designing long-life engines for home biomass energy systems 3

[chucksk]

I am most interested in tackling engine cylinder and valve wear issues. How do you reduce wear in the head area? Also, would dual spark plugs per cylinder be of any benefit? I have taken a look at split-cycle engine designs, as they seem to offer some efficiency and wear benefits. Ideally, it would be nice to reduce the maintenance intervals to a point comparable to any other type of home heating system, and maximize the efficiency of the engine for electrical production. Please offer some suggestions!!

 

[chucksk]

Thanks Globi5 & Mike!! Finally getting some time to take a look at the Swiss machine - got pretty busy with work for a while. It should be instructive to see how well their engine is holding out.
Mike, maybe you're right, but I have a hunch that engine durability issues can be addressed, and most of the problems stem from cost-cutting measures on the part of manufacturers - insufficient filtering of oil, lack of lubrication at start-up, cold-engine starts, etc. It might be quite a challenge to turn a regular engine into a spit-cycle to improve efficiency, and perhaps that's a bit of a stretch for a home system, though it could be important in the near future, when skyrocketting energy costs in all sectors drive demand for high-efficiency and high value systems.
I love truly balanced engines - something about a machine that doesn't bounce and vibrate at certain RPM's just seems like good engineering, and I'll bet that has some effect on engine life as well. It would have to be very quiet too. Anything louder than current heating systems would be unacceptable, so the muffling of exaust gasses is very important. In fact, I'm wondering if the spit-cycle engines, utilizing the Miller effect, wouldn't eliminate some of the exaust noise issues, as there's less "pop!" coming out of the exaust valve area, when the gasses get to expand more fully..
Anyhow, thanks & more later!!

 

[globi5]

At least the engines mentioned all have a turbocharger, so this 'pop' is already partially muffled.

 

[mishar]

I would focus on refining that fuel rather than on special engine.

 

[chucksk]

Oh, thanks!
I didn't realize turbochargers reduced the exaust pop, but that does make sense! I could go with a conventional engine, and add a turbocharger - true. But the spit-cycle design looks easy enough to create from a modified engine, it is very tempting to try. And someone has to, or the car would still be a carriage; the airplane a dream.
Mishar, I'm not quite sure what you mean - are you suggesting I fractionate bio-oil made from biomass, or clean the gengas to remove ash, soot, and resins? The latter is not too complicated, well documented, and certainly a must! The former might be a possibility as well, though that requires more pressure vessels, fractionating towers, and catalysts. I thought about a mini-refinery like that; but what would the neighbors say?
Anyhow, thanks for the suggestions!
Sincerely,
-Chuck.

 

[mishar]

I meant getting rid of CO2 and N2.

 

[chucksk]

Wood gassifiers work by passing combustion product gassses & pyrolysis products back through a hot bed of coals to generate the mixture of simple fuel gasses + "inert" gasses. The N2 comes with the atmosphere, and unless I use pure oxygen or some other process, will be there in the fuel stream. CO2 is from all the flame chemistry, a result in part of the combustion that keeps the coals hot, and perhaps it could be reduced a bit? But will probably always be there.
It's a very well studied field, so reducing the CO2% in the mix would be challenging!
One thing I did discover - Kohler offers / will be offering a new line of small Diesels. Diesel compression ratios would be more ideal for wood gas owing to the gas's high octane rating, and the higher efficiency of diesel engines. Engine life in excess of 5,000 hours is not unheard of for some of their engines - one critical part of making a successful unit. There was something I had looked at about internal harmonic balancers built into the engine - just vague recollection, but it's nice to see this in small engine designs.
Anyhow, that's all I know right now. Happy December Everyone!!

 

[dicer]

"Diesel compression ratios would be more ideal for wood gas owing to the gas's high octane rating,"

Did you know that high octane has the opposite effect in a diesel engine? Octane and Cetane are inverse, a diesel engine desires high cetane. High octane in a diesel will cause more severe knocking. Also how are you planning to introduce the fuel into the combustion chamber? Spark ignition?

 

[tommy75]

I think you could take a look at a book called the "Pegasus Project". It's about all the small gassifiers Hitler had installed on the German war machine during WWII. They had switched to these because of the oil cutoff during WWII.

Regards,

 

[globi5]

The reason why high compression engines (such as diesel) would be well suited for wood gas application is because of the low energy content of wood gas (N2, CO2 in the mix).

It's basically like running an engine with a half open throttle (knocking won't be an issue). By increasing the compression ratio, efficiency of the engine will be increased.

Not being able to get rid of N2, CO2 is not the problem. You simply need a larger engine to generate the same amount of power (engine weight is not really a concern in this application - so who cares).

