Correct Plating For A New Engine Design

[MikeMM]

I'm working on a new type of internal combustion engine I designed and I need some help with deciding what coatings to use. The engine is part rotary and part recipricating and makes use of water injection and for that reason no materials that have a potential to rust can be used. Most of the engine will be made out of aluminium for this reason and because it's cheaper and because the engine doesn't need as much structural strength as a conventional engine. However, aluminium has lousy wear caracteristics so I am planning to coat some parts with other materials.

There are 2 places where I'm concerned with wear. The first is with the piston and the engine block the second is with the combustion chamber and rotor. I'm planning to use chromemoly piston rings but I am not sure what I should coat the aluminium block with. I'm considering nikasil but from what I have seen it seems kind of expensive. Are there other materials that would do an acceptable job without costing quite as much and what type of thickness would be needed for those materials or are there places that do the nikasil for a reasonable price? Basically I'm not trying to build a race car or anything but I am planning to use this prototype to demostrate the fuel efficiency of this design to potential investors and companies interested in licensing it. The engine has a far higher theoretical effiency than conventional engines so I am not really concerned about miniscule performance differences between coatings just as long as they do an acceptable job. I should also mention that the forces and gas pressures inside the cylinder should be less (about 1/2) than a conventional gasoline engine so there should be less friction.

For the combustion chamber I am similarly considering nikasil or else possible alternatives to nikasil but I also need to pick a coating for the rotor which I guess would have to be something different since from what I've read it's usually not a good idea to have the same type of material rubbing against itself. Whatever coating is used for the rotor should be the softer material since the rotor is more capable of compensating for wear. The rotor will be turning at 1/4 the rpms of the crankshaft and the rotor and the combustion chamber will have a very wide contact surface.

Finally, I know that some engines with nikasil had problems with corrosion when higher sulfer fuel was used in the past. I am planning to run this engine on propane gas. I was wondering if anybody knows how much sulfer is added to propane as an oderant and if the amount is more or less than is in gasoline or diesel so I know if this would be a danger to nickel.

If anybody could provide me with any suggestions it would be very helpful.

thank you,

Mike

 

[DVE]

Hello Mike,
Try to find out information from companies such as Sulzer-Metco, Whitford (Xylan), Kolbenschmidtt ... which supply coatings to OEM. I am afraid to be not very helpfull because I expect that you already know all of them but I think it is interesting to look first on what "others" are using as you can directly benefit from their experience.
Good continuation,
DVE
... By the way, if you´re european citizen, good luck with your investors ...

 

[MikeMM]

Thank you for your help DVE. I should have mentioned that I'm from the USA specifically southeast pennsylvania. Unfortunately that still doesn't make finding investors easy since most of them specialize in computer or other non-engine stuff.

I should have mentioned that I've looked into nickel and industrial chrome plating a little bit because they may be cheaper than nikasil since nikasil is sort of a specialty. Anyways one guy I talked to about electroless nickle plating said that nickel has poor adhesion to aluminium and didn't recomend it for that reason. That suprised me because nikasil is largely made of nickel. Is there some way nickel plating can be used? Does anybody have any experience with nickel or chrome plating and how they perform?

thanks,

Mike

 

[tbuelna]

MikeMM,

Nikasil requires special electrodes for its application (it's electrodeposited). Companies that apply Nikasil are usually only prepared to coat round bores. Nikasil also requires a specialized honing process to finish the surface after being applied.

Coating and finishing flat or irregular surfaces with Nikasil would likely require a substantial investment in tooling to produce a quality surface. So I doubt it's what you're looking for.

You can apply hard chrome, one or two mils thick, to aluminum and give it a light hone to finish it. It's hard and corrosion resistant. The only drawback is that it will eventually flake off. However, it may last long enough for your purposes.

Good luck.
Terry

 

[schmidtj86]

Water is a product of combustion in engines, and I'm pretty sure there have been thousands of people who have run water injection on a normal engine and have had no problems with rust. In general, the heat of the engine will vaporize most of it, so it's not likely to see sitting pools of water (but sure some condensation will take place as it cools). If any metal that can rust sits out in the elements for a while, it will rust, but with regular use, like a car engine, rust doesn't seem to be a problem for the moving/sliding parts. I'm not here to tell you to try to do anything in particular, just that I wouldn't concern myself so much with rust, unless the application calls for extended down time in a rust happy environment.

 

[MikeMM]

Thanks Terry that might be a good way to go for the prototype since I just need this to run for long enough to demonstrate the engine and dyno test it. Although I don't know if something that flakes off would be good when this eventually goes into production.

