Lean burn engine (E85?)

[serialk11r]

Originally Posted by Juho

BMW N43, N45 and N46 engines atleast are running on 105 to 112C coolant temperatures.
112C being an "eco mode", while the temperature will drop to 95C when going high load.

So it's very possible to run without major issues at higher temperatures.

I could possibly try at some point +100C coolant temperatures, if the thermostat just allows it.

You may want to make sure that the ECU won't retard ignition timing at 112C.

[Juho]

Yes, good point.

I have already modified the ignition retard / coolant temperature / intake air temperature map, so it doesn't retard ignition untill more than 60C intake air temperature or more than 110C.
But testing up to 112C, if the thermostat only allows that, would of course require zero'ing the ignition retard @ 110C or adjusting the temperature value higher.

[Juho]

Sadly, no progress at all on avg. fuel economy.
Even though it is now possible to maintain the speed as low as 6-7l/100km momentary fuel consumption @ 100km/h.
This is mostly because I retarted intake cam as much as possible (120 centerline, instead of around 106-110).. vvt (vanos) is great, when it works. I did service both; intake and exhaust vanos. New seals and rings.

And did try as lean as lambda=1.30 at 60-70km/h and up to 1.40-1.45 at 100km/h accidently, when I tested my alpha-n maps (maf not connected) .
- lambda=1.30, no missfiring but lacking power -> maybe could try more advance or intake cam advancing?
- lambda=1.40 still no missfiring, but even less power, so no benefits.. also could try different ignition advance and intake cam advancing
- lambda=1.45, missfiring, but there is that possibility the bank 2 (4-5-6 cyl) is running even leaner so not saying the lambda=1.45 is the limit as for missfiring.

Did try, and currently running the NGK BKR6EQUP spark plugs which are platinum plugs.
Platinum should work as a catalyst for ethanol, but I'm quite sure I don't have enough compression and/or heat to cause pre-ignition because of platinum.
I did notice the engine not being as sensitive for random missfiring, but that may be because of their different design versus Bosch FR7LDC+

Main problem is the engine being a bit unstable on power output.
It can maintain sometimes speed (100km/h) as low as 6l/100km momentary fuel consumption and starts accelerating when more throttle given, so the momentary fuel consomption is 8l/100km.
I haven't yet figured out what is causing that. If I had possibiliy to record in-cylinder temperatures and pressures, maybe that would help me.. but not possible on my budget and limited time.

Anyways, I'm quite sure I've hit the limit where I need to start doing mechanical changes to improve my fuel economy which isn't too bad.
Increasing engine tempereture did not improve fuel economy 'at all', which is actually quite odd. And I haven't been able to reach higher than 96C at 100km/h or even at lower speeds because the engine doesn't seem to build heat at lean burn mode as much (cruising at low/moderate load).

It should be very interesting to test with high compression ratio and faster squish velocity, if I it would be possible to run the engine succesfully with leaner than lambda=1.40

But I do need a standalone ecu and two wideband lambda sensors, because:
1) no safety features, what may already be fooling me and limiting fuel economy gains because fuel trims are limited to +5%, and running the engine fuel trims maxed out to achieve lean burn (not possible to adjust target afr on Siemens MS42)
2) both banks require logging, since the engine will be near missfiring when going very lean mixture, and only standalone ecu can work at that (to keep the mixtures stable enough)

Luckily there is cheap standalone ecu available which is near 'plug and play': speeduino for m52tu/m54.
Other benefit is I can throw away the MDK throttle body and go mechanical (which isn't good for FE tho but reliability: yes), which has caused some problems earlier and not really trusting it.. if the MDK fails = goes limp home mode 2: the car won't move faster than 10km/h if at all.

[serialk11r]

Do you wanna post some tables from your ECU? My hunch is because you have double VANOS, the engine probably has considerable internal EGR, which limits your ideal lean-ness. Maximum efficiency would come from retarding the intake cam quite a bit, and running as lean as possible.

A small amount of residual exhaust gas can help bring temperatures up and help ignition, but the more EGR there is, the smaller the temperature change and the slower the mixture burns. Whatever is left in the cylinder when the exhaust valve closes is probably all you want.

[Juho]

Yes, of course.

Stock maps:



Modified (14-06-2021):



It seems to be very difficult to tune this engine, possibly because of the ecu safety features?? which I am unable to trace if there are any active when noticeable power loss is present.
Today, on the morning I thought my changes made it worse - again.
When I started again later, and started driving back to home the engine was working a lot better and fuel consumption was at some point quite good and was able to hold the speed even at 6-7l/100km momentary fuel consumption (not always tho) and around 70-80km/h was steady at 6l/100km.

About hour later, again same thing, much worse fuel economy.

Logging could be possible, but for some reason the software seems to freeze sometimes after 5-15min logging and won't work untill I start it again after waiting about 10min or more, having obd2 cable disconnected from car.
I do have quite a lot of log files, and every single log file tells the ecu follows exactly the ignition and fuel maps, so the random powerloss shouldn't be because of safety features.

