E85 Worksheet
04-10-2012, 01:21 AM
#1
E85 Worksheet
I discovered there was a single gas station with e85 in town so I decided to put some in the tank for that little safety factor. Driving home changing nothing I was about 10% lean. In theory if you tell the PCM what the real stoich is everything else should be fine since PE, and BE values are based on the stoich value (those numbers are actually desired equivalence ratio, fyi). So if you know the new stoich everything is fine, but how do you know if you dont fill completely up with e85 all the time?
I made this worksheet assuming a few things:
1.) You know the current stoich value of your fuel. If you dont you can use your wideband or trims to find out. When the fuel trims stabilize, you are at lambda=1 (stoich), so whatever your wideband reads at this value is your stoich afr. Using my worksheet you can approximate the percentage of e85 is in your tank.
2.) I use premium 93 which is advertised as having up to 10% ethanol content. I find it is actually about 5% based on what my trims and wideband tell me, so this is what I called normal gas.
3.) You fill your tank completely up when you go to the gas station. It can be a combination of gas and e85, but the total you add can not be more than your defined tank volume. I didnt put in an error trap, so dont put in wrong values!
4.) Thinking in terms of lambda makes everything much simpler, especially when you are not using a pure fuel. Luckily, gasoline and e85 make max safe FI power around lambda = 0.75, but you can change this as you like. I figured most guys using E85 are FI anyway. Lambda = AFR divided by the Stoich AFR. So Lambda=0.75=(11.025/14.7).
5.) The idea with this worksheet is you update and save it every time you fill up, since I assume you have your laptop with you and can easily change the stoich value in the tune at the same time so the tuning is close. You also need to input the previous stoich value (unless you run the tank 100% dry) so it can properly calculate your new stoich based on what you added and what was already in the tank. If you do not do your own tuning (EFI Live or HPT), this wont be much use to you as you can't immediately change your tune. It will also not be as much use if you always fill up with e85. Also, if your truck is "flex-fuel" it has a sensor in the tank that detects the alcohol content and adjust to a different stoich point automatically.
I havent tried it yet but the math should work out. Let me know if anyone finds it useful
I made this worksheet assuming a few things:
1.) You know the current stoich value of your fuel. If you dont you can use your wideband or trims to find out. When the fuel trims stabilize, you are at lambda=1 (stoich), so whatever your wideband reads at this value is your stoich afr. Using my worksheet you can approximate the percentage of e85 is in your tank.
2.) I use premium 93 which is advertised as having up to 10% ethanol content. I find it is actually about 5% based on what my trims and wideband tell me, so this is what I called normal gas.
3.) You fill your tank completely up when you go to the gas station. It can be a combination of gas and e85, but the total you add can not be more than your defined tank volume. I didnt put in an error trap, so dont put in wrong values!
4.) Thinking in terms of lambda makes everything much simpler, especially when you are not using a pure fuel. Luckily, gasoline and e85 make max safe FI power around lambda = 0.75, but you can change this as you like. I figured most guys using E85 are FI anyway. Lambda = AFR divided by the Stoich AFR. So Lambda=0.75=(11.025/14.7).
5.) The idea with this worksheet is you update and save it every time you fill up, since I assume you have your laptop with you and can easily change the stoich value in the tune at the same time so the tuning is close. You also need to input the previous stoich value (unless you run the tank 100% dry) so it can properly calculate your new stoich based on what you added and what was already in the tank. If you do not do your own tuning (EFI Live or HPT), this wont be much use to you as you can't immediately change your tune. It will also not be as much use if you always fill up with e85. Also, if your truck is "flex-fuel" it has a sensor in the tank that detects the alcohol content and adjust to a different stoich point automatically.
I havent tried it yet but the math should work out. Let me know if anyone finds it useful
Last edited by Atomic; 04-10-2012 at 01:40 AM.
04-10-2012, 11:49 PM
#6
If you figure out what your current stoich is based on your narrowbands you can approximate pretty closely what your current percentage is based on that reference table in the sheet. Also knowing the stoich of "gas" in your area. If you change that value in the sheet everything will be correct since that cell is referenced.
Trims also went from around 10% to around 0%, and injector duty cycle went up ~5% so I know its injecting more fuel.
The value of this spreadsheet is really in the 3rd or 4th tanks after adding either gas or e85 to whatever is currently in the tank. The first time is easy to calculate by hand, after that it gets more complicated.
A little disappointed it didnt a better reception from the locals :/
Trims also went from around 10% to around 0%, and injector duty cycle went up ~5% so I know its injecting more fuel.
The value of this spreadsheet is really in the 3rd or 4th tanks after adding either gas or e85 to whatever is currently in the tank. The first time is easy to calculate by hand, after that it gets more complicated.
A little disappointed it didnt a better reception from the locals :/
Trending Topics
06-15-2012, 11:23 PM
#9
How are you calculating the new stoich with your wideband? Run in open loop and do the math on the error between the previous actual ratio in open loop and the new one with the E85? Do you have your gauge display lambda units as opposed to AFR? Seems like using 14.7 for blends of E85 can be confusing.
