Originally posted by DR. EVIL
will running propane injection make up for some of the lack of fuel when I run higher boost levels (like 24-26psi)?
To a limited degree- my O2's with propane are .88 instead of .84-.86, so the difference is quantifiable. To the extent propane induced richness becomes an issue due to displacing intake air, you can turn up the boost to cram in more air and even things out. It has been a matter of patient tuning/adjustment with the amount of propane injected. I run stock injectors with an upgraded turbo at 20-21 psi and no FMIC, and this combo is generally deemed impossible on 93 octane in the DSM world. Most folks at these boost levels require 25% larger injectors and FMIC, so the propane obviously does provide extra fueling. It even works well at reasonable knock suppression after my stock smic begins heat soaking badly.
BTW, propane works to delay the onset of knock due primarily to better turbulence and more even fuel distribution in the chamber. "turbulence within the combustion chamber helps prevent "hot spots" from forming, which can create detonation and it prevents "dead spots" where molecules of air and fuel are left unburned" "The injection of propane, a completely homogeneous gas, mixes with the non- homogeneous air/gas charge and improves the burn characteristics and therefore reduces detonation caused by unburned end gasses. The end result is an engine less prone to damaging detonation."
The propane results are not from cooling impact, IMHO, especially based on some measurements I did awhile back- here is what I posted on this in another forum:
It is true that propane liquefies at minus 45*. But, the bottles used in the kits currently marketed are designed to provide VAPOR, not liquid. They draw off the top of the cylinder, from the vapor, not the liquid. To confirm the temperature of the propane leaving the tank, I opened the valve of the 5# tank wide open (outside of course, up on the edge of the porch roof of my workshop, so the heavier propane would drop and I would not be breathing propane) and watched the thermometer drop from ambient 55* to 10* over the span of about a minute. It would not drop past 10*.
I repeated this with the full 25# tank, but using the LH thread to ¼” NPT adapter since the 25 is the new style and does not flow gas without the adapter in place. I kept the valve wide open for over 2 minutes and could not get the thermometer to drop below 27*. Nor did the thermometer ice up like it did from the 5# tank. I attribute this to the smaller orifice of the adapter- can anyone think of any other reason?
In the 25# experiment my finger was partially in the path of the propane and I assure you I was in no danger of frostbite. It felt cool, but not bitter cold like minus 45 would. I pressed my finger against the adapter opening and was able to block the flow without great difficulty. It felt like maybe 60 to 80 psi- that could be calculated fairly easily if I had the right formula.
This “experiment” seems to indicate that any claim that vapor propane exits the tank at minus 45 is inaccurate. Thus, the cooling benefits of vapor propane seem to have been overstated. However, I do not doubt the cooling benefits of liquid propane- the 5# tank had a layer of frost on the bottom half from the liquid inside converting to vapor, about 5 minutes after experiment number one.
Joe