waterinjection.info  

Go Back   waterinjection.info > Injection Theory (what it is and what it does) > Injection Mixtures

Reply
 
Thread Tools Display Modes
  #1  
Old 05-04-2013, 01:18 AM
Flr Power Flr Power is offline
Member
 
Join Date: Apr 2013
Location: Canada
Posts: 62
Default Water Methanol AFR Calculation

Can anybody double check the math I have done here please?
I am not sure if this is the right way to calculate the ratio of AFR change when injecting 25 % by weight of water methanol. What would be the real AFR change?
I am injecting 510cc/min of W50/M50 by weight for 2040cc/min of petrol at peak power.

510/2040=0.25; 25%/2 = 12.5% or 255cc/min of injected methanol.
14.7 petrol stoich and 6.4 methanol stoich = 8.3 total AFR change; So 8.3x.125=1.04 AFR change?

Is the math good? Will injecting 12.5% methanol combine with petrol would give me an AFR change of 1.04?

So it looks like I would need to trim 7% petrol from my fuel map when I fully inject right?

Last edited by Flr Power; 05-04-2013 at 01:19 AM. Reason: Mistake
Reply With Quote
  #2  
Old 06-04-2013, 06:05 AM
Howerton Engineering
Guest
 
Posts: n/a
Default Re: Water Methanol AFR Calculation

I'm not quite following one part of your calculation. I think you are off by twice as much. Here's how I do it, and it has been pretty close in practice:

Say for 2000cc of fuel injector, you jet at 25%(500cc of meth) and spray 100% meth. I don't use ideal stoich AFR, but power AFR, which is 12.5 for gas, and 5.5 for meth. So meth is about 44% of gas, for simplicity I tend to round down to 40%.

So if you jet at 25% and use 100% meth, that's like 10% more gas(40%). 10% more gas is roughly 1.0AFR in most situations.

Now for jetting at 20% and using 50/50 that's 10% methanol, which is about 4% more gas, or .3 to .4 of an AFR change.

On paper this may look funny, but we have been pretty accurate at predicting AFR change and providing proper jetting over the years.

NOTE: One thing to remember is the margin of error on whatever dyno you may be using. Some will have a issue with a .2 to .3 repeatability so many runs and proper load bearing dynos are needed to measure accurately.
Reply With Quote
  #3  
Old 06-04-2013, 06:41 PM
Flr Power Flr Power is offline
Member
 
Join Date: Apr 2013
Location: Canada
Posts: 62
Default Re: Water Methanol AFR Calculation

Ok, thanks, I had some numbers wrong in there.
So the right numbers are: I inject 12.5% meth x 0.44=5.5% more gas or around 0.5 AFR change.

I was close but not enough it seems since now it looks like I have to only trim 5.5% gasoline from my main fuel map at full load/boost.

Last edited by Flr Power; 06-04-2013 at 08:21 PM. Reason: Correction
Reply With Quote
  #4  
Old 09-04-2013, 10:27 AM
Liborek Liborek is offline
Junior Member
 
Join Date: Nov 2009
Posts: 9
Default Re: Water Methanol AFR Calculation

Quote:
Originally Posted by Flr Power View Post
I was close but not enough it seems since now it looks like I have to only trim 5.5% gasoline from my main fuel map at full load/boost.
Charge cooling effect can increase air mass trapped in cylinder which would partially compensate for increased fuel value. It depends on accuracy of determining actual airflow into the engine.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +1. The time now is 12:02 PM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.