Ceramic coated exhaust pipes? No thanks - Ferrari

[john.r.davies]

We've had threads before about ceramic coating for exhaust pipes, and if they work or not. Well, now we the word, literally from the horse's mouth. And not just any horse, but the black rampant stallion of Ferrari.

 

This month's Racecar Engineering features Ferrari's 2014 F1 power unit, the 059/4. It says "The exhausts swathed in thermal protection, something that Ferrari did not do for much of the season, baffling many as this lost heat ...the recoverable energy" And a picture of said swathing, not a ceramic coating, but a fireproof fibrous jacket, covered with a reflective outer surface. Pics of previous examples of the same engine show it wrapped, with fireproof bandage.

 

If Ferrari with the largest F1 budget of all, don't use ceramic coats, why should humbler souls like us?

 

John

Edited October 5, 2015 by john.r.davies

[RogerH]

....they just don't understand......

 

 

Roger

[John Bracher]

Perhaps even they can't afford to have it done??

 

Envy is such a nasty emotion......

[Don H.]

I might be more interested in what the teams at the front of the pack are doing... just spending the most money doesn't prove much! (smile)

 

In reality, one of the arguments I've heard against wraps (having no personal experience myself) is that they can accelerate corrosion. That matters for a long-term installation. For something in place for less than a few days it's probably more expedient to simply wrap the exhaust than have each bespoke piece ceramic coated.

 

What I take away is that the physics around heat management is sound, but there are multiple engineering solutions to the problem.

[john.r.davies]

Field leaders? Mercedes haven't been so forward, but here's the 2014 Mercedes-AMG PU106A Formula 1 hybrid power unit.

And what's covering the exhaust manifold? It sure don't look like ceramics, Toto!

 

John

 

 

[Don H.]

No, it doesn't look like ceramic coatings, John. At least not that one can see. Absence of evidence is not evidence of absence.

 

On the other hand, it would not be a surprise if that custom-made insulation IS ceramic -- just fibers, not monolithic coatings.

 

I seem to recall that advanced ceramics might have been one of those fields of materials development that were closed to F1 in the interests of cost control. Like metal-matrix composites. Dunno if that applied to coatings or not -- I'll need to review the regulations.

[Don H.]

The 2015 F1 Technical Regulations permit ceramic coatings under certain conditions. Exhaust systems are specifically approved.

 

5.16 Materials and construction – General :

5.16.1 Unless explicitly permitted for a specific application, the following materials may not be used

anywhere on the power unit :

a) Magnesium based alloys.

b ) Metal Matrix Composites (MMC’s).

c) Intermetallic materials.

d) Alloys containing more than 5% by weight of Iridium or Rhenium.

e) Copper based alloys containing more than 2.75% Beryllium.

f) Any other alloy class containing more than 0.25% Beryllium.

g) Tungsten base alloys.

h) Ceramics and ceramic matrix composites.

5.16.2 The restrictions in Article 5.16.1 do not apply to coatings provided the total coating thickness

does not exceed 25% of the section thickness of the underlying base material in all axes. In all

cases, other than under Article 5.16.3(b ), the relevant coating must not exceed 0.8mm.

5.16.3 The restrictions in Article 5.16.1(h) do not apply to the following applications :

a) Any component whose primary purpose is for electrical or thermal insulation.

b ) Any coating whose primary purpose is for thermal insulation of the outside of the

exhaust system.

...

Edited October 5, 2015 by Don H.

[hoffman900]

The question you should be asking is what alloy is their exhaust system?

 

Ceramic coating is really only ever seen in racing circles on mild steel.

 

Stainless doesn't require it. This is why you see high level racing exhausts constructed with it (where iconel doesn't make sense from a cost / benefit standpoint).

 

Racing 101 - Question everything you see and there is more to it than typically meets the eye.

[john.r.davies]

I think we knew they were approved, Don.

 

But a ceramic coating is a completely different kettle of physics from a woolly jacket of fireproof ceramic fibres, that are there to retain a layer of still air about the heat source and prevent convection, plus a reflective covering layer to minimise radiation. The hype about ceramic coating involved the third means by which heat travels, conduction, which is almost always the least important.

 

John

[Don H.]

