A question about flash boilers....ish

[toad281]

I am working on a model steam engine and was considering building a flash boiler. Question arose in my mind, why not heat the cylinders and flash to steam inside them? I am sure someone has thought of this before, but I cannot seem to find any discussions on the subject. The cylinders and pistons on my model are made of cast iron so I do not think heat would be an issue. Regulating pressure would be my greatest concern I would think. Any have any experience with this type of system?

 

[mcostello]

Would the water flash to steam fast enough to run an engine?

 

[toad281]

I am not sure. I came upon this thought while thinking about positioning the cylinders in the exhaust stream to help keep them up to temperature. Doing so would perhaps aid in the need for less robust lagging. That led me to, why not heat the cylinders directly and use them to flash the system. It is just a thought at this moment, but I thought I would ask the question here and see what others think about the prospects. Maybe someone has tried this already.

 

[Toymaker]

Just thinking about your design, seems like you will need to inject the water into the cylinder(s) in much the same way as fuel injectors shoot fuel into an ICE, yes?
How do you plan to keep the water in a liquid state as it sits in the injector waiting to be sprayed into the cylinder? If you chose to use a single throttle-body injector you will have the problem of keeping the water in liquid state until it's inside the cylinder and the intake valve closes.

I don't see a workable solution.

 

[Steamchick]

Hi Toymaker, I suggest (from the weird notions in my head) that if a simple system was used like a diesel injector, then the pre-pressurising of water to a pressure such that the water in the injector doesn't boil, would cause the injector to permanently open. But Modern cars etc. use "pre-pressurised" fuel suppliers an piezo operated high speed valves to operate when the injector injects fuel. So that sort of system should work with the water pressurised to a high enough pre-pressure. An interesting concept, but with the limitations of technology, Steam Engineers simply used Higher temperature steam from superheating, and lagged cylinders. Then the heat used in the cylinder is mostly the superheat, and less condensation occurs. The hot exhaust wet steam was used efficiently either to force the fire, or pre-heat the feed-water. But when Turbines became common, the superheat temperature was raised further to ensure the expanded exhaust steam was still dry. Drops of water can be very damaging to turbine blades.
But to the original question, of Flashing water to steam in the cylinder, I don't think there is adequate heating surface of a cylinder wall at the start of a stroke to supply the heat you can get into the cylinder when feeding steam... so my answer is "probably it won't work" (sensibly). Simply, because feeding superheated steam into a cylinder has been found to be the technically practical way to maximise heat into the cylinder (for expansion and conversion of the energy to mechanical power).
You may note the evolution from the early "steam return", atmospheric engines of Hackworth's era, through low (James Watt) then high pressure steam (Richard Trevethick) to generate the power, was more or less followed with "combustion" engines, where the exhaust gas from (coke) furnaces filled "atmospheric engines", then ways of filling the cylinder with combustible mixtures and firing from an external source were created, later becoming internally fired as the engines that we use today.
But an interesting idea...
K2

 

[TinkerJim]

I am not sure. I came upon this thought while thinking about positioning the cylinders in the exhaust stream to help keep them up to temperature. Doing so would perhaps aid in the need for less robust lagging. That led me to, why not heat the cylinders directly and use them to flash the system. It is just a thought at this moment, but I thought I would ask the question here and see what others think about the prospects. Maybe someone has tried this already.

I seem to remember reading about something along these lines in an article in Model Engineer long ago.

I checked the scribbled index cards I still had and found this:

“Boilerless Steam Engine” by Hall in Vol. 132 (1966) on pages 762-4.

I no longer have this issue but maybe someone can find it if you are still interested.

 

[Jasonb]

It does seem he(Hall) got small engines to work OK, single acting with an exhaust valve the water was injected just before TDC just after the exhaust vale closed so little pressure to overcome and the cylinder head was heated causing the injected water to flash to steam ar TDC running at around 1500rpm

 

[toad281]

I would love to read that article. I will do some more research and see what pops up. Thanks for the replies. I did find this.. www.cyclonepower.com

 

[minh-thanh]

It does seem he(Hall) got small engines to work OK, single acting with an exhaust valve the water was injected just before TDC just after the exhaust vale closed so little pressure to overcome and the cylinder head was heated causing the injected water to flash to steam ar TDC running at around 1500rpm

Jasonb .
Do you have the link of the video ?

