Dutch
Veteran Member
VW reports the mass air flow in mg/stroke(?) while manufacturers like Bosch and Pro-Flow report in kg/hour.
How do I convert one to another?
How do I convert one to another?
kg/hour conversion for air mass
- Thread starter Dutch
- Start date
GeWilli
Top Post Dawg
milligrams to kilograms is the easy part
that is a straight conversion.
The Revs to hours can be done.
R is rotation of the shaft per minute - convert that to an "instant" number by saying at X revs it turns (x)*(60) times per hour or -- value per hour . . .
make sense? Now I htink I might have confused myself . . . I'll play around with it but I think it should be a matter of factoring and coverting revolutions into hours . . . and since you can't really get a good instantaneous value over an hour the mg/rev is a more sensitive measurement and possibly why VW uses that instead, allowing for more precise regulation.
that is a straight conversion.
The Revs to hours can be done.
R is rotation of the shaft per minute - convert that to an "instant" number by saying at X revs it turns (x)*(60) times per hour or -- value per hour . . .
make sense? Now I htink I might have confused myself . . . I'll play around with it but I think it should be a matter of factoring and coverting revolutions into hours . . . and since you can't really get a good instantaneous value over an hour the mg/rev is a more sensitive measurement and possibly why VW uses that instead, allowing for more precise regulation.
Dutch
Veteran Member
Did some calculations too:
Suppose the engine is doing 900RPM.
That's 900/2*4=1800 strokes per minute or
108,000 strokes per hour.
- factor 2 because of the 4-stroke operation:
one active stroke every 2 cycles
- factor 4 because of the 4 cylinders
Suppose I read 340mg/stroke from the ECU at idle
That's 340mg/stroke*108,000strokes/hour=36.7kg/hour
Let's check:
1.9l engine at 900RPM
1.9l*900/2=855 l/min => 51,300l/hour
Air is 1.29g/l so 51.3*1.29=66.2kg/hour(?)
Error of a factor 2 because I have to calculate 900*4=3600 strokes per minute or is the cylinder air pressure when the intake valve closes 36.7/66.2=0.55 bar?
I think the latter. Looking at the TDI data of an AFD engine (tdi-technik-eng.pdf referenced many times in this forum): 75kg/hr at 1300 RPM.
1300RPM/900RPM*66kg/hour=95kg/hour That's to much. That can't be true because at 1300RPM the turbo is doing at least something, resulting in more than 95kg/hour.
With the same pressure: 1300RPM/900RPM*36.7kg/hour=53kg/hour
With 0.78bar in stead of 0.55 due to turbo: 0.78/0.55*53=75kg/hour.
And 75/53*340=480mg/stroke at 1300RPM doesn't seem to be way of.
Who can confirm this or show the correct calculation?
Suppose the engine is doing 900RPM.
That's 900/2*4=1800 strokes per minute or
108,000 strokes per hour.
- factor 2 because of the 4-stroke operation:
one active stroke every 2 cycles
- factor 4 because of the 4 cylinders
Suppose I read 340mg/stroke from the ECU at idle
That's 340mg/stroke*108,000strokes/hour=36.7kg/hour
Let's check:
1.9l engine at 900RPM
1.9l*900/2=855 l/min => 51,300l/hour
Air is 1.29g/l so 51.3*1.29=66.2kg/hour(?)
Error of a factor 2 because I have to calculate 900*4=3600 strokes per minute or is the cylinder air pressure when the intake valve closes 36.7/66.2=0.55 bar?
I think the latter. Looking at the TDI data of an AFD engine (tdi-technik-eng.pdf referenced many times in this forum): 75kg/hr at 1300 RPM.
1300RPM/900RPM*66kg/hour=95kg/hour That's to much. That can't be true because at 1300RPM the turbo is doing at least something, resulting in more than 95kg/hour.
With the same pressure: 1300RPM/900RPM*36.7kg/hour=53kg/hour
With 0.78bar in stead of 0.55 due to turbo: 0.78/0.55*53=75kg/hour.
And 75/53*340=480mg/stroke at 1300RPM doesn't seem to be way of.
Who can confirm this or show the correct calculation?
GeWilli
Top Post Dawg
I'm not seeing where you are taking in boost quantity?
1 rev = 2 cylinder fillings
these things use the MAP more than the MAF for fuel quantity it seems. . . air volume will be easier to calculate from the MAP data I would think . . . no?
1 rev = 2 cylinder fillings
these things use the MAP more than the MAF for fuel quantity it seems. . . air volume will be easier to calculate from the MAP data I would think . . . no?
Dutch
Veteran Member
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> 1 rev = 2 cylinder fillings <hr></blockquote>
Yes, so 900RPM is 1800 strokes or cylinder fillings per minute.
I don't know how to do calculations with MAP.
I think boost will have to be taken into account at higher RPM's. My 110hp TDI does somethink like 1000mg/stroke at 3000 RPM WOT.
For that you need about 1.6 bar in the cylinders at valve close and 2 bar in the manifold. 2 bar is the maximum manifold pressure if I'm right.
I'm still struggling a little with the numbers. Not sure I'm correct. Have to get a labtop and run the vagcom while driving.
Yes, so 900RPM is 1800 strokes or cylinder fillings per minute.
I don't know how to do calculations with MAP.
I think boost will have to be taken into account at higher RPM's. My 110hp TDI does somethink like 1000mg/stroke at 3000 RPM WOT.
For that you need about 1.6 bar in the cylinders at valve close and 2 bar in the manifold. 2 bar is the maximum manifold pressure if I'm right.
I'm still struggling a little with the numbers. Not sure I'm correct. Have to get a labtop and run the vagcom while driving.