Carbon issues with direct injection engines

[jlee]

Direct injection produces more power and better fuel economy. The trade off right now is the carbon build up on the intake valves. It may be, as you just alluded to, a need for a totally reformulated type of gasoline, so deposits do not build up as easily. You can thank all of this crap on Obama and the EPA wanting better (and it is not really much better) fuel economy.

http://www.caranddriver.com/columns/csaba-csere-why-mileage-hasnt-improved-in-25-years-column

Twice as much power, average 5 seconds shorter 0-60 times, and hundreds of pounds more weight...the improvements are probably more substantial than you realize.

 

[bruceb]

More power is always better. Better to have it on hand if you need it, than not to have it when you do. As to vehicle weight, some of that can be mitigated by use of more aluminum in suspension pieces and body panels. All aluminum engines can also save weight and some minor changes in overall gear ratios would improve MPG while not signifigantly hurting accelleration.

 

[GDI Tech]

Direct injection produces more power and better fuel economy. The trade off right now is the carbon build up on the intake valves. It may be, as you just alluded to, a need for a totally reformulated type of gasoline, so deposits do not build up as easily. You can thank all of this crap on Obama and the EPA wanting better (and it is not really much better) fuel economy.

Dead on correct Bruce!!!

Here is GDI in a nut shell VS port injection. Port injection the fuel was introduced int he port of the runner of the intake manifold just before the intake port on the engine. It used pressure of 45-50 PSI. This also sprayed the fuel into the port just as the exhaust valve closed and then the intake valve closes and the piston begins the compression stroke where it rises and compresses the air/fuel mixture. The compression ration with port injection was limited to app 9.5:1 for 87 octane, and 10.2-10.5:1 for 93 octane (the higher the octane, the less "explosive" the fuel, and the more controlled the burn so it allows for higher CR). What happens though is this mixture can "pre-ignite" or "detonate" prior to spark ignition due to high heat, low octane, oil mist present, etc. so when this occurs, the knock sensors detect this before the human ear can hear (in the old days we called this "ping" and knew timing was to far advanced or to low of octane fuel) and the ECU pulls timing advance until it ceases, but the most efficient power and economy comes from optimum timing advance, etc. So, as gasoline as a fuel does not burn very complete during combustion, the catalytic converters are relied upon to further burn these by products. So, the port injection technology had reached it's limit's for power and fuel economy as well as lowering emissions. Enter the "government". They mandated all auto maker develop more efficient engines that not only get better fuel economy, but also reduce emissions. This was not possible with existing proven port injection, and the auto industry was "forced" to adopt gasoline direct injection before it is perfected. The irony of this is after 10-15k miles the average GDI engine now produces as much or more in emissions and gets the same or less fuel economy than a similar sized port injection engine did, but don;t use common sense when we are talking regulatory agencies.

Now, enter GDI.. The fuel is now delivered directly into the combustion chamber and not until milliseconds before ignition, so combustible mixture is not present (except now that they are adding small port injectors back in to try and combat the coking) prior to ignition, so detonation is nearly eliminated (oil mist can still combust from the PCV vapors) and much higher compression ratio can be used (11.5:1 is the current GDI standard, but Audi and others are as high as 18:1 in the lab) and lower octane fuel. The fuel is now brought from the tank to the HPDI pump with a lift pump, and then a mechanical HPDI (high pressure direct injection) pump takes it up to 2,000-3,000 PSI and the fuel is atomized much finer, and the combustion s much more complete and efficient. Less emissions, more MPG, and more power from smaller displacement engines. All sound amazing, right? BUT, as back in the carbureted days, there is now no fuel spraying directly on the back sides of the valves (why top tier fuel or any in tank additives are now a pure waste as it never touches the valves) cooling and keeping them clean. Back in the 60's and 70's, coking was such an issue and wearing of valve guides, etc. the Feds mandated detergent minimums be in all fuel sold for street use and that addressed it well, and then when port injection came along and the valves were now cooled and kept clean (detergent fuel cannot clean an already coked valve) by the direct spray of fuel near constantly on the valves, and the era of needing a "valve job" at 30-40k miles disappeared the way of the dinosaur, or so we thought. SO for the past 3 decades or so techs have not been taught any of this as it was assumed they would never need it. Now we have it back worse than ever in the history of the internal combustion engine.

