Ceramic Coating

[Mark(The Miser)UK]

theoretically if you can keep 100% of the heat inside the chamber it would be extremely efficient.  but that's kind of impossible.

It's a ceramic head then...
And an electric heater for the driver...
A coil round the exhaust would suffice I think

[jtanguay]

but you can't reach 100% efficiency with ceramic can you?  rather you need something that actually reflects the heat.

[greg123]

Some coaters dual coat, first an insulating coat, then a heat reflective coat.

Re not coating the pre-cups, I respect the experience of those that have done it and don't advise it, but it cannot be correct to say it keeps heat out.  Correct, it keeps heat out of the pre-cup - BUT it retains the heat inside the air within the pre cup where it is wanted.

The pre-cup heats by cooling down the air inside it, if a thermal barrier is placed over it as a coating it will no longer cool down the air inside it so well - this is the reason why a lot of people have used it in low compression diesel engines (search on the web) as it effectively restores some of the heat lost when dropping CR.

I would argue that other than a small thermal loss, it won't improve the burn IF the air was already hot enough to ignite the diesel anyhow, pre coating.  More gain would be seen on an engine of lower CR or some other issue causing lower air temp in the pre cup.

If any negative effects were seen, something must be wrong.  All things being equal, it's a good thing to do as reduces thermal stress on the head and pre cup, improves efficiency and sustains the air temperature in the pre-cup better.

[saurkraut]

i'd like to agree with you that putting a heat barrier/reflective coating in the pre chamber makes all the sense in the world.

Tragically, it appears we have emperical evidence, from some one that has invested alot of time and money into experimentation, that says otherwise.

I guess we need to figure out why it doesen't work, and attack the problem from that angle.

Apearently, a swirl chamber (or something else) at 198 F aids in combustion.  So what ever the air temperature rises to, from compression, it needs another 198 degrees to do something to succesfully complete the combustion process with the equipment we have now.

Are the swirl chamber walls mearly heating the air a few degrees more in the phemto second that the air is in contact with it?

Is the air being pre heated in the intake tract?

Does a hot injector give a better spray pattern?

The TDi engine seams to work just fine at a much lower CR.  The gosh darn things even need glow plugs in the coolant to keep the driver and passengers alive in frigid climates.  Why can this engine do this?

Higher injection pressure?

Different combustion chamber?

Any thing else? pilot injection?

Do we need a TDi pump to run an IDI motor at the same CR as the TDi?

[Mark(The Miser)UK]

but you can't reach 100% efficiency with ceramic can you?  rather you need something that actually reflects the heat.

Silver coat the ceramic?

[saurkraut]

I wonder if its the temperature of the injector.  The ceramic coating insulates the injector, and there is no water jacket in the area.

Any one have one of those opticle temp sensors?  Try aiming at a warmed up injector boss, and then about an inch away where there is water jacket.

[Mark(The Miser)UK]

i'd like to agree with you that putting a heat barrier/reflective coating in the pre chamber makes all the sense in the world.

Tragically, it appears we have emperical evidence, from some one that has invested alot of time and money into experimentation, that says otherwise.

I guess we need to figure out why it doesen't work, and attack the problem from that angle.

Apearently, a swirl chamber (or something else) at 198 F aids in combustion.  So what ever the air temperature rises to, from compression, it needs another 198 degrees to do something to succesfully complete the combustion process with the equipment we have now.

Are the swirl chamber walls mearly heating the air a few degrees more in the phemto second that the air is in contact with it?

Is the air being pre heated in the intake tract?

Does a hot injector give a better spray pattern?

The TDi engine seams to work just fine at a much lower CR.  The gosh darn things even need glow plugs in the coolant to keep the driver and passengers alive in frigid climates.  Why can this engine do this?

Higher injection pressure?

Different combustion chamber?

Any thing else? pilot injection?

Do we need a TDi pump to run an IDI motor at the same CR as the TDi?