...a ceramic coating is a completely different kettle of physics from a woolly jacket of fireproof ceramic fibres, that are there to retain a layer of still air about the heat source and prevent convection, plus a reflective covering layer to minimise radiation. The hype about ceramic coating involved the third means by which heat travels, conduction, which is almost always the least important...

 

I agree completely with this, John!

 

PS: In my house in the upcoming winter, conduction is probably the least of my concerns regarding my heating bills. But in the case of ceramic coatings on exhaust, maybe there's a different way to look at it? The heat from the exhaust of a racing car has to travel through the wall of the exhaust pipe first (via conduction) before radiation and convection (plus a tiny bit of conduction) then distribute it. If one were to have a perfectly insulated exhaust pipe, would it not eliminate the need for radiation and convection control?

Edited October 5, 2015 by Don H.

[john.r.davies]

Hoffman,

D'ye know the story of the racing yacht, built with a white hull and black decking? Exactly the opposite of the owners instructions, but discovered far too late to correct it.

The Owner tells his competitors that the black hull increases zephyr speed, thanks to the hot air rising across the sails.

Nice one, Owner!

But yes, don't believe everything you see, and nothing you are told about racing.

 

Thanks for your point about materials. I looked up the thermal conductivities, and found that they are significantly different, so I'm surprised.

Carbon steel 36-54 Watts/metre/degree K

Stainless steel 16-24 W/m/K so about half?

Iconel 11 W/M/K about a quarter?

That is something I had no idea about - very interesting!

JOhn

Edited October 5, 2015 by john.r.davies

[hoffman900]

The answer lies here:

 

..................Density............Specific Heat..........Conductivity

..................(lb/in^3)...........(BTU/lb/F)............(BTU/hr/ft^2/F/ft)

 

Steel.(1020).....0.283..............0.10....................27.0

SS (304)..........0.290..............0.12.....................9.4

SS (429)..........0.280..............0.11....................14.8

Inconel (600)... .0.301..............0.106....................8.6

 

 

Last I checked, F1 cars had the budget to not have to use mild steel exhaust tubing.

[Don H.]

...Racing 101 - Question everything you see and there is more to it than typically meets the eye.

 

My favorite story here is the development of the Gurney flap.

[hoffman900]

Right, but you're missing the point. SS304 and Inconel, it's pointless to ceramic coat. F1, top tier NASCAR, and the like use Inconel. It's stronger than SS which means you can use thinner tubing (lighter), and conducts less heat. Mild steel really needs ceramic (think Zircotec or Swain) to realize similar benefits.

Edited October 5, 2015 by hoffman900

[MadMarx]

I really don't know why to coat anything?

I prefer to radiate and conduct as much away as I can.

[hoffman900]

I really don't know why to coat anything?

I prefer to radiate and conduct as much away as I can.

Chris,

 

Dyno with your hood closed and you'll feel differently. This is especially true with a non crossflow cylinder head....

 

The other is to keep the speed of sound higher through the exhaust tract. The retention of heat tends to be a bigger deal when dealing with alcohol fuels.

Edited October 7, 2015 by hoffman900

[MadMarx]

I never was interested on hot air under the bonnet on a dyno which doesn't exist if you zip down a lane at 120mph or more. Theoretical problem which might be something for road cars in town traffic but not for race cars.

 

You are right with sonic speeds and the dependency of temperature but that is a matter of pipe length and if you would need a broad band of power.

if your gearbox is short stepped then you shift all 500 rpm so the downside of loss of gas temperature in the exhaust and the change of pipe length is no real world problem anymore.

 

The main reason for run no wraps or coatings is cylinder head temperature. If a exhaust pipe is wrapped or coated then temperature is held in the pipe steel.

Steel conducts to the head over the mounting flange so the head gets a lot warmer just from the exhaust pipe. If the pipe cooled by wind from driving your head stays colder, and you get a better volume efficiency = more power.

 

First rule - get writ of heat as quick as you can.

[hoffman900]

Chris,

 

How sure are you of the underhood temperature at speed?

 

The head is iron and is plenty hot already. The proximity of the exhaust port to the intake port really makes it a mute point. You want to keep as much exhaust temperature in the actual tubing. Coatings, differently alloys will allow that and transmit less heat to the flange and subsequently less to the intake manifold. Less heat soak = higher VE.