I have posted these before, but these show the basic fuel introduction types:



Here is a relatively late model BMW from BG's site showing how serious this is at low mileage, and the 2015-2016's are not much improved:



Here is a 2015 Corvette with GM's latest designs in combating this at 20k miles. This is before and after a manual intake valve cleaning, so no, NO automaker has this solved, not even close, and GM's head engineer for the Corvette, Tadge, is still stating there is NO reduction in power or economy from this and it does not exist. Same as all other automakers.

So. as you can see, tons of advantages of GDI vs Port injection, but one huge negative, and the industry has gone to great lengths to keep this information from the consumer and deny it even exists in most cases. It is up to the new vehicle purchaser to either take steps to avoid this, or trade the vehicle before the issues become real noticeable. Most daily driving consumer will never know this, and when the symptoms become obvious (random misfires, hesitation when accelerating from idle, lazy throttle response, and poor fuel economy and drivability) they will trade for a new vehicle and pass the problems on to the next owner. The corvette owner is an Aircraft engineer, and he was under the impression there was no noticeable power loss, and this is because this comes on gradually and most do not notice until it is severe. He could notice the regained power though after the cleaning.

Hope this helps!

 

[Denly]

More power is always better. Better to have it on hand if you need it, than not to have it when you do. As to vehicle weight, some of that can be mitigated by use of more aluminum in suspension pieces and body panels. All aluminum engines can also save weight and some minor changes in overall gear ratios would improve MPG while not signifigantly hurting accelleration.

Respectfully disagree. Why anyone need a 250hp sedan(which most V6 produce more in 2016) is beyond me, what is the speed limit again? A 130hp compact can handle legal hwy speed +20% in NA without issue with 4 people.

90% of the people can not handle 200hp at full throttle, detune the engine to make it more reliable and more efficient is my preference.

 

[NetWareHead]

so detonation is nearly eliminated (oil mist can still combust from the PCV vapors)

GDI Tech thanks for your input in this thread. Forgive me for asking a question that I posted before your joined the conversation but it pertains to the excerpt from your recent thread I quoted.

So, detonation can still happen with GDI and that depends on the quantity of PCV fumes present in the intake charge. And thats because these combustibles are present during the compression stroke.

There was a mention of some manufacturers opting to use a port injector and a direct injector; the port injector spraying fuel on the back of the intake valve for sole purposes of cleaning it. Wouldnt this introduce fuel into the cylinder during the intake charge and all of the issues associated with detonation? You will get a washed clean backside of the intake valve but perhaps canceling the beneficial effects of GDI?

And here is a bit of speculation from me. At some point, compression ratios are going to get so high, what will be the point of a spark plug? Couldnt gasoline engines using GDI be compression ignited like in a diesel engine?

 

[bruceb]

You can do that if you like, I want a vehicle that can get out of it's own way and out of the way of any others. For me, off the line times from a stop to decent speed are very important. Much easier to cross roads with traffic both ways and to merge onto highways.

 

[Midwayman]

ALL auto makers GDI engines have this and none have stopped it.

There are articles on every engine as long as techs have posted their findings, but all automakers deny this:

http://mbworld.org/forums/c-class-c...-up-new-direct-injected-mercedes-engines.html

http://www.benzworld.org/forums/w204-c-class/2462321-gdi-intake-valve-carbon-fouling.html

Lot's of examples, but the best is to Google: "GDI Intake valve coking" and click on images. You will find actual pictures of most any engine you can imagine showing what is really occurring, and remember, NO port injection engine will show coking at all, even after several hundred thousand miles due to the detergent fuel constantly cooling and keeping them clean. Once the deposits form detergent fuel cannot clean what has already formed.

I assume this is in response to me. I already read those threads and the images aren't a MB engine. One of those threads actually had the quote I was reading about the injector positioning.

"I did a little poking around and found this... and it looks good... maybe! The new DI engines are designated M276 and M278, (V6 - V8). Both utilize the same head design although the V8 is turbocharged. But for our discussion, we are more interested in the set up of the injectors, which are piezo-electric direct petrol injection and the location of the intake valves relative to the injector. The new engine has a reduced V-angle between the cylinder banks, 60 now vs. 90, making the engine naturally balanced, enabling the designers to eliminate the friction hogging balancer shaft. The fuel efficiency numbers are truly astonishing for this engine, more than 24% more economical than the previous engine!

