Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[KBIO]

Hello.

I better open , here, a new post on my boiler to avoid to spoil the Xrad's one.

[KBIO]

Hello.

As I said, I have a Scott boiler, as per A.Rayman drawing and if the performances are OK for conventional engines, I am a bit limited in steam production.
I read George Flash Steam topic , long time ago already and I find it very interesting.
But I do not want to go Flash Steam. Too tricky and expensive for my capacities.
I did what Xrad suggested and I have to do some tests.
To answer to George, my engine is a twin cylinder = 3cc with cylindrical distributors. It runs  7500 RPM at 5 bar with air, on the bench.
The RPM drops when I put the boat in the water and I have another problem here:
-Large propeller : Propshop 4 blade , 60 mm and long pitch ==> engine stalls but boiler pressure steady.
- 30mm speed boat 3 blades propeller and boiler's pressure drops.
But we'll come back about this later. As well as on the burner design and the lubricating with super heated-dried steam at 7 bar.
Concerning the burner. I am in liquid phase and as, I have no check valve on the tank, I start with 1 or 1.5 bar inside the tank, and the coil around the burner heating up, gives me 2 or 3 bar after 3/4 min.
Here are a few pics of the boiler:

[KBIO]

2nd set of pictures

[KBIO]

Hello!
Resuts of my last test.
I get up to 5 bar within 3 min. My main concern is that I get fire back if I open up the gas supply valve a bit too much.
I have to be very careful until the system is hot.
I have a pressure reducer which holds on the back pressure inside the tank until it is empty. Going up from 1.5 b to 2.5 b after 5min.
Now that I know how to reduce pictures, I can feed you some!
Next test will be conducted with a propeller and the boat inside the pond! Hopefully.

My next question is: do I have any advantage to leave this big opening around the burner. I wonder if I do not let too much fresh air to enter and allow cooling down.
Don't know!
Thanks for you cooperation.
Cheers.

[ooyah/2]

Yves'
Unfortunately  your boiler is not to A Raymans design but much shorter,the design shows the boiler at 10" long
 ( 250 mm ) and the coils at 25 mm centers not the 15 mm shown on your pic.
As xrad has said ,your coils are touching each other and should have a space between them to allow gas circulation,also in one of your pics you show ceramic insulation which has the coil impression on it and this will not allow the gas flow through the casing and all around the bottom coils, also there is no super heater coil going into the casing to dry the wet steam which needs the flame of the burner to reach the super heater which will increase the power of the wet steam.


I very much doubt if you can achieve a constant supply of steam to power an engine to give a high speed to a boat.
Also as I have already said that L.P.G. is not the right type of fuel and that paraffin under pressure should be the fuel to use.


I referred you to my flashsteam thread not suggesting that that was the way to go but to have a look at the pump arrangement to pump the fuel and water.


Having said all of this it's very much an experimental road that you have to go down to find the correct combination to get a boat to go fast and if you wish to stay with L.P.G. that is your choice.


I do hope that this is of help.


George.

[KBIO]

Good (rainy) morning!
Thanks Ooyah for those explanations.
My boiler is not exactly the Rayman's size, as I was planning to run a 1.5cc engine. Unfortuntly, there was not enough torque to run my boat, and I decided to install a 3 cc.
I guess that I have to start from scraps and build the real Rayman's . I 'll follow what you say on parafin burner. I never used one and this will be the oportunity to start.
Main thing is to stand a good steam production at 7 bar for a 3/4 cc engine during 10 min. The choice of the propeller will be another problem at this time.
I'll have to work out a lubricating device for this configuration, (as super heated steam do not condensate and do conduct heat).
I have another idea, (another brilliant one, probably! )
At the end, I reconsider everything and starting from the boiler, I can build, around,  the boat I need ==> Long & thin or light and flat?
Light and flat requires a lot of power to take off the water.
Do you think that steam would have any interest without all those discussions???
I appreciate you help; Thanks.
Regards.

[KBIO]

Hello!
I've been through all your posts
I have some material at disposition and I propose the following for my boiler.
Similar to the Rayman's drawing, but :
body : brass tube 9"      (230 cm) long
                              2.36" (60 mm)  Diam
10 x 1/4" (6 mm) copper loops (which is about the same surface heated of the Rayman's).
I shall leave about 3 mm between each coil = no contact in between.
The exhaust will be a 40mm elbow from the plumbing shop.
The super heater coil will be 3 ft long as per drawing but 5 mm diam (>3/8"), instead of 6 mm.
Thanks for your comments or suggestions , before I ask my bud' to do the silver welding.
Regards.

