Myth? Lean mixtures will cause engine damage
 

Doing a bit of research, it looks like lean mixes alone do no harm, but at low rpms and high load, lean mixes can lead to detonation and its the detonation that can damage pistons, burn valves etc.

This is why the Civic VX lean burn does not damage the engine and why the Honda insight can go up to 40:1 under cruising conditions and do no damage.

Here are a few good reads:
Aircraft engines and leaning/richening mixtures (pilots do this all the time when they change altitude)

A discussion amongst engineers on the subject "Running lean and melting pistons"

Combustion temps actually decrease as you get leaner and leaner

https://www.huygens.org/sape/pilotage...s/image012.gif

When I first heard about the EFIE devices and clogged fuel injectors, I wondered why ppl weren't killing their engines since these would cause one or all cylinders to go lean. The above links explain the lack of damage. If the above info is correct- as long as you have a functional knock sensor (so the ECU can retard timing as needed), leaning an engine a moderate amount should be a safe way to gain MPG as long as you do not ignore the sounds of detonation.

These are my thoughts assuming that the above webpages are accurate.

On a related note- here is a lean burn engine design which claims to be very efficient.

Bourke engine
Another Bourke site

Wow I have been saying this forever... THANKS!

As long as the engine is under very little to no load there should be NO problem!

For example, at idle! Or cruising!

I plan to modify an EFIE to work only when I am under (let say, I still have to do more testing) under 20% throttle.

So it would not be active when under load, acceleration, going up hills, etc. But would in constant driving, or simply idling.

And yes, it would increase MPG A WHOLE LOT and it does burn cooler, think about it, there is a lot more air in the cylinder...

The Civic VX/HX can run lean because it was specifically designed and tuned to run lean. You can't take a Civic DX or EX motor and run it as lean as the VX. The fuel wont spread evenly, hence it wont burn evenly. The fuel fails to ignite and you get lean misfires if you go any leaner than 16.5. At medium load 15.5 is the limit. And yet the Civic VX/HX can run 18:1 and still accelerate.

This is why:

https://suspendedhatch.thecarthing.co...-E_diagram.gif

Closing one intake valve causes the air to spiral in to the combustion chamber, in essence stirring up the sparse fuel evenly. You also advance the ignition timing quite a bit and decrease the load placed on the engine by eliminating weight and accessories that drag on the crank.

It's difficult to damage an engine at light load. Why? Because it's at light load. It's self evident. You can get pre-ignition, detonation, misfires etc at light load just as you can under heavy load.

Those websites make generalizations but that info doesn't apply to all engines. Engineers have been successful at creating engines that run at both extremes of the parameters of gasoline.

So what is so special about the vx engine that makes it be able to ignite so well?

Piston design? Ignition Design?

Its my understanding that there are several conditions that must be met before the VX will go into and stay in lean burn including throttle position, temperature, vacuum etc.

I thought part of the VX lean burn system has to do with the swirl of the incoming charge by the position of the two intake valves, but suspended hatch will have to help us out.

The old Honda CVCC system (1987 was the last year for it) is ideal for being leaned out because the rich mixture in the precombustion chamber is easy for the spark plug to ignite and its combustion can more easily ignite a cylinder full of an extremely lean mixture.

Some modern cars use the ECU to achieve basically the same result.
My car runs in lean mode when the cruise is active and after 15 seconds of steady state input.
Not sure how lean exactly but the FE is impressive for what it is and does.

Sort of related there is an item on the Autospeed site (www.autospeed.com)
at the moment.
The article address is:
https://www.autospeed.com/cms/A_110767/article.html

Cheers , Pete.

Thanks Pete- that was a good article

Oh and if anybody is planning on doing this (like me), it is a very wise idea to go with an aftermarket ignition module like MSD or the such.

These devices can multifire below a certain rpm, which is what you need to be able to light those lean mixtures (and it is exactly what the Honda insight does, multi fires the plug).

Just a heads up on what I have learned through my research in order to get my engine to lean burn safely :)

Fuel system design is the most important!

I posted a rather large pic.

Honda pistons are pretty much standard. Honda ignition systems are mediocre at best. The pent-roof combustion chamber shape has a lot to do with it but it certainly is not unique to the D15Z1. It's pretty much standard across the entire Honda lineup since the early 80's.

I have an AEM Twin Fire (CDI multistrike ignition system) on mine as part of converting it to direct fire.