Another possible reason is DISA, which is a simple vacuum and solenoid controlled flap closing and opening intake manifold section depending of rpm.
It should be closed at below 4000rpm, but my DISA has a small vacuum leak so it doesn't work.
I did "fix" it to try if there was any effect; only noticed worse fuel economy because it required more throttle.
But it failed after a short time again.

I do have a theory, that the DISA may suddenly close/open, causing odd behavior. Since the problem is it doesn't hold vacuum well enough.
Another possible reason is MAF signal is bad / incorrect randomly.

[serialk11r]

Stock intake VANOS looks completely fine to me. You may consider retarding the first 5-7 columns a little bit to stabilize lean burn. I would set the first column to 120 down to 3500rpm and then gradually drop it to 112.5.

Exhaust I think you have the right idea, though I don't understand that little 100.12 island. I would keep the last 3-4 columns stock, and basically shrink that blue/purple island towards the right since you don't need the exhaust dilution to reduce your pumping losses anymore. At medium load, a little bit of overlap is helpful for raising charge temperature and combustion speed. E.g. at 2500rpm, I would set that row to something like 105 105 105 102 100 97 94 92 90 90 92 95.

[Juho]

Thanks for the advice, I'll try that and let you know how it works.

The 100.12 island is actually small accident, when I tried 105->100 (turns into 100.12)->90.
Earlier tried even 82,5 , but it was clearly worse in every section expect around 4000rpm at more than half throttle went lean and caused small missfiring -> something changed because needed more fuel.

[Juho]

- worse fuel economy, mostly around 9-10l/100km at 100km/h
- atleast by feel not noticeable more stability, requires quite a long time before the fuel consumption drops to around 8l/100km at 100km/h

So the engine doesn't seem to like intake timing around 110-116.
120->116 and fuel consumption increases.

It's happy around 100 and 120 centerline. Atleast based on my testing (not enough, tho!).
I might remember wrong, but at 120 timing it was easier to reach less than 8l/100km momentary fuel consumption.

Another odd thing is, that when I had the thermostat broken, I reached 7.9l average fuel consumption and coolant temperature was around 82-83C.
If I remember correctly.

Higher than 96C is not possible without grill block.
I have the thermostat set at 105C low load, and I was able to log radiator outlet and coolant temperature sensor readings.
Based on that, thermostat was not open; radiator outlet temperature was around 70..75C. Fan starts spinning +90C outlet temp.

There is the possibility, that with aftermarket ecu I could be getting very different results since I cannot be 100% sure the Siemens is not activating some kind of safety modes.

Another thing I really should check, how free the wheels etc are actually spinnings.. how much drag is coming from the complete drivetrain when driving:
Rear differential oil
Gearbox oil
Bearings ?? (rear right is making noise, replacing by the end of month)
Wheel aligment (not good, adjusting when I replace tie rods (tie rod nut is rusted and couldn't open with little bit of heat; easier to just replace than heating them until red).. also by the end of month)
Aero ?? Still haven't got the full undertray.. maybe I'll just fabricate my own, they cost a bit too much for plastic that probably breaks in less than 1000km because of unbeliveable ****ty roads..
Tires, used Michelin energy saver 205/55R16

And for engine modifications, I think better fuel atomization could help at lean burn even more.
I've been looking at Bosch EV14 373cc/min@3bar injectors that have 12 hole spray tip and sprays split in two ways.

Stock injectors may already be quite bad already.
Bigger injectors mean shorters injector pulse widths, so that is not a good thing. But small injectors are restricting cold start enrichments, which is a problem for ethanol engine when it's very cold (like -20C ... -25C)

[serialk11r]

Er, did you run more lean? I don't get why your exhaust map looks like that at all btw, why don't you start with the stock one and change the cells one by one?

You basically want to shoot for ~3-5% hot exhaust dilution (typically the OEM shoots for 10-20% on a double VVT engine) and as high of a lambda as possible. It's like running a high cooled EGR dilution rate but with air.

That's however assuming you have free control over lambda and are able to run richer at very low loads where fuel isn't burning as quickly. If you are limited to a lower lambda for practical reasons, then you want a little more exhaust overlap. At any given speed and load, you know you've reduced internal EGR if you reduced overlap compared to stock, so I would look at the maps in "difference" mode.

[Juho]

I'm getting random missfiring when I lean more, and it gets a lot more unstable (probably due to missfiring but not as much to be noticeable enough expect as loss of power).
Lambda=1.25 +/-0,05, what I'm running, and low load (100km/h 130..150mg/s) about lambda=1.10-1.15 since it didn't seem to have any negative effects compared to lambda=1.05.

I did drive most of the time with stock vanos maps, before doing anything for them. Only ignition and fuel maps modified for lean burn.

What I'm most interested, is how it works at 100km/h since it seems to be more difficult.
Load is 165-225mg/s and 2500-3000rpm maps are most commonly used cells at 100km/h
Sometimes 130-150mg/s, but usually not possible to keep the speed around there.

Exhaust advanced to 105 has been so far most stable at low loads (<150mg/s) at higher speeds, so that's why I set it up to 105 at low load.