Motors Steam engines - engineering opinions needed

Hello,

Currently into the idea of building a steam engine, I have come up with a simple design:



Just need people's opinions as to whether it would work.

Basically the two valves slide within the valve guides, when pushed up by the cam they open.

So when steam goes into the intake, it pushes the piston down, then the intake closes and exhaust cam opens at the start of the piston's upward stroke.

Any engineers about who can give me some advice?

Cheers!

 

You wont get enough momentum into the crankshaft to clear the steam out of the piston.

You've got sevral(that i know of) choices
These are two of them
Either add a valve that when the crank gets to the bottom it sprays cold water into the cylinder this cause the steam to condense and the vacuum pulls the cylinder back down again
there is exhaust value, these do have tendency to blow up when the water fills the cylinder(iam not quite sure how they got around that little bit) but if you only building a small one then it should at the worse pop the top off this how the original steam engines worked.

My preferred method and not too difficult to construct would be to have two cylinders with a common cam shaft but set up so that when one cylinder gets to the top the other is at the bottom of it cylinder that way one pushed the used steam out of the other.

See http://www.howstuffworks.com/search.php for some basic princples and
http://science.howstuffworks.com/steam-technology3.htm

 

No need to - that design has an external condensor fitted so depending on what the inlet steam pressure is the upstroke of the piston may actually provide more power. Furthermore, some railway steam engines use exactly this system (external condensers aren't practical - nowhere to reject the heat to).

That's effectively a Newcomen engine, while the external condensor he has fitted is a Watt style engine. The Watt variant is much more efficient, and avoids the need to get rid of condensed water from inside the cylinder.

No reason there should be any water in this system, depending on steam conditions - if this uses dry steam, any condensate you get will evaporate again as the thing warms up. Wet steam is bad news in any case.

Irrelevant as already discussed - this uses an external condenser.

Couple of problems I can see:

1) How are you going to seal the piston? The reason I ask is that condensers only work well if they have no air in them. Normally you achieve this by running steam through the system for a while with no cooling on the condenser, venting to atmosphere. You then stop venting after the steam has driven all the air out, and turn the cooling water on. If the piston seals are poor, you will have an air flow into the condenser and it won't work properly.
2) Safety. I can't emphasise enough just how dangerous steam generators are if you don't know what you're doing. Make absolutely sure that you pressure test everything to substantially higher pressures than you intend to reach using cold water with no air in the system before you turn the heat on. The problem is that if a boiler bursts, because the water inside is at substantially higher temperature/pressure than 1 Bar/100 °C when the pressure drops to 1 Bar a substantial amount of the water will turn to steam spontaneously. The whole process is highly explosive, not to mention that boiling water is thrown all over the place in the process.
Best way of dealing with this - in addition to testing whatever pressure vessel you use with cold water - is to ensure you have a safety valve that is known to work at a particular pressure.
Easiest way of getting a safe steam generator is probably to buy a pressure cooker and tap a hole in the top for your steam pipe. Provided your connection is done properly and you test it, you should be pretty safe.
3) Control. At the moment you have nothing to stop this engine running away and shaking itself to pieces once it gets going. The only load on it is internal friction, and I would expect something like this to be inherently badly balanced so vibration will be a major problem.
If you can I would suggest some sort of governor - the centrifugal governor has historically been used for things like this, and will let you automatically shut off the steam supply if the speed goes too high.
4) Not sure on the scaling of that drawing, but those valves look way too small for the piston in that drawing. Also, as per the piston you need to make sure they seal quite well.

If you want any specific numbers (e.g. temperature of dry saturated steam at a particular pressure, which is what you'll get if you don't heat the steam again after it leaves the boiler) let me know. I've got a full set of steam tables and the like lying around the place.

 

What pdf27 said is totally correct. What ever happens you really really don't want water condensing out.

