air gets sucked into the system via a vacuum. when you present positive pressure, how does air get sucked into the system? obviously the fuel pump doesn't send pressurized air through the system??? (lift pump isn't an air pump)
The positive pressure is in the fuel line, yes. I am not talking about sucking air through some joint in the fuel line or in some other magic location. I am refering to the fuel pump pick-up (in the fuel tank) getting exposed to air do to fuel tank slosh. It will injest a burb of air (or air entrianed diesel) even thought it is not an air pump. You can move air and fuel through the fuel line to the fuel pump. The air travels in the line with the fuel. BTW - the air would be at the exact same pressure as the fuel sorounding it. Have you never lost fuel prime from a steep incline and low fuel level? It does not matter weather you have an electric inline or not. All the inline pump does is help you purge the system using the same old fashion way but much faster.
Anyways, I will say it again, I simply brought this up to make sure the original poster understood the importance of not loosing prime in a diesel engine. I have also included short link to a basic airplane fuel tank systems Q&A that discusses a few options. There are systems that will work 100% of the time. For a diesel application, personally, I would not do anything short of a bladder system (as I mentioned earlier).
http://www.newton.dep.anl.gov/askasci/eng99/eng99417.htm.
again i'll say this ...
the exact same system used to remove air in a gasoline injected aviation fuel system can and will work in a diesel aviation system .
and btw any air that does make it to the injection pump , is easily burped out by the injection pump it's self ..... don't believe me ... take one apart and look at it closely .
you have to dam near starve a ve pump for fuel before it starts to push air .
but again it comes down to the lift pump and how it is set up .
as long as the lift pump is pushing a decent volume of postive pressure fuel to the injection pump there is no issue , even if that fuel is mixed with air bubbles .
but there is a slim chance of that even happening with a proper fuel system / tank up stream of the lift pump .
and i apologise to tomlaudato for messing up his thread
this is what i am hoping for more info to make an informed judgment
the more discussion on any and all of he places where trouble might surface is welcome please anyone jump in and help with any thoughts
tom laudato
I believe who says the VE pump is a "simple system" has never opened or seriously messed with one.
gasoline MPI electronic system can be 10 times more simple and reliable!
two injectors for cylinder, each bank with its own fuel rail, filters, pumps and tanks.
a main ECU and a failsafe one that has its own battery.
thats why a lot of diesel systems can't be aviation certified, to introduce some redundancy one had to fit a second injector in there somewhere. (or a way to make sure a single one could not compromise the engine in any way)
what i'd be thinking of , is a 1.6 turbo , with head studs and main studs , aaz metal headgasket .
maybe a set of compund turbo's ...... maybe a k26 off of a mercede's feeding into the stock vw k24 , to help keep a decent amount of boost at altitude .
the to offset the power pulses , run the 1.6 at a higher rpm than one would run one of the larger engines .
maybe a 1.9 idi camplate in the 1.6 pump .... maybe even mercedes nozels on the injectors .
i left a bunch out ... but this should get the wheels turning .
I will leave the other topic alone now. I am intrigued by your idea of using a 1.6TD with mods. Why would you go that route vs. a 1.9TDI? You mention running it a higher RPM. In fan/propellor/pump applications HP is related to the cube of the speed (RPM). So to run a bit faster in RPM, you need a huge amount more HP. Are you suggesting a smaller prop to compensate?
I don't believe the air in fuel would be a problem. I ran my rabbit out of diesel one time. To get it going I only bled two injectors, the other two self bled. I think bleeding 'em only saves the starter some cranking.
Also, as soon as you lose fuel to the pump you'll know because your timing advance will fail due to lack of internal pressure, and you will lose power. But if you can keep it windmilling I think it'll fire up again.
On a normal airplane the prop will windmill so you wouldn't need to crank it. You actually need to slow to a stall to stop the prop. But the diesel is harder to turn over plus the prop speed reduction would make it harder so it might be a problem.
My two cents.
in that case just pitch the nose forward... you'll surely get that diesel goin :lol:
one other suggestion to eliminate all those problems would be to create positive pressure inside the fuel tank. that way the fuel is 'pushed' through the system
a two tank system would be nice
I know that some diesel's have a mechanical on/off switch, eliminating the 12v start stop solenoid. I'm not sure if that modification is available for the Bosch VE pumps.
Does a turbocharged engine make sense without a variable pitched prop?
Also, the 1.6 diesel engine had a nice large airplane looking thrust bearing. The TDI's only have very small banana looking thrust bearings. I hope you aren't planning on bolting the prop right onto the TDI's flywheel... How much power can you reliably expect at 3200 RPM with the 1.9 TDI engine anyway?
I know you can put a mechanical stop on the VE44's used in the Cummins 5.9/3.9, I think the same would apply to the VW TD's. The pumps looks very similar side by side.
Is the thrust bearing in any of the VW TD's or TDI up to this useage? How many pounds of thrust are we talking about? All pulling on the crank. Perhaps mounting the prop on a jackshaft with a proper thrust bearing would be wise. There would be no thrust on the crank then. Unfortunatley, with the price of extra weight.