Tuning - using efilive & WB O2s, and EGT and CHT

[Gelf VXR]

Before I start I'll just say what I'm about to write is the culmination of my conclusions derived from searches on the web. Feed back and corrections are most welcome.

Tuning - using Efilive & WB O2s, and EGT and CHT

I’ve been searching on Google and on other forums, and there doesn't seem to be many people taking this route? I bought Efilive so that I could learn to tune on the road but never felt I quite got there. I’ve had varying degrees of success dialling in the MAF and VE map, non-conventional route (both together), getting my LTFTs nice and tight, but never felt happy with the feedback from the engine for tuning spark advance.

From what Ive read EGT's sometimes get written off as a tool because they have been used to dial in fuelling without much success (carburettors), maybe from before when WB's weren't so readily available? the stigma holds it seems. Monitoring CHT & EGT for the tuning is standard practice with aircraft engines, and CHT tuning appears to be popular in the carting world, lack of dyno facilities I suppose led to necessity.

So I'm away working with time to mull over the timing feed back problem when i came across an interesting article id seen before, attached.

"Effects of Ignition Timing, Equivalence Ratio and Compression Ratio on RDH Engine Performance"

The research on a spark ignited engine amongst other things demonstrated the effects of the above on IMEP, PICP, ISFC and EGT.

EGT reduces as IMEP increases to its maximum, or the Knock limit. However EGT alone can not pin point peak IMEP.

So further searching looking at EGT sensors drew my attention to CHT sensors and what CHT can tell you, like your AFR is tuned to maximum flame front speed, and timing at minimum for MBT, less time for heat transfer to the cylinder head.

So here goes, I wont to try and put together a 101 for tuning with Efi flash scan, WB O2, EGT and CHT. - Continued next post

[Gelf VXR]

Some important points to note

The melting point of aluminum is 660 degrees centigrade,1220F.

The operating temperature of the catalytic converter is 650~870 degrees centigrade, 1200~1600F.

Actual combustion temperatures are around 2000ºC or about 3630ºF.

Peak combustion temperatures occur at stoichiometric combustion, EQuivalence Ratio = 1 (AFR 14.63:1)

Peak flame front speed occurs at richer than stoichiometric combustion EQ≈1.1 (AFR13.5:1≈13.1:1)

Minimum Indicated Specific Fuel Consumption occurs at richer that stoichiometric combustion EQ≈1.1

Peak Indicated Mean Effective Pressure occurs at richer than stoichiometric, EQ≈1.1, peak flame front speed combined with minimum timing advance, means less chemical energy is used compressing the combustion mixture and maximum work is applied pushing down the piston with minimum heat lost to the exhaust.

Peak IMEP occurs at richer than stoichiometric combustion EQ≈1.1, because of reduced O2 available to convert CO to CO2, at stoichiometric combustion two CO molecules will absorb one O2 molecule to become two CO2, gas volume is reduced from three to two molecules reducing peak cylinder pressure. However, some chemical energy is lost to the exhaust, CO is a fuel and heat energy lost from combustion is released when oxidizing CO to CO2 in catalytic converter. This also explains why richer than stoichiometric combustion is cooler.

Peak IMEP occurs at EQ≈1.1, when Cylinder Head Temperatures are at minimum and Exhaust Gas Temperatures are at minimum, as a result of less heat transfer to cylinder head and less heat wasted to the exhaust.

Peak EGT occurs at EQ = 1 with too little ignition advance, peak combustion temperature with excessive heat energy lost to the exhaust.

For a commanded EQ ratio, EGT decrease as ignition timing advances, increments reduce closer to IMEP

For a commanded EQ ratio, as ignition timing advances either before and after peak IMEP, (too advanced) EGT will decrease notably with onset of detonation.

Peak CHT occurs at EQ = 1, peak combustion temperature.

CHT will decrease with leaner or richer EQ ratio, lean for economy and rich for power, because of lower combustion temperatures. (Pilots of smaller aircraft with air-cooled engines typically lean for economy EGT 38C or 100F lean of peak (stoich), and rich for power EGT 38C or 100F rich of peak (stoich))

For a commanded EQ ratio, CHT will increase with too much ignition timing advance, increased cylinder pressures and work on compression, pinging then detonation, leading to melted pistons.

