Mini steam turbines -- convert a turbocharger?

[swyves]

I am involved in a project taking place among small communities in rural Peru, mainly in rainforest areas. Population density is low, there is no road infrastructure, and development levels range from third world towns to uncontacted tribes. Power is a major problem. Solar is expensive and not well suited to a rainforest; there's no wind, no hills for hydroelectricity, etc etc etc. Fuel is hard to obtain and expensive. Biofuel infrastructure is not operational.

What I'm wondering is whether we can make low cost steam turbines, perhaps by cannibalising turbochargers (using the exhaust turbine) or superchargers (running them backwards) from vehicle salvage, and get the shaft to do some useful work, for electricity or rotary power in smaller communities. Efficiency is not really an issue; there's no shortage of dead wood we can burn to generate steam. However, the system does have to rugged and field maintainable, preferably with minimal training. If we can get 50W, we can at least get a radio running for each community. With a kilowatt or two, we can really make a difference, maybe with lighting, water purification, even local light industry. As a pipe dream, if we could get a system weighing in the lowish hundreds of kilos (or less) to generate 10kW or more, then this can be used to power boats, which are the only means of transport in the region.

The aim is that with steam, anything can be used as fuel. Even installing basic ethanol distillation in this region is difficult and expensive, and the number of people who could benefit from any fixed installation is small as the population is so spread out.

So, is it feasible, or are we (a) not going to get anything, (b) going to get so little power that it's pointless, or (c) going to kill our turbines in seconds and have systems that won't keep working or chew through parts too fast. Low cost is the main concern; anything technical is going to be expensive here, but raw materials are not too bad and we can easily hire skilled welders and metalworkers (though don't expect much in the way of CNC out here). I'm hoping we could get truckloads of old turbos from broken vehicles to import from the USA.

Any thoughts, or indeed suggestions for totally different systems, much appreciated.

 

[racookpe1978]

Looking at the video's of the (many!) small fixed base and portable steam engines at that site above, I'm beginning to think the portable steam tractor with power-take-off driver for saws, generator, water pump, thresher, stone crusher, irrigation pump, corn husker, mill, lathe, etc, etc, etc - and as a tractor or steam RR or truck engine is most adoptable. Adaptable too.

If the fix bed is what's required for a village or remote mine or farm or business, buy the standard kit with no wheels. If the truck/tractor car/bus is what's needed instead of a farm and business implement, don't run the PTO.

Simple, standardized run-of-the blacksmith shop repairable parts. Power from 2-6 Hp up the 30 to 50 to 150 Hp.

 

[JStephen]

If you look at the old steam tractors, they were very low-powered compared to the weight, and had this annoying tendency to blow up when used improperly.

Something to watch out for on the hobby-type steam engines is that most of them probably are actually run very few hours. So you never really know how well the lubricating systems are set up and all. It may be a great little engine, but can you run it 20,000 hours without an overhaul? Or does it take a machinist building a new engine every 200 hours? (If I recall, one of the downfalls of the steam locomotives was they spent about 30% of their time in the shops being overhauled and all.)

As an alternate to lawnmower engines, you can buy new air compressors (just the compressor part, minus the electric motor and tank), that would be equally adaptable. In either case, you're liable to have lubrication problems when putting it into steam service.

 

[ornerynorsk]

I'd have to agree with the other posters suggesting wood gas generator running a small engine.

 

[swyves]

I'm liking the sound of the wood gas, but the small steam engines are a good option too. For any of these projects based on old ICEs, we can get hold of motors very easily and cheaply -- Peru is full of imported Chinese motorbikes with 125cc or 250cc engines, mainly 2 stroke but some 4 stroke, and 10hp agricultural engines. Car, bus, and truck engines are also available.

Reliability is the big concern, I guess. If I get little power from a big heavy engine, then I can live with that; but if it's going to need a mechanic to come out and fix it every few weeks, we might as well just send him with a few jerrycans of gas and run regular engines. And some of these villages take a week to get to, so maintenance is the real bugbear.