That is a good point schmidtj86 except that this engine is a non - 4 cycle design. I don't want to go into too much detail since this invention is not yet on the market but the way this engine generates power is very different than a conventional internal combustion engine. The water is used to cool the combustion gasses and create a vaccum. The amount of water that is injected in fact would be greater than the amount that could hypethetically boil so the parts will always be exposed to some liquid water.

thanks,

Mike

 

[MikeMM]

One other idea I had. Does anybody know if hard anodized aluminium would work? I think they use it in hyraulic cylinders sometimes but I haven't hear of it being used in this application.

thanks

 

[CoriolisForce]

Mike, I ran across a process that Hinson does to their clutches that may come in handy. It's called "akadize" which to me seems just like a hard anodize. It seems to work great on the parts that hinson makes. It may be worth checking out.

http://www.hinsonracing.com/store/product.html?prod_id=259

http://www.lovattprocesses.com/index1.htm

 

[dwedel]

As I don't know too much about your aplication, I'm not sure I can be of much help. We do have aluminum compressor pistons 28" diameter and some others at 11" diameter that are hard anodized. This allows the carbon filled teflon rings and rider bands to seat without eating away the aluminum. The maximum temps the teflon can stand is 300-350F. I assume the anodizing is good for those temps.

We have bought pistons like this from both an OEM and a specialty shop and it seems difficult to find people to maintain an consitant anodizing process. I haven't studied the process too much, but it seems difficult to find consistant procedures and standards on the web. Perhaps this is just my lack of research, but it seems to be more of an asthetic finish, thus it is more black art, and less science.

Like I said, my opinion, and limited experience.

dwedel
Hotrod Big Engines!

 

[SMOKEY44211]

You can run rings against a high silicone alloy aluminum. The Chevy Vega engine of the early 70's, one of the versions of the Chevy ZL1 CANAM block and many of the Briggs + Stratton offerings are a few that come to mind that have done so successfully. I'm not sure how it would fare in the rotary but it seems logical that it sould be up to the task.------Phil

 

[magnograil]

You might look into flame spraying tungsten carbide. I plan to use this on the rotary I am building (uses alloy sideplates). It is available in varying hardness. You will have to diamond grind it flat afterward. Grind shops I checked said they could not hold the alloy housing on their surface grinder magnetic chuck (obviously never heard of a steel plate and bolts) so I have to do it myself on the mill.
Flame Spray in San Diego said they could do the coating. They also do a sprayed ceramic coating that might work in your application.
Forget about TiN coating. I had one endplate coated ($$$) and it came off with my fingernail.
Electrolizing is a form of hard chrome that can be done on aluminum without peeling.
Hard anodize will grow the surface dimension so you need to compensate.
Nikasil like tungsten carbide has to be diamond ground which is why it is typically done on round cylinders.

 

[MikeMM]

Thank you everybody for all the good suggestions. As soon as I have all the drawings finished I'm going to get some quotes on the different coatings you guys mentioned.

It appears though that the cheapest option for some parts would be to hardcoat anodize (which is slightly different from some other anodizing techneques)the aluminium and from what I've found out it would seem like it would work well. Aluminium oxide is one of the hardest materials known to man so it shouldn't wear out very easily. Also it coats onto the surface evenly so the surface finish doesn't change much so it should be possible to hone a cylinder before anodizing it although it could also be diamond honed afterwards. There's also no cohesion problem. And although I couldn't find the friction coefficient of anodized aluminium I did find it for saphires which are also aluminium oxide and it was fairly good. It's also pretty cheap.

The only reason I am cautious about using it is because no conventional engine I know of uses it even though it appears to me that it would have advantages over iron liners, like being able to use all aluminium so you don't have a difference in thermal expansion, and yet not cost any more than them. Obviously there must be some reason. Does anybody know what that reason(s) might be for not using anodized aluminium?

 

[CCycle]

MikeMM
For the first iteration of a new cycle use anything you can get your hands on. You will have a dozen changes before you get around to firing the engine. Aluminum is probably the first choice. Gray iron is a great choice and it is readily available in many sizes, rectangular, rounds and cored rounds. By all means avoid making the first prototype of stainless or hastalloy.

If you are condensing exhaust using direct contact water with no phase change you are going to use lots of water. If it is single pass the corrosive build up will not be enough to worry about.

 

[optimum]

I do know that much about coatings but Goodridge offers their aluminum hose ends in electroless nickel which are subject to wrenching on. It holds up in this application as well or better than traditional red & blue anodize. Maybe they have a different process.

http://www.goodridge.net/maincat2002/SECTION4.pdf

They call it electroplate in their website but my catalog calls it electroless nickel so who knows.
Tim

 

[shbazjinkens]

I've thought of using water injection to gain power from the subsequent vacuum (some early steam engines operated on this principle) but when you do that with an engine you effectively ruin your means for getting rid of CO and NOx emissions. The catalytic converter only works with a lot of heat.