If you can get a copy of an h-s diagram for water/steam it would help you alot as you can plot on it the states at different points in your system. For steam tables google is your friend but this site has them:
http://www.efunda.com/materials/water/steamtable_sat.cfm

However this will only give you data for dry saturated steam. To prevent water forming you are going to want to use superheated steam so that you don't form wet steam. (You have to love the terms wet and dry saturated steam). Again refer to the charts for this not the tables.

There are many ways of making steam engines more efficient but what you have should be ok.

On the throttling front, as wikipedia says, centrifugal throttles actually spawned control theory because they are not very simple and so need some thought.

Looking at your basic plan working out how to do this could be done entirely in theory and probably should be implemented with a micro-controller (a very very simple one would do). I can help with this if required.

 

Missed the Condenser bit in his design sorry.

I think two of them apposing each other would be the easiest design no messing around with condensers and not as difficult to build as a double action on. But i think with a bit of googling there's properly quite a few DIY, that would your best bet.

 

the design is not bad, the tricky part will be building it leak-tight.

 

The way railroad locomotives dealt with the issue is to have two cylinders 1/4 cycle out of phase. That way one is always in the power stroke which pushes the other one closed.

 

We used to have a small toy one; it's cylinder was about 10mm dia, 50mm long. It was single cylinder, with the boiler putting steam in one port, and the exhaust just vented to atmosphere. As the end of the piston rod went in a circle, it caused the cylinder/piston to oscillate (much like a pendulum), so at one angle it received steam, and at the other angle it's port was open to the atmosphere.
Hard to describe sorry!
But essentially it didn't use condesners, and was the simplest design ever, and worked really well!
This looks an awesome project so please do a log!

 

I've got a similar air powered one sitting around at my parent's house. The cylinder is pivoted about halfway up, so when the flywheel rotates the bottom end of the cylinder moves from side to side in an arc. The inlet and outlet ports are set up on this sliding surface such that they are covered when not in use and exposed to the port on the cylinder when needed. That actually worked quite well when this surface was greased, but I wouldn't want to risk that with steam. Kind of elegant though - the whole thing only had 3 moving parts (cylinder, piston and flywheel).

 

Ah a much better description thank you

 

you could have a simpler version where you have holes in a flywheel where on the upstroke it opens the outlet valve and vice versa.

 

I've been thinking and I am now considering going with a Tesla Turbine (apparently this can be made out of old hard disk platters). A well-designed one can (according to the man himself) make 300hp from a box no larger than a car battery.

Basically, this is going to be mounted on a push-bike with an electric transmission, and run from waste vegetable oil. It's just for a laugh and as a sort of proof-of-concept, plus I'd imagine a few people would find it funny if I turned up to a motorcycle rally on it.

So here is the idea I have so far...

The turbine will be connected to a 48 volt generator which is then connected to a 48 volt gel battery bank.

The battery bank will be connected, via a P.W.M controller, to a motor which drives the rear hub via a chain.

The idea is that the batteries act as a 'float', so the bike can accelerate away just using the batteries and then the turbine will spool up and take over.

For this I will need to monitor the battery voltage and control the turbine's throttle. So whenever the system voltage drops below 48 volts (as it will under initial acceleration), the turbine will speed up to provide the extra power, which will recharge the batteries. This will also enable the turbine to keep running at idle when there is no load, without the need for a clutch or gears.

Does anyone have any comments about this system? Do you think it would work well?

For the generator I am planning to use a modified car alternator, and a standard 48 volt motor for the drive motor. I'm only aiming for 500 watts or so, for a top speed of about 15-20.

 

The Tesla Turbine sounds an interesting idea. I don't know if you'd be able to get 500 watts out of an HDD platter though...?

 

I've seen one in action at the PRIME show. They're not as effiecient as they theoretially could be and you have to be carefyl about what you feed them. On the other hand, the one I saw got up to 11,000 RPM on compressed air.

The distance between the platters is absolutly critical as is the balance.

That said, if you can make it work there must be video!