[tadd]

Awesome feedback, thank you all! Awesome info!

I am a huge propane fan, so hearing other fuel thoughts and having a discussion is really great. We are having a nice wave of low gas prices but I think that will eventually come to an end...

IMHO the advantages to propane are:
1. Super clean burning. It is a simple hydrocarbon with no hetro-atom (N, S, O, ect) functional groups. Unlike methanol or ethanol you don't get nasty side products like formaldehyde out the exhaust. Also it doesn't leave heavy combustion byproducts in the oil. Look at any forklift. Oil needs to be replaced due to wearing out rather than from contamination.

2. Reasonable storage. Since it stored under pressure, it doesn't spoil since nothing can vaporize away. Plus it liquefies, so you get great storage (800:1 expansion ratio), and does so at reasonable pressures/temperatures. Standard propane tanks are burst tested at only 350 psi IIRC. This is very doable pressure compared to to methane which does not liquefy with just pressure and needs 10k psi storage solutions to store the gas (or special cryogenic if you want liquid). The other darling is hydrogen which has the same issues. Propane tanks are also one hell of a lot stronger than a sheet metal gas tank current found on standard gasoline cars...

3. Propane has been a motor fuel for a long time and it is the only alternative fuel that already has a large full scale distribution infrastructure in place.

4. Propane can equal the usable energy density of gasoline. If the motor is built for propane (read high CR), you can achieve energy use parity. Even though propane has less energy per gram, because of its 110 octane rating, you can harvest more of the stored energy.

5. Propane antique cars are exempt from emissions testing because they are so clean. At least this was the case 15 years ago.

6. Propane can be generated via water gas shift reactions. This way out there, but we could take CO2 from the air and mix with water at high heat and have a closed carbon cycle for our transportation industry.

The only 'con' to propane is that the octane rating is temperature dependent. For manufacturers that have sold propane vehicles in the past, they have set the engine to the worst case use scenarios. For example International Harvester had propane trucks as an option in the 80s. Just incase someone had their truck stuck in a field, and working it hard to unstick, they set the CR at 8:1. Worst case use. So it got really poor mileage and didn't sell for squat. This can be avoided by utilizing liquid propane (LPG) vs gaseous propane (as the bulk of most propane fuel systems utilize).

LPG utilizes the latent heat of vaporization to keep the charge cool and maintain that high octane rating vs gaseous systems that pre-warm the liquid to vapor before use.

Siemens worked extensively with LPG in the late 80s early 90s. They did all sorts of wear testing because propane has no lubricity. Gasoline is low, but propane is even less. Anyways, from what I have read from their work, the only issue with utilizing a stock EFI injector is that they would split from the elevated pressure as they were only designed for 150 psi use. If the propane was chilled to lower the vapor pressure, stock injectors worked great. Anyways they did a run of re-engineered injectors to deal with increased pressure. They are findable, but hens teeth today. You think lash cap rockers are hard to come by, LOL!

The other issue for a LPG system that costs to much, and thus has hindered for general application, is the pump. As stated, propane has zero lubricity. This means a pump made from very hard materials. Pumps are typically several thousand. Since propane generates its own pressure with temperature (phase diagram), you need to pressurize 50 to 100 psi above whatever temperature you think your engine bay will be at to ensure liquid delivery to the injectors. There are two ways to do this... pressurize by heating the propane tank and letting the phase diagram do its thing naturally, or add a pump. To avoid the expensive gear drive pump, I would like to side step this by using a hydraulic accumulator and just use a small air compressor to pump up the system. Use two accumulators to swap back in forth during refills. Then utilize a regular forklift (43#) aluminum tank or two in the frunk. Although not as much volume as a conformal tank, you could then use a propane service. Say two tanks in the car, two empties at home along with two full ones ready to swap in. Last time I did the math a forklift service worked out to about $1.50 a gallon.

If you have a reference flieger on the 'gumming up' with propane, I would love to see it. I have never, ever heard of such behavior with propane. As for the DFI, I had considered them because they are operationally rated way over any pressure that would be required for propane. As for the spray pattern, I agree it would be less than Ideal, but it will vaporize anyway in the 'hot' head... unless maybe you are driving in Minot ND in the dead of winter. Had a buddy send me a pic of a coffee cup of liquid propane because it was -44F there! Yikes.

Love to hear others thoughts on this as this is a personal passion of mine...

t