I managed to hijack my own thread about joining metal together, so thought I should start a proper thread here.
Without re-gurgitating ALL of the previous thread, this upcoming stream of gibberish will be my attempts to make a flash steam powered model boat.
In the 1930's and the 1950's flash steam was quite popular here in the UK to power very fast model boats - hydroplanes. Speeds in excess of 100mph were recorded. Of note is that in the 1950's, a model hydroplane was designed around what people THOUGHT might go fast. Compared to todays high speed boats, the old hydro's have more in common with bricks that racing boats.
I wanted to build a very fast boat - 100mph plus, so got interested in diesel engines. While I was looking at that area, a very wise man indeed called Circlip brought me beer and told me about flash steam.
Flash steam SHOULD be simple. Get a length of pipe. Wrap it in a coil. Turn your propane torch on the coil so it glows red hot. Pump water through the coil - steam comes out.
No messing about fabricating boilers and whacking poor defenseless pieces of copper plate around. No acres of silver solder. No boiler tests. No risk to life and limb if they pop. Couple that with the fact that they can produce HUGE amounts of very hot, very high pressure superheated steam, and it looks like a winner.
Sadly, they are almost too good. The old boys who used to run the racing boats were, at the time, right up against the limits of engineering and materials for a "garden shed" sort of project.
steam pressure has been known to reach 4000psi and many boilers working pressure was 3000 psi. tempurates were running at up to 800 degrees c.
This means that the engine and ancillories need to be special:
Newtons laws say that every reaction has an equal and opposite reaction. So if the pressure in the flash tube is 3000psi, then you need to be able to pump water into the tube at a higher pressure than this. Thats a seriously strong pump for a model.
At that temp and pressure, the steam is absolutely bone dry, so a good quality super-heat oil is needed. Again, you need to force this into the steam - you can't put it in before the boiler - and that takes serious pressure as well.
The engine itself needs to be a work of art. How do you build an engine to cope with these pressures? And keep it light? And make it power a boat to over 100mph? All to fit in the palm of your hand?
So, I'm going to attack the problem in stages. burner. Boiler. procrastination, engine, procrastination, ancilleries.
This thread will be where I post either my disasters or my sucsesses. A wise person recently told me that he saw little point in posting "half arsed rubbish" on forums like these. And in 99.99% of cases I agree. I like seeing a working rocker engine as much as the next man, but I don't usually have any interest in the "I was in such a rush to get pictures onto Mad Modder that a made an utter mess..." sort of threads.
However, my thinking here is that, baring a couple of examples, flash steam hasn't been touched very much for 60+ years. There have been some very sucsessful models, but not a lot, and not a lot has been written about them, or their build.
That has caused me real issues, so I'm going to put all my mistakes, as well as any sucsesses, up here, so that Google can find it for anyone else to follow in the future - mostly so they know what NOT to do.
OK - I thought I would post a C-O-C picture of a basic racing flash boiler here first. Then describe it a bit, and then show you my own version, and ask some questions to see if anyone is interested. If not, I will keep posting stuff, but ask less questions, as resounding silences are bad for the soul...
Basic flash steam boiler:
There is a coil of pipe between 30 and 60 foot long - say 2" in dia. This is held in a boiler case made of steel plate - open at each end.
A parrafin burner directs a flame down the middle of the coil of pipe. Water is fed into the tube, and rapidly converts to steam. As it progresses further down the pipe, it superheats.
Due to the fact that the boiler is in a boat traveling at about 100mph, the burner is very carefully tuned so that it doesn't go out. This involves deflectors to control area's of high and low pressure around the boiler.
A paraffin/petrol mix seems to be recommended as it develops a lot of heat and also and made to work at high pressure to aid in not going out due to air turbulence. A number of propane burners were used, but from what I understand these were more fussy and tended to go out at speed more often.
This design is based on a totally open bodied boiler casing and a separate burner.
I have been thinking about a slightly different design, whereby the burner is removed completely, and the body of the boiler case is turned into a combustion chamber. The "chimney" is used as a negative pressure system to pull the flames through the length of the chamber and out, keeping the flames burning fast and hot.
Basically, vauporised petrol/parrafin would be forced into chamber, along with an air stream, causing high levels of mixing. This would be ignited using spark plugs ( a friend has suggested childrens sparklers as an alternative ) and then the flames would hold within the chamber.
The water coil would be entirely within the flames, for the entire length, and so should get very hot indeed. The water feed would begin at the "chimney" and a smaller coil in this chimney would act as a feedwater heater. The chimney would have a fairly steam rake backwards, away from the direction of travel of the boat.
The petrol/parrafin feed line would enter the boiler case where the flames occur to vauporise, and then move towards the injector.
Sorry for the poor description, I have added another C-O-C sketch which (may ) help...
I *THINK* the second design will be less fiddly to set and keep running, once it is set up right, but it's a total shot in the dark. The more traditional design I have seen designs for, and so, even though I would be using my own designs, there is a well tested foundation to work from. The second I think may have been used, but I have not even seen a diagram for it, and know nothing of it's practicality, or it's methods of tuning, but it FEELS a better design.
What do you guys think?
I'll be doing some of this over the weekend, and will write up what happens
Any thoughts/comments most appreciated.
Steve