Apparently 'over swirling' is possible as it encourages more gas to be cooled from the chamber sides and reduces the burn quality.The VW swirl chamber is based on a Ricardo patent AFAIK from at least 60 years ago and in the 50's was regarded as one of the best of the IDI's efficiency wise.

Surely what makes an engine do work, is not the flames from the fuel but it is just a matter of heat... Extra heat expanding a particular volume of air. So arguably an infra red lightbulb  could do the same thing.
Initially I couldn't see how the swirl chamber could heat the air; but I guess it can whilst air is cooler than the chamber. But what is the temp of the chamber walls? what with the coolant trying to suck the heat out. Heat will of course go back out of the air as the compressing takes it beyond wall temp on its way up to 600 deg C. Fuel burning only raises it up another 300 deg C or so,
Where did the rapidly cooling walls get their heat from? Obviously it came from the previous 4 strokes or at least the power stroke. Thus  in the continual process the present power stroke will be 'robbed' of heat for the next cycle.  
Ceramic coating will reduce heat loss so the same coolant will be able to remove more of the heat that does pass  (2/3 of non ceramic setup) and so there will be less heat returning to the air from the chamber walls  but with a 1/3 more heat staying in the chamber that doesn't seem a problem. If peak air temp in the chamber is higher in the ceramic case then turning the fuel down should result in similar temperatures to original setup.
Reducing radiator size could help; or using pure antifreeze (which although it boils at a higher temperature actually has a lower SHC than water).
I don't like the idea of higher and higher injection pressures  just seems like extra energy wasted and extra strain on the pump. Neccesary perhaps for absolute power but for economy not required. Somewhere I have a book that suggests that over atomisation can lead to poor burning. Perhaps its linked to times of lower injection volume where the droplets can get lost in the excess of air and slow the flame front...

However efficient these TDI engines appear; I'm not getting the vibes that they will be long life engines.,,,
Rant off

[saurkraut]

No rant detected.  I'd really like to cermaic coat my prechambers if there is a noticable, measureable bennifit.

we can pontificate all day long about how it should be bennificial, but we have a member of this fine community that has gone where no man has gone befor, and actually ceramic coated everything but his socks.  The results are that ceramic coating the swirchambers of the VW IDI diesel does not work.

I am inclined to trust Dave's observations that ceramic coating the swirl chambers on the IDI VW Diesel engine results in lower performance.

From his varied posts on the subject:

it does not result in better fuel milage

it does not improve cold starts

on a stricly performance only VW idi diesel, it gives no bennifit, but actually reduces performance.

He has no motivation to report an untruth.  I don't suspect he used the wrong coating.

I could write a couple of paragraphs on why ceramic coating the swirl chambers should work as well.  And with my plans to build a low compression VW 1.6TD engine, I really would like to ceramic coat the swirl chambers too.  I contacted Swain Technologies (http://www.swaintech.com/), sent them pictures, talked at lenght over the phone about it, and although they have never done a diesel swirl chamber befor, they felt it was a do-able process and should yeild noticeable bennificial results.

But with Dave's experimental results, I am inclined to begin my build without ceramic coating the prechambers.  Its not an expense thing, its a performance thing.  I can't drink the coolaid and jump on a band wagen thats heading no where.

I honestly suspect that the ceramic coating is not causing the bad results because the wall of the swirl chamber are at a lower temperature.  I suspect that the cooler wall of the swirl chambers are causing an unintended consequince to something else, and thats causing the poor performance.  No good deed goes unpunished.

If VW screwed up the swirl chamber design and they have to be at 190 F to run right, we're screwed.

If there is something else whe can fix, or modify, i'm in like flin for cermamic coating the swirl chambers.

Does any one have one of those point and shoot temperature measurement thingies?

[greg123]

Tragically, it appears we have emperical evidence, from some one that has invested alot of time and money into experimentation, that says otherwise.

Maybe the member can post a bit more info, wasn't it more that he couldn't measure the difference - which if only looking at changing the coating on the pre cup without changing anything else, unless measuring mpg carefully over 2,000 miles would be hard to get an accurate figure on - given that a FULL engine treatment of multiple coatings gives UP TO 5%?

