Author Topic: Wood burning truck! (Read 80216 times)

beenthere · « **Reply #120 on:** February 13, 2007, 11:48:19 pm »

So if we find the area of the truncated cone at 2.25" (or diameter would be 9½" halfway up). The area ½ way up would be 70.88 in sq, and that times the height of 4.5" would be 319 in cu.

I'll check the math, but it's how I would do it.

Yep, this volume is similar to getting the volume of a log, by measuring the end diameters, average them to get the diameter halfway along the log, and use that diameter to calculate the log as if it were a cylinder, rather than a truncated cone.

You might need more than that volume, dat right?

SwampDonkey · « **Reply #121 on:** February 14, 2007, 06:06:28 am »

Why not just V_cone = 1/3x(Area of Base)x(height), of course you'de have to estimate the length of the cone missing to come to the apex of the cone if it existed and deduct that area.

Area _base= pi x D²/4

farmerdoug · « **Reply #122 on:** February 14, 2007, 06:45:18 pm »

SD has the right idea.

Here is the formula for the area of a truncated cone.

V=1/3*pi*h(radiusone squared+(radiusone*radiustwo)+radiustwo squared)

V=1/3*3.142*4.5(2.5squared+(2.5*7)+7squared)

V=342.87 cubic inches

Checking my math is a good idea as it is a little rusty. Now how do you get super and subscript again?

Beenthere, your idea works in two dimensions but the third kills it.

Farmerdoug

farmerdoug · « **Reply #123 on:** February 14, 2007, 07:14:31 pm »

Paul,

If you make all of the nozzles the same size them I come up with nozzle diameter of .244 inches, so lets just call it a 1/4 inch. You have to remember that changing the diameter of a circle changes the area exponentially.

Total=32(pi*r squared)

1.5=32(3.142*r squared)

.04687=3.142*r squared

.014919= r squared

.12214=r

Diameter=r*2=.24428 inches

Now my math is rusty so it needs to be checked.

Farmerdoug

SwampDonkey · « **Reply #124 on:** February 14, 2007, 07:36:11 pm »

Even simpler, easier to measure diameter.

V_{truncated cone}=1/12 x π x h (d₁² + d₁d₂ + d₂²)

π=3.14
h = height
d₁=diameter top
d₂=diameter bottom

farmerdoug · « **Reply #125 on:** February 14, 2007, 08:02:43 pm »

SD,

How did you get the super and subscripts?

Farmerdoug

SwampDonkey · « **Reply #126 on:** February 14, 2007, 08:09:18 pm »

You'll _see them ^above the _smilies in ^the posting _editor.

Just hilight the text before clicking the ^sup or _sub icons.

Jeff · « **Reply #127 on:** February 14, 2007, 08:11:20 pm »

Donk ya made me dizzy.

farmerdoug · « **Reply #128 on:** February 14, 2007, 08:16:16 pm »

SD, thanks ^for pointing _that out. I _never even ^saw that.

Farmerdoug

Paul_H · « **Reply #129 on:** February 14, 2007, 08:43:13 pm »

Farmerdoug and SD,
I sent you both IM's with more info.I cut and pasted from a woodgas site.

I'm still trying to figure out how the plans came up with the 1 1/2 square inch nozzle area in the Am chart and what is the corelation between that and the 8, .38 nozzles + the 8, .27 nozzles.

It has to do with the volume of air needed by a 302 cu in engine running at 2800 rpm.
My limited understanding of the nozzle sizing has been explained as holding your thumb over a garden hose.The volume coming out is the same but there is more force.The air in the hearth zone is supposed to cut,or penetrate if you will (?)

The term used is "superficial velocity"

farmerdoug · « **Reply #130 on:** February 14, 2007, 09:07:34 pm »

Paul, It looks like someone did calculations or trail and error to get the ranges shown on your graph.

I can understand the 1.5 squared inch air inlet area. It is sized to provide the optimum inlet for the air to fuel ratio in the burner to provide adequate gas production for your size engine.

Now as to the two sizes of nozzles. I see that in your picture one is pointed horizontal and one is pointed vertical. They maybe sized different to keep the burning in the chamber area for concentration of heat. I cannot tell which size is which but I would bet the vertical maybe the smaller one. We will need to make the same correlation for your 32 jets too.

In the email you sent me Max was calculating the top of the cone and height also based on fuel flow volumes to the engine. I am assuming that you have already decided on the height and diameter from your earlier post?

Farmerdoug

Paul_H · « **Reply #131 on:** February 14, 2007, 09:45:51 pm »

Yes the height and diameters are correct for the engine size and RPMs.

Here are a couple of quotes from Mother Earth News from whom I bought the plans.Then the modified them again and drilled an extra hole on top of each of the 16 nozzles giving 16 horizontal and 16 vertical.