Thanks again for all the thoughful and innovative suggestions!

 

[KENAT]

While it might be possible to come up with a 'steam' solution, I think berkshires wood-gas is perhaps the most promising given what you've told us.

It's not just maintenance but also potentially safety concerns.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

JStephen,

The original steam engines on ships were inefficient for their size, and their boilers blew up regularly. Eventually, they learned that wood was not a good material for boilers. Then they learned that iron and steel boilers had to be manufactured skillfully, then they learned how to analyze and manufacture them.

An efficient steam engine runs at high temperatures and pressures, requiring reliable analysis and fabrication techniques. This is an issue for safety as well as efficiency, and might be a good case against steam.

JHG

 

[CH5OH]

stirling engine, trust me I am a docter (lol)

http://www.youtube.com/watch?v=2LOcyjZthsg

 

[swyves]

The thing with Stirling cycle engines is that engineers love them, everyone always bigs them up, always considers them, then people suck their teeth and end up not using them. At any given time there seem to be zillions of companies developing them, but never a production model to be found. But hey, I'm open minded. Find me a way to make or buy one that can compete with a cheap, used, ICE running low pressure steam or wood gas and fine. As mentioned, we have nothing like the facilities, expertise, or money necessary to develop an engine of our own.

 

[CH5OH]

thing is they don't have a market for it,in developped countries ICE engines have a 100 year research ahead and a fuel infrastructure to support them.
I suggested a stirling because you are on a low budget,without mechanic support, without fuel infrastructure.
OK, I put my mc Gyver hat on and give it a try:
1.go to a scrapyard and get 2 motor blocks of a mass produced (popular) car (4 in line design)
block A will have 3 cylinders acting as the hot cylinders 1 cylinder will be converted to act as a compressor.
block B will have 3 cylinders acting as the cold cylinders 1
cylinder will be converted to act as a compressor.
2.the cylinders used to charge the engine with air should be located on the opposite site of the cooling water inlet.
To convert the 4 stroke cycle to a compressor cycle, you have two options:modify the camshaft so the cams are mirrored or modify the drive train from 2:1 to 1:1.
Next you need to provide 3 way ball valves, which give the following operating modes to your 2 cylinder compressor:
2.1.charging motor with air (starting and toppig up): both inlets of the cylinders are connected to open air, the outlets are connected to the motor circuit.
2.2.charging wood combustor with air (running): the outlets are connected to the wood combustor.
3.design a motor frame to support the two motor blocks and to interconnect the two crankshafts via the open gear, which was used to engage the starter motor.(one starter motor can be removed).The opposite cylinders of the two blocks should have a 90 deg crank angle difference
4.hot cylinders:the cooling inlet of the block is connected to the exhaust of the combustor, the cooling outlet serves as the exhaust of the motor.The valves on the ports not facing the other block should remain closed (remove their cams on the camshaft.the other 3 valves (of the ports facing the other block) are removed and the hole were the valve stems used to be are plugged.
5.cold cylinders:the cooling circuit is left in place (pump remains, thermostat valve is replaced by a dummy (so cylinders are cooled as much as possible).Same story on the valves,facing ports removed, other three remain closed.
6.regenerators:basically a cavity with a gas volume equal to the volume of one cylinder, stuffed with SS demister mesh.The three regenerators connect the opposing cylinder ports of hot and cold motorblock.Hot motorblock and regenerators need some insulation on the outside.Provide a tiny little pipe between the regenerators, so static pressure of the three cylinder pairs remain the same
7.interlink the two oil sumps and use the converted radiator on the cold block to cool the oil
8.wood combustor:an empty gas bottle (a tall one)is converted to use as combustor (before cutting remove the valve and fill with water)
bottom sectionrovide a port to remove ashes and to get the woodcharge going, this port is also used to make a starting fire. provide a connection to the compressor.(you might need a compressed air storage tank to facilitate starting (provide a flow to heat up the hot block)
mid section: this section is separated from the bottom section with grating.while stuffing the combustor with woodchips/sawdust, a pipe is placed in the centerline of the combustor.Once the woodchips/sawdust is compressed, the pipe is retracted, leaving an air channel.
top sectionrovide a port to load the combustor and to put and retract the centerpipe.Provide a line to the cooling water inlet of the hot motor block,provide a blow off valve on this line to discharge excess of heat.
if you need more power,build more machines to the same specification.Remember diversifying a design only increases the profit of the supplier.
I believe the proposed design is called an alfa type stirling

