Flex Fuel Fudging - Table 2 VE numbers

Hi all

I've just started with Link's Modelled Multi, and have started noticing a trend where my Table 2 numbers are approximately 10% higher than my Table 1 numbers.

I figure this shouldn't be the case since it's not airflow that is different, it's the fuel that's different.

This probably isn't a problem in general, but I had to fudge the cold starting tables by adding a 3D axis Ethanol(%) and removing 10% fuel from E80 to get the Lambda back to where it should be to keep cold start happy.

This leads me to believe the model has a 10% discrepancy in it's calculation.

Questions...

Fuel charge cooling co-efficient - Both are set to 10c as per Link's starting point. In general, Is there a better or differing starting point for E85?

If an injector is rated at 1000cc @ 3bar lets say, What solvent is used to test and is it representative of both gasoline and ethanol?

Am I barking up the wrong tree, would these things not account for this magic 10% VE differential I'm getting?

Thank you for reading

Mike

There will be small changes in VE due to various effects, mostly scavenging related due to different EGT and volume of exhaust gas produced.

However it sounds mostly like your injector flow rates are set wrong, most injectors will flow 7-15% less ethanol compared to petrol.

Thanks for the response Adam

Should I try wiping 10% out of my Table 2, and 10% off my Multi Fuel Flow Rate, eliminate my cold start fudge, and re-tweak the VE table?

It's important to understand that any VE fuel model is only a model and hence some level or inaccuracy can be expected. For this reason alone you can expect to need slightly different values in the second VE table. Then of course there are the very minor effects on the actual VE that can be expected from moving from gasoline to E85. Lastly as Adam mentioned, you can expect the injectors to flow less on E85 compared to gasoline due to the viscosity of the fuel.

Generally with the modelled multi fuel mode I find that the off boost areas of the second VE map end up quite close to the first VE map (perhaps within 2-5%) however as you transition onto boost the error seems to be a little worse, requiring perhaps 5-10% larger numbers. This is obviously hard to correct with injector flow alone. In your case if you're seeing a consistent 10% variation then you could do a pretty good job of rectifying this with the injector flow on your second fuel.

As with a lot of tuning topics, there's no right or wrong way to go about this. Potentially addressing the error in the second VE table may give you more control because you then have the ability to use the blend ratio table to address any error that creeps in between your two fuel blends (while this table should in theory be linear, often the blend deviates slightly in my experience).