 

The only place you want to get rod of heat is through the pistons, valves, and the cooling system.

 

Subscribing to your theory would mean everyone (including NASCAR, F1, etc) should be using mild steel exhaust systems and underhood heat is a non issue due to flow in the engine compartment. Tsking your theory to the extreme mean building cooling fins on the block and head. The evidence in practice is weighted heavily the other way.

Edited October 7, 2015 by hoffman900

[MadMarx]

I'm not familiar with Nascar designs because they have special rules to cope with and that might need a wrap or a coating. Also F1 might have some special problems with their cars.

Not to forget, if they use a special alloy that doesn't conduct or radiate then this would be the optimal stuff.

My suggestions referring on the Porsche results with 917 and later cars where many tests were made on exhaust wraps and coatings and all cost more power than they helped.

As I run a normal SS pipe and can't afford anything special the best help for me is to run a free pipe.

 

BTW....I measure a lot on my car, putting cameras everywhere....I've measured the temperate under the bonnet and the higher the speed to colder it gets.

Edited October 7, 2015 by MadMarx

[MadMarx]

Chris,

 

......

Subscribing to your theory would mean everyone (including NASCAR, F1, etc) should be using mild steel exhaust systems and underhood heat is a non issue due to flow in the engine compartment. Tsking your theory to the extreme mean building cooling fins on the block and head. The evidence in practice is weighted heavily the other way.

 

I think a coating from inside and not outside would be a great solution. The exhaust gas stays hot, the tube stays colder, small conduction to the head.

But who can coat the inside of a tube and how long will it last before bits of the coating break away?

Edited October 7, 2015 by MadMarx

[hoffman900]

Chris,

 

Both levels use Inconel. See my 3rd post for the details of why.

 

Air flow through the engine bay is not good. Drag increases with the square of speed. You want the radiator opening to be as small as possible.

 

NASCAR actually pre pressurizes their cooling systems to a higher pressure than in race trim so they can run very little radiator during 2 lap qualfifying. Raising the pressure increases the boiling point.

 

I'm sorry, Chris, but I am just not following your logic.

[MadMarx]

I'm sorry, Chris, but I am just not following your logic.

 

No problem, many people don't.

 

 

NASCAR actually pre pressurizes their cooling systems to a higher pressure than in race trim so they can run very little radiator during 2 lap qualfifying. Raising the pressure increases the boiling point.

 

This would mean, that they run higher water temperature what will hurt the intake charge.

[hoffman900]

The manifold runners are separated from the base of the intake manifold. It's not really an issue for them. The cooling systems are unsurprisingly incredibly efficient.

 

But using your rational, yes, the hotter water could hurt intake charge, just like a tube that conducts more exhaust temperature and radiates more heat because of it, adjacent to the intake manifold will cause underhood temperatures to increase and heat the intake manifold runners.

 

The more heat you keep in the exhaust (and not in the tubing), the more energy is preserved in the system.

The more heat you keep in the exhaust gases, the less is radiated to the engine bay and the intake manifold. Power losses in the double digits have been measured.

The less heat you radiate, the less underhood airflow you need to reduce heat soak. Less airflow decreases drag substantially.

 

These aren't air cooled engines. Keep the heat in the combustion chamber and the waste gases and remove it through the oil cooler and radiator.

Edited October 8, 2015 by hoffman900

[MadMarx]

If you are talking about V8 engines - and all have the basic design, the exhaust headers are on the sides, while the intake is on top.

The drag comes from front, blows out the heat of the engine and the exhaust to the rear, somewhat under the car or over the windscreen.

I don't think there comes much up to the intakes. An easy way to protect the intakes from radiation is to polish them mirror like on the outside.

They stay cool from that.

 

NASCAR Chevy - no wraps:

Edited October 8, 2015 by MadMarx

[hoffman900]

Chris,

 

They use inconel for their tubing. It has 1/3 the conductivity of mild steel. More exhaust heat stays in the tubing.

 

There is a lot more going on airflow wise in a NASCAR. Watch when they hit oil dry and how it blows out the wheel wells.

 

That said, they feed VERY little airflow through he engine bay. To control heat, you use something like inconel, or if close, you use wraps and shields as well.