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fuel tank baffles

fuel tank baffles

fuel tank baffles

(OP)
I wasn't sure where to post this but here goes.
Fuel tank baffles.  The application is a dirt/sand hotrod. 140 hp 650 pounds wet...one fast over sized go kart. This thing has a 950 cc MC motor and trans plus about 5:1 gear reduction so it can really accellerate. Live axel independent rear end. It will go up or down about anything normally found very quickly. out run most dirt bikes. Burn the tires on pavement.

The tank in question is about 4.5 gallons rather tall narrow and a little long. The bad part is that the intank fuel pump had to be mounted in the front of the tank. It is still the lowest part of the tank however by several inches. picture a flattened wedge with the point in the rear and about 1/2 way up the max height.
 
This motor on a bad day in the crotch rocket is supposed to get better than 20 mpg going very fast.  So figure 60 mph 20 mpg 3 gallons per hour.

Even at 2.5 gallons in the tank  there is over 7 inches of fuel over the pickup point.

Even if the kart could maintain 1/2 g for a length of time there would still be fuel over the pickup assuming the fuel surface would be 45 deg to level. Verified with SW design picture.  Now if the kart goes up a steep hill say about 35 degrees and the acceleration is very small ...it would take say 30 to 60 seconds to get up the hill, the fuel will be at something like level to the ground or about 40 degrees maybe 45 to the bottom of the tank. At this point there is a question as to whether the fuel will still be over the pickup.  So install a baffle.  Not hard when building a tank.  The question is...how big should the baffle openings be.???  Keep in mind how fast you could empty a 2 gallon can with unlimited venting through the standard gas can opening.  30 seconds ?? maybe. I haven't tested it yet.  The point being that only a small hole is really necessary at the bottom of the baffle with a larger hole say 1/2 way up and another right at the top to aid in filling to the full mark. You don't want much flow thru the baffle.. right??
A simple solution is a trap door over a little larger hole or holes. This would be closed going up and open going down. More or less closed on the level.  Even if this leaks some going up hill, it still will not pass gass (you know what I mean) very fast so the pickup will remain covered for the time required. right???

whattaya think.???

RE: fuel tank baffles

<pshew> Is there a question in there somewhere? ;)

I would size the lower holes to be slightly larger than required for the amount of fuel being burned at full throttle.  Add mini trap doors and you have about the best solution little money can buy.

Being an engineer, I'd go with some wacked out idea that measures fuel level... as the level goes down balloons fill up each section of the tank to effectively shrink the total size, forcing the remaining fuel to linger around the pickup.

But that's just me :)

Dan - Owner
http://www.Hi-TecDesigns.com

RE: fuel tank baffles

Thought About foam in the tank?

have you got a loose pickup in the tank that can slosh around with the fuel?

RE: fuel tank baffles

Why not a fuel bladder or cell with a foam insert?  The foam will reduce the amount of slosh.

RE: fuel tank baffles

did you try an external pump with an accumulator ?? If you have an angled bottom tank with the pickup directly in the lowest part of the tank it should feed the external pump without a problem. Then throw in a fuel accumulator to feed the system when the pump cavitates.

RE: fuel tank baffles

(OP)
Well, this thing turned out to be a real football.  We argued almost a whole day about it and got nowhere.  I finally said let's just build a header tank and install it inside the main tank.  This tank has a siphon tube on it and carries about 1 gallon so there is enough fuel to run for a long time by itself.  The fuel pump turns out works like a fuel injection supply pump on a car complete with a return line.  The crotch rocket is fuel injected.  I put a separate filler cap that is sealed from the main tank to aid in filling the header tank.  as fuel is used from the header tank it is replaced by siphoning from the main tank.  We use them in model aircraft all the time. works great.  Well we tried out the new tank an it works like a charm.  You can stand the tank on end and it still will flow properly.  Just a lot of work to make the think.  There must be 10-12 feet of TIG weld on it.  Looks cool though.

RE: fuel tank baffles

Hmmm, just had a brainstorm...  

What if the fuel was in a bladder with no air at all ?  As fuel is used, the bladder just shrivels up to nothing. If there is no air for the fuel intake to gulp, it can only get fuel, even if the vehicle is complely upside down or accelerating wildly in any direction.

Never seen this done, just a crazy idea that has just come to me at this moment.

Filling it might be interesing, but once full and completely purged of air, I think you could see a solid fuel flow with no air bubbles no matter what.

RE: fuel tank baffles

Prius does that in the states. I'd guess many motorsports do it too.

Cheers

Greg Locock

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RE: fuel tank baffles

(OP)
We used to use bladders in our model air planes before they got so big.  An ounce used to last forever it seemed. Now 4 oz a minute is normal and the jet guys use way more than that. Some of them carry a gallon or more of kerosene.

This kart is to be relatively simple so making or getting a blader made is a little beyond the scope of the project.  The header tank works really well.  We were going to put a flexible pickup in the tank but it's just an unnecessary complication.

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