Sparkplug heat range & alcohol / ethanol fuel
 

With alcohol fuels (ethanol and methane), is there any data out there on the effects of the alcohol % and impact to sparkplug heat range. I presume that there is some inverse relationship between alcohol content and appropriate plug temp range due to the inherent cooling and octane advantages of those fuels. But we all know how that assume thing usually goes...

Tried scouring the interwebz, but I couldn't find any authoritative sources (e.g. SAE docs). For lack of comment here, guess I'll give this question one more shot on my build thread.

seems to me it’d still apply equally for the very same reasons, but just my possibly not-informed opinion.

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The one i know about is not heat range, but plug material. its SAE 892061 "Pre Ignition Phenomena of Methanol Fuel M85 by the Post Ignition Technique"

the two important points are that Platinum plugs are "highly susceptible to surface ignition" and that alcohol was less stable, it pre ignites at a lower temperature

$30 later interesting, I learn that it's not just platinum, but that "..it's not recommended to select noble metal (e.g. platinum AND iridium) as electrode elements for spark plugs use with methanol-fueled engines" but, "...noble elements can be used in the spark plug element in gasoline field engines". However, since M85 is substantially chemically (e.g. corrosive) different than E85 (not to speak of E50), I'm unsure of the actual risk of NGK R7420 iridium plugs in my application.

As for the heat range to ethanol % correlation, the search continues...

that only asserts running the coldest plug possible and you’re probably already there or close.

then again, how often do we hear of E85 preignition issues? :dunno:

Agreed. And then I started to speculate if the pre-ignition risk might apply to 100% meth WI, though this isn't my application.

So to the original question, I'm coming up with a 'goose egg'. Given that, I'll finalize my way forward on my build thread.

not very, but its been done!

its also true (according to the papers) that 100% alcohol is more prone to this kind of thing than the mixes, which is why they were running the mixes

on gasoline the hot spark plug seems to be one of the issues, so once you put cold plugs in it, and make sure its not inductively cross firing, or having RFI/spark leakage issues, it seems like that goes a long way toward getting rid of detonation/preignition. i would think it best to keep the cold plug, and see if its too cold :)

currently running 60% 93 pump and 40% eth with 1320 cc of 60% meth, 40% water.

the ground straps on my Denso 5720 10 heat range plugs were completely clean so they were too hot.

today, i swapped in some Denso 5722 11s and the strap was half clean which means they are on the money heatwise.

i also noted that my knock readings dropped significantly. they weren't high to start with but lower is...

running mid 500 ATM

perhaps this might be of help

Exceptionally helpful Mr. Colemon! Especially since I'm looking at similar fuel composition (E50). I had assumed starting with R7420-10.5 and checking plugs. While I'll only be at mid-400rwhp, your data give me more confidence that I should be well within the heat range ballpark. Many thanks!

BTW, I was actually coming back here to post a possible lead I found on another forum. The proposed inference is that there is no significant heat of combustion reduction with E85, as it just produces more energy at the same combustion temp.
The Hot and Cold of E85 vs Gas: A Theoretical Analysis - 6SpeedOnline - Porsche Forum and Luxury Car Resource

Power Rating Spark Plugs and Each Ignition Option:

BUR9EQ on Factory FD Ignition - 400whp
BUR9EQ on Factory FC Ignition - 425whp
BUR9EQ on Factory LS1 Ignition - 375whp
BUR9EQ on Factory LT Truck Ignition - 425whp

IGN1A = 650whp or 32psi on 2 Rotor is where I like to keep them. No more.
IGN1A = Under 9000 RPM. Use CDI After that.

IRE01-29, 31, 32, 35 - 600+whp, No Issues
R7420 10, 10.5, 11, 11.5 - 600+whp, No Issues

CDI The World. It's the right option for anyone wanting over 8500 RPM and/or 25+psi of boost.