Let's look at the pix...

Click the image to open in full size. M276 V6

^ See where they placed the direct injected fuel injector?.... TDC! Now look at this picture...

Click the image to open in full size.
M278 V8 but same head design.

^ You can better see in this picture that because of where the piezo electric injector is located, (not to the side but above the intake valves) Kevibk2 may have hit the nail on the head! The intake valves (the larger ones) are perfectly located to take full advantage of the injectors spray pattern cleansing properties. "

I don't doubt there are some issues, but either the M276 is too new (5 years on the w204) or its just a not a widespread problem like some models. I searched all the usual tech sites specifically as well. Only model a found direct pictures of was their diesel DI engines. (There may be more, I was searching for w204 or M276 stuff specifically.)

 

[shabby]

Elite Engineering and the RX systems are available for most any vehicle, but some may need "creative: thinking in mount locations, etc. But they have good tech support to guide most anyone.

What makes these catch can's so special compared to a typical catch can you can make from a pop can? Is it the media inside to trap the oil or the fact that they seem to have 2 inlets and an outlet?

 

[Mark R]

And here is a bit of speculation from me. At some point, compression ratios are going to get so high, what will be the point of a spark plug? Couldnt gasoline engines using GDI be compression ignited like in a diesel engine?

There is a lot of work going on into this. The problem with direct injection is that it results in a stratified fuel-air mixture. This results in soot (particulate) production where micro-droplets of fuel exhaust all the air immediately surrounding the droplet, and the fuel in the core of the droplet burns with inadequate air present. Because of detonation, they also produce high NOx emissions.

With spark ignition, ignition timing is simple. With diesel compression ignition you can control this by injecting the fuel only at the point of ignition. However, if your fuel is already vaporized and mixed in the air, how can you control ignition timing? This is actually a very difficult problem. You can control it to some extent by air-fuel ratio, but in general, it's completely chaotic and affected by all sorts of parameters, engine temperature, heat soak in the pistons, oil blowby, etc. It also only works over a very narrow range of engine speeds and loads - too slow, and you get pre-ignition. Too fast, and your cylinder pressures spike too high.

However, this so called homogeneous charge compression ignition (HCCI) engine design would be able to operate on a gasoline fuel, get diesel level efficiency with gasoline level particulate and NOx emissions. As a result, there is a ton of money going into researching this.

Rumour is that some F1 teams have managed to get HCCI working under certain conditions, with the engines switching to spark ignition outside of the HCCI range (HCCI engines sound like diesel engines when operating in HCCI mode). As the precise designs are closely guarded secrets, no one really knows for sure, but the best guess is that they use pistons with a "nipple" in the center. The nipple fits into a recess in the cylinder head, forming a second combustion chamber with very high compression. When the cylinder reaches TDC, temperatures in the small combustion chamber ignite the fuel, starting to push the piston down. Then when the nipple disengages the recess, the flame escapes from the high compression chamber into the main chamber, igniting the rest of the fuel. To disable HCCI and enable spark ignition, a decompression valve in the high-compression chamber reduces the compression to stop compression ignition. A spark plug in the main chamber takes over.

 

[Engineer]

OT: Why does octane matter in DI engines since the gas isn't being compressed during the compression stroke? Since the gas is already compressed and being sprayed into the chamber at nearly the top of compression, wouldn't it act as a coolant at that point (leaving no chance of pre-detonation)?

 

[GDI Tech]

GDI Tech thanks for your input in this thread. Forgive me for asking a question that I posted before your joined the conversation but it pertains to the excerpt from your recent thread I quoted.

So, detonation can still happen with GDI and that depends on the quantity of PCV fumes present in the intake charge. And thats because these combustibles are present during the compression stroke.

There was a mention of some manufacturers opting to use a port injector and a direct injector; the port injector spraying fuel on the back of the intake valve for sole purposes of cleaning it. Wouldnt this introduce fuel into the cylinder during the intake charge and all of the issues associated with detonation? You will get a washed clean backside of the intake valve but perhaps canceling the beneficial effects of GDI?

And here is a bit of speculation from me. At some point, compression ratios are going to get so high, what will be the point of a spark plug? Couldn't gasoline engines using GDI be compression ignited like in a diesel engine?

