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Engine Materials

Posted by Bill Gatlin 
Bill Gatlin
Engine Materials
November 16, 2004 07:00PM
Hello,

In the engine I'm designing, the third stage sees steam at about 500 deg F. or less. In order to get an efficient expansion I'm looking at using a teflon piston surface and cylinder liner to lower heat transfer. The teflon would be working against graphite packing with oil lubrication.

Two things I'm hoping to accomplish with this are low heat transfer and very low friction especially since at the lower pressures at the end of expansion in the third stage the trad-offs between extra work output and friction start to become dubious.

So, does anyone have any knowledge of how these two materials might work together as far as wear or durability? Any other suggestions?

Thank you--------------Bill G.
Rolly
Re: Engine Materials
November 17, 2004 04:08AM
Bill I think you should be looking at ceramic coatings, and reheating of the steam to the low pressure cylinder.
Rolly
George Nutz
Re: Engine Materials
November 17, 2004 04:53AM
Bill,
Agree with Rolly on this one. The new ceramic thermal barrier/reflective coatings are very efficient. Also most triples without reheat did not noticably better in steam rate than good compounds. With reheat and a good vacuum on the exhaust would do much better. For instance the Doble triple with LP reheat had a very low steam rate---in the 6+# area??. This was not any better than the WIlliams poppet valve unaflow with its automatic valve and very low clearance volume however. A good attempt could be made with a compound with reheat with a cylinder volume of 4:1. Compounds and triples are difficult for automotive use unless the LP cylinder has an automatic receiver charging valve---something Doble never totally perfected.
So good of Earl to find you a reasonable Stumpf book, wouldn't mind having one myself.

George
D K Nergaard
Re: Engine Materials
November 17, 2004 05:39AM
Many moons (about 500) ago, I built an engine out of scrap metal to run on low pressure saturated steam. The cylinders were brass, so I tried Teflon packing on the pistons. Even at the pressure I used, 15 psig., the Teflon wore rapidly, aggravated by its high coeffecient of expansion. When things were cool, the pistons were loose as a goose!
The thing was only built as a toy, so effiency didn't much matter. It and an ex laundry boiler burning coal were placed in a 13 foot boat with side wheels which we christened "S. S. Asthmatic".
Bottom line. I cannot recommend teflon for steam packing. Even at low temperatures, it tends to flow under pressure.
Rolly
Re: Engine Materials
November 17, 2004 07:11AM
Teflon should not be used as packing as we normal do. As David stated the expansion is great. If there is no room in the packing box it will wear rapidly and also gall the shaft.
Attached is a drawing of how the packing gland should be configured for Teflon. I have seen this used with very good results. The Teflon is installed as a solid disk with a slide fit. When it expands it will wear as shown on the drawing. You need the room behind the outside diameter for expansion. I have never tried it as a piston ring.
Rolly
Attachments:
open | download - teflon packing Model (1).pdf (2.8 KB)
Bill Gatlin
Re: Engine Materials
November 17, 2004 08:20AM
Thank you guys for your feedback.

So it looks like teflon is out.

Can the ceramic materials be used also on the cylinder walls? Would they work with the piston rings sliding across the surface, or perhaps graphite packing with oil? I've not found any reference to their use on the cylinder walls themselves. It would be great if ceramic would work here.

The first stage cylinder would vary from about 10% to 80% cutoff, while the second stage cylinder expands by around 3.5. They are set up uniflow with an extreamely small transfer port volume. Transfer port volume to the (or a) third stage would be a noticable amount, however.

Since this is just beginning layout I haven't worked out recompression in the second cylinder yet. The first recompresses to inlet and the inlet valve provides pressure relief into the steam chest.

Contemplated inlet conditions are 2000 lbsa and 1200 deg F. This I believe is what's neccesary to get the kind of efficiencys a modern engine needs. The "theoretical" efficiency of the cycle allowing for 10% energy loss in expansion is in the neighborhood of 5.4 lbs steam rate.

I am of course having the usual problems with the third stage as at 80% cutoff the steam needs much further expansion and at 10% almost no third stage is needed.

