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Stirling Motor Electric Co-Generation with Rocket Stoves?

                              


Joined: May 12, 2012
Posts: 1
I'm imagining attaching a Stirling Motor to a rocket stove.

One thing I'd like to do with a rocket stove is to use cold, outside air for the combustion, rather than drawing indoor air. This creates a very accessible cold-side for a Stirling motor, as cold air passes in through a duct, with the hot-side being at the chimney. One side-effect of this, too, is that the Stirling motor could be hand-cranked to generate heat in the chimney before lighting the stove, to start the convection process and produce less smoke.

One other design modification to the rocket stove I see is in using used fry-grease from restaurants as fuel. I read that the bronze-age Minoans perfected an olive-oil fueled bronze forge where an oil reservoir was channeled into a drip system, dripping drops of oil into the fire. The drops are small enough that their surface-area to volume ratio was high, and burned quite nicely. They used their lowest-grade pressings to fuel these systems, reserving the higher grades for food and lamp-oil. In our day, used fry-grease can be painstakingly filtered, dehydrated, and processed into bio-diesel; but in a much simpler process, straight used fry-grease (with some filtration) could be channeled into the combustion chamber of a rocket stove to power an external combustion "engine", such as a rocket stove paired with a Stirling motor. This could provide a fair amount of electricity along with heat during Winter months and at night when solar is much less available.

The biggest problem I see is the lack of a decent commercially-available Stirling motor generator.
Max Kennedy


Joined: Feb 16, 2010
Posts: 462
Location: Kirkland Lake, Ontario, Canada
Old idea. Good luck in finding an appropriate stirling at anything approaching a reasonable price! If you find one actually in production, not just a promise of production, let me know. As for the oil furnace, doable. Here's just one example;

http://journeytoforever.org/biofuel_library/ethanol_motherearth/me4.html


It can be done!
Marcos Buenijo
pollinator

Joined: Dec 18, 2011
Posts: 583
Location: Southwest U.S.
    
  12
Arcas EarthSoul wrote:One thing I'd like to do with a rocket stove is to use cold, outside air for the combustion, rather than drawing indoor air. This creates a very accessible cold-side for a Stirling motor, as cold air passes in through a duct, with the hot-side being at the chimney.


The mass flow rate of air required to cool the engine is much greater than that required to support combustion in the furnace. Therefore, if the cold side of the engine were contained in ductwork, then a large blower fan would be required to cool the engine and only a very small percentage of that air could be delivered to the furnace. The fan would consume a lot of mechical energy. NOTE: Describe what goal you have in mine (electricity generation, cogeneration, etc.) and maybe I and others can suggest other possibilities.

Arcas EarthSoul wrote:One other design modification to the rocket stove I see is in using used fry-grease from restaurants as fuel... In our day, used fry-grease can be painstakingly filtered, dehydrated, and processed into bio-diesel; but in a much simpler process, straight used fry-grease (with some filtration) could be channeled into the combustion chamber of a rocket stove to power an external combustion "engine", such as a rocket stove paired with a Stirling motor. This could provide a fair amount of electricity along with heat during Winter months and at night when solar is much less available.


Pure vegetable oil can fuel many Diesel engines very well (of course, it must be highly filtered, but dehydration is not normally required). I say save the oil for a Diesel since they're a lot more efficient and cost effective than any Stirling engine. Even better, fuel a Diesel with wood gas by using only just enough oil for ignition (if you're not familiar with wood gasification, then inquire and I'll link some resources).

Arcas EarthSoul wrote:The biggest problem I see is the lack of a decent commercially-available Stirling motor generator.


Forgive me, but the bigger problem is the almost religious zeal so many seem to have over Stirling engines. Sure, there are advantages... mainly these include low noise, multi-fuel capacity, clean combustion, and ability to use solar thermal energy. However, an efficient and compact design is going to be expensive. A better choice in my opinion would be to develop modern piston steam engines.
Marcos Buenijo
pollinator

Joined: Dec 18, 2011
Posts: 583
Location: Southwest U.S.
    
  12
Waste oil genset (may also use waste vegetable oil): http://www.phoenixpowergroup.com/phoenix-generators/phoenix-10-generator/

Video of waste heat engine used in the waste oil genset: http://www.youtube.com/watch?v=6NPpelLCIkk&list=FLGwhQCvpMjlp50BoPU3LtFA&index=2&feature=plpp_video

These are overkill for individual use, but after the waste heat engine is finally released, then I expect smaller versions may be made. The most important component for individual use is the engine, and you can see from the video how simple the design is. The price should be low after mass production.
Max Kennedy


Joined: Feb 16, 2010
Posts: 462
Location: Kirkland Lake, Ontario, Canada
Cyclone power, maker of the WHE has been promising much for a very long time but has nothing but prototypes. Don't hold your breath!
Warren Weisman


Joined: May 03, 2012
Posts: 28

Whispergen offers a commercially-available Stirling engine gen-set for luxury yachts for marinas where generator noise is prohibited.

http://www.whispergen.com/main/HOME/

They are about $6,000 installed and run on diesel and produce only DC electric and of course hot water.

