LPG section
I wil be running LPG with a Vaporised Sequential Injection System. http://www.prins-lpg.com/en/products/vsi/index.html Have you looked at any liquid injection systems? - MembersPage/RichardBarrington
Stage one plans:
Use Prins vapouriser, injectors and use VEMS to control the amount of fuel.
Problems:
LPG doesn't have a steady fuel pressure in the fuel rail. So I will have to make req_fuel scaled according to the 1/sqrt(lpg_pressure). There is no need for an extra variable, since req_fuel is already there! All that is needed is 1 bit to enable the lpg_pressure dependent scaling (maybe 3 bits so the mcp3208 channel can be chosen: well, 1 byte might be more future-proof). You can add a variable at the end of config. Actually, the same would be suitable for gasoline as well, if one trusts his fuel-pressure sensor.
Pressure in the fuel rail isn't constant because off the liquid to gas transformation and the volume flow trough the vapouriser. By a fuel cut off, liquid gas is still in the vapouriser and increases in volume building more pressure. These effects are much to big to compensate with a pressure tank and are much bigger then the pressure fluctuations in a petrol injectorrail. A solution for this might be adding a pressure regulator with a blow off valve in the injectorrail. Or atleast a pressure relief valve set at about 4 bar. Problem with a higher pressure then 4 bar the injector won't open anymore.
Where to blow off if pressure is too high? I guess no one wants it go to free air. The gas won't go back to the tank fulfilled at 200 bars. How do factory systems overcome this problem commonly? Limiting the regulators flow depending on the (regulated) pressure might be a solution?
Why not to free air? Connect a hose to it a let it flow to a safe place like the wheel arch. This will never be much LPG and because you are moving there are no problems. [Economy and fuel-economy. This is a bad solution IMHO] I know this would be the solution by LPG-systeems-developers. But due to emissions and regulations they can't do this. Their blow-off valve is redirected to the intake manifault. [Haha, that's what I call unmeasured gas :) ] It's idd not the best solution but I will come up with more solutions. I will make this work!!
The pressure in the tank will never exceed 25 bar there is a pressure release valve on it which opens at 25 bar. This valves redirects the pressure to the open air! [Ooops, I thought about CNG pressure, you're right. 25 bar is not too much! I guess you can find injectors withstand that pressure. Look for diesel and modern gasoline (f.e. on FSI) engines! Direct liquid injection without pressure regulation (but measurement of coz) -that's cool :)] Would deff be cool maybe something for a new project :)
-That's OK, just checked; FSI injectors are using 110 bar system pressure, don't know the flow however..
Only CNG tanks have higher pressures like the 200 bars you are talking about. CNG (Compressed Natural Gas) and LPG (Liquid Purafied Gas) are very different! The pressure in a LPG tank at minus 20 degrees celcius can be as low as 2 bar. Depending on the amount of propane/methane mixture.
Future problems:
Injectors are too small. They have some big CC motors running on LPG, but yeh, might be an issue. Could potentially double them up? - MembersPage/RichardBarrington
Vapouriser might be too small. (Might have to use two of them.)
I'm pretty sure I will or I might have enough with the biggest hand made ones but those are >150 euro's a piece. (92cc)
- I don't know customers prices, not my department :) You can send them an e-mail if you want to know. -Did that, no answer :( They might to be busy with larger volume OEM deals... don't take it too personally. Pricing compared well to aftermarket EFI stuff last time I checked, but best to ask for specific prices and supply application information (make it easy for them!). With globally rising petrol prices, we might have more luck approaching this as an "official" VEMS initiative. I've talked to Prins before, so why don't we make an LPG page and sort these issues out? - MembersPage/RichardBarrington [good idea! :)]
Please mail me a list with your needs and I'll see what I can do for you: Jan_Saenen @ hotmail.com
Second stage:
Add an other base map to Vems. I want to be able to run on petrol too.
Problems:
This option isn't available jet
Running both high and low impedance injectors. Do you have enough injector outputs to run them all sequentially, or will the injectors be fired in parallel? - MembersPage/RichardBarrington
They won't be running at the same time. I wan't to be able to switch to petrol now and then and those are high Imp. The LPG injectors are low. So at first this won't be a problem cause first I want to run LPG only. At the moment I don't really know how to make this work without reconnecting and loading a new map.
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