustment.

There's a couple of Youtubes showing the conversion. In the first one, I explain to a small group of people what we are going to do and the second one, shows the engine running.

Tuesday, February 09, 2010

Keep the home fires burning

Freshly emancipated from my job in the city, I have reverted into suburban Victorian mode.

The 3 hours not spent battling with commuter trains are now either spent asleep or doing something useful.

This year we have had the addition of a wood burning stove and backbolier in our living room. This helps keep the core of the house cosy and offsets the amount of gas that we use. However, it must be stated that keeping a woodstove stocked with wood can become a distraction to other activities, more a labour of love.

Whilst man has been using wood to keep warm for millennia, there is a certain amount of skill needed to use it efficiently. Open fires are notoriously inefficient, and even some stoves have much to be desired. In the 21st Century, new wood based fuels are becoming available, and some of the mechanical handling associated with wood fuels can be automated. For the moment, I'm happy and contented to lie on the heath rug and gaze into the embers. Here's a few notes on how I keep this one burning.

Whilst you can just go out an buy a load of logs from numerous local log merchants, the quality is often dubious and you will need somewhere dry to keep them whilst they continue to dry out. Logs are often supplied quite chunky - meaning that further splitting is needed to make them more manageable for the woodstove -- despite its 18" log-length.

Another source of wood is from waste constructional timber. There are many loft conversions going on in this area, and I happened upon a load of roof timbers which were being skipped in the next road - so I offered to liberate them for nothing. These are generally older than 40 years - and so are not contaminated with pressure treatment or wood preservative.

Having cut the longer lengths into 6' pieces, so that they would fit in the back of the van, I hauled a van load back around the corner. These timbers are a nominal 5"x2" but when they are sawn the size is actually about 47 x122mm. They are probably Douglas Fir, and are very dry - so split easily with a hand axe. They are however full of roofing nails and felt tacks - so have to be handled a little carefully with leather faced riggers gloves.

After getting them home, they need to be chop-sawn into a suitable size for the stove. My chop saw has an end stop at 250mm - so this determined the average sawn length. Each 6' timber was sawn into roughly 7 pieces, carefully checking the path of the blade for nails and tacks before committing to the cut.

Once cut, the 10" lengths are split with a hand axe into two, generally unequal parts. These "halves" will burn rapidly and release their heat quickly. For a slower burn, whole pieces are used.

Eight of these 6 foot timbers will provide enough wood for two 12 hour burns. If we are both home, and the weather is cold, we light the stove in the early afternoon and keep it fired until past midnight.

The process of cutting up and splitting the roof timbers takes on average 30 minutes including the time to get out the chop saw, carry the timbers to the cutting area and tidy up afterwards.

The box on the left contains 30 of the 10" pieces and weighs 22kg. This gives the wood an average density of 511g/litre, and I have seen these pieces vary in mass from 500 to 800g.

The calorific value of woodfuel is approximately 4kWh/kg so the box represents about 88kWh of energy. Unfortunately, a basic cast iron woodstove is not a particularly efficient converter of wood into heat - so roughly half of this energy will reach the occupants in the room, the rest will be lost up the chimney. This is however about twice as good as an open fire.

Wood can vary in moisture content, depending on how it has been stored, and different species have different calorific values and burn rates. Better stoves do exist, but what is needed is a change in the technology in order to get the most out of wood. This is where wood gasification comes in.

Wood gasification is the conversion of woody biomass into a mixture of flammable gases, which can be burnt at optimum efficiency in a modified stove or burner. Woodgas primarily consists of carbon monoxide CO and hydrogen H2, with small amounts of CO2, methane and half of the mixture consists of the inert nitrogen from the atmosphere. Woodgas varies in calorific value from between one eighth to one sixth that of natural gas. Wood gas can be used as an engine fuel for riunning vehicles, generators and other machinery. In principle, it should be possible to run a whole household heated and powered from woodgas. Well that's the plan.

Next week I travel to Berkeley, California to learn all about wood gasification and how to build wood gasifiers. There is a project planned to convert a Lister diesel engine to run on wood gas using a spark ignition conversion - so that's what I'm hoping to do, learn how it's done and bring the technology home.