Air density correction - new method

[TheSilverBuick]

Just as a data point. Running the MS2 B&G code for years, and more recently the latest MS2/extra code as it comes out. I live at 6500ft, often drive to sea level and occassionally higher. Run from single digit *F to triple digit *F. I have a second baro sensor for real time corrections. My intake air temp sensor is a plastic open element GM part held in by a rubber grommet behind the air filter in the air filter housing on an old Buick V8. I've never had any problems maintaining AFR's at the same load/rpm point once I calibrated my baro table at every ten or so kPa increase in atmospheric pressure (as I drive off this mountain, I've datalogged atmospheric pressures from 65kPa to 103kPa). The intake air temp sensor reads what I'd expect for engine bay heat. When the air temps are below freezing it reads in the 30's*F or lower and when the temps are above 80* it gets upwards around 110*F-120*F.

[braineack]

I feel the current method is just fine the real issue is the sensor location. I moved my sensor to right after my air filter and retuned the truck and it ran great when I tuned it at 20degs and checked it again at 75degs and the AFR was almost perfect. The amount of heat that the air absorbs will stay consistant for a given air volicity so the VE table will take care of the heat the air asorbs. This is with a 2.3 turbo ranger running 30psi of boost,water/meth injection. The truck is driven daily 150 miles a day and has 90,000 miles of mega squirt driving. It just recently passed emisions with the sensor by the air filter .

I moved my AIT sensor just aft of the intercooler, from just behind the radiator, just before the throttle body.

While this did indeed help, I can still watch my AIT sensor climb 10-20-30-40° AFTER the motor has been shut off. Because of this I must use the MAT corrections table to cancel out any effect the ideal gas law code wants to pull. Even if I idle for 10 minutes, the temperatures still wont drop off unless I'm actually cruise, as there is no enough flow across the sensor to drop the temps back to ambient. Even assuming the temps are legit in reporting back the the MS, the code is too aggressive.

This works fine to correct this issue of hot restarts, but, without the ability to decay the corrections off, when I'm in boost I overfuel fuel like crazy depending on the ambient tempertures outside. It is especially apparent if I'm strapped to a dyno. Because I have the MAT corrections table configured in a way to add back fuel when the temps climb, it dumps in extra in boost. coupled with a hit day where ambeint might be 90-100*, the additional 10-20° the turbo adds just wastes gas.

MSI had the ability to decay the clt-based air density corections table (set to AIT) which is what I always used without an issue, but MS2 and MS3 do not have the ability. This is the only sore-point I have with the MS...hot restarts are elegant and the solution I use is a band-aid that causes other issue.

[racingmini_mtl]

Even assuming the temps are legit in reporting back the the MS, the code is too aggressive.

I might be annoying with this but saying that the code is too aggressive doesn't make sense. Physics is what it is.

So while I agree that the results are not what they should be, you have to realise that the problem is not about using the correct equations for a physical property but rather how anything around this might be skewed in some way or for some reason. So thinking about it this way and wording it accordingly will be more useful in solving this issue.

And by the way, talking about the ability to decay corrections off does make sense.

Jean

[SvenCS]

And by the way, talking about the ability to decay corrections off does make sense.

Does not the MAT corrections table effectively already do this? As your heat soak temps start coming back to normal running temps the amount of correction also reduces back to zero - assuming the curve is set to start adding correction above a MAT temp appropriate for that particular days ambient temperature.

[braineack]

Even assuming the temps are legit in reporting back the the MS, the code is too aggressive.

I might be annoying with this but saying that the code is too aggressive doesn't make sense. Physics is what it is.

So while I agree that the results are not what they should be, you have to realise that the problem is not about using the correct equations for a physical property but rather how anything around this might be skewed in some way or for some reason. So thinking about it this way and wording it accordingly will be more useful in solving this issue.

And by the way, talking about the ability to decay corrections off does make sense.

Jean

I absolutely understand this point, and have already talked it over with Ken at large in the past. Dunno what else to say or how to put it; it's just my experience. moving the ait to outside the engine bay was a vast improvement, going to seq injection and being able to idle at 16-17:1 helped even more ;)

[jsmcortina]

Recently I've exposed the actual air density calculation as a tuneable curve: http://www.msextra.com/forums/viewtopic.php?f=125&t=46816

I still think that the MAT/CLT concept has to have some merit, even though it seems nobody has yet had much improvement with it !

One factor that might be throwing off testing is that the VE table and warmup will almost certainly need re-tuning once MAT/CLT is enabled. We all seem to agree that the air in the cylinder just before the intake valve closes has to be a different temperature from the measurement on the MAT sensor. With regular non-alcohol fuels, this actual temperature is going to be hotter than we measured.

1. On a cold day with a cold engine at startup.
Say 0C outside temp, and 0C actual temp.

2. On a cold day with a fully warmed up engine and a remote air temperature sensor, there will be a large difference at low rpms.
Say 0C outside temp, and perhaps 100+C actual temp.
At at theoretical zero rpm, the ingested temperature will surely be equal to the engine temperature. Heywood cites an example of modelling an intake manifold as a 1.4kW heater.

3. Same deal at high rpms
Say 0C outside temp, and perhaps 30C actual temp ?? (guess)

The difference between 1 & 2 is presently handled somewhat by warmup enrichment. We have to apply a lot of WUE when cold in part due to this airdensity difference. EDIT: Not sure WUE will be any different.
The difference between 2 & 3 is presently handled through the VE table.

2 & 3 in particular highlight what I think I'm getting at. Our air temp sensor still says 0C, but the actual temperature ingested is wildly different. (24% absolute.)

Using MAT/CLT would likely alleviate a lot of the low rpm or idling "heatsoak" issues because the air temperature (it seems) is already dominated by the engine temperature. If we've already tuned for that reading and set the MAT/CLT curve to take little account of outside MAT at low revs, then the impact should be greatly reduce.

Perhaps the curve should be MAT/CLT% vs. air flow.
air flow = MAFMAP * RPM or MAP * VE * RPM depending on the algorithm in use.

However... all of this needs testing. Testers would need to start from a guessed MAT/CLT curve. 100% CLT at 0rpm to 100% MAT at infinite RPM. What are the numbers in between?? Then re-tune WUE and VE. Then see how it behaves in hot traffic and hot vs. cold days.

James

[Peter Florance]

A little late to the party but I'm wondering if a correction table by load might be helpful.
On a turbo car with water to air intercooler, you may be limited on MAT sensor location. The engine could suffer terrible heatsoak at low load and therefore require a modified air density correction value.
At high load with mass flow large enough to overcome engine heat, the normal correction might work ok and yield predictable AFR under boost.

[Matt Cramer]

A little late to the party but I'm wondering if a correction table by load might be helpful.
On a turbo car with water to air intercooler, you may be limited on MAT sensor location. The engine could suffer terrible heatsoak at low load and therefore require a modified air density correction value.
At high load with mass flow large enough to overcome engine heat, the normal correction might work ok and yield predictable AFR under boost.

I've been trying to work out this mathematically, and it looks as if you could come up with a curve adjustable by two points that would use IAT, CLT, and mass flow readings (or for speed density setups, a sort of "reverse MAFMAP") to calculate a projected "real IAT" number from that data. I had sent James a file on how such an algorithm would work.

At least in theory... we've been thinking about testing out how well the curve actually works on our 5.0 Mustang, which has some big heat soak issues.