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Discussion and questions related to the course Understanding AFR
I am wondering what would be an optimal AFR target for an engine running on pump gas and water-methanol injection?
Thanks in advance!
There is no a fixed figure, it depends mostly on the engine load and the time the load is applied so it will very from engine to engine. But as far as I remember AEM manual for water/meth kit was telling to set afr 1 point leaner than the best power afr ( should be found before kit installation) as a starting point and then slowly bring it to the best power afr...
you may lean out your ecu target by 1 point just make sure you have equal fuel distribution from cylinder to cylinder.
i just dont recommend going leaner than 12 afr, i usually target 11-11.5 because of the local weather and fuel.
i feel like afr 10.3 or lambda .70 is a good starting point with methanol you can even go richer.
Hmmm. That is very strange to hear. The entire purpose of water/meth injection is to cool down the combustion chamber for optimal ignition timing so additional fuel wouldn't have to be used fir cooling purposes. Lambda 0.7 seems to be way too rich with water meth injection - never heard of such combination... I'm sure the mbt ignition timing can be reached with much leaner air fuel mixture than lambda 0.7...
you can reach mbt timing with any afr using wmi this is not the issue my worry is pre-ignition and egt, its rare if you knock with wmi you can just add more methanol and solve this issue,
i once tested afr 12.5 on the ecu and dual #6 nozzles from snow performance which was afr 11 total using 100% wmi ratio, it made the most power with this afr with no knock at all, but im not sure if it safe because i wasnt monitoring egt or taking into account of pre-ignition.
more methanol is usually better because you dont lose alot of power like with other fuel you only gain cooling and with wmi maybe more power.
so i think afr 12 + methanol with total afr of 10.3 is a good starting point, i have not tested using more methanol than dual #6 nozzles but maybe there is more to gain and not just due to timing, i know that when we switched to e85 we made even more power than 100% wmi
240 Methanol Tuning consideration webinar has some useful information but sadly there is not enough information for wmi.
I can speak only about Mitsubishi examples I came across as I'm not doing other brands. In my experience using wmi completely eliminates the issue of pre-ignition and egt. I would never concern too much about these two things when using wmi because of its great coolong properties ( wather and meth both have very high latent heat of vaporisation index ) that alows us to adbance ignition timing towards MBT thus reducing egt even with very hight boost level... But this is just me...
Thanks for the response!
I am not an experienced tuner, but I think that sounds more logical to set lambda target one point leaner than the best power lambda. The car is an Audi RS 3 8V 2018 with a 2.5L TFSI DAZA engine.
If that was me I would try a few different afr figures with low boost just to see how the engine responds to it. I remember one case when changing afr just 1 point reacher resulted in 30 whp gain with just 1.4 Bar of boost... It is very informative process that tells you what kind of fuel curve your engine likes...
Thank you for the advice!
I just went through webinar 240 about methanol tuning- i think it is strongly about using pure methanol (2.5-3 times more than gasoline) that would have issues with pre-ignition. In our case it is still oump gas with additional methanol and water which is a different ball game to me...
Some of you may be at cross-purposes, as Georg pickup up on - the gentleman from Qatar seems to be discussing a PURE methanol running engine, not a petrol/gasoline engine with water-methanol injection.
Without actually knowing significantly more about the application, amount of water/methanol, etc, it's difficult to make a suggestion. I'd probably leave everything as-is and see what the engine package actually wants, then work from there.
Remember, while most injection systems are fixed in output - actually falling off as the boost increases* as the pressure head increases - across the rpm range, the fuel demand of the engine is going to be increasing with RPM! This means it will be richer at lower power - rpm/boost, and leaner as power - boost/rpm increases, if you just pull 'x' percent of fuel out.
*If the reservoir is strong enough, you may be able to boost reference it to maintain flow rate.
just to clarify we were running 95ron pump gas with methanol injection no water, as fuel and octane booster, we were using killer chiller for cooling so we didnt add water (iat was 88f).
the issue with using too much water is misfiring or you will find the engine is struggling to rev up as if it hydro locking but there is no issue with running more methanol injection only until you go too rich.
the nozzle charts provided by aem and snow performance are good starting range but you can go bigger until you find mbt or misfire.
i just rewatched 069 water/meth injection tuning webinar, and Andre was targeting lambda 0.8 with both methanol on and off, he had the closed loop correct the lambda back to 0.8, it pulled 14.5% so thats is about lambda 0.91, so roughly 1 point.
but yes there is too many variables when using wmi, the water to methanol ratio, the power, the heat, etc only a dyno can tell what the engine would like the most
Well, that is the reason why it is used 50/50 by mass - water removes most of the heat from combustion chamber and takes care of pre-ignition and knocking problem whilst methanol is delivering additional oxygen without decreasing knock threshold...
If the car you are tuning uses closed loop all the time (has widebands instead of narrow bands) you might want to do the opposite and command a richer mixture.
My advice is to start with your non Meth inj tune and test how much power it makes, then add your meth injection you dont want to make it so if the meth system fails you are going to be too lean, but you also dont want to make it so it looses power when the meth comes in. Usually you can go richer without loosing power when using meth (it applies to meth injection too).