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Old 11-26-2008, 05:36 AM   #1
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some interesting research

so firstly this isn't spam

some guys may have figured out a real working bolt on device to improve fuel economy...i know hard to believe. the claims are not 40% or some dumb crap, we're talking ~5% improvement here. totally reasonable. they actually put some small electric current over two metal screens in fuel injectors to reduce the viscosity of the fuel for both diesel and gasoline...resulting in a finer mist of fuel coming out of the injectors. nothing is for sale yet, but here's the research paper. thought you guys might enjoy this one

http://pubs.acs.org/doi/full/10.1021...98?cookieSet=1
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Old 11-26-2008, 05:57 AM   #2
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The link is broken, but removing the dynamic part of it makes it work for me:
http://pubs.acs.org/doi/full/10.1021/ef8004898
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Old 11-26-2008, 06:05 AM   #3
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the problem with that is that I can get those types of gains with a properly placed piece of plexi glass. I understand that you can do both and go above and beyond

I think that price would be a major deciding factor in how well that product does and if the auto makers started offering it as an option in an automobile...or even standard equipment
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Old 11-26-2008, 06:22 AM   #4
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So, if I understand correctly, they think this could be retrofitted to existing vehicles or easily put into new ones without major technology changes. Neat.

They mention this while leading up to the idea they present:
Quote:
Although 100 bar is not extreme pressure yet, this injector, known as the Delphi Multec 10 GDi muli-hole fuel injector,(4) would require substantial changes of the fuel lines in vehicles, because current gasoline vehicles can only sustain a fuel pressure less than 3 bar.
Here's what I don't understand about that, and about existing technology: Why does the whole system have to be pressurized? Why can't it simply move fuel in appropriate volume from the gas tank to the engine, and pressurize it where it enters the fuel rail? I also still don't understand why fuel injection systems must have a return line sending gas back to the tank...
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Old 11-26-2008, 06:48 AM   #5
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Quote:
Originally Posted by theholycow View Post
I also still don't understand why fuel injection systems must have a return line sending gas back to the tank...
I always thought it was because the high pressure pump needs plenty of fresh fuel flow to help cool itself. That and many engines use a vacuum operated pressure regulator that needs somewhere to "exhaust" the excess pressure when the injectors need fuel at low pressure.
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Old 11-26-2008, 07:05 AM   #6
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Originally Posted by BEEF View Post
the problem with that is that I can get those types of gains with a properly placed piece of plexi glass. I understand that you can do both and go above and beyond
sorry to be rude, but plexiglass? who what where when how wtf??
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Old 11-26-2008, 07:21 AM   #7
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First of all, 100 bar *is* extreme pressure in the automotive fuel world. Today and yesterday. But it's very rare and only exists on direct injection AFAIK.

Quote:
Originally Posted by theholycow View Post
I also still don't understand why fuel injection systems must have a return line sending gas back to the tank...
Here's the thing. Fuel Injection pumps are relatively small, but generate a lot of pressure and flow volume. Therefore, they are horrible at heat dissipation.

There are two possible ways (well maybe more) to keep the pump from overheating. The first way is to reduce the work done by the pump, but this requires some fancy electronics to match pump voltage to engine demand and so on. But you'd still probably create too much heat for the pump to last. The second way is to rely on the fuel to cool the pump internally, but in order to do this you have to have full flow all the time and just return any extra back to the tank.

So that's how it works- the pumps run at full volume all the time, and the regulator just returns the leftover to the tank.

Most modern cars also submerge the pump in the tank for the same reason, to keep the pump cool.

I've burned up some electric pumps with just a few seconds of running "dry". Don't run out of gas in your FI car or your fuel pump can be damaged pretty quickly.

-BC
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Old 11-26-2008, 08:03 PM   #8
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Most fuel pumps don't really generate that much heat however. Submersion is all they really need for cooling. The problem with running dry of course is the loss of the cooling medium, but if GM ever got smart and put low fuel shutoff switches on their pumps like so many other manufacturers, this would not be a problem. They would rather have you pay for a replacement however and make you feel all the more stupid for running out of gas! And they still wonder why they are having trouble with market perception of quality.

Anyway, back on track, because fluids compress to a high pressure with minimal reduction in volume, even high pressure pumps don't really generate that much heat to deal with. Just look at any hydraulic pump for aircraft or heavy machinery. The amount of cooling applied to them is relatively slim for all of the pressure they generate - and it is usually air cooling which is far less efficient than liquid.

The larger issue is in pressure control and blowing out the seals of the compressor when not adequately controlled. The same thing applies to even the lower pressure systems of today, which is the reason they shut off after the initial priming when the ignition is turned on and the motor isn't running. It is also why hydraulic pumps are paired with limit bypass valves in the hydraulic cylinders. But that's comparing closed hydraulics to an open system, so I don't want to confuse the issue any further than that by trying to compare pressure regulation.
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Old 11-26-2008, 08:13 PM   #9
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Quote:
Originally Posted by theholycow View Post
I also still don't understand why fuel injection systems must have a return line sending gas back to the tank...
They say it's because the fuel pump delivers a steady supply of fuel which
is generally in excess of that which is required by the engine, but I am like
you in that I have always questioned this apparently stupid technology.

Like the 'air pump' as a smog-reducing device, used to inject air into the exhaust,
not that this reduces the actual amount of pollutants, it simply dissolves them
into enough air so that it 'cheats' the smog machines into thinking the car is a
low pollutant so long it emits below a certain amount per cubic foot of air.
But it's still the same amount of pollution, just air has been added to it...

So we know they'll cheat to make it work.
Gas return lines almost sounds like some thing along that trend.
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Old 11-27-2008, 04:00 AM   #10
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Quote:
Originally Posted by Snax View Post
if GM ever got smart and put low fuel shutoff switches on their pumps like so many other manufacturers, this would not be a problem.
Wouldn't that indicate that other manufacturers wouldn't need returns on their fuel injection systems?

IMO, they should all have simpler cheap low pressure pumps at the tank and a pump right near the fuel rail to pressurize it. That would probably be barely more costly or complex than running the whole system pressurized, would increase safety in accidents, make fuel filter replacement (and fuel line service) easier, and allow them to easily implement higher pressures.

Often I see something like that and think it's a pretty crack-headed way to do things, but there's usually still something I'm missing...these companies put a lot of money and a lot of expertise into R&D.
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