I am surprised at the much lower steam rate of an auto engine using reheat. Do you know what temperatures and pressures the Doble triple was working at? Any idea as to how reheat effected the throttle responce? Thinking it would slow it down a bit.

If I dump the third stage idea entirely and add more expansion to the first and second stages, what would be a good area of temperature and pressure to stop expansion at without wreaking overall efficiency too much?

I think I'm starting to see Jerrys idea that combinations of cuttoff and throttling are more efficient than either by themselves.

Thank you------------Bill G.

Mike K.
Re: Engine Materials
November 17, 2004 03:28PM
What about brass rings in a cast iron or steel cylinder? Perhaps you could use a baked porcelain enamel coating on the cylinder wall and then use soft annealed brass or bronze rings with some graphite lube. The Troy Type E manual mentions the use of a beeswax/graphite mixture instead of cylinder oil during engine break-in. If this is done properly, the manual claims that no cylinder oil will need to be used for the life of the engine as the beeswax/graphite allows the parts to wear together perfectly. These engines have iron/steel cylinders and pistons with no rings.
Bill Gatlin
Re: Engine Materials
November 17, 2004 06:29PM
Mike, brass or steel against cast iron with any kind of lubricant is a good wearing, low friction combination. Add nitriding as a coating on either the rings (steel) or cylinder walls and it gets even better. Nitride against chrome is a very good combination. This is what I'd like to use in the first two stages. See the website for Lycoming engines for their use of these.

The thing I'd like to cure in the possible third stage in particular is heat transfer from the steam to the cylinder walls. I would think this becomes more of a problem in this stage because of the potential of wet steam. It seems to me that water droplets in contact with cylinder surfaces would transfer a lot more heat than dry steam would. Teflon being hydrophobic and a poor conductor of heat as well as very slippery was the reason I was looking at it. Of course from the experience others have had with teflon it's out as a cylinder wall. Quit possibly the oil itself would be hydrophobic enough to limit water droplet contact, especially the new Mobil gear oil that Rolly found.

A question now becomes an insulating cylinder surface which wears well or could we just heat it with pressurized water from the economiser? Gotta kick that around, because being the last stage would also be adding heat to the exhaust.

The Troy engine sounds interesting, especially about using no rings. How does this work when thermal expansion is taken into account?

This is fun------------Bill G.
Re: Engine Materials
November 17, 2004 06:51PM
Bill the F doble in the green monster it ran 850 f and 1600 psi the Williams ran 1000 f and 1000 psi i am going to tie 1100 f 1300 psi
Bill Gatlin
Re: Engine Materials
November 17, 2004 08:39PM
Howard,

Both the Williams at 1000 F at 1000 psi and yours at 1100 F at 1300 psi fall on my expansion line from 1200 F at 2000 psi. So I think my estimate of 5.4 lbs/Hp-Hr is not too far off.

If your engine is an efficient expander you should be well under 6 pounds.

At full on, what do you think your exhaust pressure and temperature will be?

1100 F is starting to push on material limits. Even though the engine will run cooler than the inlet steam, the valves at least may get quite hot.

Are you planning to use any special stainless steels or other materials?

Thank you for your input-----------Bill G.
Mike K.
Re: Engine Materials
November 18, 2004 08:16AM
I think there is a bit of clearance between the piston and cylinder when the Type E is cool and that closes up as it warms to operating temperature. I haven't run my engine yet so I don't know. Maybe there should be rings and my engine just doesn't have them. The Troy-Engberg Type E usually only operates at 140 psia so the steam is only about 350 deg F, so expansion is minimal at best.

For your third stage, Bill, how about a cylinder sleeve of very thin metal surrounded by a cast block of insulating material? The sleeve would be there simply to provide a hard-wearing smooth surface for the piston to ride on and the actual stresses encountered in the cylinder would be borne by the mass of clay or teflon or other insulating material that surrounds the sleeve.
Re: Engine Materials
November 18, 2004 05:49PM
Bill the engine you sing is the1952 Williams 264 in3 1000 1000 6.5 pound rate ex temp 300
ex20 psi absolute is the block steel
Bill Gatlin
Re: Engine Materials
November 18, 2004 09:46PM
Howard, I've worked out some rough math on the conditions of your Williams engine according to the data you've given me.

