Home Power Prius, dual fuel

I guess my first question would be whether the same injectors at the same injection pulse width would flow an appropriate amount of natural gas. Maybe by adjusting a pressure regulator carefully enough you could get it in the ballpark, and the ECM's ability to learn a fuel trim (within ±20%) could do the rest, but things might be a little ungraceful right after switching from one fuel to the other.

At least when stationary the car doesn't generally throttle up above maybe 4 kW output or rev above idle speed, so maybe it would be simpler to regulate the natural gas supply to cover those conditions than it would be if you wanted to cover the whole range of normal driving conditions.

The conditions at the intake ports are negative pressure, so my first guess would be that you can get the needed flow at residential pressure or below, but that's just a guess.

You could use Techstream to see what your current injection pulse width is on gasoline, at idle and when charging the battery in Park, and then experiment with an identical injector to see how much natural gas it delivers at the same pulse widths and various pressures.

How tight are you with your insurance agent?

Got a plan to prevent mistakenly driving the car away while the natural gas line is attached?

 

Take a look at this old post

Toyota Prius 2nd Gen. - converted to LPG hybrid | PriusChat

 

You can check out either of these types.

Generac.com

Plugoutpower.com and use promo code 7373

http://www.RedBullet.net

http://www.ProjectLithium.com/?ref=mG0GE

http://www.Pulstar.com

http://www.PlugOutPower.com
Use code 7373

 

Sure; it'll do that by regulating the number of milliseconds each injector is open for it's cylinder's intake stroke. The ECM knows how much liquid gasoline at 43 psi will flow through the injector per millisecond, and it knows how much gasoline makes a stoichiometric mixture with how many grams of air, so it can calculate how long to hold the injector open. It can trim its calculation by up to 20% either way if the oxygen sensor reading after combustion says it wasn't spot on.

So your mission would be to look up what's the corresponding stoichiometric ratio for natural gas to air, and figure out what gas pressure will push that much gas through the fuel injector in roughly the same amount of time as for the right amount of 43 psi gasoline would flow. If you are able to supply the injectors with gas at that pressure, then the car's normal modulation of the injector pulse width will probably be able to get you the mixture you need.

However, sitting here in my armchair, I haven't any idea what "that pressure" will turn out to be, and the answer could determine the practicality of the idea.

The thread linked in #3 is interesting, but different in a couple of ways:

• It uses liquefied propane, not natural gas. (From my limited-experience with natural-draft water heater burners, LP requires both a higher pressure and a smaller orifice compared to NG.)
• It is designed for use under actual driving conditions.

Again, I'm hopeful that your plan to use NG only when stationary might simplify some things. The controller for driving might need an extensive 'map' of injector timings to cover the whole range of engine RPM and power output. As you will only need to cover the idle to roughly 4 kW range and only roughly idle RPM, possibly something less elaborate will suffice.

Their system needs to vaporize the liquefied propane, whereas your natural gas is already gas.

They use separate injectors for the gaseous fuel. It would be nice to find a simple way to get the car's existing injectors to flow the appropriate amount of NG ... but maybe the characteristics are just too different, and it doesn't work out.

Interesting project!

 

The car's fuel pump produces about 43 psi, but that's what it takes to force a liquid (that we weirdly in the US call "gas") through the injectors.

Your mission would be to find out what pressure would be needed to force an energy-equivalent amount of natural gas (an actual, you know, gas) through the same injectors in the same amount of time.

Maybe it would be high, maybe not. I haven't tried to back-of-the-envelope it.

The joke part was that there even is a carburetor, right?