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Lean burn

A long time ago I read about something called “lean burn”. Has anyone heard of lean burn?

Chrysler’s first electronic spark control system which came out in the mid-70’s was called the Electronic Lean Burn system. It was a pain to keep working right and they were often replaced with conventional carburetor/distributor combinations.

Greasyjack is right, I had one in a 79 Newyorker 440 CID and it was a headache. But for that matter most systems in the early 80s were headaches.

Honda dallied with lean-burn for awhile with their high MPG Civics.
Google is your friend.

There are lots of variations on this - more recent versions are ‘stratified charge’, ‘hcci’, etc…and wikipedia has a number of articles on these.

In th e’70s manufacturers were experimenting with different ways to reduce emissions and improve gas mileage. One way was to “lean out” the mix, because less fuel per volume has the capability of producing fewer unburned hydrocarbons and carbon monoxide molecules. The marketing guys used this terminology to attempt to differentiate the cars with the terminology.

In truth, all vehicles became “electronic lean burn” systems. The key to getting good operation with less hydrocarbons per volume was to get the droplets of fuel that entered the chambers as small as possible, providing more surface area per volume of gas thus allowing more of the hydrocarbon molecules to be in contact with oxygen for a faster and more complete burn. That not only reduced the unburned hydrocarbons and the CO2 out the exhaust, it also made better use of the energy available in the gas molecules, allowing less gas to be added to the instream, changing the gas vs oxygen ratio per volume, meaning a leaner mix and improved gas mileage. This was, as we know, ultimately accomplished with multiport fuel injection controlled by sensors feeding signals into a computer program…electronic multiport fuel injection.

Thus, every engine today uses an “electronic lean burn” system. Fortunately, they’ve figured out how to do so much more successfully than their early attempts.

I guess another variation is that some pre-OBD-II GM’s with fuel injection supposedly had a “lean cruise” mode that would lean out the fuel mixture while cruising at highway speeds. But supposedly this caused some drivability issues (like if you stomped on the gas while cruising, the engine would stumble) and so the mode was turned off by default, but it could be turned on through some sort of computer wizardry and would result in better highway economy.

I honestly don’t know if the above is true, though. To a certain extent it sounds like an automotive urban legend to me.

You mean my post? It’s just simple physics. The way to reduce emissions and improve gas mileage is to get the most out of the energy contained in the gas. The way to get the most out of the energy contained in the gas is to burn it as fully as possible. In the limited time available in a power stroke, the best way to do that is create as much surface area as possible in contact with oxygen and to have plenty of oxygen in contact with as many hydrocarbon molecules as possible. That’s done by spraying under higher pressure the gas as close to directly into the cylinders as possible. That’s done with electronically controlled multiport fuel injection. Now they’re experimenting with spraying it directly into the cylinders via direct injection systems.

In a nutshell, that’s what it’s all about. And that’s all “electronic lean burn” systems were. It’s marketing hype for what everyone was developing by necessity anyway.

I just meant that the story I’d heard about lean-cruise being a hidden feature on 80’s and 90’s GM products sounds little fishy to me.

What is the very recent technology Chrysler got from FIAT in regards to a complete induction system (from cylinder head up)? They are first going to fit it too 4 cyl and them move up the displacement and number of cylinder range.

Seems to me the word “lean” was in the title decription

Oh, okay. I’m totally in the dark on that one. I wouldn’t doubt it, though. In their efforts to comply with constantly tightening fed regulations a lot of shakey stuff was tried. This whole metering game is a fine balancing act.

The game ain’t over. Wait 'til the CO2 regulations begin…

Lean mixtures at cruise transmitt a “hunting” feeling back to the driver, very annoying.

An over-lean mixture burns slowly…Slow enough that the exhaust valves are bathed in fire and are quickly destroyed. Exhaust gas temperature is a good way to monitor when this point is reached. Aircraft engines that have adjustable fuel mixture also have an exhaust gas temp gauge to prevent engine damage…

Honda, in the 70’s, had a CVCC (controlled vortex combustion chamber) that got the job done WITHOUT a Catalytic Converter. He (Honda) offered the design to Detroit free, but they turned him down. They had already sold Congress and the oil companies on the converter and unleaded gasoline so they could get ten more years out of their antiquated V8 pushrod engines.