 

[Jasonb]

Toad, check your messages

They did not have video back in 1966

 

[Steamchick]

Seems my computer is developing Dementure... when I clicked the cyclone power link is didn't work and said it is "out of memory". - (I have just had "MajorStuff" do a new version of their Search programme... - just my luck they have dumped all the data from NASA's main computer onto me in the process!) - So where has my memory gone? I can't remember the answer to that one... Answers on a postcard please, in case my computer is about to crash!
K2

 

[minh-thanh]

check your messages

I did not receive your message

 

[Jasonb]

Toad, check your messages

Message was to Toad281

 

[HMEL]

I am working on a model steam engine and was considering building a flash boiler. Question arose in my mind, why not heat the cylinders and flash to steam inside them? I am sure someone has thought of this before, but I cannot seem to find any discussions on the subject. The cylinders and pistons on my model are made of cast iron so I do not think heat would be an issue. Regulating pressure would be my greatest concern I would think. Any have any experience with this type of system?

My opinion but its fairly strong based on experience. Not a good idea. One of the most violent explosions I have seen was due to extreme fluctuations in temperature. Cast iron expands and contracts as all metals do. The forces generated are very high and exceed the mechanical properties of the metal. Its not the heat so much as the variation in temperature. Now you should know that there were engines made where the fuel oil was injected with water so the steam added to the power but the engine did not fire constantly. They were used in agriculture and I called them oil pull engines. This may be the wrong name but its what I knew them as. Engine clearances depend on an operating temperature. Also there is a water chemistry issue. You will need pure water as any solids in the water will stay in the cylinder. In fact knowing the water chemistry you can predict just how long it takes for the solids to fill the cylinders. Now I dont think the engine would run long enough to fill the cylinders as they would probably jam in a relatively short time do to the solids build up. Probably best to continue with a flash boiler unless you are determined just to see what happens.
HMEL

 

[toad281]

My opinion but its fairly strong based on experience. Not a good idea. One of the most violent explosions I have seen was due to extreme fluctuations in temperature. Cast iron expands and contracts as all metals do. The forces generated are very high and exceed the mechanical properties of the metal. Its not the heat so much as the variation in temperature. Now you should know that there were engines made where the fuel oil was injected with water so the steam added to the power but the engine did not fire constantly. They were used in agriculture and I called them oil pull engines. This may be the wrong name but its what I knew them as. Engine clearances depend on an operating temperature. Also there is a water chemistry issue. You will need pure water as any solids in the water will stay in the cylinder. In fact knowing the water chemistry you can predict just how long it takes for the solids to fill the cylinders. Now I dont think the engine would run long enough to fill the cylinders as they would probably jam in a relatively short time do to the solids build up. Probably best to continue with a flash boiler unless you are determined just to see what happens.
HMEL

There is something I did not consider. Cast will fracture [I am picturing like glass] when exposed to rapid changes in temperature. Interesting. Thanks for your insight

 

[Richard Hed]

I am working on a model steam engine and was considering building a flash boiler. Question arose in my mind, why not heat the cylinders and flash to steam inside them? I am sure someone has thought of this before, but I cannot seem to find any discussions on the subject. The cylinders and pistons on my model are made of cast iron so I do not think heat would be an issue. Regulating pressure would be my greatest concern I would think. Any have any experience with this type of system?

tHERE is at least one person working on a 6 stroke engine in which four strokes are the usual ICE of intake, fire, exhaust, air but the other two strokes are injecting water for power strokes AND for cooling. This engine does not have a radiator. I know the fellow made at least one and was trying to sell it to GM but of course they were not interested in anything lilke that. Others have tried similar things. I thimpfks it's worth a try. Also other types of ICE-steam too.

