Opinions on alt fuel system

[Denton]

So I’m bored of waiting for an ethanol station, and I’ve driven past propane refilling stations. Propane has all the same octane benefits, and when injected as a liquid, has comparable cooling qualities. As an added bonus, people have been using it as a fuel for years and there is already a large knowledge base.

So I’m thinking about a secondary fuel system and control for OBD compliance.

So I’m thinking about a horizontal forklift tank in the trunk or underneath. Should hold about 8 gallons. Standard straps should make refilling a breeze, and they’re cheap enough used to have a couple for hot swap.

Next, standard lines should be available from like Parker or wherever.
Since everything will still be liquid, I should be able to get away with this:

It is rated for gas and alky so pane should be okay (?). It has a 1:1 boost reference and the return port would be piped to the vapor fitting on the tank. I haven’t done the math to check orifice sizes and pressures, but with a range of 30-100# this should be fine.

I may need to add a filter and lockout. I’d like to talk to people who have more experience w/ propane.

For control I want to use any one of the progressive nitrous controllers that reference MAP and RPM. (Megasquirt if I want to get fancy) I had some reservations about nitrous solenoids acting fast enough, but if they are close enough to stay stoich on a big dry shot, it should be able to reliably run an engine.

Standard Nitrous Solenoids:

plumbed to one of those clever injector riser ports

or nitrous express makes one too that I can’t find a pic of.

but that should make it simple, and just under $800. That sounds a little high, compared to a gasoline fuel system upgrade.

Figuring you drive 20k per year, and use 87 octane @ $2.95/gal…
AND that pane has %75 energy density compared to gas and sells @ $2.20/gal, you would save a whopping $0.37 per year by using propane.

So you’ll never get the difference back day to day, but you’d have race fuel in the tank at all times.

Anyone else think this is feasible?

[BrockwayMT]

No.

How are you going to meter the fuel? By cycling the nitrous solenoids only? How long will they last in continuous duty? You are right you need to meter the LP based on flow. In fact that’s really the only thing you need the meter the [mass flow of] fuel by.

What are you going to use for a fuel pump? You’ll need to run pressure as high as 400 or 500 psi to maintain liquid at underhood temps. You need to constantly return liquid fuel to the tank to maintain homogenous liquid fuel in the lines - you can’t meter properly if there is vapor in the fuel rails. You need a way to purge the vapor from the lines before you start it.

[Denton]

[quote=“BrockwayMT,post:2,topic:27895"”]

How are you going to meter the fuel? By cycling the nitrous solenoids only? How long will they last in continuous duty? You are right you need to meter the LP based on flow. In fact that’s really the only thing you need the meter the [mass flow of] fuel by.

[/quote]

Duty cycle is a good question I haven’t found an answer to. For metering are you suggesting something like a rising rate FPR? The only propane vapor regulators I have found are limited to 5psi in boosted applications.

[quote=“BrockwayMT,post:2,topic:27895"”]

What are you going to use for a fuel pump? You’ll need to run pressure as high as 400 or 500 psi to maintain liquid at underhood temps. You need to constantly return liquid fuel to the tank to maintain homogenous liquid fuel in the lines - you can’t meter properly if there is vapor in the fuel rails. You need a way to purge the vapor from the lines before you start it.

[/quote]

A purge kit would be easy enough, but I’m confused about pump and pressures. Looking at vapor pressure graphs illustrates your point. My original thought was that at ambient temps, I’d have about 90 psi pushing on the liquid, and that should provide enough delta. I could route the return in copper alongside the regulated line, and insulate all lines with HVAC line insulation, but I don’t know if that would keep things cool enough to stay liquid without going to high pressures. As to the homogenous liquid in the return line. If I’m using a tank with a liquid pickup and vapor return, why would the return need to be liquid?

All this begs the question, all these kits the diesel truck guys use; are they all unregulated liquid at tank pressure, or are they all injecting vapor into vaccum only? What about the fuel system on the CNG civics?

[BrockwayMT]

Those kits for diesel trucks use vapor. The ones I’ve seen don’t even use a converter. For the small amount of propane they use they are just drawing vapor from the tank like a gas grill does.

CNG is delivered as a vapor in CNG engines. The fuel is never liquefied, only carried as a high pressure vapor.

You don’t need to return liquid to the tank. To run a liquid injection system you need to keep liquid at the injectors. To do this you need to circulate the fuel at the injectors so, especially at low duty cycles, the fuel sitting in the lines doesn’t pick up heat and start to vaporize. It will pick up heat from the engine anyway, but by sending it back to the tank you are using the tank is a heat sink. As the engine runs, say for hours, the tank will slowly get warmer.

Thus you need a pump to generate the high pressure to hold liquid in the lines. Then you would need a regulator/convertor that would lower the pressure back down to storage level to go back to the tank. Thus with this arrangement of pump (compressor) and nozzle you have effectively created a refrigerator that takes heat from the engine and deposits it in the fuel tank.

For the reasons aforementioned, liquid LP injection is difficult. Most all systems are vapor systems. The easiest way to do dual fuel is to put a propane carb upstream of the gasoline carb or fuel injection plenum. then when you want to run on LP you just turn the gasoline off and the LP on. It is kind of a clunky systems with lots of hardware, but that’s how dual fuel lift trucks and aerial lifts and other industrial engine applications do it.