How to reduce NOx emissions on diesel engines. 3

[Spek]

How can we reduce NOx emissions for medium speed diesel engines. 1500 - 2400 kW / 1200 - 1500 rpm.
What are the regulations.

 

[Docengineheat]

Whoa!!

That's a question that the diesel engine companies are asking with great gusto. You're not from Caterpillar or Cummins, are you?

First, I'm interested in what applications you are looking at. The power range you listed -- 1500-2400 KW -- is roughly equivalent to 2000-3500 hp, or about the size of a diesel engine found in a locomotive.

Second, how can you decrease diesel engine nitrous emissions? You need to either 1) lower the combustion temperature, or 2) add some type of catalyst that removes the nitrous from the exhaust.

The easiest way to lower the combustion temperature is to use cooled exhaust gas recirculation. This decreases the oxygen content, and hence slows the rate of combustion, resulting in a lower temperature and nitrous production. Unfortunately, you will also take a 3-5% efficiency hit.

A somewhat more complex method is to boost your intake manifold pressure and add variable valve timing to allow delayed closure of the intake valves. This is also known as the "Miller cycle", and is the basis for Caterpillar's ACERTS technology. Used with an aftercooler, this markedly lowers the temperature of the air in the cylinder at full compression, and thus lowers the resulting combustion temperature. The claimed advantage of this approach is that you don't take a fuel efficiency hit, but the results in the field are not convincing as of yet.

In case you didn't know, there is a rather fascinating story of the EPA vs. the diesel engine manufacturers concerning this very issue. The manufacturers have paid out better than 1 billion (that's b as in boy, or 1,000,000,000) dollars in fines since 1998 because of diesel engine nitrous oxide issues. The last I heard for this year Caterpillar has paid out $87 million just in the first six months of this year for selling engines (some non-ACERTS ones) that didn't meet the EPA requirements.

The second method, which is getting a strong look now, is SCR's -- selective catalyst resorbers. Urea seems to work fairly well, but must be replenished. The systems that work for gas ignition engines don't work on diesels because of the high oxygen content of the exhaust.

Finally, even as we speak there is a "Diesel Engine Emissions Reduction" (DEER) conference being held in Rhode Island. These are annual events. Check out their website -- they usually post summaries of the action:

http://www.orau.gov/deer/

Good Luck!!!

 

[DonClark92586]

Hi
I'd be very interested to know what you think of the bulk fuel additive product from biofriendly.com - see their website. They claim an 84% reduction in NOX among other things.
If you have any experience to share on this product, please email me at "DonClark" the at symbol "mchsi.com".
Thanks, Don

 

[jmw]

The EPA is good at handing out fines!
Another way to clean up NOX is to use plasma discharge in conjunction with catalists. This is currently under trial. A search of Google using "exhaust gas plasma discharge provides a substantial number of hits including