Yes, I covered this in a few posts in this thread, but that is the main negative to the port injectors. They now create more detonation and more incidence of knock retard function pulling timing. This less power and less MPG. Then in studying these new engines with the port injectors added we agree seeing only a minor reduction in the rate. MarkR has the answer 100% correct to the compression ignition. Gasoline is far harder to control the point of ignition than diesel fuel. But he goes into great detail, and has it correct.

On the Mercedes engines, most all have changed injector and spark plug locations, have added multiple fueling events, variable valve timing events, etc. and we still today in the ones we get to tear into see excessive coking. No one has it cured, but no need to argue. (not you, midway man) If in doubt and you wish to see instead of take the "PR spin" press releases is to remove your intake manifold (takes minimal tools and only app 1 hour total to remove, inspect, and reinstall. No new gaskets needed as all are reusable) and see the proof right there with out having to trust in anyone claiming so. That simple. All of these changes have helped in small amounts, that we see VS the early 2000 GDI engines that were horrible, but any deposits forming on the valves disrupts air flow and creates unequal A/F ratios between cylinders as well as the wear these hard abrasive deposits are drawn into the softer guides. Something we have not seen prior for 30 or so years.

What makes these catch can's so special compared to a typical catch can you can make from a pop can? Is it the media inside to trap the oil or the fact that they seem to have 2 inlets and an outlet?

There are several principles that must be taken into consideration for effective air/oil separation, and any container with 2 fittings will trap some oil due to condensing alone. Then the internal volume has to be a minimum of app 16 oz to allow the flow to slow to the point of allowing droplets to fall from suspension. The Venturi effect creates suction that pulls liquid through and out most cans. The Bernoulli principle creates lift that also will pull droplets out and through. You need both coalescing separation and condensing, and then finally gravity most also come into play. The outlet of any separator must be at least 3" vertical from where droplets are separating inside. So if you look at most Catchcans sold, they are either just empty containers with fittings:








Or some screen inside but the inlet and outlet right next to each other, and as any flow seeks the path of least resistance, most of the vapors just exit and are never routed through a system internally:



Then you get to the more expensive "billet cans like moroso/diablo sport/pahsetek/JLT, etc. (most are made by one company for over 20 different brand labels) where they are too small as well as they have media that traps the oil and compounds tight against the outlet so most is sucked right out from the media:




So none of these take simple flow dynamics into consideration.

Then some use a simple air compressor water separator and buy them for $12 and sell them for hundreds$ with their label stuck on, but as you can see add anther and they do a very poor job as well:



The ones I mention all use a patented design that has the flow of foul vapors go through distinct steps that each do a portion of the job. The vapors first flow into a main coalescing chamber with stainless steel mesh. Then most is removed through this forst step. The vapors then flow into the main condensing and collection chamber, before passing a lower disc baffle that causes all to make as much contact with the outer cooling wall before again slowing into a secondary condensing chamber and another disc baffle to again make contact with the outer cooling wall to give one final condensing shot before entering a separate outlet chamber. These are the only ones that the dirty/foul oil laden vapors never mix with the cleaned vapors exiting. All others the vapors mix so there is no way to be effective:



Most judge a purchase on appearance and price and they like a small size for fitment, but never look into what makes a system effective or not, and unless you actually do a test such as this one (JLT had the thread locked) they never know as all containers will catch some oil.

Read this test a JLT can owner did:

http://themustangsource.com/forums/f726/jlt-vs-rx-catch-can-results-part-2-a-532449/

There are more as well if you search.

There is a lot of work going on into this. The problem with direct injection is that it results in a stratified fuel-air mixture. This results in soot (particulate) production where micro-droplets of fuel exhaust all the air immediately surrounding the droplet, and the fuel in the core of the droplet burns with inadequate air present. Because of detonation, they also produce high NOx emissions.

With spark ignition, ignition timing is simple. With diesel compression ignition you can control this by injecting the fuel only at the point of ignition. However, if your fuel is already vaporized and mixed in the air, how can you control ignition timing? This is actually a very difficult problem. You can control it to some extent by air-fuel ratio, but in general, it's completely chaotic and affected by all sorts of parameters, engine temperature, heat soak in the pistons, oil blowby, etc. It also only works over a very narrow range of engine speeds and loads - too slow, and you get pre-ignition. Too fast, and your cylinder pressures spike too high.

