Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Cooled EGR vs Water Injection vs Super Lean

Isaac Zackary · 06-16-2015, 02:02 AM

Thanks for the posts, because I've learned a few things so far.

First of all, hottest EGRs occur just lean of stoichiometric (14.7:1). But after leaning out even more combustion temperatures do subside just as if it were running on EGR. At which exact AFRs it does this on this particular engine I don't know, but others with this engine have indicated about 16:1 and leaner. I might get an EGT gauge in the future, but being it's an air-cooled engine the CHT gauge I have might be a pretty good indicator of what's going on.

I guess for now I'll shoot for a 16.5:1 to 17:1 AFR while cruising. That seems safe enough for this particular engine. It's the WOT I'm not sure what to do with yet. I really don't like the idea of running a 13:1 or richer AFR for high load. I could try to go even leaner than 17:1 in order to avoid detonation and ultra high EGRs. Looks like cooled EGR would have about the same effect anyway. Water injection would do the trick but that's not that easy to work with.

I guess EGR has been so popular not because they couldn't get a lean burn to do the same as far as combustion temperatures go, but because that way the exhaust gases are always depleted of oxygen, which is necessary in order to reduce NOx in the common three way catalyst (which I don't have).

One assumption, being this is a carbureted engine, is that it'll be very important to control intake charge temperatures. If I set it lean on a cool time of day if it gets hot then it will be running richer. I have a thermostatic air cleaner, but it's vacuum operated, so it stops regulating heated air at WOT. Maybe I'll need some sort of vacuum pump, unless I go with EGR or water injection as WOT detonation control.

One more question. What would be more fail safe? The popular method has been to enrich the mix to around 12.7:1 or so. But obviously a clog in the carburetor or faulty fuel pump can make it go lean. EGR can get clogged over time, or the linkage could fail. A lean burn could go rich if an air bleed got clogged or with a change in altitude. Water injection could cause lots of problems if water ran out or a pump stopped working or if it kept working when it shouldn't.

06-16-2015, 02:02 AM	#16 (permalink)
Isaac Zackary Full sized hybrid. Join Date: Apr 2015 Location: Colorado Posts: 602 Suzy - '13 Toyota Avalon Hybrid XLE 90 day: 37.18 mpg (US) Thanks: 369 Thanked 108 Times in 84 Posts	Thanks for the posts, because I've learned a few things so far. First of all, hottest EGRs occur just lean of stoichiometric (14.7:1). But after leaning out even more combustion temperatures do subside just as if it were running on EGR. At which exact AFRs it does this on this particular engine I don't know, but others with this engine have indicated about 16:1 and leaner. I might get an EGT gauge in the future, but being it's an air-cooled engine the CHT gauge I have might be a pretty good indicator of what's going on. I guess for now I'll shoot for a 16.5:1 to 17:1 AFR while cruising. That seems safe enough for this particular engine. It's the WOT I'm not sure what to do with yet. I really don't like the idea of running a 13:1 or richer AFR for high load. I could try to go even leaner than 17:1 in order to avoid detonation and ultra high EGRs. Looks like cooled EGR would have about the same effect anyway. Water injection would do the trick but that's not that easy to work with. I guess EGR has been so popular not because they couldn't get a lean burn to do the same as far as combustion temperatures go, but because that way the exhaust gases are always depleted of oxygen, which is necessary in order to reduce NOx in the common three way catalyst (which I don't have). One assumption, being this is a carbureted engine, is that it'll be very important to control intake charge temperatures. If I set it lean on a cool time of day if it gets hot then it will be running richer. I have a thermostatic air cleaner, but it's vacuum operated, so it stops regulating heated air at WOT. Maybe I'll need some sort of vacuum pump, unless I go with EGR or water injection as WOT detonation control. One more question. What would be more fail safe? The popular method has been to enrich the mix to around 12.7:1 or so. But obviously a clog in the carburetor or faulty fuel pump can make it go lean. EGR can get clogged over time, or the linkage could fail. A lean burn could go rich if an air bleed got clogged or with a change in altitude. Water injection could cause lots of problems if water ran out or a pump stopped working or if it kept working when it shouldn't.