I guess we need to figure out why it doesen't work, and attack the problem from that angle.

Can't argue with that ;-)

Apearently, a swirl chamber (or something else) at 198 F aids in combustion.  So what ever the air temperature rises to, from compression, it needs another 198 degrees to do something to succesfully complete the combustion process with the equipment we have now.

This can't be so, on full compression the air is way higher temperature, a chamber round it at a 'cool' 198 will do nowt but cool the air down.  The chamber only gets hot via ROBBING the air of temperature.  Put 10 metal spoons in your cup of tea, leave them there for a minute.  All the spoons are now warm.  But your tea is now also warm, not hot.  The heat travels to something cooler - the warm spoons don't warm the tea up - they sap the heat of the tea to keep them warm.  Put your tea in an insulated chamber (flask) and it stays hot all day.  Compared to combustion and compression pressures, a pre-cup is always cold - so I cannot see in any possible way or form that it's 'heating' the charge up!  If bad running resulted, or no improvement, either the issue was caused by something else (changing too many things at once) or too small to measure the improvement, or a poor coating, or something we don't yet understand.

Are the swirl chamber walls mearly heating the air a few degrees more in the phemto second that the air is in contact with it?

And where would they get this heat from, unless it's taken OUT of the compression/combustion air - thus reducing pressure/temperature in the cylinder?

Does a hot injector give a better spray pattern?

Now that is a good question, quite possibly - it is done via heating the fuel on oil engines as without it they can't spray good enough.  Seeing as how with decent compression a car will start fine on a cold engine/injectors I think the answer is 'no' though, perhaps there is some small efficiency to gain by heating them - this would need practical testing.  Most people suggest they are 'hot enough' in the head but one could feed them with diesel at 100c pretty easily.  I don't think it's worth bothering with this line much though, my 'seat of pants' conclusion.

The TDi engine seams to work just fine at a much lower CR.  The gosh darn things even need glow plugs in the coolant to keep the driver and passengers alive in frigid climates.  Why can this engine do this?

 My argument on the other thread and generally agreed on in techincal papers is they don't have the compression and friction issues an IDI has with the pumping losses in and out of the pre-cup.  This results in the increased efficiency.  The increased injector pressure and different spray putting the energy in via the fuel rather than the swirling air to allow good fuel/air mixing enables them to run without a pre cup/swirl and at the lower compression ratios.  I think very high injection pressures on the smaller volume of a pre-cup may result in diesel hitting the walls (bad for mixing/power/engine life) and thus better suited to the lager 'bowl' in a DI piston.  Pilot injection is a way of managing noise and emissions on a di, as well as reducing the strain on the bearings as the compressed and ignited charge isn't released in a 'jet' from the pre-cup 'slowly' like on a idi, but explodes at once over the piston directly - the idi's are kinder from a shock wave/bearing load point of view at the expense of some efficiency (typically 10-20% compared to a di).

Do we need a TDi pump to run an IDI motor at the same CR as the TDi?

I haven't worked out what would happen.  Would be interesting.  I think there would be issues with the space being too small for the spray pattern produced by the di pressure/injector.  IF one enlarged the pre-cup to the size of a di bowl, maybe this would work (this would also give the same di compression ratio).  One could then perhaps drill a big entry/exit hole to the pre cup and make pumping in/out easier and approach the efficiency of a DI.  Of course you would also have the noise and loading issues of a DI if you did that, presuming it would run and you are not trying to fire the fuel through the alloy of the head or something ;-)

Seems like a good experiment though?  Anyone taken the pre-cups completely out and seen if the engines will run?  Lol.  We need a re-usable copper or metal head gasket for an experimental engine!  The cost of new bolts and gaskets puts me off tinkering more than anything else.

