How to calculate octane impact of 50/50 WMI?

[Asbjorn]

Is it possible to estimate the octane increase of running 50/50 water methanol injection like below (idea by @CNM135i)?

I did one log with WMI before going back to 100% water and reducing nozzle size to 225cc (thanks to @F87Source)

Here are the results:
RON 98 WI 20C amb 6200rpm: -6% stft
RON 95 WI 14C amb 6200rpm: -5.5% stft
RON 95 WMI 20C amb 6200rpm: -12.5 stft

375cc nozzle
WMI = 50/50 water meth
WI = 100 water
16psi / 7deg timing / 11.4 afr @6200rpm

If methanol is 115 octane, and RON95 is 91 octane, would this mean that with WMI the effective average octane is

12.5 - 6 = 6.5% stft difference
115 - 91 = 24 octane difference
6.5% x 24 = 1.5 octane increase
Resulting in 91 + 1.5 = 92.5 octane

 

[doublespaces]

I prefer to just add all the numbers together and punch that in as my answer.

What are you aiming for? I always saw meth as an IAT helper and tried to avoid the octane aspect.

 

[Asbjorn]

I prefer to just add all the numbers together and punch that in as my answer.

What are you aiming for? I always saw meth as an IAT helper and tried to avoid the octane aspect.

I run WI now, and my aim is to finish my ron95 and ron98 maps with that.

Then @CNITUSRJ sent a picture that he had found RON101 in China, although at a gas station very very far from my city.

Then I started to cry, and my friend comforted me with a glass of meth on the rocks... this led to the above napkin calculations

 

[F87Source]

Hmm interesting, I personally never liked to rely on methanol for octane. I always tuned the car for pump gas then used meth for cooling and an added layer of security. The reason behind this is because if the meth doesn't distribute evenly through all 6 cylinders then one cylinder may get knock.

 

[rac]

Is it possible to estimate the octane increase of running 50/50 water methanol injection

yeah, kind of. but there are complications regarding mixed delivery methods (DI versus port and other) that you would need to guestimate through. It's no napkin exercise.

start thinking in terms of what the different fuels and water can do for you regarding in cylinder heat removal. pragmatically, your water injection by weight will be limited by the ignition system and practical tuning capability of being flash only on a load bearing dyno. more water needs more experienced tuning and understanding of what the water is actually doing. that's why most hobbyists find tuning for meth easier and more productive.

there are lot of good resources and reading material on the aquamist forum.

i hope you are not using charge pipe only WMI?

 

[rac]

so my napkin numbers would suggest ~15% (by weight ratio to fuel) of 50/50 WMI would be ballpark as affective as E50 if the E50 was delivered in the same location (which it wouldn't be - but for simplicity sake).

 

[Asbjorn]

yeah, kind of. but there are complications regarding mixed delivery methods (DI versus port and other) that you would need to guestimate through. It's no napkin exercise.

start thinking in terms of what the different fuels and water can do for you regarding in cylinder heat removal. pragmatically, your water injection by weight will be limited by the ignition system and practical tuning capability of being flash only on a load bearing dyno. more water needs more experienced tuning and understanding of what the water is actually doing. that's why most hobbyists find tuning for meth easier and more productive.

there are lot of good resources and reading material on the aquamist forum.

i hope you are not using charge pipe only WMI?

Im actually not using WMI, I just did one log with 50/50 meth, and then went back to pure water. I inject inside charge pipe after FMIC.

But you raised a different topic just now. Tuning for WI. I had no idea this was a thing. The only difference I see on the logs is slightly lower iat and afrs that do not return to 234 as fast as normal after wot. What are the topics to be aware of and to notify my tuner about?

 

[rac]

in which case ~10% WI / fuel ratio would yield a similar outcome (again napkin numbers). but I would not dump all of that in the charge pipe. I would strongly encourage you to go direct port set-up, and if you want use a 7th small injector in the charge pipe. also set yourself up with a fast acting valve and controller so that you can control flow in proportion to fuel flow as you would with a PI set up and PI fuel map.

water both stabilisers and slows down the flame front, and it also makes the fuel harder to ignite.
so if you keep everything constant (boost, timing, AFR), at some point you will see reduction in power because your timing is getting further away from MBT, and you might start misfiring (maybe not enough to throw codes but it will show early signs in power loss).

the timing needs to be advanced to account for a slower flame speed and you need a lot more spark energy to make sure you get reliable ignition as the water goes up (which really when you think about it also works in your favour regards detonation). keeping a really rich AFR (so that excess fuel does the cooling), makes things even harder for the ignition system and because water is so much more effective at cooling you can afford to dial back the excess fuel and run leaner AFRs. but these are bold moves for a remote tuner on a customers car - if I were tuning it, how would I know what quality of installation your WI is? what's the fail safe for a plugged injector? an inline flow meter might help give some comfort.

a lot of people wouldn't make significant tuning changes for fear of various failures and so you might stop adding water prematurely when you cant tolerate the amount of power you have started to lose.

