Ethanol Content and Stoich Question.

[k4nnon]

Hey all, Quick question about ethanol content and stoich. When i last tuned my car it was on summer blend about 83-85% from our local pumps and regularly tested to be pretty consistent at that percentage. I recently installed an ethanol content sensor in the car and its reading the winter blend at 66% currently which seems correct. Now with the winter blend being at 66% should i change my Stoich values in my fuel setup to reflect the e66 or leave the values at what they were when i tuned last on summer e85? Thanks for any help or input..

[koracing]

It depends on how your car was tuned.  If it was tuned with modelled multi-fuel with two fuel and timing tables interpolating between them then there should be no need to do anything as all parameters are already being interpolated for any point between the two tables that were tuned.  Are you having any issues that prompted you to check and/or decided something needs changing?

[k4nnon]

1 hour ago, koracing said:

It depends on how your car was tuned.  If it was tuned with modelled multi-fuel with two fuel and timing tables interpolating between them then there should be no need to do anything as all parameters are already being interpolated for any point between the two tables that were tuned.  Are you having any issues that prompted you to check and/or decided something needs changing?

Hey thanks again for the input. My car is SD and tuned on one fuel only so non multi fuel just modelled fuel equation on summer blend e85. My stoich value in the fuel setup is 9.8:1 for e85. Just wondering if i need to make this value more like 10.9:1 to reflect e66. vehicle runs well as is no issues but if the stoich value should reflect the E content than i want to correct the fuel setup so that everything stays best as possible.. Thanks again for the input.

[Adamw]

The problem is it is not just the stoich ratio that changes, fuel density will change, injector flow rate will change, fuel density temp coeff will change, VE may change a little.  So this is the advantage of multi-fuel mode it can seamlessly adjust all of these based on fuel composition.  

Without doing a lot of calcs and guesstimations it is hard to say how far out the fueling will be with the change from 83% to 66%.  Probably what I would try initially if the AFR is significantly off target after the fuel change is just changing one factor by the average percentage error so that the AFR at medium load/medium RPM is back close to target.  Hopefully the error is mostly linear and you will end up with AFR in the ballpark under most conditions.   

So to say that a different way with an example, lets say your AFR was on average 10% richer than target with the new fuel, then reduce say the engine capacity by 10% which will remove 10% fuel, then check if AFR is acceptable over a range of RPMs/loads.  

[k4nnon]

13 hours ago, Adamw said:

The problem is it is not just the stoich ratio that changes, fuel density will change, injector flow rate will change, fuel density temp coeff will change, VE may change a little.  So this is the advantage of multi-fuel mode it can seamlessly adjust all of these based on fuel composition.  

Without doing a lot of calcs and guesstimations it is hard to say how far out the fueling will be with the change from 83% to 66%.  Probably what I would try initially if the AFR is significantly off target after the fuel change is just changing one factor by the average percentage error so that the AFR at medium load/medium RPM is back close to target.  Hopefully the error is mostly linear and you will end up with AFR in the ballpark under most conditions.   

So to say that a different way with an example, lets say your AFR was on average 10% richer than target with the new fuel, then reduce say the engine capacity by 10% which will remove 10% fuel, then check if AFR is acceptable over a range of RPMs/loads.  

Hey Adam, thanks for the information, thats a bit more in depth and understandable. The car has ran great no issues and i dont think the difference in ethanol content has caused the tune to be out really. If it is running slighty rich or lean its only slightly and the corrections adjust to where its not noticed. I plan on setting up multi fuel in the near future and was the reason i installed the ethanol sensor. As of now everything seems great so im just gonne leave it. Thanks again for the information.