Achieving target Lambda with flex fuel

[Hodgdon Extreme]

Starting with E10 fuel, I tuned out my VE table and was seeing less than 5% closed loop correction; usually more like ±2%.

Configured multifuel parameters as below - my thought was this should allow me to run any blend of alcohol from 10% to 99%:

I was expecting this to "just work", but during testing, I discovered this resulted in being lean of target lambda by almost 10% on ~e45 fuel. After adding more pump e85 into the tank, my ethanol content increased to 63%, and that resulted in me being lean of target lambda by about 12-13%.

At first, I tried changing injector flow rate for fuel 2 by multiplying by 0.88 (because I was about 12% lean of target). This seemed to work pretty well - but it seemed to richen idle/light load more than it did the moderate/heavy load.

Read elsewhere that Haltech pre-populates their equivalent to the Link blend ratio table, so I reset injector flowrate back to 1332 cc/min and used Haltech settings for the blend ratio table:

This resulted in being even leaner than I was to begin with.

Frankly, this non-linear relationship between fuel 1 and fuel 2 doesn't make any sense to me, especially for fueling. Perhaps it makes sense for spark, as 40% ethanol provides most of the knock-resistance that 80% provides...but the table from Haltech is reversed from that.

Anyway, what is my move here to calibrate flex fuel properly? Is there anything wrong with simply scaling injector flow rate until I'm achieving target lambda? If so, why does that seem to effect light loads differently than high loads? I'm using the published injector data from Injector Dynamics for the 1300cc units.

 

[Confused]

When you run multiple fuels, you need to tune first with your lowest ethanol content you'll run, then again tune a second table, which will be with your maximum ethanol content you'll run.

 

Then, the two tables will be blended together based on your current ethanol content (determined with the sensor).

 

This is all explained in great detail in the Help under the Multi Fuel tuning section.

[Hodgdon Extreme]

Thank you for reply. I've read the Multifuel portion of the manual. It mentions a second VE table may be required.

Are you saying that in your own experience, achieving good results with flex fuel - and hitting lambda targets with both gasoline and ethanol blends will require the 2nd VE table?

[Confused]

Unfortunately E85 isn't available here, but every post I've seen here with multi fuel is using multiple fuel tables...

 

One thing that I've just noticed, you mention you tuned the VE table on E10, but in the blend table you're starting from 0% ethanol with 0% blend, and at E10 (where you tuned) you're already saying to blend 8% towards the second fuel - if the value in the E0 and E10 cells is 0%, then ramping up to 100% blend at E85 might give you a closer result?

 

As I said, unfortunately no first hand experience, but I've been reading posts here daily for 3 years now!

[Timboj]

I'm no expert, but I spent a few weeks going through this myself to blend 98-E85. I ended up using two tables with pretty disparate values.

I think the other call out is that there are so many variables that contribute to your final AFR. Modelled tries to simplify this by using values for the variables which are then fed into conditional algorithms. Any error (and there will be error) can be amplified depending on the other inputs. Using a single table and asking the blend ratio to take care of it sounds fine in theory, but it's not practical for typical users (again, not an expert).

Unless you've been able to validate that all of your input values are 99.99% accurate (or whatever), then the VE table won't be an accurate representation of your actual VE. Instead it becomes a useful point to tune out the error with the final air/fuel mixture. Then if you've got closed loop, that takes care of the rest.
 

[Adamw]

If the injector characterisation is good then you generally dont need a 2nd VE table.  Flowrate for the injectors will be quite a bit lower for ethanol.  I have never tested a ID1300, but as an example an ID1000 will flow about 850cc/min ethanol Vs 1000cc/m with petrol.  

If the actual flowrate is unknown then you can adjust it experimentally at medium load/medium RPM until the measured lambda is close to target.  If you have some error at idle still then this likely means there is some deadtime or short PW adder error also.   

[Hodgdon Extreme]

Thank you everyone for your thoughts.

I set stoich for fuel 1 to 14.7:1. I set stoich for fuel 2 to 9.1:1. I rescaled my multifuel blend table 1:1 from 0 to 100. My thinking here is I want the flex fuel to work from E0 to E98...
I found that setting injector flowrate for fuel 2 at 1332 * 0.83 = 1106 cc/min is pretty darn close. I'm achieving target lambda everywhere except for conditions under 2000rpm and under -60 kPa MGP. For those light load/speed conditions - I'm 4-5% rich.

Before I can draw any real conclusions, I think I need to switch back to gasoline and retest because my VE table was developed with fuel 1 stoich set to 14.1:1. Can't help but notice there is a 4% difference between 14.7:1 and 14.1:1...