Quote

Then, to solve the bridging problem, we oriented the
outlet tips of the manifold pipes so that the "odd" eight point
straight upward ...and the remaining "even" nozzles aim inward,
toward the center of the hearth opening (see the illustration). The
benefits of this arrangement are twofold: The horizontal jets provide
combustion air for oxidation at the entrance level ...while the
vertical outlets reduce the size of the chunks of wood about to enter
the hearth by cutting away at them like miniature torches, thus
eliminating the possibility of having a "logjam" block the flow of
fresh fuel.

Quote

the 250-cubic-inch powerplant used in our Chevrolet truck
(which turns at about 2,800 revolutions per minute at 55 MPH, the
speed at which most of its mileage is logged) requires an overall
nozzle area of 1.237" (horizontals 0.36", and verticals 0.26" in
diameter) ...a nozzle-to-hearth separation of 5-1/2" ...and a hearth
restriction width of about 5-1/4". (Generally, the total nozzle area
should be 5 to 10% of the overall hearth area.) To size the openings
in the nozzles, we simply drilled holes of the proper diameter
through 16 pipe caps, and threaded them over the feed-tube outlets.
Likewise, the orifice at the base of the hearth (that platform, by
the way, is fashioned from a No. 5 cast-iron frying pan) was made by
boring a series of adjacent holes in a circular pattern and then
knocking out the resulting "plug". In any case, the dimensions given
are merely guidelines, and-should you wish to construct a unit of
your own-you can likely extrapolate from these figures according to
your engine's displacement and working speed, and still come out in
the ballpark.

farmerdoug · « **Reply #132 on:** February 14, 2007, 10:21:46 pm »

Paul,

I will assume that you have sized the hearth where you want it.

I back figured the nozzles and found a 2-1 ratio in area. So I recalculated your nozzles and have the two sizes for the 32 nozzles as;
D=.206 inches
D=.282 inches I guess the arrangment of the sizes are up to you as I have not seen anything that states otherwise.

Farmerdoug

Paul_H · « **Reply #133 on:** February 15, 2007, 12:09:01 am »

I should have posted this earlier.It explains superficial velocity.

Woodgas Link

Paul_H · « **Reply #134 on:** February 17, 2007, 11:20:44 pm »

Farmerdoug has been helping me a lot through IM's and a phone call to make sure the proper calculations have been done for the hearth size and nozzles.He has a very good understanding of how the generator works and I hope he will jump in and explain it as he did for me in laymens terms.Through this we realized that I had omitted info that is crucial so here are a a couple more charts.

I also realised today while preparing to weld up the air pipes that I mis-measured the nozzle ring diameter.It is 12" diameter not 14" as posted the other night so I may have to make changes.

farmerdoug · « **Reply #135 on:** February 18, 2007, 12:15:33 am »

Paul,

I will expand on what we talked about when I have a little more sleep.

To answer your last question I will take a stab at it right now.

According to the graphs you have posted you need a 5 inch nozzle high and a 5.33 inch hearth. I am assuming that you have to calculate the top diameter based on a 60 degree angle.

Now I will calculate it based on a 5 inch height and a 5 inch hearth that you all ready have.

Tan°= opposite/adjacent

Tan30°=opp/5

.5773=opp/5
2.8865=opposite side for a 60° angle

so top diameter is
hearth+(2*opp)
5+(2*2.8865)=10.773 top diameter

since your hearth is a little smaller than needed you will probably be okay with the 12 inch top diameter.

If you had a 5.33 inch hearth then the top diameter would have to be 11.103 inches so you are close at 12 inches.

If this does not click I will try again tomorrow.

Farmerdoug

Paul_H · « **Reply #136 on:** February 24, 2007, 11:40:17 pm »

Got the weekend off so I had a chance to fit the air tubes and weld things together.The nozzle ring is 12" diameter and the nozzle-hearth separation is 5".
It was a fiddly job to measure and fit the 16 pipes and weld them at 4 points each but I'm 3/4 done.

I welded the pipes and cut of the excess.This picture shows 8 welded and cut off and the other half ready to weld

This next one is looking inside from the top.The 16 pipes sticking up from the bottom will have a 90° elbow pointing toward the center with a hole sized for a nozzle.The cast iron frying pan in the center is the hearth(sorry Norm

)

A view from the bottom.The hearth will have a grid of 1/8" Stainless steel rod as a grate(1 rod already in place) The woodgas will come down through the hearth and the air tubes will help cool the gas and the combustion air coming in through the tubes will be preheated in the process.

I hope to get some more welding done tomorrow afternoon.Aint it a cool looking contraption?

Jeff · « **Reply #137 on:** February 24, 2007, 11:54:11 pm »

If I had to guess what it was cold, id say it was out of a Jet engine.

Ianab · « **Reply #138 on:** February 25, 2007, 12:20:08 am »

When do you install the Flux Capacitor

Moonlight · « **Reply #139 on:** February 25, 2007, 12:31:33 am »

That looks pretty neat Paul

I'm proud of you for building it. It looks complex.

I really like the smileys on here.

News:

Author Topic: Wood burning truck! (Read 80216 times)