 

[swyves]

Wow -- very impressive. That looks practicable; I'll go through it in more detail, and give it a go if possible. At the very least it'll be an interesting experiment.

 

[CH5OH]

well,
ahum... I did some calculation and you might want the scrap the proposed design for following reason (I guess you're right with regards to the stirling cycle):
a dreadfull power output, reason being:
stirling engine uses a temperature swing
ICE,gas turbine, steam turbine uses a temperature and pressure swing
so back to the drawing board:
1.find a 4 stroke engine
2.convert to a two stroke design,half the cylinders work as compressor, half as expander(camshaft modifacion)
compressors should be on the up stroke, while expanders are on the down stroke
choke the inlet flow to the expanders, by seriously reducing their inlet valve lift (cam shaft design,trial and error)
4. pay enough attention on the sealing of the ports on the combustor, so it can be pressurised (pressure swing depends on valve choke inlet expanders)
5.use a filter mesh on the outlet of the combustor
6.oil and water circuit remains intact.
good luck!

 

[CH5OH]

remark:
if you're able to provide excellent sealing on the combustor,the maximum obtainable pressure swing is limited by a single stage compressor design (about 8 bar) and the spring load on the inlet valves of the expanders (probably<8bar)

 

[CH5OH]

I attached a sketch for the cams

 

[berkshire]

Why fabricate a Stirling engine from used automobile parts.
Find a junkyard engine that runs, and run it on wood gas you will have half the conversion work to do.
You can also run a Honda generator set on wood gas with very little additional plumbing.

http://www.woodgas.net/files/FEMA emergency gassifer.pdf

B.E.

 

[CH5OH]

proposed solutions and their problems associated for SWYVES project:
convert a turbocompressor to use as a steam turbine:
-requires a turbocompressor,a furnace with boiler, super heater, feed pump, level control,safety valves,flow regulating valve, PTO involving coupling and gearbox

convert a 2 stroke engine to use as a steam expansion machine:
-not feasable because 2 stroke engine uses normally oil in the fuel to lubricate the crankshaft, before entering the cylinder (2stroke without valves),using as a steam expander, wet steam will destroy crankshaft bearings.

convert 2 4 stroke engines to stirling:
-to much motor mass for usefull power output

use a gasifier with modified 4stroke engine(ignition timing, carburation):
combustor:
H+O2>H2O
C+O2>CO2
CH4+5O2>CO2+4H2O
gasifier:
H2O+2C(charcoal)>H+2CO
CO2+C>2CO
CH4+O>CO+H4
+well proven design (thanks berkshire for excellent info)
-providing combustion gas with a constant quality
-handling CO (poisonous)
-fuel preparation=chipping+dehumidification

use a combuster and a modified 4 stroke (camshaft)
combustor:
H+O2>H2O
C+O2>CO2
CH4+5O2>CO2+4H2O
expander (motor):
pressurised H2O(steam)+CO2(hot) expands to atmosphere
+combustor is easier to construct than gasifier
+fuel preparation=chipping
-continuous operation requires 2 combustors
-re engineering a camshaft
-design not proven (innovation gots us away from living in caves though)

 

[katmar]

swyves, here is a link to another person working on low-tech steam turbines.

http://www.green-trust.org/steamturbine/steamturbine.htm

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