Exhaust Heat Recovery - Steam Power

[mwebb]

Originally Posted by LeakyIdeas View Post
drip a small amount of water into a tube at 500F

it expands to about 1600times it's volume,

heat a small rc motor to 500-600F and small amount of water is injected a few degrees ATDC, it will expand 1600 times and force piston down

if what is above is true
a small solenoid with a piston can be tasked to force "a small amount of water"
thru a reed valve into a chamber ON the hot exhaust , when that water converted to steam that could be routed to a diaphragm which would expand
with a rod to harness the movement, after the diaphragm moves up
it would expose a hole to
vent the steam, spring closes diaphragm to rest position , repeat .
if there was more energy in the diaphragm movement than needed to operate the solenoid
you would have something .

[jdgFirefly]

Originally Posted by LeakyIdeas

Wouldn't it depend on your source of input? if you have for example a limited rpm range and low torque, by increasing the size of the flywheel you are storing more energy per rev, and when it's small you can get it up to speed, which in this case may be needed as i think it wouldn't have the torque to get a large flywheel started... kind of like having a gear box built into the flywheel.

but we don't have any movement yet so it'll be "a nice problem to have" :-)

Why do we need a flywheel for this application?

[Patrick]

Originally Posted by LeakyIdeas

if you have for example a limited rpm range and low torque, by increasing the size of the flywheel you are storing more energy per rev, and when it's small you can get it up to speed, which in this case may be needed as i think it wouldn't have the torque to get a large flywheel started... kind of like having a gear box built into the flywheel.

Yes, it might help in that aspect (matching flywheel speed closer to the desired range of the alternator). But you can't put less energy in and get more out. You can only get out less energy than you put in.

[Daox]

I did some more testing this morning (I also got my videos to work with audio, here is the link to my first video's post if you wanted to rewatch it).

So, I altered the alternator setup to include a wire to the voltage regulator on the alternator now so it can regulate things properly. The 3rd pin I had talked about in my other post does go to the warning light on your dash to indicate when the alternator is not working.

On this test, I tried an air drill I had laying around. I looked for the specs on it but found nothing. But, the voltage did get up to a usable level which a good sign. However, I'd imagine it would fall as load on the alternator is increased.

http://www.youtube.com/watch?v=URzBIfi9NHU

I am starting to think that air tools are not the way to go. To get the power we need the flow rate must be very high. With the steam system I am thinking it would be better to go with a higher pressure & lower flow setup. I'm thinking at 250 psi you only need 1/2 the flow vs 125 psi. My thoughts to back to a home made turbine and some simple piping with a pipe plug and hole drilled in it. Thoughts on the high pressure low flow vs low pressure high flow?

[Patrick]

Originally Posted by Daox

My thoughts to back to a home made turbine and some simple piping with a pipe plug and hole drilled in it. Thoughts on the high pressure low flow vs low pressure high flow?

I think a turbine would have to be very precisely made - probably beyond the capability of home-made tech. Also, I think it would have to run at a very high speed to make any usable power, necessitating a gearbox to reduce rpm to match that of the alternator.

IMO, an easier system (and more likely to work), would be to use a positive-displacement engine (a small lawnmower, weedeater, or chainsaw engine) and convert it for use with steam. The rpm ranges match the alternator more closely and most of the precision parts are already machined.

Here's an example of a converted two-stroke engine. Of course this would need much more refinement. http://www.youtube.com/user/GREENPOW...12/dI-Zl7nEzA8

[Daox]

I agree a positive displacement pump would be ideal and likely more efficient.

The weed wacker engine is an interesting one. Too bad I just gave away my old one haha.

With positive displacement pumps you have a problem with how to lubricate it. Any ideas how to solve that?

I still like the turbine idea because its super simple (besides making the turbine, which I do think a DIYer can do). RPM would definitely be something you'd need to test to get right. You'd have to select a range of PSI that would be useful and if it dropped below that close the jet to rebuild pressure. Of course, we may have to do that with a positive displacement pump too... I dunno, I still just like the simplicity. Less moving parts, no friction, no maintenance basically.

Anyone know how industrial power generators work? Most power plants use heat to make steam to generate power.

[Dr. Jerryrigger]

I don't know how much power you can get off of one of these, but it looks like it might have enough torque if the RPM's were reduced with a gear or pulley. I think this one would melt with steam, but the basic design, and even sizing of this looks like it might work out well.
instructables Tesla-Turbine

[RobertSmalls]

Not a lot of power out of this one:

http://www.youtube.com/watch?v=yuPMZ...eature=related

[jdgFirefly]

Power plants typically use the Rankine cycle with steam turbines, they can get a bit complex with super heating and reheating stages but its all based on the simple Rankine cycle. Smaller scale power plant with more intermittent use might use gas turbines or even diesel engines.

I'm sure you can build a working turbine at home, but it will not have the same eff as an off the shelf PD motor that is converted for steam. If the air drill took 4cfm at 120psi to turn the alternator would a DIY turbine take less CFM to do the same job? Not likely. A turbine is a vary simple machine but to make it eff one must pay close attention to the shape of the the turbine blades. Like how tweaking the aerodynamics of your car can greatly affect FE the same is true for the turbine blades but to a greater degree because of the higher velocities and the importance of the force vectors.

Someone mentioned earlier about using a old lawn mower engine by simply welding a second set of lobes on the cam. This is a good Idea and probably the easiest way to make a high eff motor. Ideally you want to let in the high press steam close to TDC then close the intake valve and let it expand to BDC. So in addition to adding extra lobes It would be ideal for good eff too grind the intake lobes to only open for a short time at TDC. The steam motor will have a expansion ratio that is the same as the compression ratio, so on a typical engine you can expand the steam 8:1. This would mean that on a open system 118psi would be the optimal press anything above that press will have leftover steam press at the bottom of the stroke anything under and it will over expand creating a vacuum. At 118psi and 8:1 the pressure approaches zero as the piston approaches BDT, this might be optimal eff but there must be a point of diminishing returns so having the pressure a little higher wouldn't be a problem. Also if you want to run higher press more eff you just have to increase the compression/expansion ratio.

The two stroke motor wouldn't be vary eff because full pressure steam pushes the piston unit the ports are uncovered and the steam is released at full pressure. The motor has to compress the remaining steam as it returns to TDC. Plus how do you lube it.

[Daox]

I completely agree the turbine won't be as efficient. However, it might just be efficient enough to make a simple DIY system that works. With that said, does anyone have any info or knowledge about turbines and how you could make a semi-efficient one at home?

Everyone feel free to do testing on your own ideas. I have my own goals for this. If I can get free battery charging I'll be happy (for now ). More power would be great, but that adds more complexity to it since what do you do with that extra power now? There are tons of things you could do, but thats an entirely different project. My first goal is just to get something that works.

I definitely need to do some reading up on the Rankine cycle. I really don't fully understand it.