Super Simple Fuel Metering

[kjjohn]

I was pondering how to deliver fuel to my new hybrid in a simple, low-pressure metering device, when I thought of this idea: Instead of having a separate meter pipe with two valves, you could simply seal the chamber with a burst disk/piston, then have no meter pipe, instead just put a ball valve in between the regulator and the chamber, and set the regulator to the pressure that is required in the chamber (which will be very low). To inject the fuel, just open the ball valve, and when the fuel pressure in the chamber equalizes the pressure you set the reg to, the fuel will automatically stop flowing into the chamber. You can then close the ball valve, and fire.

[inonickname]

For this to work you would need a completely leak free chamber and an extremely accurate low pressure regulator. Not really feasible.

[kjjohn]

I guess I probably should have posted this under hybrid discussion, as it applies more to hybrids than it does regular combustions. With a 6x mix in a 130ci chamber, the reg would need to be set to about 4 psi, which I don't know exactly how accurate a regulator could be a such low pressures like you mentioned, but for oxyacetylene welding, I always set the acetylene reg at 5psi, which is usually easy to get accurately out of a welding reg.

[mark.f]

Take a look at the Hybrid Fueling 101 sticky. It describes the same thing.

[Technician1002]

Starting with a low pressure regulator and modifying it to the desired pressure isn't difficult. Hint, start with a BBQ regulator. Nominal pressure is 11 inches of water column which is about 1/3 PSI. With a proper spring replacement and adjustment screw, this can be set and fixed to the desired pressure.

[kjjohn]

Actually, I was just thinking of using a standard MAPP regulator, then adding an extremely accurate low pressure gauge to get an accurate pressure.

[metalmeltr]

Look for high quality regulator designed for use in hvlp paint guns, these guns operate at pressures typically below 15psi so these regulators are very precise at low pressure.

[D_Hall]

Actually, I was just thinking of using a standard MAPP regulator, then adding an extremely accurate low pressure gauge to get an accurate pressure.

It's not enough to have an accurate/precise gage. You must also have an accurate/precise regulator. Sure, the gage helps, but if you have a cheap reg all it's going to do is tell you just how badly your reg sucks (hint: for a lot of industrial applications a reg that's good to 5 psi from one usage to the next is considered acceptable).