# How bad do we need a pressurized fuel tank?

by dE_logics
Tags: fuel, pressurized, tank
P: 4,780
 Quote by chayced I agree with Chris. A pressurized fuel tank regardless of where the pressure came from is a bomb. Look up "Fuel Air Bomb" if you doubt me. That's why we have a pump.
...................? Why does it have to be pressurized with air? Even if it does have air, it will only ignite if the stoichiometric ratio is right.
 P: 336 they already are pressurized thats why every 2-3 years your car needs a new gas cap to pass inspection and they don't blow up that much now, and theres plenty of O@ in there already dr
P: 2,043
 Quote by chayced I agree with Chris. A pressurized fuel tank regardless of where the pressure came from is a bomb. Look up "Fuel Air Bomb" if you doubt me. That's why we have a pump.
 Quote by Cyrus ...................? Why does it have to be pressurized with air? Even if it does have air, it will only ignite if the stoichiometric ratio is right.
IT doesn't matter what its pressuried with, the air is in the atmosphere. If your fuel tank explodes for some reason (admittedly an event that would never happen) the fuel would vapourise and mix with the air, then explode.

My main conern was that in the event of a crash and failure of the tank, a standard pressure fuel tank would just leak out. A high pressure tank would actively eject it's contents onto the surroundings (especially with a system that tried to maintain its pressure) you'd have a fuel fountain. It's more of a fire risk than a bomb risk.
 P: 336 if it was pressurized with fluid, as opposed to gas, then the forced ejection of fuel would be minimized. add a rubber bladder that the fuel resides in, and is pressurized from the outside of the bladder, and risk becomes minimal, if not safer than the current single layer tin can we currently use dr
P: 2,043
 Quote by dr dodge if it was pressurized with fluid, as opposed to gas, then the forced ejection of fuel would be minimized. add a rubber bladder that the fuel resides in, and is pressurized from the outside of the bladder, and risk becomes minimal, if not safer than the current single layer tin can we currently use dr
That's what i'd do to minimize risk.

Only problem then is one of economics. Bladder + pressure vessel is way more expensive than a pump. You'd also need a locking fuel rig with valves, unless it's purged then repressuried after delivery.

Edit: just thinking every fuel line would have to be a high pressure fuel line.
 P: 336 I really can not see any significant advantage in the pressurized system. early race cars and aircraft had manual pumps to pressurize the tanks, and we can see where that went. as you said, the costs of the tubing alone would drive the $up significantly and high pressure tubing is also a bear to bend artisticly vs thin wall tubing. AN fittings and braided flex tubing would also probably be needed. dr  P: 735 The whole pressurized arrangement is extremely cheep and sorta simple (sorta). To fill the tank you can release the pressure using manual force or a small motor (the smaller the motor the more time will take). Point is we have definite advantage with gaseous fuels right?  P: 735 Actually the whole tank can be made air less...though doing that will make it more complex and expensive.  P: 336 I just priced a replacement fuel pump for my intrepid.$191.00 the pressurized fuel tank, lines, assys needed to upgrade would probably be significantly more. not cost effective. how about looking at water systems (especially well water) that could be a place that the pressurized systems may be a better fit. I think your idea has merit, just wrong application dr
 P: 735 I think it will cost less than $191...around$80 - \$100. It has just 1 moving part, that too isn't hard to manufacture...no need of extreme engineering. Actually the manufacturing cost will be very less. The most expensive part is a constant force spring. Ok...it might not have any advantage when it comes to liquid fuel...but we don't have 'pumps' (only air compressors) for gas...
 P: 2,043 It's not the cost of the compression system that stings you. You are talking about pressurising the entire system (not just part of it, which is what happens atm). The cost of keeping a high pressure system safe and reliable is where it starts getting expensive. Eg, low pressure fuel lines can be rubber hoses, with clips to keep them attached. High pressure hoses have to have proper connectors and need to be strengthened.
 P: 735 Oh...I see.
 P: 15,319 Isn't a pressurized tank of fuel a Very Bad Thing? Pressuring the fuel using a pump means that, unless the pump is active, you don't have to worry about pressure. But if the tank is pressurized passively, you're sitting on a bomb.
 P: 735 We've already discussed that.
 P: 336 a vented, unpressurized tank is probably more dangerous. vaporization can take place easy from vibration/aggitation. positive pressure could keep the fuel below its vapor pressure thats why the tanks are slightly pressurized now. it cuts "random emissions" from the car just sitting in the heat dr
 P: 336 on the drive home yesterday, the critical design flaw surfaced (impending pun) the surface area of the interface between fuel and pressure would need to be constant, to get constant output pressure. that would mean the tank would need to be exactly the same shape and size from open to full. The fuel would also have to stay pretty much level all the time. Most fuel tanks are non-uniform in shape, often smaller at the top, and lengthening out at the bottom. this could greatly effect the whole car design as the gas tanks are "designed to fit in the leftover space" dr
 P: 735 The design needs to be a of constant geometrical, that's the only way it will work. The volume can be trimmed off to give it a constant geometry...this will be a major drawback. The flue level in bikes matters significantly...you can actually feel the difference.

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