The overall expansion ratio--------- 27
Inlet pressure-----------------------1000 psia
Inlet temperature--------------------1000 deg F
Inlet enthalpy-----------------------1505 BTU/lb
Exhaust pressure---------------------20 psia
Exhaust temperature------------------300 deg F
Exhaust enthalpy---------------------1192 BTU/lb
Work---------------------------------313 BTU/lb

Same expansion ratio-----------------27
Inlet pressure-----------------------1000 psia
Inlet temperature--------------------1100 deg F
Inlet enthalpy-----------------------1563 BTU/lb
Exhaust pressure---------------------20.5 psia
Exhaust temperature------------------378 deg F
Exhaust enthalpy---------------------1227 BTU/lb
Work---------------------------------336 BTU/lb

Gain in HP output -------------------23 BTU/lb or 7%
Extra heat added---------------------58 BTU/lb or 4.4%
Extra heat rejected------------------35 BTU/lb or 3.5%

Thirty nine percent of the extra heat added is converted to work in this temperature increase from 1000 deg to 1100 deg. Not too shabby.

Thanks Howard, a little data can go a long ways----Bill G.

Re: Engine Materials
November 19, 2004 05:12PM
Bill your clothe to Williams speck
Bill Gatlin
Re: Engine Materials
November 19, 2004 06:44PM
When considering materials to make the cylinder block and heads out of for an engine running 1200 deg F and 2000 lbsa the first thing that comes to mind are some of the high temperature stainless steels. It seems that in particular the inlet valve, cylinder head and the steam chest surrounding the inlet valve would need these high temp materials.

A friend of mine, who used to be a machinist said that good old cast iron working against steel valves (rotary) would still be a viable combination at these temperatures, that cast iron and steel or brass are suprisingly slippery with almost anything for lubrication.

Now Howard is planning to run the Williams engine up to 1100 deg F with steel parts. So the question becomes; at 1200 deg inlet is stainless an overkill? If it is at what temperatures would one need consider it?

Thank You--------------Bill G.
Re: Engine Materials
November 20, 2004 08:35PM
BILL the Williams has stateless par it valse tried cer amics rings and no oil the new Williams company is working on a compound and numbers ard closest to you
Bill Gatlin
Re: Engine Materials
November 20, 2004 11:10PM
Thanks Howard,

I wasn't aware that anyone as a company, meaning money, was actively working on a new design.

The numbers I've chosen seem logical because much over 2000 lbs and we may start to loose the advantages of a lamont boiler. Thought of going up to 2500 lbs to try a reheat cycle but the gains seemed too small for the extra stress.

1200 degrees F looked like a good upper limit material wise for boiler tubing to stay away from more exotic stainless steels. Also expanding down from too high a temperature makes the exhaust pressures too low and the temperatures too high so efficiency is lost.

Much more efficiency can be gained by designing a good expansion down to saturation at 200 deg F than by raising the temperature above 1200 deg., I believe. This is where a well designed compound might start to shine.

As you well know designing an engine for 100% output is easy. When designing for a dynamic range with variable cutoff the end of expansion is all over the place. Multiply this by the several stages of a compound and balancing them gets tricky. The first stage expansion ratio varies by a lot and the next stages are fixed. The last stage can vary from putting out one third of the work to not being needed at all.

I've got faith that I can find the answers to it.

Thank You and may the world find you well----------Bill G.

Re: Engine Materials
November 21, 2004 07:06AM
Bill & Mike,

I have been researching prospects for non lubricated engines and here is what I have come up with.

