Lean burn on automotive natural gas engines
Lean burn on automotive natural gas engines
(OP)
Hello All,
I would like to know if anyone has experience on the increase of efficency and emissions with natural gas automotive engines running on lean burn.
Also if any advice for vendors that can supply GM vortec 8.1 turbo or Ford 6.8 turbo on lean burn.
I would like to know if anyone has experience on the increase of efficency and emissions with natural gas automotive engines running on lean burn.
Also if any advice for vendors that can supply GM vortec 8.1 turbo or Ford 6.8 turbo on lean burn.





RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
Is this off-highway on on-highway?
For off-highway, would the engine be driving a gen-set?
j2bprometheus
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
In short, it was a bust, the cost of required improvements to turbocharging, ignition and air fuel control just wasn't economical. In the end all of the units we tried went back to stoich with three way catalysts.
Since then there have been some improvements in the offering for electronic ignitions and better lean burn AFRC's, but I'm not sure the base engine designs have improved enough to make lean burn work effectively without high fuel consumption and poor part load performance.
Mike L.
RE: Lean burn on automotive natural gas engines
When running lean burn, the AF ratio must get past the NOx curve to be effective, but power drops off considerably, making a turbocharger almost mandatory. You MIGHT get by without it but dont expect any power miracles. When running in lean burn mode, maintaining the AF ratio is especially critical, the slightest deviation can result in almost immediate engine damage.
One company I am aware of offering lean burn fuel systems in either natural gas or propane is Continental Controls (no personal affiliation).
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
franzh, I know you are generally well informed about gaseous fueled engines, so this statement surprises me.
Though full-size natural gas transit applications are now migrating toward stoich-EGR for emissions reasons, lean-burn engines have been the norm (Cummins-Westport, Deere, not to mention European & Asian OEMs) from the 90's through the present.
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
With the expected benefits of learn-burn providing better fuel economy and longer engine life due to the lower engine temp what reasons are preventing the use of learn-burn on Gensets.
RE: Lean burn on automotive natural gas engines
- block load acceptance is better with rich burn (or so I'm told)
- altitude capability is better with rich burn
- it's more difficult to get stable operation and complete combustion running lean burn in a small-displacement engine... perhaps something to do with the ratio of volume to surface area
Lean burn IS widely used on gensets 18L and up, even in the US.
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
First, what emission target are you trying to reach? When we went thru this exercise most of the industry thought 2 grams of NOx was way low, we were trying to hit 1 gram and in some cases 0.6, it is NOT twice as hard to get half as much, it's a lot harder.
In some cases fuel consumption was actually worse with lean burn configuration.
Rich burn with three way catalyst is always a loser in the exhaust temperature part of this, in some cases we had to derate engines due to the thermal problems, mostly valve life.
Engine startablity, in general seemed we had fewer starting and getting on line with rich burns than lean burns, especially in parallel to grid applications.
Engine durability, usually the winner here is lean burn, mainly because of impacts of the higher exhaust temps, however, in some lean burns the margin to detonation was pretty close, and we seemed to have more failures in lean burns than in rich burns, especially early on. Detonation protection systems usually only came on larger engines because of cost, but we did apply some aftermarket units on a couple with mixed results.
Maintainability, I have to say, overall a rich burn was easier for most technicians to deal with, the operating margins seemed wider, and some guys could keep an engine in compliance just by watching the differential temp across the catalyst. Also the AFRC for rich burn used automotive exhaust sensors, cost and reliability was much better. As lean burn has become more common some of these issues have improved, but most lean burn engines have more complex control systems and are more affected by ambient conditions and fuel quality than the rich burn engines seemed to be.
This experience is somewhat old now, and from a tough emissions market, but in genenral I think still pretty accurate.
RE: Lean burn on automotive natural gas engines
The newer Cat G3516s can reliably hit 1.0g/hp-hr or 0.5g/hp-hr (depending on setpoint) without NOx aftertreatment. 1.0g/hp-hr will be the fed. limit in the US starting next summer.
http://cat
RE: Lean burn on automotive natural gas engines
NOx sensor feedback is very new, and in it's early stages, as with charge density, had lots of issues that always didn't live up to the promises. Larger engines (with larger price tags)can afford the newer and more complex controls, along with the base engine engineering to make lean burn work as well as it does. As an example, the CAT G3520 has 3 ECM's, a temperature sensing module for exhaust temps, a fuel mass flow controller (Woodward Raptor), two other Woodward actuators (throttle and compressor bypass), a detonation sensor per every two cylinders, a handful of pressure and temperature sensors, and lots of wire and connectors tying it all together. Not to mention the millions of dollars spent actually making it work in the field.
The original poster asked about auto derived NG engines, and the experience shared above was centered around those particular types of engines.
