Eric Hysteric wrote:
Thank you guys! Very interesting discussion and a lot of informations and links!
I was a littlebit surprised, as i couldn't finde a fuel return line at the carburetor.
A very simple way to cut the fuel supply when the engine is not runnig (in case of an accident)would be an emergency shutdown by a standard relais and oil pressure sensor. No oil pressure = no power at the fuel pump.
Or by the D+ signal from the alternator to relais and the relais switches the fuel pump on and off.
That's part of what I was suggesting. I need to work on it more conceptually. Mostly to see if there's a way I can break it or find a weak point that could result in an unacceptable failure. (Yes, there is such a thing as an acceptable failure ... sometimes called a deliberate fault.)
Alternator connection not acceptable. Can explain if you'd like but explanation will be somewhat lengthy. (Involve how battery, voltage regulator, and alternator works together as a system during normal operation.)
Here's the tentative analysis:
1. Power from ignition switch => normal operation of electric fuel pump. Switch on implies pump on, switch off implies pump off.
2. Manual switch within easy reach => emergency shut off if vehicle operator is capable.
3. Oil pressure switch and relay => emergency shut off if vehicle operator is rendered incapable.
Emergency condition logic:
-- Manual switch is fastest due to linear operation. (Ergonomics)
-- Ignition switch is slower due to rotational operation. (Ergonomics)
-- Oil pressure/relay is slowest due inherent oil system lag.
Notes at this point in project:
a. Pump control system needs to be simple. Right now, I have it at three additional components, not counting ignition switch and pump.
b. Significant issues exist related to using oil pressure. May not be doable or may require additional components and an unacceptable degree of complexity.
On fuel return line topic: If I recall correctly, your dual fuel conversion has a valve for shutting off gasoline when running on propane. If so, fuel return line definitely advisable if still using mechanical engine-driven fuel pump. May be easier to shut off pump simultaneous with valve closing if you're using an electric fuel pump.
Aside: Do you have a oil pressure gauge or indicator light? (A question leading to more discussion in the future.)
