Lean Burn dangerous or not?

To meet the 'new' emissions requirements back in 1979, I was working with a team of automotive engineers on designing the perfect solution... a lean burn engine that met all the American emission requirements...

It was progressing nicely and showing the positive effects of lean burn, i.e. reduced emissions, reduced fuel consumption and so on...

Then the death knell was dealt to us as Johnson Matthey produced the catalytic converter at a reasonable price!!

So any engine could meet the emission requirements... unfortunately, the engine has to run rich - higher fuel consumption, and the catalytic converter only started to be effective after it had warmed up to operating temperature, many minutes after the engine had started and had the choke full on for cold start...

So anyone who shouts that catalytic converters were the best choice is nuts!!! They burn up fuel far more than a good design of lean burn engine, and the emissions for the first several minutes of driving are horrifying!!

John.

Would that have been the Ford engine????????????

Yes, get rid of the converter and our fuel consumptions would have been 10/20% less. Politicians dont seem to bother with 'little' things like that.

Today,what is the environmetal cost of the increased fuel consumption AND of the construction on the converters???? What, hoisted on their own petard, never.

You wrote "I'm sure part of the loss is due to be excessively rich mixture necessitated by the catalytic converter."

Why should this be so? A cat needs only to have a source of hot CO to allow it to heat up and do its work as far as I am aware. Even a "Lean Burn" engine, still does not burn 100% of the fuel that passes through it......if it were so lean that no CO, only CO2 passes out of the engine, a major need for the normal cat is completely gone.....or have I missed it somewhere????

Georgee - we had a number of different engines to modify and play with but the principle engines were the Ford ones...

They were specially modified by Ford to run on the then new unleaded petrol, as well as to withstand the extra heat from running on a lean mixture.

We showed that running lean resulted in emission and fuel consumption reductions that would have made it far better than catalytic converters... Fuel savings would have been over 20% of an engine running with a rich setting to get a 'cat' up to working temperature.

John.

Hello Electroman:

From the responses in this forum there seems to be a little controversy over the benefits, or possibly I should say the amount of benefits from a lean burn system. Since you have some official experience with these systems I thought I would see if there were any numbers floating around from way back when.

Circa 1979 myself and a few friends had 900 Kawasaki's, by adjusting the metering rods on the carburetors slides to a fully lean position we were able to fine tune the cruise mixture with the idle screws. The net result after a little experimenting leaning the cruise air fuel ratio as much as possible without getting a lean misfire netted about a 15% fuel economy increase.

I'm sure that we would have been able to lean out a little further with a better ignition system i.e. long-duration or multi-spark,Obviously we weren't using anything but seat-of-the-pants tuning an inspection of the plugs and pipes as our guides. Also there is no way of knowing how close to an optimum air fuel ratio of the factory had set the bikes up for.

So I guess my question are, did the lean burn systems you were working with come close to, or exceed that 15% figure for increases in fuel economy? What was the air fuel ratio that you were striving for on cruise?

Also I can only rationalize a slightly lean mixture, just lean enough to make sure the fuel is completely utilized are there any benefits to going leaner than that?

Hi YWroadrunner, I should start off by saying I was designing the electronic control unit for this venture and the details for using lean burn was mainly left to the automotive combustion expert engineers. But from what I remember...

At the stoichiometric point of air : fuel mixture the emissions are minimised, running to rich vastly increased the hydrocarbon outputs and running it lean increased the NOx outputs without the hydrocarbons...

The main difficulty back then was controlling the engine and measuring the parameters - with fuel injection only just becoming an affordable way for a family car and being the only way to set the air:fuel ratio accurately - Carburetters were just not good enough.

We managed to get emission reductions to meet the new 'California codes' The test engine a Ford Fiesta (as well as a few other types) on the test bed showed a performance equal to having it run on a slightly rich mixture and a good improvement in fuel economy, about 10% I seem to remember...

Then our work was dumped when the catalytic converters became a reality, even though for the 'cats' to work correctly the exhaust must have excess hydrocarbons in the emissions which means the engine HAS to run rich, this made the fuel consumption worse by a good 10%...!!

So if we had gone ahead with a lean burn technology the result would have met the then forthcoming emission requirements as well as giving a 20% fuel saving in running costs!!

The whole team was very disappointed with the acceptance of the catalytic converter... But a few of us did re-map our own car engines to run on lean burn and save a fortune in petrol / gas costs before having to change our cars...

The engines used for testing were supplied to us by Ford as specially modified to run on unleaded petrol (a new thing then!!) and with coated valves and pistons to disperse the heat of running lean.

Hope that's of some interest?

John.

By definition "lean" would mean less fuel than is needed for optimal combustion. Most engines have been designed to run "rich" because of inferior fuels, elevations, temperatures, octane levels, sensor limitations and the list goes on.

In my pursuit of performance, I would tune as close as possible to the optimal mixture. I have lost several motors prematurely to the lean mix. Pistons, valves, and head gaskets were the main reasons and there were also signs of cylinder wall wear possibly due to a scavenged cylinder burning the oil or leaving soot, I'm not sure.

Is it dangerous? Certainly can be to your motor!

Have a read of A.Grahame Bell's book 'performance tuning 4 stroke engines' their is adetailed discussion on fuel ratios, burn requirements and various systems in use. lean burn is being used in modern cars, particularly those using oxygen sensors. Maximum power usually requires a slightly rich mixture. This is because the limiting factor is oxygen supply. A rich mixture means the engine is burning every molecule of oxygen. Stratified charge engines burn the charge more efficiently, lessening the need for additional fuel, meaning they will run leaner at maximum power. That is where direct injection is good as it lets more air into the cylinder.

The second posting by guest pretty much reflects my experience. Peak power is obtained with a optimal air fuel ratio. Running slightly on the rich side cost very little in power and buys a safety margin.

So for maximum power output lean is dangerous. If you're talking more of a cruise power you've got a much larger safety margin, a lightly loaded engine should easily tolerate a lean condition.The question then is how lightly loaded, and how lean.

The mixture on a aircraft engine is adjusted by using a exhaust gas temperature gauge. The old rule of thumb for a moderate power setting was too richen the mixture to obtain a 20° drop from peak i.e. 20° rich of peak. When the price of fuel increase some manufacturers of new aircraft engines would allow you to go 20° lean of peak, at a low cruise power setting, (I don't remember the maximum percentage of full power) in the interest of saving fuel.

In any case the rule never change for full power everything went to the firewall mixture, (full rich) propeller and throttle. In other words ba... to the wall.

Yes it can be dangerous to the engine's health- the thing is that expert engineers have optimised all settings to work together, incl materials- when an inexperienced person alters settings, in the vain hope of extra power, m.p.g etc, as promoted by generalised after market books etc- disaster is certain. I still have a ball valve operated by cable & lever connected to ported vacuum- when I used it on a Ford Fairlane 351, by opening the valve on cruise, ie leaning the mixture, there were no discernible differences in op at the time- but the exhaust valves were burnt, needing a cyl heads recondition.

If an engine was designed from day 1 to have a hotter (leaner) burn, then all the components that are directly affected by higher temperatures (valves and pistons primarily) have to be designed to allow this extra heat either not to affect them (better materials), or the design must allow for easier/quicker heat removal (hollow valves with special fillings that take the heat away from the end and transfer it to the cylinder head quicker) for example.

Pistons can be cooled with oil jets from below as is done in many modern Diesel engines, basically any Diesel that has a Turbo needs this, but even a petrol engine could make use of such a system to cool the pistons in a lean burn (hotter) engine. Whether it is done in such petrol engines I cannot say as I have not had the luck to see such and engine taken apart!!

I am personally convinced that the extra lubrication to the cylinder walls and pistons alone from such a system contributes heavily to the long life of the engine as a whole anyway.......

But you do need an oil pump with a far higher capacity than normal, to use such a system in the first place......as well as a sump with more oil and possibly an oil cooler as well......as have most modern Turbo Diesels!!!

But basically, the engine MUST be designed to allow lean burning, modification of engines not so designed will often result in failures as several posters have noted......

Better internal cooling, more engine oil, better engine oil etc etc must always be planned first....

god morning andy, as usual the experience of one may not be accepted by the wisdom of another.

we owned a english built 1967 vauxhall with a 70.7 cu.in. engine and a 1968 with a 97.5 cu.in. engine in it. the 70.7 had the head taken off and a ).003 shim gasket plus the regular hasket in it, putting a larger rad from the '68 in the fron and using a oil filter which should have gone on the '68 drove many mechanics nuts if they saw it. the air injection reaction pump was and a gas under low pressure valve plus the pcv were the only emission control devices this had. the buffalo chevy dealers would refuse to accept that the small changes we made kept the exhaust valves from melting at the stems and the car being able to get from buffalo to rochester on about a gallon and a half of gas, somewhere near 50mpg. don't know the metricated distance but the paddock guys thought i was breathing fuel fumes.

you can't buy a emission system of that design today, you can buy all kinds of .... that costs a whack of a lot more that has a expected operational lifetime and even higher replacement cost when it leaves you out in lower tackaracky with your .. half frozen ion a snow storm though.

'da ber

Actually I was answering more for the people who had experienced problems, not those who had made modifications and not had problems......you are finding a problem with what I wrote that does not exist I feel, or possibly I should have directed my comments more carefully for some......

The engines you modified were either so well designed that your modifications were still well within their capabilities or you used the engine in such a fashion that did not "strain" its possibilities in any way.

Changing parameters on relatively modern engines which are probably designed to run on the mechanical limits can often result in unwanted problems, that is what this blog was all about really....

Either way, I believe you that you did not have problems from your mods, well done. Need I say more?

Lean burn is very dangerous. That is why manufacturers play it safe and run on the rich side. Aftermarket tuners can usually draw 10-15% RWHP gains through leaning out the A/F mix on a naturally aspired engine.

That sensor you speak of is currently used in the performance tuner world. It's called an exhaust gas temperature sensor. The driver can monitor the temps and when they get above a certain point, the driver backs off (or some tuners can be programed to back off the engine automatically.) However, anyone playing with tuners will dramatically reducing the engines lifespan.

Think of an oxy/acetylene torch. High acetylene (fuel) and low oxygen is used for brazing. Medium amounts of both gasses is used for welding and high oxygen and low acetylene (fuel) is used for cutting. By running your engine lean your applying the same principle as a cutting torch.

By now you have a very good survey of opinion on the dangers of lean burn.

Excessive heat and engine component failure are likely under sustained high load conditions.

High particulate and NOx emissions are a separate and more complex issue.

The most efficient method of increasing power, decreasing emissions, protecting engine components, and increasing fuel economy to about 125% of typical values is to inject fine water droplets into the air intake of virtually any vehicle.

The water droplets due not require compression so they do not create a load on the compression side of the piston stroke. They do form reform into high pressure steam after compression and combustion and so they add power to the expansion stroke.

The heat the droplets consume in the phase transformation reduce the combustion temperature which prevents heat related component failures and the formation of NOx. Particulate formation is suppressed due to on the fly Thompson process fuel reformation as part of the combustion process.

This simple solution works well with power enhancing techniques such as turbos, blowers, nitrous injection, and stochastic hydrogen oxygen infusion from on the fly electrolysis.

Turbo lag may be slightly increased due to reduced waste heat in the exhaust. Electrically powered blowers do not have this limitation. Nitrous injection is notorious for burning components and otherwise blowing engines and so is only used for short durations in high performance applications.

Stochastic hydrogen oxygen infusion increases overall combustion heat and so improves engine power output generally but the majority of its effect in safely improving engine performance has to do with its easier ignition and faster flame front speed of propagation.

Further information on water injection and on the fly water electrolysis supplementing conventional fuels in slightly modified engines is widely available on the net, and kits are available from Canada and elsewhere. Combining the infusion and injection techniques typically produce increases in fuel economy in the 135-150% range. This approach works for both diesels and Otto cycle combustion engines and has been fairly extensively tested in cars, trucks, and planes. Freezing of the water in winter cold is the most troublesome problem reported by most users.