My engine is designed with a nickel silicon carbide bore that is spray plated and ground to finish on a iron liner. yes iron has great lubricarion prpoerties in many applications but when not running, the light film of rust scares me with it's abrasiveness. The Nikisil bore will not corrode and is much more wear resistant. Swain Tech coatings will be ceramic coating the piston and rod assembly with a lubricant type of ceramic on the rod and piston sides (skirt), and on the piston crown, the coating will be a ceramic thermal barrier that greatly reduces heat transfer. I looked at Nitriding and use to have many crankshafts nitrided after grinding but modern materials accomplish the same function with better overall results. The complete heads will be coated on all surfaces, including ports with thermal barrier ceramics as well as the heads of my stainless poppet valves. In an IC engine, it is virtually inpossable to burn a hole in a piston with such thermal coatings and it may be possible to use such treated aluminum pistons in a high pressure and temperature steam engine. Swain Tech can build up worn pistons with the ceramic coatings up to about 0.004 inches. About 60 % of the cylinder barrel has shallow channels cut around the inside to prevent contact with the sleeve, and the resultant heat loss, and I will have these areas coated with a thermal barrier as well. My first piston rings will be phosphor bronze bushing material cut to size but plasma and molly coated rings are available in my bore size.

The inlet valves (unaflow) are EV8 stainless with a hard coat that requires virtually no lubrication when run in phosphor bronze guides, both supplied by Kibblewhite Engineering, a supplier of valve parts to the after market automotive, motorcycle, ant ATV markets. I have seen this combination work very well in large displacement, high performance, air cooled motorcycles for well beyond 100,000 miles. If a bit of lubrication is needed at the valves, it is easy to use a felt type of wiper that contains a bit of synthetic oil and is feed with an ocassional drop or two.

There are many plain type bearings that are lubrication free but the bottom end of my DA engine is open and uses sealed ball bearings everywhere but the wrist pin and the rollers for the crosshead, where the most heat is. Here I have many choices including some Garlock brand materials. Swain Tech coats plain bearings with a lubricating ceramic that is said to prevent failure in the event of an interuption in lubrication. I am considering all the bearings to be non lubricated to significantly reduce the mass of the moving parts.

Somewhere on a forum someone asked if there were bearings that could use water as a lubricant, well all fluids can be used as a lube, that includes all gasses and liquids. Just the bearing can't adversely react with the lube, like rust and it must be proportioned so as not over load the lube. To accomplish non lubricated standards is sometimes easier with modern technology than to engineer for marginal lubricants.

I have to consult with an engineer at Swain Tech Coatings for more information as to the compatibility of certain coatings working together and I will post what more I find.

Beware of coatings that are called ceramic but are nothing more than glorified paints. Swain Tech is a major supplier to NASA and they developed the first practical ceramic coatings to be commerically available. They are huge in NHRA and Nascar circles. They even ceramic coat parts like valve springs to hasten the sheading of oil. There are some dyno tests that show a noticable increase in performance when an IC engine is coated to reduce friction and prevent power loss through heat loss.

Peter Heid
Bill Gatlin
Re: Engine Materials
November 21, 2004 11:33AM
Thanks Peter,

I believe your information will be very useful.

Although I'm not far enough along with my design yet, having an idea in mind of the materials and technology available to work with has a great effect on the outcome.

One of the materials I would like to investigate as a lubricant is hexagonal boron nitride powder. It is totally inert and will work to any temperature concievable in an engine. It's lubricating properties are much like graphite powder. It is included in the mix of a number of high temp materials to make them self lubricating, with a coefficient of friction of about 0.2. I first ran across it on a NASA website about self lubing gas turbine bearings.

I envision it also filling any gaps between piston,ring, and cylinder walls to effect a better seal. Any thoughts on that one would be appreciated.

Do you feel free to part with any data on your engine, such as inlet temp & press.? Is it a compound? The grooves cut into the cylinder barrel to prevent heat transfer is a good creative idea. Are they straight or rifled?

Thanks again Peter-------------Bill G.
Garry Hunsaker
Re: Engine Materials
November 21, 2004 02:12PM
Does anyone know of anything in print on these high tech coatings? Personally, I am looking more for something that says, here is what it is, this is what it will do, and these are it’s basic engineering characteristics. I have run across a few sights, that after the first sentence, they immediately drop into a high level mathematical projection of what they think the materials might be capable of, but I am more interested in what can I do with these materials now.