http://www.icpig.uni-greifswald.de/proceedings/data/Mizuno_1

While attempting changes to the engine set-up may help, as indicated above there are sometimes some penalties so exhaust gas treatement can limit the constraints on engine operation by helping maintain efficiency.
However, when considering diesel engines of any size another aspect is that of fuel viscosity. Fuel viscosity affects the droplet size formed by the injector. Too low a viscosity and a soft non-diffusing aerosol is produced. This tends not to mix well with the air and to burn incompletely (without excess oxygen) and in the wrong place. On the other hand, too high a viscosity results in large droplet formation. This time the droplets tend to travel too fast and again mix poorly with the air. Again, the droplets burn in the wrong place. In burners this is usually on the boiler tubes. It results in excess soot and increased risk of tube burnout.
Usually viscosity is regulated by fuel heating. The use of viscometers for viscosity regulation is standard practise in large diesle engines burning heavy fuel oil but they have been used for turbines enbling them to burn IF30 fuel instead of the lighter MDO. On one high speed ferry this is said to enable saving of around US$2-5000 per day.
Look at the specification for any diesel and you will see that viscosity is variable within quite broad limits. To date, the problem with using viscosity measurement to control fuel heating has been limited by the available technologies to the heavier fuel oils. However, new technolgies (vibrating fork etc._ offer the potential to extend automatic fuel heater control to smaller engines burning lighter fuels. I would expect medium speed diesels to be suitable for this and a logical expansion of the technique from the large diesel engines. Rail traction would appear a suitable opportunity and marine diesels.
As a guide to the benefits of online automatic viscosity based fuel management, on a medium sized petrochemical plant where heavy fuels are burned in steam raising the penalties of using excess oygen to ensure combustion can be around $150,000 per annum due to the increased cooling effect of the air. Such techniques were and still are often modified by using daily laboratory viscoisty measurement and flame inspection. On line viscosity meassurement can be very accurate and yield significant savings.
So as pollution effects become more critical there are many avenues by which to address the problem. The EPA, bless them, are providing an added incentive to to solve the problems. NOTHING TALKS LIKE MONEY! This is not just a problem with engines but of burners as well and there is plenty of history on the EPA web sites of their activity in addressing pollution issues such as that of the Pueto Rico Electric Power generators where numerous fines were levied and as part of an out off court settlement many other initiatives were made. One strand of the response illicted was to fit modern viscometers on the fuel heating control. This proved very succesful.
In another thread the question of available fossil fuels was raised and the reserves of oil were identified as being substantial. Not mentions is that there exists already accessible, orimulsion (bitumen water emulsion) equivalent to another 50% of the oil reserves. The problems have been handling this as a fuel. The that available reserve and new technologies this promises to be a valuable fuel and some large diesel engine makers are already using it. Does this mean that with suitable technologies e.g. fuel heater technology and exhaust gas treatment that medium speed engines could burn heavier fuels (the limit being the ignition delay of heavier fuels?)
heavier fuels are cheaper and if they can be burned as cleanly as more refined fuels, this may help pay for the addittional technolgy to control emmissions.
Any other thoughts?

 

[Docengineheat]

Don asked:

"I'd be very interested to know what you think of the bulk fuel additive product from biofriendly.com - see their website. They claim an 84% reduction in NOX among other things."

The Product claims that it is the "world's most effective and economical solution for significantly improving fuel economy and reducing emissions."

The agent in question is marketed as "Green Plus", and supposedly works for both gasoline and diesel fuels. It is claimed that Green Plus catalyzes hydrocarbon combustion by "unbundling" hydrocarbons which allows them to burn far more completely. Because of this, more energy is released from the fuel, but somehow the increase in energy does not result in a rise in combustion temperature. Instead, it supposedly lowers the combustion temperature by lowering the temperature needed for combustion. In other words, it "lowers the amount of energy needed for fuel to burn."

The putative result of using the catalyst is a) an 11-18% increase in fuel mileage, b) about a 2-3% increase in horsepower, c) and 84% decrease in nitrous oxide, d) an 82% decrease in carbon dioxide (!!!!!), e) 31% decrease in particulates, and f) anywhere from a 40-90% decrease in sooting (black smoke).

In addition, the promotional literature notes that Green Plus has been declared non-mutagenic by a researcher at the USC Keck school of medicine.

==========================

Observations:

This product is a bunch of hooey.

First, consider the test results. The website mentions that the Southwest Research Institute (which does a fair amount of diesel engine research) has tested the substance. Yet no mention of the Southwest Research Institutes results is found. Instead, reference is made to the effect of Green Plus on black smoke from buses in Mexico City and Las Vegas.

Documentation claiming an increase in horsepower is from "the sole distributor of Caterpillar Engines" in Australia, the William Adams company. So you would expect them to study the effect of Green Plus on Caterpillar engines, right? Wrong! The sole distributor of Caterpillar Engines in Australia studies the effect of Green Plus on . . . .an International Cummins diesel truck!! Where are the results on the Caterpillar Engines?

But here's the absolute, one-hundred percent proof that all of this is absurd; It is claimed that Green Plus reduces the output of carbon dioxide by 82%, while also reducing sooting (black smoke) and carbon dioxide.

Now, normally the goal of complete combustion is to take every last single carbon atom in a hydrocarbon and couple it to a couple of oxygen atoms to form carbon dioxide. If you are burning fuel, and you're reducing carbon dioxide, then the carbon has to wind up somewhere else. And anything else that it winds up as will be a pollutant.

This stuff has been in development for 16 years at a cost of $12 million dollars?

That's a bunch of BS. If this was a legitimate product their fancy website wouldn't make a mistake as egregious as "reducing carbon dioxide 82%".

