converting VE% to engineering units

[MICK]

Hi,

Does anybody know a formular for converting VE% into engineering units.


cheers

mick

[Alvin]

Hi,

Does anybody know a formular for converting VE% into engineering units.


cheers

mick

Effeciency will not have a unit.

[redhardsupra]

yea except that our VE isn't a real volumetric efficiency, there's like temperature in there and some other things that don't quite cancel out.

[MICK]

yea except that our VE isn't a real volumetric efficiency, there's like temperature in there and some other things that don't quite cancel out.

Thanks for your reply. I have been checking out a few other excell spreadsheets that you have put together. Their pretty cool.

I can look at the relationship of a pre set figure and compair the differences (VE % TO Engineering Units) and form a table but its not quite as good as crunching the numbers in a formular ( if one was available).

So my question is. If I were to built a crossover table it would only be as good as the detail I put into it. Could I use this in a spread sheet that I have made and use it to convert VE% to Engineering Units....?


Really like the work you have done redhardsupra. Do you have any thoughts here.

cheers

mick

[redhardsupra]

yes, that's why i'm so anal about keeping things as constant as possible. i've seen changes based on fuel temperature, cooling capacity, variances in battery voltage, and other things that noone usually monitors, yet introducing 'noise' that we cannot account for emprically. having solid hardware really cleans up your signal and limits variation in your data, yielding better, more consistant results quicker.

if you wanna see the formula involved in getting the VE numbers read the 've table cracked' sticky in the pcm section on ls1tech.
i've been thinking of building a probabilistic model just to see where the biggest variances are, so we could locate the biggest sources of noise.

[joecar]

If you're reading the VE table from flash, you can select it's data units to be g.K/kPa.

From the units you can see that it's not really VE, but rather airmass scaled for absolute temp and pressure.

[superls1]

There are 4 views of which can be selected when viewing the VE table in EFILive:

• g*K/MAP
• % of Theoretical Maximum
• g/cylinder
• g/second

The last two options, g/cylinder and g/second, allow an additional attribute to be considered which is Temperature. The default value appears to be 21* C.

EFILive indicates the formula for g/cylinder to be:

g/cyl = VE * MAP / charge temp

VE is in g*K/MAP
MAP is in kPa
Charge Temp is in kPa

So in units,

g/cyl = g*K/kPa * kPa / K

g/cyl = g

EFILive indicates that charge temp is calculated as:

273.15+IAT+((ECT-IAT)*factor)

Where IAT and ECT are in C

Factor is a value that can be modified through EFILive. They indicate a range of 0 – 2 in which a value close to 0 will favor/bias IAT.


My problem with the VE Table Cracked Thread is that nothing was ever resolved in that discussion. Here are some of the formulas posted in that thread:

Posted by NoGo

VE = ((massflow * IAT / (MAP * RPM * Displacement))

Massflow: grams/sec
IAT: Degrees Kelvin
MAP: Bar
RPM: Duh!
Displacement: Cubic Meters

Posted by gameover
The PCM g/cyl calc for the VE table is:

g/cyl x 8192 = VEvalue * MAP * 51.2 / (IAT * 32)

Posted by HumpinSS

Nogo'sve% = MAF.gp/s*(IAC+273)/((346*RPM)*MAP)*212544

gameover's = Ve= g/cy * ((IAT+273)*5120)/MAP(kpa)/cyl colume/178 derived from original formula of

ve . (178.33) . (0.708 . map / (iat+273) . 5120 = 0.85 g/cyl

Posted by DVCrazyCamTAWS6

this is the expression i'm using to crack the VE in EFILIVE
({SAE.J1979.MAF} * {SAE.J1979.IAT} / ({SAE.J1979.MAP} * {SAE.J1979.RPM} * 0.0059))

0.0059 = 364ci 6.0L
0.0056 = 346ci 5.7L

Must Set PIDs to : (or will not work)

MAF = UNITS- Grams/Sec, FACTOR - 0.010000, OFFSET - 0 (limits = 0 to 530)
IAT = UNITS- Kelvin, FACTOR - 1, OFFSET - 233.15 (limits = 0 to 500)
MAP = UNITS- BAR, Factor - 0.010000, OFFSET - 0 (limits = 0 to 1.0500)

Expression : (MAF x IAT x / (MAP x RPM x DISPLACEMENT))

And there were a couple references to this VE calculation

[blandmiller]

So, if I am reading this right:

The first view is actual flow
The second is true volumetric efficiency
The third is volumetric flowrate
And the last is mass flowrate

How do you change between the various views?

[superls1]

I don't think any of them are 'truly' VE. They all have mass in them. GM's model is more 'mass-centric' as opposed to 'volume-centric'.

The good thing is that a percentage is a percentage no matter what. So, no matter your view if the PCM needs to add 10% more fuel to achieve a desired AFR you simply need to add 10% to the number in the table. The frustrating part is that if you are someone that wants to know 'how' it all actually works it is fairly complicated, and in reality you need some engineering background in: computational methods (regression, dimensional analysis, etc), thermodynamics, compressible flow, etc.

To change display units, Menu Edit->Properites (shortcut is Alt+Enter)

[blandmiller]

I have the Engineering background covered. I have just never calculated VE with any mass associated. VE has always been a percentage of theoretical maximum.