How bad do we need a pressurized fuel tank?

[dE_logics]

Imagine a fuel tank that can store fuel at pressure (it can store at pretty high pressure also) without having any component which provides it constant energy e.g. a pump (i.e energy has been previously fed into the system so as to maintain the pressure in the tank regardless of it's fuel quantity).

This can be also be used in fuel stations and aircrafts.


So, what will be the advantage of this?


I think it will make a sort of super/turbo charger.

 

[xxChrisxx]

I don't get it.

How are you going to get higher pressures without some sort of pump?

 

[dE_logics]

:D :D...it is somehow possible (maybe I'll post 'how' later)...the fuel has been maintained at high pressure and the pressure is not a function of the amount of fuel left...it's very cheep and reliable.I just want to know what will be the advantages.

 

[xxChrisxx]

Well... I really can't think of any.

I don't know why on Earth you'd want to pressurise a full fuel tank on a car.

I must be thinking/imagining something different to you, as what's in my head just doesn't make any sense to do.

 

[dE_logics]

I was wondering about increasing the power delivery per stroke.


Like a super/turbo charger...instead of forcing the fuel/air mixture in, it will force the fuel.

 

[xxChrisxx]

Turbochargers work by having more AIR in the cylinder, so as a result you have more fuel and therefore more power. Just adding fuel under pressure will not add power, just make you run rich.

For that you don't need an entire fuel tank underpressue. In cars fuel is pumped from a low pressure tank into higher pressure injectors.

Typical out of cylinder injectors run at something like 4 bar, and use the heat of the valves to help atomise the fuels. Newer direct injection engines, use high pressure rail injectors running cloer to 150-200 bar. Common rail direct injection diesels can run at nearly 2000bar.

Higher pressures, allows smaller nozzles to be used for the same flow rates, meaning more atomised fuels, but agian only a very small amount of fuel needs to be at high pressure at anyone time.

 

[dE_logics]

Ok...I know what you mean...there's an ideal fuel air mixture after which there's no use of adding more fuel to the mixture.

 

[Topher925]

Newer direct injection engines, use high pressure rail injectors running cloer to 150-200 bar. Common rail direct injection diesels can run at nearly 2000bar.

The only thing I can think is that it would allow you to get rid of the high pressure fuel pump(s) but I don't see that being a big advantage. While you are feeding fuel at a very high pressure, is at a very low mass flow rate so it doesn't take that much power away from your BHP.

 

[xxChrisxx]

That will eliminate any pumps which were previously there to do the same job...that's what I'm talking about.

I don't know about you, but I don't fancy sitting on 15 gallons of petrol pressuried to 200bar. You only need a tiny amount of high pressure fuel at anyone time.It was an interesting idea though, eliminating moving components is always a good thing, how did you plan to keep it pressurised without a pump?

 

[dE_logics]

Sorry...I got only half the message last time...some sort of bug.

Higher pressures, allows smaller nozzles to be used for the same flow rates, meaning more atomised fuels, but agian only a very small amount of fuel needs to be at high pressure at anyone time.

What I mean is that the whole fuel in the tank is at pressure...so you won't require the pump...that's the only advantage.


What about bikes and small generators (by small I mean not those colossal ones which are large enough to make you think of fitting a small pump in it)?...it will provide fuel under pressure without any pump.

 

[dE_logics]

I will post the whole thing later (I'm making the formal docs)...not only it is applicable for fuel tanks...but many other applications; providing pressure in a cheep and reliable way.

Constant pressure i.e without the pressure being a function of the fluid left in the tank.

It has moving parts...but it's negligible...point is you won't have to worry about it's life.

 

[xxChrisxx]

What about bikes and small generators (by small I mean not those colossal ones which are large enough to make you think of fitting a small pump in it)?...it will provide fuel under pressure without any pump.

You'd have an advantage in very very small things, that would either require tiny pumps.

Or it could replace things with a gravity feed, they don't use pumps but require an awkwardly placed fuel tank, so a lawn mower or something.

 

[FredGarvin]

We used pressurized fuel tanks in many of our applications already. The trouble is, Chris is right. Pressure just doesn't happen. We have to use some part of the engine to provide some source for that pressure. Of course, by doing so, there are tradeoffs like having more regulation and flow control equipment. Also you now have a pressure vessel and not just a tank. That all equates to more $$$.

 

[dE_logics]

You'd have an advantage in very very small things, that would either require tiny pumps.

Or it could replace things with a gravity feed, they don't use pumps but require an awkwardly placed fuel tank, so a lawn mower or something.

Yeah, the thing is made primary to reduce the height...or it can give pressure without any height elevation.

Thanks for the answers...I got an ideal now.

 

[dE_logics]

What about CNG tanks...their pressure drops with the amount of fuel left, with this you can maintain a constant pressure.

 

[dr dodge]

there is a big advantage. the increase in static pressure would raise the fuell above its vapor pressure. That (in theory) would decrease evaporation in the tank, and help the fuell be more meterable due to a consistant density. Down side is it should increase the temp of the fuel at the time of pressurization. In IC lawn instruments it would also stop condensation of ambient water vapor in a normally vented tank. The pressure "release" at the injector could also possibly have better atomization.

dr

 

[dE_logics]

Ok...thanks.

 

[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.

 

[Cyrus]

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.

 

[dr dodge]

they already are pressurized that's 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 there's plenty of O@ in there already

dr

 

[xxChrisxx]

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.

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.

 

[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

 

[xxChrisxx]

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.

 

[dr dodge]

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

 

[dE_logics]

The whole pressurized arrangement is extremely cheep and sort of 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?

 

[dE_logics]

Actually the whole tank can be made air less...though doing that will make it more complex and expensive.

 

[dr dodge]

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

 

[dE_logics]

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...

 

[xxChrisxx]

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.

 

[dE_logics]

Oh...I see.

 

[DaveC426913]

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.

 

[dE_logics]

We've already discussed that.

 

[dr dodge]

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

 

[dr dodge]

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

 

[dE_logics]

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.