Lean burn engine (E85?)

[Isaac Zachary]

The whole "lean is hot" and "rich is cool" theory isn't always correct. Leaner than what? Richer than what? What engine?

There is a point, usually around stoichiomentric, that an engine will be more prone to detonation. The leaner you go past that point the cooler the burn and the less pinging you'll get.

Engines never have a completely homogenous air/fuel mix in the combustion chamber either. Even with port fuel injection there will always be lean and rich spots. How the head is designed can help move those spots into places they don't make as much of a problem, like keeping it rich over the hot exhaust valves instead of a lean pocket over them. So the average AFR point of detonation is different for each engine due to these variences.

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

The whole "lean is hot" and "rich is cool" theory isn't always correct.

That's why I said "most often" instead of "always".

But anyway, also considering Christian von Koenigsegg's claims that Freevalve tech could enable a port-injection engine to run on Diesel fuel, I must confess I still take that claim with a grain of salt, yet a port-injection engine working with a controlled self-ignition is always interesting to say the least.

[djr48312]

Originally Posted by Juho

Hey, I decided to finally register here after a while just reading threads and posts that I found interested and perhaps here I can get and share more information related to what I think would be 'the key' for best fuel efficiency on engine modifications; lean burn.

Lean burn is an old invention, and what I've understood so far it could be possible to run with lambda = 1.40...1.60 if the combustion chamber, ignition and perhaps some amount of egr.. help enough with burning that lean mixture.

E85 is interesting atleast in my thoughts, and I've been running most of my vehicles with E85. Quite hard to cause engine knocking, works with ridiculous compression ratios and is cheaper than gasoline - but not enough to save any money if the fuel consumption is 25..30% more than with gasoline like it usually is.

I have been testing my current daily driver; BMW 523 E39 '99 w/ 5spd manual that I actually bought because it's easy and cheap to get ecu tuning without replacing it with aftermarket ecu (megasquirt or etc) or buying an emulator.
I have been driving around 6000km with only E85, and 2000..2500km of it with lean mixture while cruising at low load, so far no problems.

It's running on lambda=1.15 (+/- 0.05) and ignition timing at low loads is around 10 to 16 degrees more than factory tune.
2800rpm on 5th gear (100km/h gps speed) , low load = 45-48 degrees BTDC. Yes, needs a lot longer gear ratios.. way too much rpm for a 2.5 liter straight six engine.

Fuel consumption is currently about 10% more than with gasoline (95E10), which is quite good at this stage.

An interesting note:
- while cruising around 100km/h (gps speed) for more than 20km, the engine suddenly starts accelerating with same throttle amount, and I'm able to reduce the throttle so the current fuel consumption reads only 7-8 liters / 100km (true fuel consumption about 10% more than it reads) and then after a while it starts slowing down back to normal.

My thoughts are, it starts pre-igniting or it's getting fuel fumes from the tank, because of EVAP.
Spark plugs look good, no signs of knocking etc. I should actually be worried.
Pre-ignition may not be dangerous at part throttle, low load.
But I'm not the right person to tell that.. full throttle, yes - spark plugs gone.

There are some faults on the engine (and car) that should reduce fuel consumption more when fixed (hopefully soon), but after that I'm interested on going for more advanced modifications than mostly just ecu tuning.
I have a cylinder head from 2 liter variant, which has smaller valves, ports and combustion chambers.
I've already started modding it; welded combustion chambers and took the valve seats out. Bigger valve seats and valves coming, so it's possible to make the ports better.. intake port requires the most work since I'm trying to change it for 'high tumble flow'.

On factory lean burn engines, are there some clear differences in combustion chamber? Atleast Honda Insight has valve disable function(?) and intake ports made for swirl flow; which is quite odd for a 4 valve head (per cylinder) but understandable when it's disabling the other intake valve making it act more like a 2 valve head.
So in my case it's clear it's best going for tumble flow.

Compression ratio is another thing. Because I'm running the engine on E85, it's possible to benefit of quite extreme compression ratio.
I'm targeting to around 14 to 15:1 ratio, which should still work with the small cams.

Any thoughts/ideas?
If I find the previous threads related to lean burn engines with useful information, I'll post their links here.

Was your 1.15 lambda lean cruise on E85 considered a success? I have been figuring that E85 should be able to cruise on a more lean value that gasoline due to it's cooling properties and resistance to detonation.

[Ecky]

Originally Posted by djr48312

Was your 1.15 lambda lean cruise on E85 considered a success? I have been figuring that E85 should be able to cruise on a more lean value that gasoline due to it's cooling properties and resistance to detonation.

Gasoline really shouldn't have any problems cruising lean anyway. It's running just shy of stoich that's a problem, and the crossover from lean to rich. Lambda ~1.03 and above 70% load is the point to keep an eye on at typical cruising RPM.

[djr48312]

Gasoline can cruise lean as you say but shouldn't E85 be able to go to a leaner lambda value?

[Ecky]

Originally Posted by djr48312

Gasoline can cruise lean as you say but shouldn't E85 be able to go to a leaner lambda value?

I'm not certain, and I'd like to hear what others have to say on the topic.

Gasoline isn't knock limited going lean. Once you get past maybe lambda 1.05 or so, combustion temperature drops and emissions start to get clean (NOx drops). Catalysts don't work at this ratio.

At around lambda 1.3, most normal AFR sensors cease to read actually, which is what has always stopped me from running leaner. Honda uses sensors in their lean burn cars that read accurately to at least lambda 1.5, and the combustion chambers in those cars are able to combust at those ratios efficiently and reliably. I'm uncertain if ethanol can actually combust leaner, but it might just buy virtue of having more fuel per amount of air.

[cRiPpLe_rOoStEr]

As ethanol has a lower energy content, running leaner won't be so easy. I have never seen any car with a normal compression ratio actually running leaner on ethanol than it would on gasoline, not even the 2007 Chevrolet Celta that my mother had until 2014 which had a quite high compression that made it run poorly unless an extra amount of ethanol was added (just a remind, in Brazil it's mandatory that all gasoline has 27% ethanol) to "fix" the octane rating. It would lean just a little when more ethanol was added, but if it ran only on ethanol it would use a higher fuel volume.

[LostinTransit]

After we had the EGR valve replaced I've learn more about our van. it's clear that within the specs it says can run regular fuel and the e85 fuel.. so starting this weekend.. I'll be readjusting to running the efuels.. the reasoning here is after seeing both ports in the EGR caked up with carbon.. I suspect the efuels will attempt to clean out the engine. Though we'll suffer with fuel economy,.. the performance aspect will be greatly increased. one thing to is that because we removed the slat on the active shutter system.. I would if running the efules will make any difference. So now knowing I can run the efuels.. I'm looking forward to it once again. just have to be careful not to just top off the tank with 10.00 I need to wait till at least less than half a tank.

[cRiPpLe_rOoStEr]

Not sure if ethanol would clean up the EGR ports, but most likely it will decrease carbon buildup.