 

[Jasonb]

Having read the article about the direct injected engines at 1500rpm I doubt you would see much in the way of rapid temperature changes as the engine would not have time to cool and then get heated again if it is going through the cycle 25times a second. As the head is heated that would be warmed up first to working temp with a gas burner so again no instant rise in temp. Not a lot different to running a hot tube engine.

Lets face it water flashing to steam is not going to create any more rapid temp changes than seen in a model IC engine where the fuel is ignited inside the cylinder and I don't see many models failing.

Not sure about the comment of solids building up, most would go out the exhaust and what if different from any "solids" being carried into the engine from a flash steam boiler to one where it flashes in the cylinder? may possibly get a small amount of scale on the "hot" part of the head I suppose

 

[Steamchick]

Solids in steam from hard water are akin to running an ICE engine without an air cleaner. In my early motorcycling days, running an open carburettor with a Belmouth (5% more power? I hoped!) And I measured 0.003 in wear after 10, 000 miles. But modern cars run superb air cleaners and just don't see wear that loses compression or passes oil in 10 times that distance. All minerals wear cast iron bores. But I can't see a problem using distilled water - especially on a model for "demonstration only" running.
K2

 

[HMEL]

Having read the article about the direct injected engines at 1500rpm I doubt you would see much in the way of rapid temperature changes as the engine would not have time to cool and then get heated again if it is going through the cycle 25times a second. As the head is heated that would be warmed up first to working temp with a gas burner so again no instant rise in temp. Not a lot different to running a hot tube engine.

Lets face it water flashing to steam is not going to create any more rapid temp changes than seen in a model IC engine where the fuel is ignited inside the cylinder and I don't see many models failing.

Not sure about the comment of solids building up, most would go out the exhaust and what if different from any "solids" being carried into the engine from a flash steam boiler to one where it flashes in the cylinder? may possibly get a small amount of scale on the "hot" part of the head I suppose

An IC engine is quite different as the heat is leaving with the hot gases. This allows the cylinder wall temperatures to stay fairly constant. Water has a very great capacity to absorb heat and even in boilers there is a delta on the tube wall of a constant 70 to 100 degrees But I suspect it will be like quenching steel. As for the solids I have seen them close off superheater tubes. The heat transfer to the water would most likely be by conduction which implies wall contact. and that would definitely change the temperature of the metal big time.

 

[Steamchick]

This discussion appears to me to be like trying to decide what size and shape of logs to throw onto the fire, to warm a pan of water, when everyone else is blowing sawdust into a boiler with air....
I am sure someone could make a water injected engine work, although I cannot see the advantage or useful reason "why", but of the thousands of different ideas that have gone before, the historical record shows what people could make work, and their failures were "lost" as useless.
I do accept, there may be some hidden gems of history that didn't work because of the available materials, or other reason, but if there was a way of making this water injection engine work thermodynamically, and efficiently, then I fervently believe it would be in the record somewhere.
Considering that the earliest Jet engines, (Non-Whittle that is) were really use of the directed exhausts from hugely powerful supercharged or turbocharged aero-engines and similar (Like the Napier Deltic, Sabre, etc.) through jet nozzles at the rear of aircraft, then someone decided that reciprocating engines were not the best combustion chambers for a jet, so then Rolls Royce believed Whittle's ideas and are fundamentally what we have today, I think that is an example of how the apparently crazy ideas have all been explored and developed to the point where the "survival of the fittest" rule has left us the technological world of today.
Remembering the that steam is (like electricity) a means of transmitting power, not a fundamental source of power leads us to burning fuel inside the cylinder, rather than generating steam inside the cylinder. We all know: Fuel burning in a firebox (combustion chamber) to generate steam, then to utilise the power from the steam, has become fuel burning inside the engine as a combustion chamber (at higher pressure than the conventional steam plant), to generate power directly. I.E. cutting out the steam power transmission from combustion chamber to cylinder. Thermodynamically, there is no advantage to generating steam inside the cylinder, simply to eliminate the boiler and plumbing.
Sorry to put a damper on this discussion.
K2