"Q: What is Multi-Strike?
A: Multi-Strike is the process of firing the spark plug multiple times at low RPM to aid in idle quality, throttle response and engine start up. The AEM CDI can deliver up to 8 full energy spark events sequentially."

https://www.fuelly.com/attachments/fo...a6755b2c38.jpg

12.8-13.2:1 is the max power mixture range. Not sure about economy.

My friend melted 2 or 3 pistons in his 250cc mx motorcycle before he realized he had leaky crank seals, making his bike run lean. Of course he was hammering it to death every time. Thing was he said it was running GREAT, really fast, and then nothing. From what I've seen, I concur...

Engines always run their best right before they die.

Gasoline direct injection engines can run as lean as 65:1 according to this wiki:
https://en.wikipedia.org/wiki/Gasoline_Direct_Injection

Most put out more power when there into a little detonation.

Really? I've read that they're pretty good at what they do... That it's not generally necessary to upgrade them for most performance applications. Are you saying that because you had problems when running a modified lean-burn setup, or because you're annoyed that it doesn't fire 15 times every other cylinder stroke?
Really, I don't think it's fair to compare factory equipment to an aftermarket setup when modifying the engine beyond its intended range of operation. If the engineers had expected the engine to run particularly lean, they would have upgraded the ignition to cope. Newer Honda lean burn engines have two spark plugs per cylinder, and each plug has its own coil/ignitor unit assembly. The separate ignition assemblies not only add redundancy and therefor reliability, but also divide up the work load so plugs could conceivably be fired multiple times (maybe they already are?) with just a tweak of the ECU programming.

This graphic shows 16:1 as having the best economy.

https://www.huygens.org/sape/pilotage...s/image002.gif

On a related note, supposedly NOX emissions go up when you run too lean, but based on the graphs at the beginning of this thread, it seems that running ultra lean would have lower combustion temps and therefore lower NOX emissions than a stoichiometric ratio.

Your forgetting that as you go leaner there are more oxygen molecules available to react with the 78% nitrogen in the air and the combustion temperatures are still in the thousands of degrees.

Wouldn't the ratio of oxygen to nitrogen remain the same regardless of the volume?
The "Lean" aspect applies to the volume of air relative to the volume of fuel so although the volume of air is decreased the actual mixture of the air does not alter.

Cheers , Pete.

That's true before the mixture burns. Once ignited only the oxygen combines with the fuel to produce combustion. If there's left over O2 in during combustion (eg lean mixture) it will try to latch onto other molecules, such as nitrogen.

That makes sense DRW, it also explains how EGR helps reduce NOX emissions (less free oxygen in exhaust to react with nitrogen).

I suppose running ultra lean WILL increase NOX emissions.

Hmm...so there's all this nitrogen reacting with oxygen...I wonder if there's a way to persuade it to make N2O and separate it out from the rest of the exhaust, then feed it back into the intake.

I don't know about separating it, but that's more or less what EGR systems do. They mix some exhaust into the intake stream, which replaces some oxygen-rich air in the cylinder. Less oxygen in the mix means reduced NOx emissions.

Yeah, but that's NOx, not N2O...

Actually, that isn't how EGR works. EGR works because the extra inert gasses in the chamber absorb energy from combustion and the combustion is cooler because of that(also gives more to expand from heat of combustion). Additionally, the extra gasses take up space in the manifold and reduce vacuum a lot like our WAI are doing.

The actual oxygen/fuel ratio never changes with EGR. All stock EGR cars still run 14.7:1 on freeway cruise which is where EGR is active.

Yup, thats what he kept saying...

so why not compensate the lean with hho??

I'm leaning out my mixture with map enhancement, o2 enhancement, and wai

HHO won't help. It's a stoich mixture.

Uh... What? Warm air intakes work because they reduce the density of the air being pulled into the engine. Lower density means there's less oxygen (and nitrogen for that matter) per volume of air, so less fuel needs to be injected to reach a stoichiometric ratio. Manifold vacuum is unaffected by the temperature of the air.
No, the volume of air/fuel mixture being pulled into the cylinder during each intake stroke is reduced. The mixture is diluted by the exhaust gasses. Less air and fuel being burned means less heat released in the cylinder, lower combustion temperature and therefor reduced NOx emissions.

I think dkjones was saying the same thing on the vacuum issue- just in a different way. If you use WAI vs. no WAI, on the same stretch of road at the same outside air temp, you would need to open the throttle more to maintain speed with WAI (since, like you said, the air/fuel takes up more space). Opening the throttle plate slightly more would mean slightly less vacuum.

