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Calculated airflow as ignition axis


Dan Bailey

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Hi guys,

A couple of things which would be quite nice additions to "load" axis in fuel and ignition tables would be as the title suggests, calculated airflow - if not effective cylinder filling or something of that kind as an option for the ignition table axis... so for sake of argument, if you were using the modelled fuel equation mode then you could have MAP x VE as a load axis.

Another one which would be nice would be MAP / EMAP as an axis option for tables & logging.  I'm sure there were others which have occurred to me, but those are ones I'd definitely quite like if they were options :D


Thanks.

Dan

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Hi Scott, 

Calculated Airflow: Perhaps being pedantic, but having the option of doing a timing look up based on closer to the actual mass of air going into the engine - I guess mimicking a MAF setup.  There are 4d overlays which I do when tuning to deal with things which could effect VE from the base VE map "describes".  At this stage for the most part it's possible to just mimic the same adjustments by doing overlays of the ignition table as well, but if there was a way of having the ignition table look up done based off what the air mass / cyl calculation (so basically incorporating VE + 4d/5d table correction, MAP and IAT) to get look up into a singular timing table.  I figured it shouldn't be a huge wish list item as it is already a thing which appears to be calculated and can be logged.

 

MAP / IMAP: Is already an option with other ECU options on the market, VE table lookup is done based off a ratio of MAP / EMAP but the fuel calc done the same as it is currently.  I'll elaborate more when I have a bit more time, but it is another thing which seems to/sounds like it results in being able to dial in a nice tune easier - flattens out the fuel table and also becomes easier to update a map after mechanical changes

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Just out of curiosity, is the fuel runtime value "Air per cylinder measured" only a value from a MAF input, or is it calculated if using speed density (I don't have a working engine to check). You can span a table off that.

Or is the speed density calculated one "Air per cylinder estimated", which is not (currently) on the list of axis options?

or ... are neither the answer this thread is looking for?

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Hi Dan,

I've referred this on to the engineers, here is what they had to say:

The "Air per cylinder measured" parameter is a value only from a MAF input.

The "Air per cylinder Estimated" parameter is calculated from the MAP sensor. 

The engineers are happy to add "Air per cylinder Estimated" to the table axis options and will put it on the list.

Scott

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Hi Scott, thanks for the response - I was just getting back to this...

Yeah, I found that "measured" existed, but not "estimated".   

Actually, if it were an option (I just pulled estimated airflow/cylinder out because it was an existing parameter which was arguably a better load measure than just MAP) would be:

 (MAP x VE) / IAT

I think there are different "nicknames" for that by other brands, but it basically adds up as meaning that the ignition table look up is done off cylinder filling at that moment but is still semi-intuitive to work with as it is normalised - the airflow numbers would be relatively arbitrary by comparison.  Apologies for not making the first post a bit clearer in regards to what  was hoping to achieve.

Cheers,

Dan

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Actually, if it were an option (I just pulled estimated airflow/cylinder out because it was an existing parameter which was arguably a better load measure than just MAP) would be:

 (MAP x VE) / IAT

I think there are different "nicknames" for that by other brands, but it basically adds up as meaning that the ignition table look up is done off cylinder filling at that moment but is still semi-intuitive to work with as it is normalised - the airflow numbers would be relatively arbitrary by comparison.  Apologies for not making the first post a bit clearer in regards to what  was hoping to achieve.

The parameter name  "Air per cylinder estimated" would indicate to me that VE & Charge temp are probably already factored into it and will give you exactly what you are looking for.  Maybe Scott can confirm by trying a demo on his simulator by adjusting charge temp input only, then adjust VE only and see how/if they affect the "estimated air per cylinder" parameter.

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Absolutely, I understand that - so it'd be fully usable and do the basic thing I was looking for with minimal change, it's just that the calculation I showed gives a more intuitive and "consistent" number to work with.

For example, the load axis would end up looking a LITTLE like a KPA load axis with (MAP x VE) with scaling for temp correction...  well the way I pictured doing it.

So to just pull numbers out of the air... if your MAP was 202kpa, your VE was 110% and your IAT trim was +2% - perhaps you'd end up with 202 x 1.10 x 1.02 = 227 MagicLithUnits and it'd be a familiar looking scale... and one which would arguably be more portable, if you know what I mean?

On the other hand g/cyl is locked to that engine's displacement etc.  

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So to just pull numbers out of the air... if your MAP was 202kpa, your VE was 110% and your IAT trim was +2% - perhaps you'd end up with 202 x 1.10 x 1.02 = 227 MagicLithUnits and it'd be a familiar looking scale... and one which would arguably be more portable, if you know what I mean?

On the other hand g/cyl is locked to that engine's displacement etc.  

Interesting topic for sure and Im curious enough to try to understand more about it...    I'm not sure I agree with the "familiar looking scale" comment though.  For instance at idle and cruise - say where you typically have 50Kpa & 50% VE, then wouldnt your load axis number end up something like 25 - how would that be a familiar looking scale or more portable?  I can see how it will make the table flatter but that seems only because the axis scale has been exaggerated. 

Obviously airflow is the best load source but it rarely be practical to work with.  For instance how would you tune such a table?  With a more traditional load axis you can use a dyno to hold MAP and RPM constant to tune a cell but with this suggested load axis, your tuning cell would drift around as soon charge temp increases.

If you have some experience with another ecu brand that uses this strategy can you PM me the details just so I can try to understand better how they use it or what the idea behind it is?     

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Interesting idea. 

I see one big problem. If you change your VE Fuel Table, you change your ignition in the same time. Think that could be quite tricky to tune. And I'm wondering how consistent such a tune is. For example everyone knows the problem with heated up IAT sensor after a long idle period or warm start.  Of course it should be possible to tune such a model, but i doubt that it saves you tuning time. 

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  • 2 months later...

Random update on this as I was putting in some quality time looking at axis options... and I wonder if a suitable measure is already there.

- there is a parameter called Load (Abs)

- if one googles "Load_ABS"and SAE, there is what looks to be an extract from the SAE standard saying its basically an estimation of cylinder fill (takes into account MAP, standard baro and temp) (click here if keen)

- subject to engineering confirming, it is probably a good measure for ignition? 

Load (abs)

The estimated engine load as based on SAE standards.

If Load (Abs) is 100% this means the cylinder is 100% full at atmospheric pressure. If Load (Abs) is 200% this means the cylinder is 200% full (it has 1.0 bar of pressure above atmospheric pressure).

For Load(Abs) to work correctly the Engine Capacity must be set correctly and the ECU must have a working calibrated MAP sensor.

 - while it can be selected as a fuel axis, I can't see how it would work as I think VE is an input into Load (Abs).

 

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