running lean

[beef_bourito]

I was just wondering what the actual dangers are when you run lean.

from what i know there's excessive temperatures and possible detonation from those temps.

now if those are the only dangers, could you not combat them with an alcohol or water injection system to allow the engine to run cool and lean and possibly save fuel?

[2.2 Straight six]

yes, water injection is a solution.

i believe years ago, someone ran a ford fiesta really lean and used serious water injection to get something like 50mpg from it.

[KiwiBacon]

I've heard that many engine meltdowns are falsely attributed to running lean. The actual cause was detonation which causes the computer to retard the spark timing so much that fuel is still burning when the exh valves open.

Hence really high exh temps leading to valve and head problems.

In which case running lean isn't the problem, detonation is. While a rich mixture will give a cooling effect, going leaner than stoich will result in a lower burn temperature.

My Nissan has a supposedly lean-burn engine (QG18DE), but I haven't been able to monitor exactly what AFR's it runs at.

[UncleBob]

Originally Posted by 2.2 Straight six

yes, water injection is a solution.

i believe years ago, someone ran a ford fiesta really lean and used serious water injection to get something like 50mpg from it.

he was using a modified engine for that, something like 14:1 compression ratio. The water injection was just to stop detonation due to low-octane fuel

Simular.....but not quite the same as simply running lean

I think he got closer to 55 or 60mpg....but then, those cars could squeak out 50mpg stock

[curtis73]

The bases are mostly covered here. Running lean alone can cause high EGTs which can be combatted with water/methanol injection, but careful consideration has to be given to the valve and seat temps. Water and methanol can cool combustion, but water reduces lubricity at the valve seat and latent methanol can increase valve/seat temps. An upgrade to severe-duty valves and better seats might be in order.

One benefit to leaner mixes is a faster flame front speed, which means you can make better use of the combustion by retarding ignition timing.

You might be interested in Singh's grooves. Do a search. Its a process where you cut a groove in the quench pad of either the chamber or the piston (or both) in an effort to induce flame swirl. There is little hard data on it, but tests suggest that it allows much leaner mixes and higher compression on pump gas. We know that swirl promotes complete combustion and improves detonation tolerance; I guess the question is, do Singh's grooves actually improve swirl?

At any rate, if you search for it you'll find tons of applicable tech on the subject of swirl and quench. So, grooves aside, that research may provide you with some interesting reading about lean burning and its effect on flame front speed and detonation.

In specific, you may want to go to www.hotrodders.com and search for Singh and you'll come up with two threads in particular that go pretty deep into the tech. Expect the typical "snake oil" opposition arguments, but its a valid theory that is yet to be supported by hard core testing.

[beef_bourito]

thanks guys, what sparked the question is that someone was telling me he read that some company had made a car that used a turbocharger and alcohol injection to get better fuel economy and more power, so i was wondering if they could have done it by running lean.

and i've read up on those singh groves before(probably from another thread here lol), they're pretty interesting.

[UncleBob]

I read that article too, I think their claims were rather....."optimistic"