Good video, well explained Rich/Lean burns...
Running Lean versus Rich - Engineering Explained
- Thread starter StevieC
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I like those EE videos, most of them are quite interesting to an amateur car guy like me.
Throw in iron big block with iron heads and you get another problem. Heat retention. Back in the day a great engine tuner was worth his weight in gold.
This topic is why I like to build my engines with a tight quench distance. (piston-to-head clearance) The flat areas of the cylinder heads exposed to the cylinder and piston are the quench areas. I like to get that clearance down to around .035-.040" as the tighter the quench, the more air/fuel gets squeezed out of that area toward the chamber, creating more turbulence in the chamber, and increasing combustion efficiency. I can run the engine leaner with less chance of knock. I've also noticed the tighter the quench distance, the more responsive the engine becomes.
I think this also only applies to gasoline. In my experience, alcohol is a completely different animal. On one of my engines, we found peak power at 11.8-12.0 AFR on C16. After switching to C85 (85% ethanol), we found peak power closer to 10.5 AFR. (converted to gas scale) Yet, the alcohol could also go leaner at part throttle. Steady part throttle at 2500 rpm, C16 wanted to lean knock around 16.5 AFR. C85 didn't knock until 17.5 AFR.
I think this also only applies to gasoline. In my experience, alcohol is a completely different animal. On one of my engines, we found peak power at 11.8-12.0 AFR on C16. After switching to C85 (85% ethanol), we found peak power closer to 10.5 AFR. (converted to gas scale) Yet, the alcohol could also go leaner at part throttle. Steady part throttle at 2500 rpm, C16 wanted to lean knock around 16.5 AFR. C85 didn't knock until 17.5 AFR.
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
Originally Posted by BMWTurboDzl
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
That would be incorrect. DI engines in the USA typically have an "ultra lean burn mode." It is typically only active when cruising at light loads and steady speeds.
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
That would be incorrect. DI engines in the USA typically have an "ultra lean burn mode." It is typically only active when cruising at light loads and steady speeds.
Originally Posted by badtlc
Originally Posted by BMWTurboDzl
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
That would be incorrect. DI engines in the USA typically have an "ultra lean burn mode." It is typically only active when cruising at light loads and steady speeds.
I've heard that before but nobody has been able to demonstrate that "ultra lean burn" in the US is the same in Europe. Basically I'm opining that a manufacturer can claim "lean burn" but I've never seen any sort of industry wide standard defining such. Especially with extensive use of turbocharging. Kinda like Chevy claiming a "study" showed that they're more reliable than Honda or Toyota.
Originally Posted by BMWTurboDzl
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
That would be incorrect. DI engines in the USA typically have an "ultra lean burn mode." It is typically only active when cruising at light loads and steady speeds.
I've heard that before but nobody has been able to demonstrate that "ultra lean burn" in the US is the same in Europe. Basically I'm opining that a manufacturer can claim "lean burn" but I've never seen any sort of industry wide standard defining such. Especially with extensive use of turbocharging. Kinda like Chevy claiming a "study" showed that they're more reliable than Honda or Toyota.
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I think he mixed up 2 temperatures which generally change in opposite directions: the peak combustion temperature which lasts only a fraction of time during the combustion and the exhaust gas temperature which is the most detrimental to the engine components.
I think most all have misinterpreted what he said. You have to overlay the chart on the right with temp and power over the chart on the left with temp and NOx. This is where you will see why he is talking lean is hot and dangerous- at full throttle, nearly EVERY "conventional" ICE ever made operates to the left of the peak of the temp trend based on the AF ratio. What the graph on the right shows you is that before power (and temperatures) start to taper off, your combustion and flame front teperatures are climbing to the highest point around stoichiometric. So if your engine is rich (10:1 or so) and you start to lean it out towards 14.7:1, your combustion temps will increase. If you have EFI and "forced" the engine to run on the ultra lean burn side (>17:1) the temps would be lower, but so would power. As you richened up the mixture towards stoichiometric again the temps would also rise, and if you didn't transition past the point of max temperature to sub-13:1 AFR you will melt parts in a hurry.
