E85Forum.com

murphinator · Joined: 08 Jan 2010 Posts: 93

I know that e85's ethanol content can vary and needs to be factored in but for the moment lets leave that as a seperate issue.

What I am looking to verify is in my case I will be blending e70 or e85 with pump fuel which is e10 anywhere within a days drive of me.

for this exercise with e85 stoich being approx 9.87 stoich ( varies slightly by reference material) and e10 stoich being approx 14.13.

lets say you are mixing 4 gallons of e85 and 6 gallons of e10 does this look correct?

9.87(stoich)X4 (gallons)=39.48
14.13(stoich)X6(gallons)=84.78

39.48+84.78=124.26

124.26/10=12.426 stoich for this blend

in other words do the fuels stioch characteristics blend in a linear fashion so simple math will yield an accurate stoich ?

I can easily change stoich in my vehicles with my tuner and currently have it set to 14.13 for e10 from the 14.68 that was in the stock tune - after making that change trims got easier to keep +or-5%

I will be monitoring afr's with a wideband but just trying to get my head clear on how to represent the blends I am running properly in my tune ahead of actually starting to blend.

TIA Cool

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PB's 1/4 mi 12.209, 117.75 trap ,1/8 mi 7.76 ,93.99 trap , 1.949 short time 4.53 0-60

I tune with HP Tuners software

murphinator · Joined: 08 Jan 2010 Posts: 93

doesnt do stoich calcs but found this calculator that gives final content of blends as well as final octane of blends

thought someone may like it Laughing

http://www.intercepteft.com/calc.html
_________________
PB's 1/4 mi 12.209, 117.75 trap ,1/8 mi 7.76 ,93.99 trap , 1.949 short time 4.53 0-60

I tune with HP Tuners software

Alcohol · Joined: 17 Apr 2007 Posts: 634 Location: Central Wisconsin

Yes - the stoich should be linear.

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

If your ecu reports fuel trims to get to stoich like most OEM ECU's do you can use that fuel trim info directly to change your tune. If you get it running right and have near 0 fuel trim at warm idle then fill the tank with new fuel and not the fuel trims have changed to +5% you know the blend has changed its oxygen demand by about 5%. If you richen your mixture across the board by 5% you should be right back to your ideal tune.

The same applies to your wide band info. Once you have a tune dialed in and know what that tune gives you as far as readings on the wide band are concerned than just make a global adjustment to the base tune as your bench mark wideband reading changes. I watched my warm idle fuel trims on the OEM ecu and with the wide band I watch both my warm idle, and light throttle highway cruise AFR and lambda.

I shift the whole tune by just tweaking the injector scaling by the appropriate percentage. To richen the whole map I just change the injector size and tell the ECU they are slightly smaller and it richens the whole map by that percentage.

Larry

murphinator · Joined: 08 Jan 2010 Posts: 93

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

If you go to full E85 you will be very close if you increase fuel flow by 30% over stock. At lower mixtures the magic number would be lower.

A really simple way to do it is draw a square with 0-30 on one axis (the vertical Y axis), and 0-85 on the other (the horizontal x axis), with both 0's in the lower left corner.

Draw a straight line from the 0,0 corner to the other 30,85 corner.
You now have a simple graphic calculator that if you know either one, you can ballpark the other.

At the end where both axis go to zero that is your fuel flow for straight gasoline. At the opposite corner where the scales read 30,85 that is the point where your mixture would be +30% at straight E85.

Figure out your true ethanol content of the mixture in the tank. Find that point on the 0-85 scale and go up to the diagonal line, then over to the 0-30 scale. Where that intersects, that is the approximate increase in fuel above pure gasoline to get you about right for the new mixture in your tank.

If you are comfortable with simple math, you will need to increase your gasoline fuel flow by about 0.35 x (percent of ethanol).

For example at 10% ethanol you should need about 3.5% more fuel flow than on straight gasoline.

At 25% ethanol you would need about 8.8% more fuel than straight gasoline etc. etc.

At 85% ethanol you would need .35 x (85) = 29.75% increased flow.

These are just ball park numbers but I hope you see the idea, but this will get you close enough that the car should not complain too much while you dial in the last little bit of fuel trims to make it right?

Larry

murphinator · Joined: 08 Jan 2010 Posts: 93

30 points on one axis and 85 on the other the graph would be a rectangle in my mind so I must be missing something, I follow the concept though

thanks for your continued assistance !
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PB's 1/4 mi 12.209, 117.75 trap ,1/8 mi 7.76 ,93.99 trap , 1.949 short time 4.53 0-60

I tune with HP Tuners software

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado