Lean buring a Natural Gas powered Reciprocating engine

[NewfieEng]

Does anyone know who can help me convert a Natural Gas powered Reciprocating Engine into a lean burning engine to reduce the emissions? I have a old Caterpillar engine that produces substantial amounts of NOx and CO and I need to reduce the emission in the area without replacing the whole engine with a newer model. What other economical methods could be used to achieve this?

Thanks,
Gavin Tweedie

 

[GregLocock]

Is this spark ignition or compression ignition? How is the gas injected?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[NewfieEng]

The engine is a Caterpillar G-399 spark ignition enigne with a carburator.

 

[Lou Scannon]

The carburetor and fuel pressure regulator are the devices you can modify to convert the engine to lean burn. Depending on what you have to start with, you may be able to adjust what you have, or you may have to replace them. There are some major caveats to converting a nominally stoichiometric engine to lean burn:
1. Power will be reduced roughly in the proportion you reduce the fuel/air ratio, unless you can increase the air flow e.g. by increasing boost pressure, assuming the engine is already turbocharged. This would necessitate investigation of the turbocharger capability. If not turbocharged, turbocharging could be added, but that would not be a small undertaking.
2. You have to go quite lean (50% excess air or more, typically) to see a significant NOx benefit. This will put the engine near the lean misfire limit, so fuel control needs to be very accurate to keep it a zone where NOx is low and simultaneously there is adequate margin against misfire. The only two ways to ensure that the engine continues to operate in this zone over time, given component wear/drift, and variation in fuel composition, is to check and readjust the mixture controlling hardware regularly using appropriate instrumentation to verify the air/fuel ratio, or use a closed-loop fuel control system. You may find there are aftermarket kits of this type for lean burn, but they will be pricey.

I would suggest you contact the local parts & service support outlet for your engine to find out what is available for converting it to lean burn. If you don't know of one in your area, try Hatch & Kirk (

http://www.hatchkirk.com/).

You could also go to Impco Technologies (a manufacturer) website (

http://www.impco.ws),

and follow links to their distributors.

 

[patprimmer]

Lean burn, gaseous fuels. I can see the holes in the pistons already.

With natural gas, you should be able to get good CO by accurate adjustment to stoic.

Maybe water injection will reduce your NOx emissions for little cost and risk. Note, I say little, not no risk.

Regards
pat pprimmer@acay.com.au
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[franzh]

Operating an engine in lean burn mode will not always result in holes in pistons. At some point after the stoich knuckle, the combustion temperature drops dramatically. Case in point:
5.6L OHV engine running at stoich, exhaust outlet temps 1250 deg F. At L=1.3, at 20 lbs turbo boost, the temp drops to 970 deg F. It is possible to run a non boosted in lean mode but at a substantial power reduction. To make it most effective it must be turbocharged.
That same engine made 450 lbft torque at 3,000 rpm at L=1.4 at 30 lbs boost.
I have seen more damage caused by rich fuel mixtures in gaseous fuel engines than with lean mixtures.
Lean burn mode is almost the exclusive rein with gaseous fuels due to its requirement for a fully homogenized air-fuel mixture. Its difficult with gasoline because the small gasoline droplets tend to clump while the relatively even distribution of NG or LPG supports a more even flame propogation.
Today, just controlling CO with a good tight AF contol is possible, but at a cost in NOx. Aftertreatments help but a precise AF control is mandatory. Water injection lowers combustion temps, but like my illustrious colleague Pat states, there is some risk of a hydraulic lock engine.
Franz

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[bowtie8]

My 2 cents

Check your emissions now, if your near Stoich or a phi slightly rich, you should see around 4500ppm CO and 3000ppm Nox. If your in the ballpark, put a Bandito Johnson Matthey CAT on it - it will knock it down to less than 250ppm CO and less than 100ppm Nox. (assuming your valve seals are good and carburation and timing is stable)

Best
John

 

[dcasto]

http://www.miratechcorp.com

Catalytic converters

A lean burn engine is a ground up proposition. Pistons, heads, everything is new.

 

[dwedel]

Ajax has a lean burn kit for their engines. New heads, precombustion chambers, and fuel delievery system. Superior has a lean burn kit, which includes heads, turbo upgrade, precombustion chambers, and fuel delievery system.

It has been done, and can be done. Do you want to pay for it. You will probably need to get a turbo as you need to force the air into the cylinders to maintain your HP ratings. Plus you will gain more scavaging and cooling effect, depending on your valve overlap. The Superiors had different cooling rates for the lean burn units.

Cat may have a convertion kit. I would say that a catalytic converter is more cost effective. However the elements are not cheap, and maintianing an A/F controller that keeps the Cat burning is sometimes tricky. (we made our own, and learned the hard way)

Miratech is good, so is Johnson Matthey.

http://www.miratechcorp.com

http://www.jmcsd.com/catalytic_converters.html

Good Luck,

dwedel
Hotrod Big Engines!
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[dwedel]

crap, hit submit, not edit ...

Make sure you price out the cost of replacing the converter elements every one to two years. If you have backfiring problems, you will want to fix them, the first time you destroy the converter elements.

dwedel
Hotrod Big Engines!
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[dwedel]

You know, go wander around the gmrc.org site. I bet they have some links to some aftermarket companies that can provide a turnkey lean burn or a turnkey catalytic converter package for you.

Just one more thought.

dwedel
Hotrod Big Engines!
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