It isn't actually the lean AFR that melts pistons as combustion temperatures are lower than stoich, it is the tendency to detonation characteristics of the lean mixture.

Maximum brake torque can be defined at the lowest combined value for ECT, CHT & EGT without detonation, for when the parameters for AAT and IAT are within defined values, for example AAT ≈ 15 C and IAT ≈ 25 C, as both will effect the final value of ECT, CHT & EGT.

[Gelf VXR]

Parts on order

EGT sensors x2
http://thesensorconnection.com/egt-p...ss_probe.shtml (non grounded as required for flash scan input)

CHT sensors x 2
http://thesensorconnection.com/cht-s...e-12-and-14-mm (grounded)

Display meter x 2
http://thesensorconnection.com/egt-p...gt_meter.shtml (with analogue output 0-5V for CHT to flash scan input)

[TDFDiesel]

Do you have an English version available as well?

[ringram]

Nice work mate. Ill be looking to see how you go with results.
You could try DVT controls on the Dyno to see if you can vary spark and monitor TQ while you are at it.
Id suggest a hub dyno would be best for that.

The roadrunner is ideal for the LS1, but the LS2 you need to look elsewhere.

How about monitoring g/cyl PID as you vary things? Id have thought if your airflow model is good that higher cylinder pressures would correspond also to higher g/cyl values..

[joecar]

Gelf, excellent thread

[Gelf VXR]

An interesting post on an Mitsubishi Evo forum tuning timing advance using EGT on a dyno. (Just a thought, the variance on the EGT he mentions could be the onset of detonation in some cylinders?)


http://www.evoxforums.com/forums/arc...p/t-61031.html
We started pulling timing until the EGT started to increase again and then slowly added it back in. we thought on the X, it is closer to 19-20* and realistically probably 20*.
The extra will make power still but the 4whp per degree will start the variance on EGT that we observed starting at 21-22*. We were down to 3-4whp per degree at that point so I left it at 19* and didnt bother adding in the extra timing.
Right now with good timing and the 11.0 we are observing-
1580ish (860*C) for 1-4
1620ish (880*C) for 2-3

[Gelf VXR]

Nice work mate. Ill be looking to see how you go with results.

Hopefully I can get some body else interested in making some trials as I'm stuck working abroad. Im very keen to get home and start logging

[Gelf VXR]

Progress is slow, getting my EGT bungs welded into the primaries in October when I'm back in UK for two weeks.

I found some useful calibrations in a 2008 LS2 HSV Club sport {B0812} & {B0814} for predicting CAT temps (EGT) from RPM vs airflow g/sec data and RPM vs EQ ratio data, using the GM data, Ive put it together with some other info from two research papers "Effects of Ignition Timing, Equivalence Ratio and Compression Ratio on RDH Engine Performance" and research paper SAE820050 "Comparisons of Thermocouple, Time-Averaged and Mass-Averaged Exhaust Gas Temperatures for a Spark-Ignited Engine. Ive created an excel sheet for predicting EGT for RPM vs g/cyl. I can not vouch for the validity of the predicted EGT without comparing to real world data, but the results don't look too unreasonable. Obviously there are limitations, you wouldn't see above ambient EGT's at 0 RPM.

With real world data comparison, regression trend formula data could be updated and it could become useful?

You can change variables for and see the effects of changes to commanded EQ ratio and timing retard or advance away from minimum best timing on predicted EGT.

[Gelf VXR]

So I had some time to log idle this week while I'm home in the UK to attend a few friends weddings.

I wanted to see the effects of idle timing on EGT (cyl 2&8), MAP, ETCTP, MAF, IPW (left & right).


Spark was set to the same value in Idle, Hi, Lo and Coast down calibrations, I used DVT to retard spark during logging, I let the PCM control the fuelling in closed loop. The idle hi and low spark were zeroed out, the PCM maintained idle rpm with ETCTP.

Some conclusions,

Advancing spark has a great effect on lowering EGT, the relationship is quite linear, but its not possible to determine MBT because EGT continues to fall even after advancing past MBT as more work (less heat to the exhaust) is done compressing the expanding ignited mixture.

I think that I should have zero'd out the minimum idle airflow during these logs to stop the PCM trying to predict airflow which caused the ETCTP to fluctuate at lower idle spark settings, causing variation in MAP and MAF.