[xrad]

KBIO: another way to 'contain' heat in the coil system is to put an 'end' plug of sheet copper at the last coil. This will force an amazing amount of heat through the coils (which is now escaping up the stack).
 
However, you must allow for the new direction of heat and open the smokebox entry to allow hot gas escape from 'coil' portion of system...or allow a gap of say about 3/4 inch from the 'end' plug to the smoke box.  See my pic.

[xrad]

Also: you need to leave a space between the baffle sheet and the coils. Your original was packed with insulation on the coils. This inhibits heat flow.

[KBIO]

Hello!
Thanks for your comments Xrad.
for sure, I'll put a casing (you call it baffle), around the coils. I shall also leave a space in between.
Concerning the copper end plate, I am not that enthousiastic as I shall have the super heater coiled in the elbow. That will slow down the burnt gas escape.Same as Rayman's or George's.
I guess , that all this depends on the burner and as, this is my first experience (second, in fact) , I want to stick to the known path and I do not want to make any error.
On the boiler, that I actually have and which performances are average, I get some fire back inside the boat when I the flamme is strong and the system not at temp.
We shall talk about the burner when, it will be time. I have my own and it works good. Still need some improvements.
Actually, what I did to hold the heat inside the "furnace" is to install the flowing "leaf". I did not notice a difference. It probably generates some turbulences , that all I can say.
Instead, I shall put one (eventually and removable) in stainless steal: shining , thin, and longer. W'll see when the time comes.
So , if there is no others remarks, I may pass order on my welding.
Regards.

[ooyah/2]

Yves.
I would suggest that you make the boiler all as per the drawing of A.Rayman.
If you put a plate inside you will get blow back from the burner and the super heater would not get the full power of the flame..


xrad,s boiler set up is excellent but not for a high power boiler such as the one that you want to work at 7 bar +


I am also a bit concerned that you are going to use a brass tube as the main cylinder barrel.
Brass tube can be used but they are a bit of the unknown when it comes to calculating boiler stresses.
Some times you can get a good solid piece of brass tube but other times it can be a bit porous and will not take the pressure and it would be a shame if you went to all the trouble in soldering it up and then it fails so if possible can you use copper tube.


If you P.M. me your mail address I can  send you a pic of a typical paraffin burner that you can make , this one was linked to a copper tank that was pressurized to 60 p.s.i.


George.

[SteamboatPhil]

Hi Chaps (been a while George) just a quick heads up, firstly before making the boiler see how long a flame you get with your burner, then reduce the OAL of the boiler so the tip of the flame will hit the superheater coil, its no good have a boiler 2 inches longer than you can get heat.
Second, Alans boiler drawing is about 1 inch too long (his words not mine ) see first answer.
I would not consider a brass boiler as you will get "leaching" and will end up making a new boiler next year.
Hope some of this helps
 
P

[KBIO]

Hello !
Thanks for your comments.
Yes, I'll stick to Rayman's boiler , but with 6mm coils instead of 8mm and I shall install 10 coils instead of 9 , on a barrel  of 9" long.
I have the material, so I wish to use it, and the performances should similar.
Concerning the barrel made of brass, we had the same discussion on this side, with the same arguments,  and I must say that I do not undertand the controversy. I have Saïto & Regner brass boilers for 20 years, and they look new. They work at +/- 60psig and I always used rain water.
The welding is no problem and the main advantage I see , is the weight. I can find brass tube of less than 1 mm thicness, when I can find only 2 mm for the copper. For a boat, it is a good point.
Now, this boiler is dedicated to a special project and the main goal is to achieve it. After......
The burner = I shall open another post  , but I understand Phil's point of vew, very well. Xrad idea seems good to me in case of a short flame. In case of a long flame, I get blow back. The super heater loops, shoulb be enough to hold on the heat without fire back inside the boat.
I shall try parafin burner, but I am a bit scary with it (leaks,..). I am not on a  flash steam project and a good burner to maintain good steam production according to the engine demand will fit my dreams.
I am still convinced that I can achieve my goal with liquid gas supply. I'll give a trial anyway!
Not easy, but exiting.
Thanks again.
Regards.
ps: George -> my mail en PM.