Which makes me wonder, has anyone run across a wear resistant coating being applied over a thermal barrier material? I was thinking if BMW could get away with direct coating aluminum cylinder walls, there might be other less heat conductive materials this would work with.
Garry
Mike K.
Re: Engine Materials
November 21, 2004 04:21PM
What's wrong with baked vitreous porcelain? How about good old chrome plating? I'm not against fabulous new high-tech coatings, but I am wondering if there is really any need to get so exotic?
George Nutz
Re: Engine Materials
November 22, 2004 05:55AM
Garry,

Go visit the Techline Coatings website as they have many coatings available that can be put on at home and baked in the oven. We used several of these products on the Knowles 16 cylinder barrel engine(steam). All sorts of heat and anti friction coatings available.
George
Bill Gatlin
Re: Engine Materials
November 22, 2004 07:10AM
George,

Could you put a picture and some specs on that Knowles engine up on another thread? Sixteen cylinders in a barrel sounds interesting. How efficient is it?

Hope all is well with you-----------Bill G.
Re: Engine Materials
November 22, 2004 07:24AM
I am ready to contact an engineer at Swain Tech and I will ask any questions that are posted here along with mine. Our business is already a customer of theirs but I have yet to contact anyone with steam questions.

I know their thermal coating for headers is 3 layers of ceramic that are 0.015 - 0.020 inches thick and reduce radiant heat by more than 50%. Our customers claim a seat of the pants difference just by coating the exhaust headers but I would have to see it on a dyno.

You can contact them from their website at [www.swaintech.com] if you want. The web site has a good deal of information and prices based on automotive parts.

As George says, you should check out Techline Coatings, I have heard they have some excellent products.

Bill,

The grooves are straight and leave ridges to support the sleeves at the top of the bore, around the exhaust ports and a couple ridges between. The sleeve is a bit thick walled to accomadate the reduced area of support. The head gaskets will seal against the sleeve which is a light press fit into the cylinder barrel. For gasket material, I plan to use stainless steel to help block heat transfer as live steam will always be at the heads with the poppet inlet valves doing all the throttling. It is locomotive style, rod driven to the rear wheel from a single stage DA uniflow cylinder on each side of the swingarm so RPM is limited. The boiler is copper so I am holding it to 350 PSI and looking for a good deal of superheat. Copper was choosen to make my job of bending coils much easer on my first project, it helps my encouragement level when individual components don't slow the overall project from difficulty of assembly. I can't argue with the heat transfer either.

To help efficiency I have designed the inlet port to be very short and with a minimal clearance volume. To over come the extreme compression, I am porting the excess pressure for a portion of the stroke to the other side of the piston where it can perform work. It should fatten my indicator curve and cut down on the lumpies a bit.

I would be interested to hear more on what you find out about hexagonal boron nitride powder.

Peter Heid
Arnold Walker
Re: Engine Materials
November 22, 2004 01:44PM
Have you considered a power recovery turbine for the third stage.....assuming some of the turbine tinkers have as good luck on the turbine side.As the piston guys seem to be having on the piston side.
Anybody got the steam rate for that William engine at critical power or critical speed.(need for figuring turbine inlet steam rate)
Granted the turbine may look more like a compressor refrigation system with the expansion applied to power for the compressor and power wheels. Instead of cooling....but I think at this stage of development. You get 132 btu /lb of steam in work with each pass thru the turbine.
The piston engine exhaust is plumbed as the reheat section on the turbine.
Roughly 10-15% of the total steam mass circulating thru the turbine.
That was asumimg the piston exhaust was 20psia@378F goiing to the turbine with no losses in piping.
Still need to work more on my steam turbine tractor to get better data on that.Since that is in fact the pressures my modified turbochargers run at as
a free turbine powerplant for the garden tractor.Don't know why ,but seen better luck with modeling a running pilot unit on a dyno for design work.Than CAD design method.....too much hot rodding with dyno saying one thing and software saying another, I guess. Just like recently.digtal time lapse photograph showed diesel injectors were shooting donuts in the spray pattern with the back part of the spray leaping thru the front at 6 times the speed conventional wisdom thought possible in most Diesel Engineering Departments..As a result Cummins among other manufacturers are working on a new injector design using data that never showed up in thier design software.
I think steam will always have those kinds of surprises as well........
Bill Gatlin
Re: Engine Materials
November 22, 2004 09:01PM
Arnold,

The first two stages of my design work together like a single stage because of the very low transfer port volume and uniflow recompression. I am doing it this way to get as fine a control of cutoff with as large a valve opening as possible. At low cutoff then the valve starts more to throttle the steam as it can't open all the way, below about 8%.

The last stage I have worked out with variable expansion to compensate somewhat for the effect of variable cutoff. I an considering a stage in between that also could use a variable expansion ratio but I can't use the same trick as with the last stage, and I don't like to get into variable stroke because the mechanical parts start to add too many complications and seem unreliable. Not as bad as trying to vary the bore on a running engine though. LOL.

That leaves varying the exhaust timing on an intermediate stage uniflow with fixed cutoff. Ok.

I'd like to see that garden tractor with a turbine. That sounds just plain cool. The veggies are gonna love it. I'd bet it will be pretty quiet.

Working with modified turbo-chargers, do you know how efficient they are as expanders? The blades typically handle 1200 deg F but start to soften at 1250. Have you run across a turbine that can act efficiently as a compressor at lower temperatures? I am of course thinking of a turbine engine running on steam, but on a modified Erikkson cycle or Joule cycle not a Rankine. At such low pressures no need for a Rankine cycle if there is a good compressor handy.

The horsepower requirments of your tractor are about what's needed to run augsillary (sp) equipment or generators all over the world. Somthing to kick around anyway.

I guess the diesel engineers never blew smoke rings before. That's what I envision the injector spray pattern to look like.

Peter,

How much superheat can you get with copper? At 350 psia you can go up to around 750 deg. Will copper take that much? Are you porting the excess compression through the piston to the other side?

I think an experiment will be necessary to check on the promise of hexagonal boron nitride. Because it's characteristics are much like that of powdered graphite below 5-600 deg in steam, perhaps running graphite in an experimental cylinder, with one piston ring instead of oil would give some indication. Then check on lubricity and if the ring seal improves with the graphite powder packing around the ring. If I had any way I'd do it myself.

I hope both of you gentlemen have a nice holiday and thanks for your input-----------------Bill G.

Arnold Walker
Re: Engine Materials
November 22, 2004 10:58PM
The jumbo jet engines that some of the light companies use are more effecient.At 60-80%.
But then in some cases the compressor section is removed for steam operation.
Turbocharger as best as I can figure are only half as good as the jumbo jet engines.

One side note......you mentioned variable displacement in a piston engine.
Most turbine are in fact variable displacement in proportion to pressure.
Part of the reason they are down right "dogs" at low speeds.
Re: Engine Materials
November 23, 2004 10:39AM
Bill,

I am using a stainless superheater from the drum of a LaMont style boiler. Copper has a temp limit of 400 dregrees F. but it is often pushed beyond that in some applications. Oh, and yes, the drum is copper with a special fitting to isolate the stainless from the copper.

I have a tube that leads from one side to the other outside the cylinder barrel. The tube is ported to the cylinder in 4 locations, two with check valves and two open ported.

Peter Heid
Jeremy Holmes
Re: Engine Materials
November 23, 2004 12:05PM
Regarding engine materials,

I have found 316L works well with 954 (alu)bearing bronze. So, for a piston cylinder arrangement, id use a forged stainless steel piston, with a 954 bronze sleeve, and moly rings. This arrangement would work well at high temperatures with minimal lubrication.

Jeremy
Jeremy Holmes
Re: Engine Materials
November 23, 2004 12:09PM
And this would only apply to a single acting engine, not double action with a short piston and a crosshead. Sorry about that Bill.

Jeremy
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