However, this so called homogeneous charge compression ignition (HCCI) engine design would be able to operate on a gasoline fuel, get diesel level efficiency with gasoline level particulate and NOx emissions. As a result, there is a ton of money going into researching this.

Rumour is that some F1 teams have managed to get HCCI working under certain conditions, with the engines switching to spark ignition outside of the HCCI range (HCCI engines sound like diesel engines when operating in HCCI mode). As the precise designs are closely guarded secrets, no one really knows for sure, but the best guess is that they use pistons with a "nipple" in the center. The nipple fits into a recess in the cylinder head, forming a second combustion chamber with very high compression. When the cylinder reaches TDC, temperatures in the small combustion chamber ignite the fuel, starting to push the piston down. Then when the nipple disengages the recess, the flame escapes from the high compression chamber into the main chamber, igniting the rest of the fuel. To disable HCCI and enable spark ignition, a decompression valve in the high-compression chamber reduces the compression to stop compression ignition. A spark plug in the main chamber takes over.

Dang Mark! Another member that actually knows what he is talking about! Very impressed. Most only look at whatever an automaker makes public in press releases and never actually look deeper into what actually is occurring, why, and how.

Your an asset to this and any other forums your on. Rare to see another that has accurate factual info to share. :thumbsup:

Lets discuss more as I in my 60's always can learn more as none of us are "perfect" and "know it all".

 

[GDI Tech]

Shabby. Got your PM but until I have 25 posts, I can't reply. I was unable to get the picture of the can you asked about, but I will state app. 99% of all we have tested are not worth installing, and several were unreal great looking and expensive, yet that was the extent. Can you send an actual picture link from say Photobucket or similar?

Thx!

 

[shabby]

This is what it looks like http://s1240.photobucket.com/user/b...1-4600-A981-12A42ECD5286_zpsmiodnx59.jpg.html uses a pa66gf35 filter to separate the oil.
Looks like a provent 100 https://industrialfilters.mann-humm...ummel/kurbelgehauseentlueftung/ProVent_en.pdf

 

[GDI Tech]

Hi Shabby,

That unit was originally designed to be used in the ventilation portion of heavy machinery where it would trap and contain and return to the crankcase of a gear box or similar. If you return what a catchcan traps to an internal combustion engine, you are also trapping far more than oil or lube. You are trapping water, sulfuric acid, unburnt fuel, abrasive soot, carbon, and ash particles and other damaging compounds that should be burned in the combustion process and exit the exhaust. These type systems when used on an internal combustion engine greatly reduce engine life by adding this concentrate of contaminates and dirty oil back into the crankcase. You can NEVER return what is caught back into the engine oil w/out serious consequences down the road from added wear and tear on the internal components. That and when we tested one of these a few years back, it only trapped a small portion of the oil your trying to remove from the PCV vapors. They work excellent in the industrial setting and applications with machinery crankcases and transmission/gear unit vents, but on an internal combustion engine would steer very clear of it.

Here is a correct industrial separation system for purifying what is trapped and returning clean oil alone to the crankcase, cleaned unburnt fuel to the fuel tanks, and the damaging contaminates to dispose of properly:

http://www.alfalaval.com/industries/marine-transportation/Engine-and-transport/Clean-emissions/


But these start at close to $10 and weight several hundred to several thousand pounds. These are the only type separators that allow safely reintroducing the oil captured back into the crankcase.

The other thing is look at the construction of these units. Plastic is an insulator and does not transfer heat well, so there is almost no condensing taking place. They reply on a synthetic fabric filter for separation, and they do a poor job as well as clog over time and then restrict the proper amount of flow your PCV system requires. Then the internal size is not large enough to prevent the Bernoulli effect from carrying droplets out the outlet.

Be very cautious of many of the solutions being sold for internal combustion engines. Far too many that are not proper. And many that can and will cause engine damage or premature wear.

Hope that helps!!

 

[shabby]

Good info, thanks. I was a bit hesitant after reading that it put the oil back into the oil pan.

 

[basslover1]

GDI Tech:

I'm enjoying your insight here, just a few questions for ya though. I own a Fiesta ST, direct injection, yadda yadda. So if I'm reading what you're saying correctly, the catch cans that are available for my car (ranging from $130-200) aren't going to be very effective at catching junk in the PCV system?