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
The so-called "rich burn" natural gas engines run in the neighborhood I think you're thinking of. rich burn, in this case, means less than 2% excess O2 - w/catalyst, between 0%-0.5% excess O2
"lean burn" would be 6% to 10% excess O2, or a lambda of about 1.5-1.8 (1.67 for the case of 8.7% excess O2)
RE: Lean burn on automotive natural gas engines
Our major issues were,
Getting enough air into the engine to get the required excess air, as Ivymike pointed out above, to get a true lean burn and meet the emissions targets we were shooting for we needed about 8% O2 in the exhaust. Finding turbo matches was very difficult.
Fuel management, we did most of our work around Impco mixers, a lot of custom fuel valve shapes got made and tried. Continental Controls was new about then, we tried some of their early stuff, never met our needs. We also played around a lot with gas regulators and trim valves, idle air bleed valves, and some other things that got a bit crazy.
Ignition systems, trying to fire a plug in a lean mixture takes a lot of energy, the Altronic DISN came along and helped that out pretty good, but we had terrible trouble with spark plug life, either due to electrode erosion or flash over at the insulator. Plus it was a pricey fix at the time.
With some Ford engines we got some help from a local race shop, one of the guys there came up with a cam grind that helped, but overall the engine got real expensive to keep running as a lean burn.
Air fuel ratio controls, mostly issues with early exhaust oxygen sensors. CAT had one, but it was REAL expensive and had poor service life, plus it needed a fairly complex signal conversion. Woodward came out with the GECO Control near the end of the project, we worked thru quite a few bugs with them and got a couple working quite well, but the overall price for a unit at 75 kW was awfully high at that time.
We did bust up a couple of engines pretty good, they had high boost pressures and high compression ratios, and at 8% O2 ran great, but if they got below 5% O2 they detonated and hammered themselves apart fairly quick.
Mechanically if we could keep the engines out of the detonation areas life was good, bottom ends were never a problem during this exercise, top ends had good wear rates compared to running rich burn. Some cam and lifter combinations didn't like the ultra low or nil ash oils (scuffing and spalling), some piston and ring pack conbinations didn't like medium ash oils (deposit rates).
The project wasn't a total bust, we learned alot about natural gas engine performance, and about ignitions and AFRC's that we turned around and applied to the larger engines with some benefits. But the objective to setup a viable and cost effective lean burn auto derived engine for generator or chiller service in our required emissions levels was never met our targets.
RE: Lean burn on automotive natural gas engines
If I were to guess the number of lean burn applications on an over the road use, they would be only a small fraction of what I see in stationary steady-state genset use.
Early spark plug failure, piston damage, and exhaust valve torching are common lean burn problems. I seldom see this occur in steady-state, but much more frequently in transient mode applications. The damage can happen very quickly, often too fast to stop the engine. Interestingly, similar damage can occur from overfueling as from lean burn.
In the early 90's, I participated in several lean burn projects, some worked well, others ate up too many pistons.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Lean burn on automotive natural gas engines
http://w
RE: Lean burn on automotive natural gas engines
The project was quite interesting but it was risky to presume that multiple egr solenoids could be economically produced within the needed dynamic range. And as expected there was very little misfire tolerance.
Turbo
RE: Lean burn on automotive natural gas engines
[b]turbocohen/b], that sounds a little extreme; care to elucidate?
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
I'm in Colorado so which R&D outfit are you referring to?
If you have more to share perhaps a new thread would be in order...
RE: Lean burn on automotive natural gas engines
Even though I was a contractor at an engine R&D lab in the early 90's, some areas were off limits to me. Windows papered over, cardboard blinders over the instrument panel, one cell even had a military guard stationed there. Sometimes, weird sounds or smells would be a give-away, and sometimes just the absence of sound could be just as telling.
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Lean burn on automotive natural gas engines
The vvt/di approach won for good reason and in the future I believe vvt/di stoich will work better than lean port cng as well. We also supported a few di cng projects over a decade ago.
Going back to the OP, a GM 6L v8 low pressure (~60 bar) DI CNG lab rat was on the road some time ago that showed some promise but thelack of funds, lower cost of port injection and little interest at the time pulled the plug. I built a few sets of DI capable cng injectors for former clients and another group of students who were competing at an sae competition. Mileage improvements and co/hc reductions were there in spades but Nox was horrific due I beleive a lack of proper chamber shape, inadequate spark heat and less than optimized placement of less than optimum injectors. The port cng injectors we built then (substantially identical to todays continental cng injector) were equipped with modified armatures, coils and pole pieces shared by an earlier DI gasonline application. Opening under high inlet pressure was not an issue with enough amp turns and drivers.. the problem imo was poor control over fuel/air preparation in the cumbustion chamber.
Just my 0.02 dinars.. Respectfully, Turbo Cohen
RE: Lean burn on automotive natural gas engines
Colorado State University's Engines and Energy Conversion Laboratory (EECL)
RE: Lean burn on automotive natural gas engines
RE: Lean burn on automotive natural gas engines
The company was partners with Siemens long ago and this group broke off after I left. They were in the same facility I worked at but they were not involved with cng until after I left..
The technology aint perfect yet, nobody has perfected gasoline or diesel injectors either, but this may be a good place to look if you are considering a lean burn gm or ford cng di application.
Good luck with your search Msantiago