Ceramic musings
First off, a disclaimer:
I’m certainly no expert (nor claim to be) on the intricacies of thermodynamics or ceramic coatings. I’m Just a guy who likes to read technical papers, bat theory around until it makes sense to me and maybe put some of it into practice once in a while.
Most of my practical experience with ceramics has to do with high speed spherical bearings and the benefits in wear and friction characteristics of that application (I trust my life to them every day). That’s why Stanadyne starting coating DS4 parts in it in newer replacement units; Superior wear and friction properties.
But I’ll do my best to give some thoughts that I feel may be relevant on the matter of a reciprocating engine. You gents will have to decide for yourself if I’m “full of it” or not…..
As I understand it, ceramic coatings are more for thermal barrier than producing power. Although there is some common ground there based on my rather simplistic understanding of thermodynamics.
Ceramic on a piston crown is primarily for protection. It provides a thermal barrier to protect the aluminum from high combustion temperatures. As I understand it, it can be as much as another 200 degrees of additional tolerance. It prevents/inhibits heat transfer into the piston material, so that is theoretically more energy available to provide MEP (translation: Mean Effective Pressure = more force pushing the piston down).
There could be some benefits to coating the precombustion chambers, but I’m a bit leery of that. Precombustion chambers are a funny bit of engineering and often don’t seem react the way you think they would for a given modification. I suspect it has to do with the fact there are so many different things going on in the chamber during any given point of the 4 cycles. Coating the chambers (all of it, not just the inserts) would form a thermal barrier and could lead to lower ECT’s. Very important in an IDI design where so much heat is retained in the heads and imparted to the cooling system. There could also be a benefit due to less energy lost in the prechamber and subsequently transferred to the main chamber, thus available to contribute to MEP at the piston "face".
The possible drawback is that heat is a part of the precombustion chambers scheme in breaking up the coarse fuel spray of the 6.X engines. The prechamber may still retain sufficient heat, it may not. Only one way to find out.....
Swirl/turbulence/tumbling is the other factor at play in the precombustion chamber. Whether the smoother coating would aid or hinder that swirl is something I’m not sure of. There are a lot of things in play when producing swirl/turbulence.
Effects on the prechamber of ceramic coating will just have to be tried and proven or discounted in a practical experiment I'm thinking. Way to complex a model to say for certain from theory. At least at my level of understanding it's not really possible to cypher it out...maybe there's some "willie coyote Super geniuses" out there that can....
Coating the firedeck (or combustion chambers if you prefer) is another area where I’m not sure there would be any measurable gains. Perhaps the thermal barrier imparted by ceramics would protect the valve bridge a little better. Perhaps not. There’s redesigned heads out there now that seem to have done away with the cracking issue so ceramics on the fire deck seems like it might be redundant at best. I would think on the fire deck you’re just looking to minimize energy loss more than protection. Given the design, I would think that to be an incremental gain at best (IE: not very much)
Where I could see some benefits in a turbo engine is in the exhaust ports, manifolds and turbine housing. Ideally, you want to expend all of the available energy (heat, pressure, etc) in the cylinder. We all know that just isn’t possible in a conventional reciprocating design. So energy not harnessed for MEP is now waste. Waste is something you have to get rid of quickly or it can impinge on the next intake charge. Coating the exhaust ports, manifolds and housing would keep the heat (IE: energy/velocity) of the waste up nice and high, by imparting less of the energy to the surrounding metal. The smoothness of the coating may also be a benefit in moving the exhaust mass efficiently(assuming the ports and manifolds are properly constructed with efficiency in mind).
An added bonus of this increased energy transfer in the exhaust in a 6.x is that it slams head on into the turbine.
Mucho Buenos.
More energy (or drive pressure if you prefer) imparted to spinning that turbine. Which spins the compressor. Which makes more mass flow. Which means more fuel. Which means more MEP, which drives the turbine, which…..well, you get the idea.
Remember, in the greater scheme of things you don’t want the “heat” in the turbo; you want it in the cylinder contributing to MEP. As I mentioned, it’s not practical in a conventional reciprocating engine to use it all so it’s waste. You just can’t harness all the energy released. Ideally; you could harness all the energy released in combustion which would pretty much make your exhaust ambient (in an unachievable “perfect” design). But you’d have to have a stroke long enough to allow the crank to extract
all the energy out of combustion for that to happen. The piston would just keep travelling until there was no more pressure pushing it down. That’s just not practical, the crank would probably need a throw measured in
feet to do that.
But oh my, the torque you would get from that! It would be like having the engine torque of a supertanker at your right foot’s disposal……ah, is to dream……:rolleyes5:
Internal combustion engines are not a very efficient design in terms of energy in for work out. But it’s the best we’ve got for now.
But, that’s what makes the turbo so viable; waste energy. It extracts more work after the fact from the waste to give you something that would have disappeared out the pipe. Keeping the energy in the cylinder is preferred for max work, but once it’s out you would prefer to get it to the turbine without loss to have a second shot at extracting work from it.
I guess you could look at a turbo as a gear head’s personal recycling program. How about that? We're "green" and we didn't even know it!
635 did have lots of extrude honing and coatings done. Unfortunately, the engine took a dump (crank bearings) before he ever really got a chance to see how the theory translates into practice.
That’s just my outlook on ceramics and thermodynamics in a reciprocating engine. Pretty simple understanding and I’m sure there are lots of “holes” in my reasoning.
Now, would I personally use ceramics?
Sure, if I had it apart, had the down time and had access to proper facilities. I’d probably look to do the piston crowns, manifolds and turbine housing. But it would be professionally applied; no “rattle can” solutions thank you. Not worth the chance of it coming apart or just not doing anything. I don’t mind experimenting a bit but when it comes to risking thousand on an engine rebuild, my risk management model is a tad to the conservative side. If I’m going out on a limb, I want solid theory behind the risk and properly constructed bits.
I’d also be looking for low friction piston skirt coatings at the same time. Plus blending, matching, probably gapless rings, etc, etc.
Remember, as I said; I’m no expert or physicist.
I could be way out in left field on some or all of this stuff…