I plan to own the car for many years and miles, and while Ford's DI engines don't appear to suffer as terribly as VW/Audi and BMW engines do, it's still a point of concern since no one has really fixed the problem yet.

 

[shabby]

This is the cheapest one for $219 http://www.eliteengineeringusa.com/elite-engineering-e2-x-catch-can/
There's another clone here http://www.mcnallyelectronics.com/Universalbr-Oil-Catch-Can-Kitbr-No-Clean-Side-Separator_p_52.html
And the original patented one is sold by team rxp http://teamrxp.com/products/ford-focus-st-rx-catch-can-ford-focus-turbo-catch-can it comes with an additional separator so that increases the cost.
It seems the internal design of the rx can is what the other clones are copying, seems to work very well.

 

[railer]

In related news:

GM blocked a warranty repair on this guys 2015 Camaro 1LE (which apparently had an oil pump failure) due to catch can installation.

http://www.camaro5.com/forums/showthread.php?t=451361

 

[Engineer]

In related news:

GM blocked a warranty repair on this guys 2015 Camaro 1LE (which apparently had an oil pump failure) due to catch can installation.

http://www.camaro5.com/forums/showthread.php?t=451361

You've got to be kidding to me!!! Didn't I read that they are now installing catch cans on the Camaro now? GM is a joke.

 

[bruceb]

That guy really should get a lawyer. How does a catch can, which only captures oil vapors, cause an oil pump to not pump oil ? ? It is not even connected to the engine oiling system.
And there is a TSB about Oil Pump Failures on the GM LS3 engines due I believe to debris left in the engine from the manufacturing process (or was it a shitty (cheap) oil pump design) ? ?
A quick google search shows many oil pump failures. Not so sure I want as LS3 engine in my new car until this is resolved.

 

[TridenT]

From what I gather, running meth will not solve this issue either. If you start out with clean valves and use meth constantly, it might increase the time between manual cleanings (brass brushes, special solvents to not be used with fuel, walnut blasting, etc.) but that's it. (Likely by just making it harder for the stuff to stick to the valves and other surfaces) It won't get rid of existing buildup though.

People tested this by taking the buildup off and then putting it various meth mixtures to see if it softened or changed. No effect, apparently.

Guys with N54's reported little to no change when they ran meth full-time.

 

[KentState]

Methanol had a big impact on my car. All but the last two valves showed any sign of build-up and that was very minimal. Being that it is only a dual nozzle aftermarket kit, I would expect something designed specifically for an engine to do much better. The biggest downside is that methanol is pretty nasty stuff and I couldn't see using it on anything meant to be daily driven.

 

[GDI Tech]

Beware of McNally or the knock-off RX branded by McNally. They are the same internally as the genuine RX, but they are cheap made in China glued together and can fall apart with use like this example:


The china copies have under the RX "extremeautoproducts" and you can see the top and bottom seams. The true RX is 100% made in the USA and tig welded together w/no seems.

This is the Patent Holder of the design:

http://www.jegs.com/webapp/wcs/stor...60&Ne=1+2+3+13+1147708&searchTerm=tracy+lewis

Billet and threaded to be able to take apart.

Meth Injection only works if constantly sprayed. As most systems are they are boost referenced and only spray when a certain amount of boost is reached. It does help slightly when used as they usually are, but not enough to correct the issue or prevent it.

Certainly does not hurt though. Just not a solution. And at $5 plus a gallon, expensive to use constantly. We purchase it in 55 gal drums and it is only $150-$175 for 50 gal. that way. (We run our Top Dragsters, Super Comp, and Super Gas on methanol).

 

[shabby]

Just got the rx catch can for my car, will be doing a walnut cleaning of the valves soon.

Btw the new 2016 camaro lt1 has a built in catch can that drains the "filtered" oil back into the pan, that must be some magical filter the got in there.

http://www.corvetteforum.com/forums...3760739-built-in-catch-can-on-camaro-lt1.html

In related news:

GM blocked a warranty repair on this guys 2015 Camaro 1LE (which apparently had an oil pump failure) due to catch can installation.

http://www.camaro5.com/forums/showthread.php?t=451361

Lolololol poor guy should of gotten the 2016 one with a built in catch can.

 

[bryanl]

Could the valves and intakes be coated with something either nonstick or is a catalyst that cleans off carbon?