 

[jmw]

docengineheat,
Great Post....
I visited the site for a look and i'm glad i read your post. I was just about to send off for some "Green Plus" when i spotted where the carbon dioxide went.... they just didn't draw it in their "Scientific Model" I was a bit mystified by the appearance of NOX in one diagram since no Nitrogen atoms appeared in the before diagram for normal combustion.
But these guys obviously have money to spend and a great track record. Take a look at the Titan process (

http://www.titanoilrecovery.com/index.html)

and the vortoil invention.... of course i am having trouble tracking independent references to these things and i have a problem with the EPA web site. I'd be interested to see their registration.
Anyway, i have better things to do for the moment, i've just received an e-mail from some guy in Nigeria who seems to have $53million legitimately acquired from his dad (whereabouts unkown) but he can't spend it in Nigeria. I've just got to send him my bank details and he'll cut me in for 25%. Must go.

 

[dgallup]

Quote:
"First, consider the test results. The website mentions that the Southwest Research Institute (which does a fair amount of diesel engine research) has tested the substance. Yet no mention of the Southwest Research Institutes results is found."

When I worked in the Mack Truck engine developement laboatory in Hagerstown MD, the owner of Roadway trucking demanded that we test the "Moleculator" or he would never buy another Mack. It was supposed to line up the fuel molecules for better combustion and energy release. Of course, it did nothing, which is what we reported. Sure enough, within a few months the adds started claiming "AS TESTED BY MACK TRUCKS". Yeah, we tested it and it was a POS.

 

[CDC]

Suppose you know this but the Nigerian money scam is a famous one...

 

[jmw]

CDC....
you're sure about this are you? You caught me just in time.
Oh well, back to the Titan people!

 

[nodnerb]

Hi,
A popular misconception with all this pollution prevention is that NOx is Nitrous Oxide. x is a variable and the two letters indicate that these are oxides of Nitrogen.

My experience with high speed marine engines (20yrs) has shown manufactuirers clutching at various straws to address this with a varied success rate. The bulk of my recent experience has been with the 3500 Series from the Caterpillar Family of engines. A lot of effort has gone into improving combustion processes including , Electronic Injection( they claim V.V.T. is coming but can't quite manage it with so many individual cyl heads at the mo) separate circuit cooling of Charge Air Coolers, increased J.W. temps and the use of Catalytic convertors. The best ones we have found are made in Sweden using a ceramic honeycomb but are were very difficult to clean. They need 7 bar air and 4 to 5 tonnes of pure water to flush out each one with 48 hrs needed to regenerate before returning to service.

The best non mechanical improvement I can see is what is known as "BIODIESEL"(a blend of vegetable oil and Diesel) it's available in the US and seems to be readily available over here in Europein Germany. A supplier there told me recently that they could ship lots of over 200 tonnes down to the Mediteranean coast for a slightly reduced price to locally tax paid fuel.

As soon as we can get an "authorisation" from Cat ( to avoid any warranty issues)and the go ahead from our offices we will try it and see what it does to our emissions.

Cheers

Nodnerb

 

[Docengineheat]

Nodnerb:

"A lot of effort has gone into improving combustion processes including , Electronic Injection( they claim V.V.T. is coming but can't quite manage it with so many individual cyl heads at the mo) separate circuit cooling of Charge Air Coolers, increased J.W. temps and the use of Catalytic convertors."

==============================

If by V.V.T you mean variable valve timing, it has arrived and Caterpillar is marketing it as the "ACERTS" technology with "electrohydraulic actuated valves" or something of that sort. I know that the C13 engine was just approved and a couple of other in the C-series are already on the market. The Caterpillar website has some information on it.

I hate to show my ignorance, but what are you referring to as "increased J.W. temps"?

 

[nodnerb]

Hi,

J.W. Temps is Jacket Water Temperatures(Radiator Water/Coolant)

I am aware that the V.V.T. was available on the newest series from CAT but have not seen anything on this for the larger engines.

I was told when doing a course at CAT that the biggest problem was with the individual cylinder head design ( 1 Cylinder , 1 Cylinder Head). They have enough trouble stopping Exhaust Leaks on these engines with all the different sections so I can understand that there are some mountains to overcome.

Cheers

Nodnerb

 

[addwrks]

Took a look at the Biofriendly site... Hmmm... reeeallly.. an additive with a treat rate of 1:64,000.., now that's potent. No self respecting additive company would go there.

They state "Generally, with our bulk formula, one ounce treats 500 gallons of fuel"... hmmm 500 x 128 ounces = 64000
That is rather bizarre, I can see 1:3,000 but not their claim.

