Intro: Paraffin Wax Vapour Stove Concept Test.
Paraffin wax (wax) tends to only get used as candles or for waterproofing. However it has great potential for being used as fuel. It has about the same energy content gram for gram as paraffin which is about 20 times more than alcohol. It doesn't matter if it gets wet and if you spill it you can just pick it up again. However getting it to burn normally requires wicks and the flame tends to be sooty and relatively cold not releasing all the energy from the fuel. If it could be vaporised and the fuel air mix be got right it could make an efficient stove. This first test was to try and achieve a sustained burn without a wick.
Step 1: Basic Design
a container to melt and vaporise the wax in, and a means of doing so. Calling this wick less is possibly not right as the initial heat source to achieve the melting and vaporisation is a standard tea light.
Step 2: In More Detail
the vapouriser and support were made from the foil casings of two 8 hour tea lights these are 38mm diameter by 22mm deep. The vapouriser was used unmodified. The support made by cutting 3 evenly spaced slits in the side of the case then folding in the edges to form roughly triangular legs
Step 3: Test
the legs of the support were place between the fuel pellet and foil container of the lower tea light that is used as heat source to cause vaporisation. The tea light was lit and checked that it remained burning (I've had problems previously when using tea lights as small burners getting air supply and exhaust paths)
the second foil casing was placed on the stand and a small amount of wax added about 2g (the residue not burnt by the wicks from 3 burnt out tea lights that was going to be otherwise reused).
Once the wax was molten attempts were made to light the vapour. This only proved successful once vapour was actually visible and required the use of a long match that actually had to touch the surface of the molten wax and act as a temporary wick. combustion was sustainable without this wick after just a few seconds.
Step 4: Observations Conclusions and Planned Improvement
Once burning the vapouriser section got hot enough to sustain vaporisation without the lower tea light.
I discovered this as when I went to extinguish it to test this possibility it had already been extinguished as all the wax in the lower tea light had melted and flooded the flame. I had already established that the distance between the lower tea light and the underside of the support was only just adequate to permit combustion.
This distance will need increasing on future designs.
I tried gently fanning the flame to see how resistant to draughts it might be. I was not surprised to discover that some draught actually improved combustion this is probably because oxygen is not available in the center of the rising vapour therefore combustion is only happening at the edges turbulence from the draught mixed the fuel and oxygen better improving combustion.
An air supply to the center of the vapouriser will hopefully have the same effect.
Step 5: Improved Support
a sort through the recycling bag came up with some small foil trays that once contained cat food . These looked to be the right hight for the burner support. I cut a hole in the center of the base slightly smaller than the foil casing I was using for the burner. This means the support is not getting directly heated so more of the heat from the tea light goes to vapourising the wax.
The sides were cut down to the base just after the radius of the corners and the resulting flaps folded in. This gives a much better air flow around the tea light.
Step 6: Air Supply Tubes
I made my air tubes by rolling strips of heavy foil (salvaged from another foil tray) around a bamboo kebab skewer. They were cut to length whilst still on the skewer using a Stanley blade(I must get around to making a back for a Stanley blade as I often use them like this and I'll end up cutting myself if I don't). To avoid collapsing the tube whilst bending to shape I twisted two pipe cleaners together and put this in the bore while I bent them. This wasn't 100% successful but it worked adequately.
Step 7: The Improved Vapouriser
with a wax pellet still in place I pierced 4 evenly spaced holes halfway up the container. The wax was removed (with the tea lights I'm using the foil container wax pellet and wick are 3 distinct units and are clearly not made by pouring molten wax into the foil container) The holes were enlarged with a biro, the air tubes inserted and the foil of the casing moulded back around them. I used the scribe and the point of the skewer. I couldn't get the fit tight enough to do without glue. I cleaned around the tubes with a cotton bud wetted with lighter fuel (white petrol for zipo lighters) and applied a small amount of 2 pack quick set epoxy resin glue to each joint. In hindsight I should probably have left it overnight to fully cure rather than just letting it set before testing.
Step 8: Second Test
as on the previous test a small amount of wax was placed in the vapouriser and the lower tea light lit once vaporisation was occurring the vapour was ignited as before. The pictures are taken without room lights as the Blue flame achieved was not overly visible with them on. (The burn mark on the work surface is not connected to the current instructable.)
Step 9: Extinguisher and Next Steps
there are three ways to put out a fire. remove the fuel. remove the heat or remove the oxygen. I would have liked to have removed the fuel just by letting it burn out but failing to let the glue cure fully resulted in complaints about the smell. I had a wet tea towel on hand in the sink as a precaution (removal of heat and oxygen) note burn mark on work top from previous experiment. but opted for just removal of oxygen by using an oversized coffee mug. The flame suffocates and by leaving in place until cool most of the smoke/ vapour is contained and the equipment remains undamaged.
I need to repeat the first test with the improved stand to prove it is the air tubes causing the hotter flame not a higher temperature vapour. However experience with wicked paraffin heaters and the how a bunsen burner works lesson from my school days says it is the fuel air mixture that controls the luminosity and heat of the flame not how hot the fuel is.
Before going on to constuct a more robust/expensive unit I need to test this ones ability to heat water. The figures I've seen in other instructable for spirit/penny stoves suggests a target of boiling 300 cc of water in under 6 minutes.
I would be looking to replicate this design in either steel using food cans and scavenged break pipe which will require brazing. or brass & copper plumbing fittings and cupronickle break pipe or model engineering supplies this would require silver soldering.
As this will take some time and I have no real use for such a stove beyond can it be done I am publishing my work so far so someone else can improve on it should they feel like it.