I agree that using EGR means less fuel used, but I think that EGR does NOT affect the air/fuel ratio, because EGR is neither air nor fuel.

If you monitor your AFR with a wideband O2 gauge you'll notice that AFR spikes rich when EGR comes on. You're displacing air with exhaust. Exhaust doesn't burn.

I said the stock ignition system on the Honda Civic and Acura Integra (as well as across most of the rest of the Honda/Acura line-up) is mediocre. I didn't say it was bad. If I were to compare it to similar manufacturers I'd give it a C. I've had 3 Civics and an Acura Integra and the ONLY part that has ever failed me has been the ignitor, the coil, or the entire distributor assembly. Your opinion is the same thing I see repeated across all the popular Honda forums. That doesn't make it a fact.

The reasons are inherent to the design. 1) The size of the distributor limits the size of the coil. One coil has to charge and fire four cylinders every rotation. Honda designs their engines to rev relatively high. As RPMs increase, dwell time (time for the coil to charge) decreases. As a result, the small coil peters out at the top end and you get weak spark.

2) Inside the distributor housing is not the best place for a coil to stay cool.

3) You have a high voltage/current coil in the same housing as the ignitor and the low voltage cam/crank sensors. Honda actually had to design a work-around of sorts so the ECU keeps plugging away even when it loses the cam signal. You find this out when you replace the stock ECU with a standalone and you can't get it to sync. Replace the distributor with a brand new OEM piece and the engine fires right up. Better yet, convert to distributor-less ignition and you'll increase the reliability of your Honda significantly.

When I looked into the various options I had for converting to distributor-less ignition, the D17A coil on plug was an obvious consideration. Unfortunately I had read numerous posts/articles that the stock D17A coils were quite weak for anything above stock power. It's not that Honda isn't capable of making a good ignition. In fact, I ended up using Honda CBR coils. But just like any other manufacturer, Honda has cost considerations when making their cars. Everyone wants to save money.

Converting your ignition doesn't give you a power increase. It can only ALLOW you to make more power. If you rev the engine high, the weak cam signal causes your ignition timing to wander. If you increase the compression or boost the engine it actually blows out the weak spark. The vast majority of Honda "tuners" wont benefit from beefing up their ignition. I did it for reliability, emissions, mpg, smoother idle, and because it made sense for my application (if you have a standalone you might as well make the most of it).

Oh yeah, and lean mixtures can cause you to burn up an exhaust valve. As you lean out from stoich your cylinder charge burns slower and as you get leaner and leaner the charge isn't done burning until the piston is well into the power stroke. When you lean to a certain point, EGT skyrockets because the charge is still burning as it leaves the cylinder which is the point at which you do engine damage.

Usually, you feel when it starts doing this because the engine loses power as sharply as the EGT rises because of the wasted energy.

dkjones,

What you are saying makes some logical sense, but I wasn't able to find any real world evidence/graphs that showed that EGT's go up as the mix gets leaner. I'm open minded enough to look at any that anyone else could find.

One of the better graphs that I found was this one (below), its shows EGT's going down as the mix gets leaner. Yes, it does show that some EGT's are maxed out as you go a little lean, but they go down as the mix gets leaner and leaner. This graph might support the idea that guys running a little lean by using an EFIE or O2 sensor extender would have the most to worry about- not those of us that are going super lean.


https://www.huygens.org/sape/pilotage...s/image012.gif

Think of all of the partly clogged fuel injectors out there on MPFI engines spraying 70-80% of what they should be spraying resulting in super lean mixes on one or two cylinders. It seems like we should be seeing lots of burned valves/melted pistons these days if lean mixtures were the culprits.

IMHO, I think that it's detonation kills pistons/valves etc. The connection between detonation running lean is that detonation can result from running lean at low rpms under high load conditions- thankfully knock sensors do a good job of helping to control detonation by helping the ECU to know when to retard ignition timing.

Actually, you'd know it if you were damagingly lean, the engine starts to feel like it is misfiring and/or just really low on power. The misfiring could be from not enough ignition energy or the mixture at the point of spark isn't enough to spark, but we are talking REALLY leaning out the engine.

I wouldn't think knock would be a problem when you are going lean, the readiness of the mixture to even ignite at all is lower and when it does ignite it's slower which is why you need a timing advancement when going leaner. I'd personally think you would have a bigger problem with knock around 12.5:1 where maximum power is to be had and the mixture is not only happy to light but once it does it burns very quickly.