[kiwimodeller]

KB10, if you want to have the best chance of making your burner work with gas then couple two gas cylinders together. The drop in temperature and therefor in pressure as gas is drawn off the cylinder is directly proportional to the surface area that it is beeing drawn from. Twice the area in the cannisters will give half the pressure drop in a given time. I have a large paddle steamer fitted with an engine to Raymans design and a conventional boiler 9" long by 4" diameter (not the Scott type). I have the Primus plumbers torch type burner and although it got up steam well after a few minutes running the performance would start to drop away as the flame reduced and the pressure dropped away. I tried heating the gas cannister and other tricks but it was not until I went to two gas cylinders that the problem was solved. I will try and attach a photo of the setup. Best of luck with your experiments, Ian.

[xrad]

Kiwi: Great idea on the gas cans! I was going to run a steam heater line to one can, but instead, I will use your set-up on my build if you don;t mind.
 
KBIO: The 'end plate' is really need to force the heat out through the coils. Without it, you will not gain the back side coil heating.  It is a balance between coil surface area heating and heat loss up the stack. As for the superheater, yes, direct heat is best, so just run a loop back through the 'end plate.'  However, if you have a very good burner with high heat capability, like the parrafin blow torch type, the heat waste is not really going to matter as much as if you had a lower heat torch and you are trying to conserve as much heat as possible... I run Isopro mix which is less heat output than my old Stuart parrafin torch...and also uses a relatively quiet burner.
 
What type of model is this going into?

[ooyah/2]

Hello !
Thanks for your comments.
Yes, I'll stick to Rayman's boiler , but with 6mm coils instead of 8mm and I shall install 10 coils instead of 9 , on a barrel  of 9" long.
I have the material, so I wish to use it, and the performances should similar.
Concerning the barrel made of brass, we had the same discussion on this side, with the same arguments,  and I must say that I do not undertand the controversy. I have Saïto & Regner brass boilers for 20 years, and they look new. They work at +/- 60psig and I always used rain water.
The welding is no problem and the main advantage I see , is the weight. I can find brass tube of less than 1 mm thicness, when I can find only 2 mm for the copper. For a boat, it is a good point.
Now, this boiler is dedicated to a special project and the main goal is to achieve it. After......
The burner = I shall open another post  , but I understand Phil's point of vew, very well. Xrad idea seems good to me in case of a short flame. In case of a long flame, I get blow back. The super heater loops, shoulb be enough to hold on the heat without fire back inside the boat.
I shall try parafin burner, but I am a bit scary with it (leaks,..). I am not on a  flash steam project and a good burner to maintain good steam production according to the engine demand will fit my dreams.
I am still convinced that I can achieve my goal with liquid gas supply. I'll give a trial anyway!
Not easy, but exiting.
Thanks again.
Regards.
ps: George -> my mail en PM.

Yves,

I know that manufacturers use brass tubing for boilers, but they know the composition and the stresses that these brass boilers will take, where as you don't know what the stress factors are in the tube that you propose to use.

Now if in doubt, would you be prepared to fire your Saito and Regnar boiler up to 7 bar, I think not.

You say that you are to use 1mm or less brass tube to make your boiler, if you do a simple calculation
 for a 1 mm ( .039" ) copper tube to operate at 7 bar ( 105 p.s.i. ) it will only take 103 p.s.i. this figure is based on a copper tube but you can't relate this to a brass tube as there are no calcs that I can find to prove that a brass boiler of 1 mm or less will take 7 bar.

If you use 1 mm or less brass tube you will be in dangerous territory.

The fuel that I mention, paraffin ,is probably known to you as kerosene and it's very much safer than L.P.G. as it has a lower flash point.
I purchase this from a hardware store or a garden center where it is used in green house heaters.

I have viewed your Y-Tube  Vid of your burner and it burns very well but I still say that it will not produce 7 bar at a constant pressure to keep your engine in power, I am always ready to be proven wrong, I couldn't do it , so go to it .
Best wishes

George.

[KBIO]

Hello!
Thanks for those warning! You make me dubious now, and most of people (not all, though) are thinking like you. 
Although, the manufacturer insures me that the brass, that he proposes to me is used in the industry at higher pressure.
The boiler , I shown in a previous post is working @ 8 bar. For how long ? That is the question!
As I shall build a bigger boat, I can afford some more weight, and I guess that I have to go to copper.
Another vanished certitude !
I see now, what is kerosen. We used it in our lamps when I was a kid during electricity shut off.
And we call it "kerosène" also.
In any case, I shall test both burners and I'll make my choice depending on the results.
Well! I still have way to go.
Best regards.



ps : George, I sent you my mail on PM.