Help me with ideas on a forced air workshop heater.

[PeterA]

I have started to make a prototype forced air heater.  I would like some input and help on a few things.

Firstly it is a piece of pipe that is roughly 9" OD and about 1 1/2" feet tall.  I have welded into the side a 3" pipe. 
  The idea is to drip fuel into that 3" pipe and the fuel should roll or dribble into the "burning" chamber as it is forced from behind by the air from the fan.

The first test burn did actually burn but man was it smokey.  I can only compare to one of these.
http://www.google.com.au/imgres?imgurl=http%3A%2F%2Fi1041.photobucket.com%2Falbums%2Fb418%2Fhq2door%2FIMAG0082.jpg&imgrefurl=http%3A%2F%2Fwww.aussiev8.com.au%2Fmembers-lounge%2F58549-how-do-you-heat-your-shed-workshop-2.html&h=1023&w=612&tbnid=RwzOub4GRyNxkM%3A&zoom=1&docid=QbxCt5MtNlyneM&ei=O-F2U_LLCoG1lQXs6oGoDQ&tbm=isch&client=opera&ved=0CFUQMygCMAI&iact=rc&uact=3&dur=271&page=1&start=0&ndsp=40

Which once up to temperature would run hot and clean. 

So I guess I am trying to get a similar amount of heat (BTU's) from my build.


So far I made up a little bowl to hold a small amount of diesel,  this was a bit a pipe about 4" OD and say 4" tall that I put about 2-3 cups of diesel into.  Then that was placed inside the bigger combustion tube and lit.

Yes it did burn, but was very smokey.  You can't see it in the photo but it was smokey smokey.

Also make up a temporary lid with a hold and 3" pipe that is just sitting on top of the bigger burn tube.  The though is that it should keep the flame inside the burning chamber more and heat it up better.

After the fuel burned out, I poured another 2-3 cups down the air intake tube.  This time that fuel was not in the inner bowl but on the floor of the main pipe.  Still burned and still smokey.
  Had a look when it stopped burning, which was not very long at all... and the smaller 4" pipe inside was a dull/slightly brighter red colour.



What is causing the smoke?  Is it too much fuel and not enough air?  Is the whole thing not hot enough yet?

[doug]

Peter,
  Welcome to the site. My guess is to much fuel. Do you have a dip tube system designed yet? I see you dumped 2 or 3 cup down the air intake.

[PeterA]

Hi Doug,

I have made up a small header tank for testing, about 2 litres.  At the moment I only have a brass "gate valve" on there, unfortunately these are no good at finely regulating the flow of the diesel/oil.  So I need to make up a needle valve from something.  I did read that you can use a standard brass tap and remove the washer plunger thing and put a needle on that.  But I don't know how easy that is to do.

[Russ]

Greetings Peter,

Glad you stopped by.  Interesting project.  I think Dougs suggestion of too much fuel is likely the cause.  Instead of modifying the gate valve, do you have access to a needle valve?

[PeterA]

Hi Russ,

I am now going to use a spray gun as it has a needle valve inside it.  To do this I will zip tie the trigger on, then it can be fine tunned from a few drops to a constant stream. 

So once I manage to setup a frame to hold the spray gun on, then I can test again.  I might have to drill out the hole in the spray gun nozzle because it may not flow enough fuel.

I am concerned that the mild steel pipe may wear out very quickly, so really it probably would be best to have a layer of refractory cement, or something to lower the temperature that gets to the steel pipe. 

So I would need to know how hot the burn is, and what the maximum temperature mild steel can handle before it falls apart.  Galling? Then work out an appropriate thickness of insulation material to protect the steel.  Later on I will add on a taller flue section, if that glows red hot that will be good.  If it wears out I can replace it easier than the bottom burn chamber.  That insulation would help to increase the burning temperature to make it burn clean too.

  1.  How hot does diesel need to burn at to burn clean and with  minimal emissions?
  2.  ""                ""                 ""               ""            ""            ""            ""   Waste oils?
  3.  How hot does my mild steel pipe start to break down at?
  4.  What is a cheap to make refractory cement (or other ) for my project?  I am in Australia so it may be harder to find products that are available elsewhere in the world? 
 

[doug]

Peter,

 When I needed a needle I bought a refrigerator ice maker plumbing kit. It had a needle valve in the kit and some extra parts I needed. I've also seen where some people have used a ball valve.

I can't say at what temperature waste oil burn with minimal emissions but, I would shoot no smoke.

The constant reheating of your mild steel will cause it to break down over time.

[Russ]

I'm really not much help on any of your questions unfortunately.  I have used a ceramic blanket material for my boiler, but it doesnt have direct flame hitting it.  They claim it will withstand 2400 degrees. 

[PeterA]

That's ok Russ.