I would not discount the benefits of fuel additives though, you don't leave home without them. These kind of claims though, make good additive companies cringe, not more snake oil...!

Gotta love the Nigerian scam... Sweet crude there though...!

 

[taylorg]

Spek mentions engine speeds of 1200-1500rpm. I would classify these as high speed sets rather than medium speed.

The technology for NOx reduction is primarily being driven by IMO regulations for marine engines, of which two methods are being used; primary and secondary.

Primary method (on-engine): Engine technology.
Redesigned combustion chambers and optimised timing etc have reduced NOx levels to those required by the World Bank (for now anyway)for land based diesel plants.
Many manufacturers are playing with the Millar cycle, but it is only just reaching the stage where it is reliable, mainly due to problems with turbochargers. One engine manufacturer in particular has a gagging order on the turbocharger supplier to stop them releasing details of the problem.

Secondary method (off-engine or downstream): SCR. Highly effective, but highly expensive (both in capex and opex), not to mention handling and disposing of the nasties. Catalyst element also requires replacement every 3 years or so.

Dismiss all supposed claims and benefits of special additives and "magic potions" - it's simply bullsh*t.
Plenty places are using differing sorts of biodiesel, but remember there are side effects of using it.

Are you using gas or liquid fuel Spek? Your options either way are limited, but remember the regulators want to impose stricter limits without putting you out of business. I have dealt with a couple of cases recently where we showed the regulator and lenders that to install secondary methods would kill the project altogether. We reached a compromise by assuring them that the best available technology would be used without bankrupting the owners.
Good luck!

 

[SBBlue]

Taylor G reported:

"Many manufacturers are playing with the Millar cycle, but it is only just reaching the stage where it is reliable, mainly due to problems with turbochargers."

========================

I find this quite interesting. You would think that the big problem with the Miller cycle would be with the variable valve timing process, which are still a work in progress. Turbochargers have been around for 40 years, and I would have thought most problems would have been worked out by now.

Can you expand on this at all?

 

[taylorg]

SBBlue,

Happy to oblige!

I was referring to medium speed engines in the above thread (I note you are Automotive). Closing the inlet valves a few degrees early for Millar cycle is easy enough. I believe Mazda employs a similar variant of the Millar cycle to some of its car engines, which they say is similar to supercharging.
The problems I've heard about with turbochargers is related to the fact that they are of new design (ABB TPL etc)and have a much higher pressure ratio. This has reportedly led to a couple of problems:

1: Rapid failure of labarynth seals etc.
2: The whole point of the technique is to lower NOx by reducing combustion temperature. However, as soon as the nozzle ring gets a bit choked the exhaust temps rise along with the combustion temperature, and hey-presto your NOx is back up again.

I know of a couple of cases where plants have had to be derated because of the problems.

 

[addwrks]

Interesting how some of you have dismissed fuel additives as a solution for emission reduction. It's hard to believe BP would say the following: "BP said the fuels would reduce emissions of carbon monoxide, carbon dioxide, particulates and nitrogen oxides and at the same time improve fuel efficiency." Wow, these petroleum engineers must be off their rocker. Read for yourself at:

http://www.planetark.org/dailynewsstory.cfm/newsid/22492/story.htm

On top of that, they invested a ton of buckaroo's $$$ into this fuel additive program they are introducing into some of their "premium fuels".

Thought I'd break you mechanical engineering types in a little easy. I am no scientist but I praise "good science". For the most part, you folks are downright brilliant in presenting your knowledge. Just wanted to lend some insight from the world of chemistry.

Keep up the good work.

 

[SBBlue]

Are they spending more money on additive research or on public relations?

I don't think you'll find anyone on the forum who doesn't think that fuel composition doesn't affect diesel engine emissions.

The problem is that most of us have also seen a long string of various additives that improve gas mileage, make the engine run longer and cooler, eliminate pollution, reduce engine nose, make the engine run smoother, improve radio reception, help the shock absorbers, make teenagers respond to reason, cure cancer, and bring about world peace. . . .all for a measily $4.00 per tank of fuel.

And you know what? We've found out that most all of this stuff is pure BS.

Good luck to BP on their latest additive research. But I'm not holding my breath that by reformulating the fuel they will be able to make present diesel engines meet the 2007 and 2010 EPA emissions requirements.

 

[addwrks]

sbblue you nailed it. more money on public relations.

NOx compliance for 2007 will most likely need the assistance of exhaust after treatment technology.