Flame-Licker Engine Construction Materials

[BronxFigs]

I want to build a Flame-Licker, model engine.

What metals will work well for:

Cylinder
Piston
Cam/Follower
Valves

Cylinder: Can stainless-steel, brass, bronze, steel, be used? Will these materials gall?

Piston: Machinable Graphite, oil-impregnated bronze bushings, stainless-steel? Must I use a ring, or, O-ring?

Valves: Steel, bronze, graphite? Valve is exposed directly to the flame that enters the cylinder.

Cam/Follower: Hardened/soft-steel, bronze, brass?

All other parts will be fabricated from materials on hand, except crankshaft.

If possible, suggest best combinations. My concern are different, or incompatible coefficients of expansion, galling, and piston sealing/blow-by as engine heats up to operating temps.

Thanks for the help.

Frank

 

[Woodster]

I found that a bronze cylinder and an aluminium piston work very well. I use an old feeler gauge for the valve. I made mine entirely from scrap and it runs superb.

 

[BronxFigs]

Woodster, nice of you to answer. Any problems with the different expansion rates between the Aluminum piston and Bronze cylinder?

Why I asked for suggestions? I have many options as far as material selection. I also want the engine to last as long as possible without anything gumming up, corroding, or burning away, from direct exposure to a flame. Condensation is also a factor.

Too many drawings call for certain materials to be used for specific parts, but almost never explain why.

My main concerns are piston/cylinder combo, and what will work best.

Thanks for all comments.


Frank

 

[BillyHill]

Here's a list of different materials and their CETs.

Coefficients of Linear Thermal Expansion

Wikipedia has one with volumentric but it doesn't have bronze. You should be able to extrapolate it using a formula (provided).

Thermal expansion - Wikipedia, the free encyclopedia

I'm curious how hot a flame eater engine will get (cylinders and pistons). Would be neat to make one out of torlon of vespel.

 

[Omnimill]

I used cast iron for both cylinder and piston on my Jan Ridders designed flameater and it works quite well.

 

[enfieldbullet]

Well, Frank,

you can just crunch the numbers if you are good with math.

give us how tight a fit you'll want and we can tell the materials that will work.

basically :

basic dimension + expansion coefficient x temperature x basic dimension < clearence + cylinder expansion

corrosion isn't really so important in such a design. it runs very underloaded. perhaps avoid ferrous materials.

that being said i love cast iron. if it's an option i'd use it. so easy to machine, corrosion resistant, abrasion resistant, heat resistant

 

[Swifty]

If I follow this right, if we use a material of lesser expansion rate for the piston than the cylinder, things should be ok. But we could be in trouble if the smaller piston expands faster than the bulkier cylinder which would take longer to heat up. Having not made any engines yet where heat is involved, not sure about the thinking.

Paul.

 

[MCRIPPPer]

If I follow this right, if we use a material of lesser expansion rate for the piston than the cylinder, things should be ok. But we could be in trouble if the smaller piston expands faster than the bulkier cylinder which would take longer to heat up. Having not made any engines yet where heat is involved, not sure about the thinking.

Paul.

i have heard of this issue. in the rc hobby people with gas enignes would lathe off a few thousandths around the upper part of the piston for running in cold climates. i would imagine with an external combustion engine you dont have to worry about it.

 

[BronxFigs]

Just this morning, I went to my "psychiatrist's-couch", called the Scrap Yard .... and bought me some Quualudes in the form of stainless-steel (304) tubing wih 3/16" wall thickness, and a bore diameter of 1.125"....enough length to make two cylinders. I have a V-Twin, Flame-Licker in mind...or, I might mount both cylinders in tandem, onto a crankcase, and use the Ross-Yoke Linkage, set-up to turn a flywheel. The Ross Yoke should be interesting to watch. I'll figure something out to work the valves that admit the flames.

I stink at doin' the math. What piston material would be the best, logical choice. I plan on honing the cylinders to a mirror finish. I'll press fit brass or aluminum cooling fins onto the stainless steel cylinders. The contrasting color of each metal should look nice.

If this engine-build turns out half as good as the engine I envision in my mind, I'll be happy.

Frank

 

[enfieldbullet]

I plan on honing the cylinders to a mirror finish. I'll press fit brass or aluminum cooling fins onto the stainless steel cylinders. The contrasting color of each metal should look nice.

If this engine-build turns out half as good as the engine I envision in my mind, I'll be happy.

Frank

Frank, that sure looks nice in my head too, i like the idea.

perhaps don't hone to mirror finish, keep the 'scratched' look for oil retention.

can you get cast iron? would be a safe choice i think. aluminum has higher expansion coefficient, brass too. steel is a little smaller but might gall.

 

[BronxFigs]

enfield....

Good suggestion. No mirror finish. That's good, less work. Had no cast iron, so I'll try the stainless. It was cheap, and, available.

Are you referring to piston materials in your last sentence of post # 10 ? Cast iron on stainless-steel. I think I may be able to get small diameter rod for the pistons.

Thanks,

Frank

 

[enfieldbullet]

yes, piston material.

you can generally find something made of cast iron that can be machined to size. brake discs come to mind but they are probably too thin for your application.

it's not too expensive to buy it from foundries either, as Continually Cast Iron.

 

[BronxFigs]

enfield:

Thanks for the clarification.

I think I need order some good cast iron stock, just to have in the shop.


Frank

 

[MikeG]

I've made two different flame-lickers. The one that runs to best, the one I take to shows, uses a Aluminum cyl and a graphite piston. You will find that condensation will form on the cyl (not alot) that's a good reason not to use anything that can rust. My other engine, a twin cyl, uses cast iron for the cyl and a graphite piston. if let stand on the shelf for long it seem to gum up. Sorry, i must of pushed a wrong button and changed the font!

Regards

MikeG

 

[jwcnc1911]

MIkeG, you got any pictures of those?

 

[dgoddard]

With respect to different materials, especially different materials for mating parts, for model engine builders attention should be paid to
-- wear characteristics,
-- chemical compatibility (Certain metals in contact promote corrosion & wear)
-- Thermal conductivity
-- Thermal expansion

The last two deserve so special attention. These engines are "heat engines" and are dominated by the laws of thermodynamics.
A basic principle is that the maximum amount of energy from a given amount of fuel (efficiency) that a heat engine can produce is governed absolutely by the temperature difference between where the engine gets its heat and where it gets rid of it. So for a flame licker engine the temperature of the flame sets the high temperature and the cylinder wall is where it get rid of it. I speak of the temperatures of the working fluid here! The hot gasses are taken in and heat is drawn out of them by the cylinder wall (primarily). Therefore insulating the intake port for the flame from the cylinderwall is a good idea. Barring that, using a cylinder with a poor thermal conductivity s a good idea. So aluminum which has a really high thermal conductivity is not a good choice but stainless steel which has a much lower conductivity is a good idea. But if aluminum is used then having plenty of air flow over the cooling fins of the cylinder is good because the cylinder stays cooler and the temperature difference between the flame an cool cylinder wall is larger. Aluminum will conduct the heat of the cylinder wall out into the fins more efficiently and it can be gotten rid of there. should the designer decide to use a water cooled cylinder then aluminum has an advantage because the ability to move the heat from the cylinder wall to the water in the jacket rapidly and do a better job in that respect than stainless steel would.

As the cylinder wall gets hotter and hotter it looses ability to extract the heat from the flame gasses and eventually the engine suffers "heat death" which is when the cooling method can no longer extract enough heat from the working fluid to provide enough energy to run the engine.

This is just one of the many issues which interplay with others to make a design effective or ineffective.

 

[Hopper]

Take a look at Jan Ridders website. He will send you free plans for flamelickers, among others, and plenty of info on the materials he uses on his well-proven and popular design.
http://heetgasmodelbouw.ridders.nu/...t_happermodellen/happeroverzicht_frameset.htm