Can't say I agree with the IAT vs CHT comparison. CHT is an air mass requirement due to low efficiency when cold. IAT affects density and to a lesser extent flame propagation speed, but in opposing directions.
Flame propagation is a difficult topic and can not be generalized that easy. There some more physical effects that have impact on flame propagation e.g, air-gas mixing in the combustion chamber, wall wetting, speed of the gas that passes the intake valve, valve overlap.
IAT reaches 60°C when the engine is idling for 30min at 10°C ambient temperature.
Once warmed up your CHT is within its normal range and has almost no effect on the engine's efficiency and can be considered constant if your thermostat and fan system are working effectively.
Talking about efficiency related to idle makes no sense !!
We better should talk about friction during idle and how to reach equilibrium with the power that the engine produces for a certain idle speed.
Because you won´t reach a steady state condition for engine friction while idle in the first 30 minutes.
If the engine reaches 90°C other things are still continuously warming up e.g. oil, pistons, valve train, all kind of bearings...
And also there are things that have indirect impact on the idle friction of the engine what´s about hydraulic steering, what´s about a cold and a warm alternator ...
And if you drove for a while some things will cool down again...
Higher Temperature could mean some things have a higher friction and some less.
And what about the things that have an even more indirect impact on the idle speed, i mean does the idle valve has the same gap at 10°C and 40% duty and 60°C and 40% .. apparently not..
At which point the IAT value comes into things. Higher IAT = less dense air, and it's quite likely that the same opening on the valve represents lower air *mass* flow. Fair enough. I'd like to see your results without IAT coming into the mix, though. The first step is a curve of CHT vs PWM duty.
In my opinion at test for this should be obsolete regarding to the things i explained earlier.
The first step is a curve of CHT vs PWM duty.
From this alone you can get a pretty good idle situation.
No, not for every engine !
This is also absolutely required for PID idle control. Another thing that's absolutely required is a matching RPM target curve.
All of this assumes fixed timing. I know you can control idle with timing, and I know timing has an instantaneous effect, unlike airflow changes, but it's more "advanced" than what we need to start with.
But i want to point out that every OEM is using spark advance or Idle !
For example my OEM ECU (Siemens FENIX5) spark advance at idle for (-10°C IAT and -10°C CLT is 22°) and (20°C IAT and 90°C is 4°) at sudden a engine load change Spark goes up
from 4° to 12°.
In any case I have two things to say:
1) You'll make a great tester for this stuff.
2) You have a bigger problem, which I'll solve first for you. (60-2 efficiency and start-up etiquette)
cool ! can't wait to test it !!
What size injectors?
Also have you verified that with IAT vs fueling zeroed out, after idling for a little bit that the fueling does or doesn't change even if the IAT starts going up? A lot of people don't notice that the IAT vs fuel correction table is pretty terrible as setup from msextra orginally
IAT vs fuel correction is a fucking stupid idea in the first place and can *NEVER* be right. Good call, though. I had assumed he meant OEM control. But perhaps he meant on M$2 for all of it, not just the bit he mentioned M$2 next to
We have to stay focused ! arguing about physical impacts won't help us to produce a stable idle control.
The best proof that theoretical thermodynamics is not working as it planned is this "MAT Air Density table " in the M$
OEM´s have realized this decades ago i saw a SAGEM S3000 correcting the fuel from 0 to 20% in 30 seconds like nothing ... based only on small band Lambda
MAT vs CLT correction *facepalm*
I think we should concentrate our efforts on the tools we have to determine correlations with idle speed and this on an empiric way !
The physics in engines differs from each other so there is no way we can keep up with this in a scientific way