This is why ultra lean burn works- the ECM is programmed to start and maintain AFRs much higher than the "peak" temperature shown in the graph on the left side, and are working in the downslope area on the tail of the chart as AFR approaches 20:1 and greater. Everything everyone learned on carburetors and dragstrips is true to an extent- but nobody would ever purposely set their equipment up to make an 18:1+ AFR, because you can't make any power there. The danger zone is all around the peak temp areas, roughly somewhere between12.7:1 to 16.5:1 air/fuel ratios depending on several factors (all cast iron was mentioned). Outside of this range you're not likely to burn an engine down, the former because you can't combust all the fuel and the latter because you can't combust all the air. Everything Jason said in that video is true.
This is why ultra lean burn works- the ECM is programmed to start and maintain AFRs much higher than the "peak" temperature shown in the graph on the left side, and are working in the downslope area on the tail of the chart as AFR approaches 20:1 and greater. Everything everyone learned on carburetors and dragstrips is true to an extent- but nobody would ever purposely set their equipment up to make an 18:1+ AFR, because you can't make any power there. The danger zone is all around the peak temp areas, roughly somewhere between12.7:1 to 16.5:1 air/fuel ratios depending on several factors (all cast iron was mentioned). Outside of this range you're not likely to burn an engine down, the former because you can't combust all the fuel and the latter because you can't combust all the air. Everything Jason said in that video is true.
Originally Posted by BMWTurboDzl
Originally Posted by badtlc
Originally Posted by BMWTurboDzl
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
That would be incorrect. DI engines in the USA typically have an "ultra lean burn mode." It is typically only active when cruising at light loads and steady speeds.
I've heard that before but nobody has been able to demonstrate that "ultra lean burn" in the US is the same in Europe. Basically I'm opining that a manufacturer can claim "lean burn" but I've never seen any sort of industry wide standard defining such. Especially with extensive use of turbocharging. Kinda like Chevy claiming a "study" showed that they're more reliable than Honda or Toyota.
Ultra lean mode is defined as lamba > 2.
Originally Posted by badtlc
Originally Posted by BMWTurboDzl
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
That would be incorrect. DI engines in the USA typically have an "ultra lean burn mode." It is typically only active when cruising at light loads and steady speeds.
I've heard that before but nobody has been able to demonstrate that "ultra lean burn" in the US is the same in Europe. Basically I'm opining that a manufacturer can claim "lean burn" but I've never seen any sort of industry wide standard defining such. Especially with extensive use of turbocharging. Kinda like Chevy claiming a "study" showed that they're more reliable than Honda or Toyota.
Ultra lean mode is defined as lamba > 2.
Originally Posted by BMWTurboDzl
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
Chrysler has Lean Burn on a lot of their engines and has done so for quite a while. Not as lean as D.I. though but lean-burn for sure.
Unfortunately he doesn't go on to tell you that automotive engines, in the US at least, don't operate in really lean conditions because of the hurdle with regards to emissions. IIRC in europe cars are running in lean burn because ULSG (10 ppm max) won't kill the cat needed to scrub NOX.
Chrysler has Lean Burn on a lot of their engines and has done so for quite a while. Not as lean as D.I. though but lean-burn for sure.
Stevie, is that because they dilute the air/fuel mix with oil vapor?
Originally Posted by SubieRubyRoo
Stevie, is that because they dilute the air/fuel mix with oil vapor?
Only the Mitsu equipped Chryslers burn oil and the sludge monster 2.7. I've yet to see any Chrysler in our family (and we have lots of them), burn any oil. My journey didn't use a drop between changes and neither does the new Caravan. The Journey got up to 10K mile OCI's (16,000km) before it was in the accident as well.
Stevie, is that because they dilute the air/fuel mix with oil vapor?
Only the Mitsu equipped Chryslers burn oil and the sludge monster 2.7. I've yet to see any Chrysler in our family (and we have lots of them), burn any oil. My journey didn't use a drop between changes and neither does the new Caravan. The Journey got up to 10K mile OCI's (16,000km) before it was in the accident as well.
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