They use about four times more fuel than an ICE, but obviously the yachting crowd is not concerned with efficiency.

Max Kennedy


Joined: Feb 16, 2010
Posts: 462
Location: Kirkland Lake, Ontario, Canada
The off grid marine generator is no longer available.
Marcos Buenijo
pollinator

Joined: Dec 18, 2011
Posts: 583
Location: Southwest U.S.
    
  12
Max Kennedy wrote:Cyclone power, maker of the WHE has been promising much for a very long time but has nothing but prototypes. Don't hold your breath!


The problem with most people who are are sour on Cyclone is unrealistic expectations. I've been following their progress for more than 6 years. Personally, I think they're right on track.
Max Kennedy


Joined: Feb 16, 2010
Posts: 462
Location: Kirkland Lake, Ontario, Canada
Cyclone should have been marketing a product a long time ago. Will believe it when I see it but won't be holding my breath. Until then it's so much vapourware!
Warren Weisman


Joined: May 03, 2012
Posts: 28

We offer small spark-ignited ICE gen-sets for home biogas, since they need no "warm up" period where they are wasting fuel without delivering any energy. However, anything for constant daily use bigger than 5-10 kW my personal preference would be a steam microturbines. One moving part, turbines operate for decades without maintenance and have a far greater weight-to-power ratio than any piston engine and unlike a steam engine do not require lubrication, which renders your condensed steam unusable (you cannot have oil in a power boiler).

Your efficiency depends entirely on your boiler design and burner, which if you know what you're doing can easily exceed 40%. The Stanley Steam Car's 20 hp boiler took only 25 minutes to reach operating temperature and got comparable fuel economy to the Model T for a long time with probably the most inefficient boiler configuration ever after a single flue marine boiler.
Marcos Buenijo
pollinator

Joined: Dec 18, 2011
Posts: 583
Location: Southwest U.S.
    
  12
Max Kennedy wrote:Cyclone should have been marketing a product a long time ago. Will believe it when I see it but won't be holding my breath. Until then it's so much vapourware!


I disagree that Cyclone "should" have a product on the market by now. Cyclone has too few resources to have completed the necessary development and testing. However, there has been enough testing on the waste heat engine to warrant an upcoming release. If they don't get that out very soon AND if it's not successful in the market, then they're sunk.
Marcos Buenijo
pollinator

Joined: Dec 18, 2011
Posts: 583
Location: Southwest U.S.
    
  12
Warren Weisman wrote:
One moving part, turbines operate for decades without maintenance and have a far greater weight-to-power ratio than any piston engine and unlike a steam engine do not require lubrication, which renders your condensed steam unusable (you cannot have oil in a power boiler).

Your efficiency depends entirely on your boiler design and burner, which if you know what you're doing can easily exceed 40%. The Stanley Steam Car's 20 hp boiler took only 25 minutes to reach operating temperature and got comparable fuel economy to the Model T for a long time with probably the most inefficient boiler configuration ever after a single flue marine boiler.


I have to respectfully disagree here. Yes, a turbine will last due to its simple one-moving part design. However, a small steam turbine is very inefficient. If enough money were thrown at it, then the efficiency could certainly improve. However, this would require multi-stage compounding, extremely high speeds, reheat staging, and heat regeneration that would take the cost way up and the power/weight way down. Throw less money at a piston steam engine and its efficiency will still exceed that of the small turbine plus show far superior part load efficiency. Please note that I'm talking about small scale systems here (generally less than 100 hp, and mostly under 10 hp). We don't see highly efficient small steam systems (turbine or piston) simply because we have internal combustion engines. However, a small piston steam system can be just as efficient as a small Diesel engine, but not without added complexity.

The concern about oil in the boiler is legitimate. However, this can be done at limited temperatures and using a properly designed steam generator. The Doble pulled it off with reasonably good success, and a stationary system could do better. Cyclone Power is getting good results with water lubrication by using actively cooled high temperature plastic piston rings. Of course, most people don't care since their products are not yet available, and that's a reasonable objection. Oil separators can solve the problem well in small systems... but again, why not just use internal combustion engines?

The thermal efficiency of a steam system depends primarily on the expander. The fuel economy of a Model T is definitely a lot greater than the Stanley except possibly under certain limited conditions like extreme stop and go driving at a very low average output.
 
 
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