 

[fmorelli]

@rac not to mention that on these cars we know that fuel quality (and consistency) is another factor to everything you've said.

Filippo

 

[Asbjorn]

in which case ~10% WI / fuel ratio would yield a similar outcome (again napkin numbers). but I would not dump all of that in the charge pipe. I would strongly encourage you to go direct port set-up, and if you want use a 7th small injector in the charge pipe. also set yourself up with a fast acting valve and controller so that you can control flow in proportion to fuel flow as you would with a PI set up and PI fuel map.

water both stabilisers and slows down the flame front, and it also makes the fuel harder to ignite.
so if you keep everything constant (boost, timing, AFR), at some point you will see reduction in power because your timing is getting further away from MBT, and you might start misfiring (maybe not enough to throw codes but it will show early signs in power loss).

the timing needs to be advanced to account for a slower flame speed and you need a lot more spark energy to make sure you get reliable ignition as the water goes up (which really when you think about it also works in your favour regards detonation). keeping a really rich AFR (so that excess fuel does the cooling), makes things even harder for the ignition system and because water is so much more effective at cooling you can afford to dial back the excess fuel and run leaner AFRs. but these are bold moves for a remote tuner on a customers car - if I were tuning it, how would I know what quality of installation your WI is? what's the fail safe for a plugged injector? an inline flow meter might help give some comfort.

a lot of people wouldn't make significant tuning changes for fear of various failures and so you might stop adding water prematurely when you cant tolerate the amount of power you have started to lose.

Thanks a lot for these explanations!

What is the quick explanation afr returns to 234 much slower after water has been injected?

 

[rac]

What is the quick explanation afr returns to 234 much slower after water has been injected?

on decel? honestly I don't know. could be many things. AFR's reading that high is kind of unique for me, I don't know how many other platforms read afrs to those kind's of numbers. its way out of reliable sensor range. I would question the lambda sensors ability to accurately determine the difference between 100 and 200 for instance since they are so far out of the normal reading scale something simple like a variation in EGT (impacted by water) could alter the sensor output. or perhaps there is actually a bee's d8k more residual unburnt fuel when you let off the gas (possibly a function of reduced cylinder temperatures). wild guesses.

 

[rac]

so far as my ~10% water by mass I was on the light side of other research I dug up for your octane increase amount. the below numbers appear to have been quoted by many researchers and they date back some decades, but its another reference point. linear increase from 90 to 100 RON with 0-40% water by weight.
40% is a lot water... RON98 + 10% water might be close to RON101 based on below.

 

[CNM135i]

It is interesting how many theories and complex the talk about WMI can get. As with anything else, going into the details reveal how complex things are/you can make them. OR - you can just dump a shit load on meth in your CP like I have done for the last 4 years and enjoy the ride My car is running tuned for both octane and volume on meth - never a single hiccup. To give an idea about the volume STFT will go -30% at 21psi before adjusting the fueling. Cyl 2 and 4 are the ones to pull timing first which I have also seen on other cars not running additional fueling.

 

[rac]

OR - you can just dump a shit load on meth in your CP

yep, could do that. that would make for a short forum thread and more work from home boredom....

12.5 - 6 = 6.5% stft difference
115 - 91 = 24 octane difference
6.5% x 24 = 1.5 octane increase
Resulting in 91 + 1.5 = 92.5 octane

if your trying to estimate how much fuel your displacing with methanol you need to take into account the ratio between fuel and methonal to reach lambda = 1 (i.e ~2.29).you need > 2x the methanol for the same lambda reading. so if the ecu is pulling 6.5% fuel to hit target, that means you CP is adding ~15% of your fuelling by meth volume (ignoring the slight density difference).

 

[CNM135i]

yep, could do that. that would make for a short forum thread and more work from home boredom....

Sorry...I'll delete my post shortly haha