[jimfoo]

While not a great insulator, tungsten carbide transfers 2/3 the heat of steel, so TC liners might help improve efficiency. Don't know what the cost would be though. While looking at TC stuff, I ran across this interesting diesel. A coal/water slurry diesel "Over 200 operating cylinder hours were run on critical wearing engine parts. The main components tested included cylinder liners, piston rings, and fuel injector nozzles for coal/water slurry fueled operation. The liners had no visible indication of scoring nor major wear steps found on their tungsten carbide coating. While the tungsten carbide coating on the rings showed good wear resistance, some visual evidence suggests adhesive wear mode was present. Tungsten carbide coated rings running against tungsten carbide coated liners in GE 7FDL engines exhibit wear rates which suggest an approximate 500 to 750 hour life. Injector nozzle orifice materials evaluated were diamond compacts, chemical vapor deposited diamond tubes, and thermally stabilized diamond. Based upon a total of 500 cylinder hours of engine operation (including single-cylinder combustion tests), diamond compact was determined to be the preferred orifice material."

[saurkraut]

Here is an old post on Dave's experience with ceramic coating:

http://www.vwdiesel.net/phpBB/viewtopic.php?t=7017&highlight=

The results appear to be measureably WORSE.  Worse milage, worse cold starts, and less power.

I can say it should work too,  but looks like Dave has done some work in this area and really broke off his pick.

i'm still wondering if the ceramic coating is the cause of some unintended consequence which is the real problem.

[Mark(The Miser)UK]

935 racer... What colour was the ceramic coating?

If you got a 5%  gain overall was that by coating everything? If so then by implication a greater gain could have been achieved by coating the 'right' part.
 A larger exhaust gave me a 30% gain.
One final point you said coating affected performance and mpg; but then your goal has been to up the power and speed hasn't it? ... Maybe ceramics help the light footed 'econo-miser' :lol:

[935racer]

Ok I am going to attempt to answer all these questions. But first off I think everyone should ask themselves, why are we trying to coat the pre chambers? Is there a problem with the way they are stock? What is the ultimate advantage you are hoping for in ceramic coating the chambers.

Greg123: Yes you are right it keeps the heat out of the pre cup its self, and than reflects the heat into the air, which is of course where the combustion occurs. I also agree that this means the pre cup is cooling the air to a certain extent, but I believe this is only on a stone cold engine, once the engine is up to operating temp I believe the purpose of the pre cup is store heat for the combustion process, one of the reasons why I believe they chose iconel for the pre chamber, instead of just making the pre cup part of the casting and keeping it Al. I could be wrong but based on my experiences that was my conclusion.

saurkraut: where does this 198degree firgure come from? I assume this is celcius?

greg123: To give more info on my tests I have done this a few times times, twice of which NOTHING else was done to the engines besides removing the head, CCing the precups (and once the chambers) and reinstalling with a new HG, I set the timing back to where it was as well. The third time I tried I also lapped the valves, and CC'd the cups and chambers.

Andrew: I tried coating the blue area you mentioned twice, no noticeable gain. And as I mentioned earlier coating the pre cup alone seemed to smoke more, I needed to advance the pump.

Mark: the coating is a silver color.

Trust me I wanted some sort of positive benefit from this, but I just had no luck. I've tried ceramic coating damn near everything on these heads, and anything where there is heat for that matter, the local ceramic coater and I are really good friends and I send as much business to him as I can but this was one thing I tried that just didn't work.

[jtanguay]

i think i'm understanding a bit more about this now.. since my car smokes more now with the lower temp t-stat than it did with the much higher temp t-stat...

and the problem could also be magnified if you're using an intercooler to cool the charge air...

[Mark(The Miser)UK]

Thanks for responding so well Dave.
Myself, I'm lookng for Samepowerlessfuelmorempg... Pepsi  :mrgreen:

Interestingly; how was the coolant temperature affected with everything ceramikked?
Perhaps if the coolant temp dropped then the way to go would be to shield part of the radiator. :?:

As silver and white coatings I believe behave very similarly; I wonder if going against intuition and using a black ceramic would produce something special :idea: