Superheated Steam

[majorm]

I am interested in learning some more about superheated steam and any engines that use it. I have found some info scattered around but not too much. I am interested in it because of the extra power it can provide. I also read that it needs pure water in order to be superheated. What I read also said the superheated steam was corrosive.

How do the engine designs deal with the added issues with superheated steam? I have used tubing and fittings such as swagelok and looking at the temperature ratings the tube drops off quick in the pressure it can hold with heat. Do any of you have any experience or know of some good places to pick up some information on superheated steam engines including materials that are good to use?

 

[aonemarine]

http://steamautomobile.com/phorum5214/list.php?1

A wealth of knowledge here.....

 

[cncjunior]

May I ask what type of boiler and steam engine are you planning on building? I am in a club that runs steam locomotives in the 1.5" to the foot. We use superheaters in most of our locos. What has been found is that the steam is dried out more than anything else and does increase the efficiency of the loco. Less fuel is used during a 6 hour day pulling passengers around the track. There might be a bit of extra power in this size of loco.

The superheater spears that we typically use is stainless steel. Older engines can be found with copper super heater tubes though they tend to waste away after a few years. My club looked into a nickel based tube that is used on stove elements but found the cost prohibitive.

To fabricate the super heaters silver solder is typical and for those with tig can use this.

In the full size locos they could only go to a certain degree of super heating temperature as the steam oil used to lubricate the piston valve and piston would break down into carbon and foul the works and also not lubricate.

As far a water is concerned, most use non hard tap water for the boiler. The only reason for not having hard water in the boiler is to stop scale from building up on the inside of the boiler as the water is evaporated. The scale typically doesn't leave the boiler. In other words it doesn't migrate down the tubes.

As far as the corrosive nature of super heated steam goes, only on non lubricated moving parts does it have an effect such as valves, pistons, throttle, etc. The one metal not to use is brass because the zinc in it is leached out and leaves the base metal brittle. This goes for any boiler super heated or not.

If you are interested in flash steam boilers look for info on the Stanley steam car. There are magazines that have the occasional article on superheated steam like Live Steam--USA or Model Engineering in the UK. Some libraries carry these mags.

There are many sources of info like searching google for model boilers, superheated locomotives etc.

Hope this helps.

Daniel

 

[windy]

As a user of superheated steam on my flash steam hydroplane I can only talk about the problems that I have had to overcome.

The steam pipe into the engine poppet valve glows red.
I do not use tap water because it blocks the steam generator with scale.
The piston, ring and cylinder can be cast iron providing clearances are suitable for the heat and speed they are running at (mine 11000rpm under load).
After I have had my runs I strip the engine to oil it to prevent corrosion that can be rapid if left.
The generator is 6metre of 1/4" 321 stainless seamless tubing welded to 6metres of 3/16" 321 seamless tubing.
The connection at the hot end to the engine is with a 60° swaged end.
The nut is stainless but fastens to a steel manifold.
If nut and manifold are made of same material they can be imposable to release after running. (Must be dissimilar materials)
The swagelock type fittings might be suitable but I have not tried them.
The picture shows the generator on test while testing a turbine nozzle.

Paul

 

[majorm]

Thanks for the replies.

The engine design is still in the air because i havent decided between a radial or a swashplate type engine. I would really like to try the swashplate since its just interesting to me. The first one will be steam or air but I would like to take into account a superheated steam future so it isnt a total redesign. For the "boiler" I want to go more the route of the monotube flash steam type. I have thought about the lubrication issue and was curious if a coating like cerakotes piston coat would be helpful or get steamed off. If it was good enough to stay and not burn or wear off too fast then it would help with corrosion and lubrication.

Paul: A turbine is out of my league right now but do you have any other pictures or info on your engine other than whats on your profile.

Daniel: Thanks for the info. Ill look up the search terms you mentioned too.

Aonemarine: Yep I have been looking at that forum for a little while. I wish it had a litte more activity but there is some good info there. I havent been on there in a week or so so thanks for the reminder.

 

[cncjunior]

Windy, that is a nice shot of your test rig. Your glowing red metal tubes definitely isn't an understatement.

I have used swagelok fittings and they are a joy to use though I have no experience with them under high temperature applications. The place were I worked tended to use welded connections where high temps were used. I could just imagine what your engine would look like if steam oil was used.

Out of curiosity, your hydroplane is it RC or manned?

 

[windy]

Windy, that is a nice shot of your test rig. Your glowing red metal tubes definitely isn't an understatement.

I have used swagelok fittings and they are a joy to use though I have no experience with them under high temperature applications. The place were I worked tended to use welded connections where high temps were used. I could just imagine what your engine would look like if steam oil was used.

Out of curiosity, your hydroplane is it RC or manned?

My flash steam tethered hydroplane is on this site http://www.onthewire.co.uk/wwind.htm

The engine is based on Bob Kirtley's with a few tweaks.
The plans can be bought from
http://www.myhobbystore.co.uk/product/17442/pisces-ii-m72

I am itching to run the steamer at its first meeting in June to see if some modifications give me faster speeds.

Paul