Sincerely,

Mr. Gee

Well Mr Gee(are you a horse?)- I completely disagree with your statements about water injection- there will not be any increase in power, mpg, or steam assist- I have experimented extensively & I can say the only benefits of water injection are to reduce detonation(by slowing down the burn rate)- & a cleaning effect in the combustion chambers- the downsides are increased corrosion, a very real chance of hydraulic lock if water entry is too high(it happened to me- the engine was no good after that- bent con rods). Remember that for every gallon of fuel burnt, a gallon of water is emitted from the tailpipe in a vapourised form when engine is warm- so any supposed steam assist has already happened!. The promoters of water injection, as with so many other "aids" are out to make money from the gullible( I was once so, as a boy). If all these aftermarket scams worked, they would be standard fittings by Auto makers!- they aren't!.

A water / methanol "mist" injected into turbo engines will cool down the air drawn in on intake. When the turbo compresses the air the water/meth will vaporize thus absorbing heat energy causing the air to become cooler and denser.

I've worked on several setups for a few very happy Subaru owners. The bigger the turbo the bigger the positive effect. The dyno shows only a 1-3% HP increase once boost appoaches its peak. The $$$ to HP ratio makes this mod worth it.

Could it be that the engines break because they also run lean when the engine is under "designed max load" (accelerating). Maybe engines are not designed to take in that much air?

I notice that some of what has been said does not stand up to scrutiny.

1. There seems to be some confusion between leaning a typical engine, vs the normal lean running condition of a "lean burn" engine. Modern lean burn engines are very similar in principal to Honda's old CVCC engines, where the overall mixture is very lean, but the mixture near the spark plug is rich. (The old CVCC required a pre-combustion chamber to accomplish this feat.)

2. Catalytic converters are not required by law as some seem to have implied. Back in the days of the first Honda Accord, American manufacturers were using catalytic converters while Honda was using CVCC. After a few years with CVCC, however, Honda found that they could no longer achieve tighter standards with CVCC, and they went to catalysts. Catalytic converters and closed loop, lambda sensing engine control systems are an efficient, economical way to achieve the competing needs of low HC emissions (favoring leaner mixtures) and low NOx emissions (favoring rich mixtures). In 1979, when John was working with Ford, lean burn alone was sufficient to meet the then very loose standards -- in fact, Honda was still meeting standards with carbureted engines then. Today, lean burning alone cannot come close to meeting emission limits, so current lean burn engines have catalysts.

3. In aircraft engines, in which you can adjust mixtures easily and manually well outside any the limits of an emission-controlled auto engine, you can lean until EGT falls (as a result of too little fuel) without doing any damage to the engine. As you can see from this article even with crude and gross leaning out of mixtures (as compared to the precise control in modern automotive engines), you will not damage an aircraft engine.

Automotive racing engines are not so tolerant of lean mixtures, requiring richer mixtures both for cooling purposes and for optimum power.

4. I think someone mentioned power increasing with leaner mixtures. It does not. In a typical engine, max power is at lambda of .9 (on the rich side of 1 which is stoichiometric).

5. Also, some suggest that emission controls have caused lower efficiencies. This is not true in practice, because the sophisticated controls that come along with catalytic converters, etc, have lead to much more precise control over combustion. My first Accord was 1.6 liters and 76 hp: 47.5 hp per liter, considered good in its day. 60 hp per liter was considered excellent then. Now, we have luxury sedans producing 100 hp/liter with essentially perfect reliability. Specific fuel consumption has improved in a similar, but less dramatic way over the years. Engines are simply much better in every respect, and much of the development that lead to these improvements came about from having to meet stringent emission limits.

Europe had a lead over America in the early days of fuel injection, because Europeans were interested in fuel economy and performance. But in the US, fuel economy has been a minor issue. Were is not for being forced into sophisticated engine controls, the American companies would be producing 8 liter carbureted engines now, just as we were in the early seventies.

My family had a 1964 389 Pontiac Catalina -- a big car even for its day. It weighed about 3600 lb. My Current Honda accord weighs about 3500 lb, yet gets almost double the fuel economy. I can drive it into a brick wall at 35 mph and survive. Do that with the old Pontiac, and I'd have been impaled on the steering column. Back in 1964 the idea that anyone would actually want to drive a 6000-7000 lb enclosed truck as a personal car was almost unfathomable.