Questions About Liquid Propane as Fuel

[thehazard]

Hi there. I have recently completed my combustion chamber and now want to move onto creating my fuel systems. In one of tech ingredients videos he mentions liquid propane as an alternative fuel choice. He describes some of the disadvantages of the fuel being the boiling in the lines causing surges and dips in fuel flow. Though from what I could take away, the disadvantages seemed pretty insignificant compared to the other advantages propane has. Namely ease of use, and simplicity in fuel delivery designs. 

Basically what I am asking is: Is their a reason liquid propane isn't widespread across the amateur designs in this forum? As I have not seen it mentioned almost at all.

If liquid propane is a reasonable fuel choice, am I correct in saying that no changes need to be made to the fuel injectors from a gaseous vs liquid propane fuel system? (I understand regulation of the fuel would be different vs the gaseous form, due to the massive increase in energy density)

My turbo has a 64mm inducer. Which is why I want more capability from my fuel than gaseous propane.

[racket]

Hi

Liquid propane can be used but any leaks can be dangerous, propane explosions happen :-(

Its easier to used liquid fuel like kero or diesel , just a decent EFI pump and a spray nozzle .

You can use the propane cylinder valve as your throttle for liquid propane use , I used liquid propane on my turboprop PJ initially www.youtube.com/watch?v=uqMn0A2aUdo&ab_channel=AndrewMartin before going to petrol with propane for starting and warm up www.youtube.com/watch?v=KVQavn_o_lE&ab_channel=racketmotorman

You might find that you'll need a spray nozzle for liquid rather than the more crude gasious devices we use .

Cheers
John

[richardm]

It' a bit out of topic but I' ll tell the story anyway .Years ago I was using a propane torch on a small job in my backyard. I had just screwed the torch to the bottle as usual and light it up. Unaware of a leak at the attachment to the propane bottle. Started the job .. fire engulfed the bottle.
Fortunate I had work gloves ,no burn I just threw the torch away from me in the grass fearing it could explode Next thing is how do you extinguish this thing?
Ran to my garage found an old blanket and smother it. Lesson learned I m now always suspicious of possible leaks and overall dont really like using propane

Propane fires are very difficult to put out. IMO no household extinguisher can do it.

[thehazard]

Thank you for the information.

I will use liquid propane for my project, and now will be extra wary of leaks during testing.

Thanks again for the help.

[racket]

You'll need to build the propane system to a high standard , annealed copper tubing with flared fittings , same as what a gas fitter would do when hooking up propane for household use , and leak test EVERYTHING after assembly .

Have a fast action ball valve in the system .

As Richard mentioned , propane can be dangerous , it was originally used in RC turbines but was discontinued after too many fires burning expensive aircrafts and engines

[thehazard]

Thank you for the specifics.

I was just going to use compression fittings on soft copper tube for the propane (that is what I am doing for the oil), of course I am not doing that anymore. I really though that compression fittings would have been good enough. So good thing I had this discussion!

[richardm]

Good decision! blog.redhedri.com/when-to-use-compression-or-flared-fittings#:~:text=Fittings%3A,major%20problems%20if%20left%20unattended.

[racket]

I have used compression fittings on my propane lines used for gasious preheating/pilot light , but theres no real pressure involved unlike if the propane is used as fuel with P2 backpressures adding to the delivery pressure .

Go flared and be safe :-)

[richardm]

Also make sure tou use the correct flaring tool for your fittings There are 37 and 45 degrees flares..ààhttps://rbisj.com/2022/08/whats-the-difference-between-37-and-45-degree-flares/#:~:text=45%20vs%2037%20Degree%20Flare%20Fittings&text=A%2045%2Ddegree%20flare%20has,used%20in%20high%2Dpressure%20applications.