 

[chucksk]

Hmm.. Octane and cetane are opposites? To me, octane refers to a standard of a given fuel's reliable combustion point and evenness of burn when compared to a mix of chemically pure octane and air; I was under the impression cetane was merely a heavier fuel compound used in Diesel's for the same basic purpose. Low-octane related knocking is caused by early or occasional random ignition before the proper BTDC point. So, how is it with Diesels? Seems like it would be less of an issue either way, as the fuel is injected?? Hmm.. more research needed..
True, it is a low energy value fuel, but because it also has a high octane rating, it can be used with a higher compression ratio. A higher octane rating means reliable combustion after spark at higher compression ratios, although maybe the mix of non-flamable gasses reduces pre-ignition as well..
Since this will be for home use, I think need only a small engine (based on calc's) running under a relatively constant load. I thought about an in-line 6, but that's too big of an engine to operate efficiently given a relatively small load.
Mother Earth News had one set up in the early eighties - a 1961 Pontiac Tempest four-cylinder engine (195 inch, long-stroke model) er.. the left-half of a GM V8 basically..
The engine was rated for 110 HP @ 3800 RPM; with wood gas fuel it delivered 70HP @ 3800 RPM's. Not too shabby!
They had it coupled to a 10-KW Kamag alternator - enough to power quite a load, but wayy more than I need! Let's see.. my rate of useage is around 8 KWH/day; I think maybe something on the order of an 11 or 16 HP engine would do just fine, with added battery buffer. Otherwise, I would be running the engine and gassifier for less than one hour per day, and needing a battery bank the size of Fort Knox! (and a bank account that size, too..)
True, I should look at the "Pegasus Project" - though, I think they were using updraft gassifiers back then, and they're pretty dirty gas generators, by comparison to the imbert downdraft design. Probably used coal mostly, as that's energy dense and plentiful in Germany..

 

[globi5]

It's true that the octane rating of wood gas is significantly higher than, for instance, of gasoline. But what I meant is that knocking is less harmful because of the far lower energy content of the fuel (similar to the HCCI concept).

Anyway, if you just need 8 kWh per day, you could simply put four of these panels:

http://www.sunpowercorp.com/Product...for_products_services/SPWR_315_com_en_DS.ashx

on your roof and be all set for the next 30 years.

(no moving parts, little complexity, no wood logging etc.).

 

[chucksk]

Thanks Globi5 - solar power I am very familiar with, and yes, this is a good solution for 8 months of the year. The remaining 4 comprise low-light levels due to our latitude, cloudiness in winter, v. cold, etc. Plus, I am interested in using wood or biomass pellets (this could be from non-recyclable paper, etc.) to generate producer gas. Hence, taking care of all the home's needs - heating, lighting, shop tools, etc., and using readily available fuel sources that are either residues from wood, or derived from waste materials. Advantages of doing so include minimal line loss, direct use of "waste" heat, closeness of the energy source to point-of-use, and stable, low fuel costs. What's lacking is reliability, and that's why I have great interest in reliable engine technologies. If service intervals could be held to a yearly or bi-yearly basis, these systems would gain immensely in their attractiveness to future buyers of heating systems. And given improved efficiency of both home and power plant, the demand on limited resources diminishes to make these systems widely practical in the near and distant future.
It would be nice to not have winter - but living north of the 45th parallel makes that a non-option! I'm thinking about better ways, and using proven technology coupled with maximum efficiency in design seems a logical way to approach our energy future.

 

[globi5]

Actually, this house is also above the 45th parallel and generates enough heat and hot water just with the area available on the roof.

http://www.jenni.ch/index.html?html/Heizen mit Sonne/MFH/Prinzip.htm

There's a 205 m3 Watertank which basically stores the summer heat to provide heating and hot water during the cold months.

You need to click on: 'Mehrfamilienhaus' to see a picture of the house.


(Obviously, this is only practical if you build your house from scratch.)

 

[TDIMeister]

Nothing in the fuel composition you stated would seem to be contributory to excess wear to the cylinders and valve seats other than the lack of lubrication, as long as your fuel does not have any suspended solids in it. This would be the same problem faced by an engine fuelled with alcohols, propane or natural gas. The other potential problem is cooling (gaseous fuels inducted at ambient temperature and pressure do not provide any charge cooling that evaporating gasoline or alcohols do).

There are lots of contemporary developments in valve seat materials, and sodium-cooled exhaust valves would help a lot. The lubrication issue can be helped in large extent through lube oil selection (full synthetics highly recommended plus there are some motor oils specifically formulated for propane and natural gas-fuelled engines) and periodic oil analysis.

If this engine is to be used in a stationary application, water injection directly prior to the intake valves could be very beneficial, especially if the engine is force-inducted to make up for the low volumetric heating energy.

IMO, however, this fuel composition would seem to be most ideal not for a piston internal combustion engine, but rather in a continuous-combustion burner in a gas-turbine or Sterling engine.

I have been doing some research and analysis into a CHP system using bio-fuelled ICE or Sterling engine that drives both an electrical generator as well as being the work-module of a ground-source heat-pump HVAC system that could operate fully off-grid as long as it has a sufficient source of fuel. Given that my full-time off-grid requirement would necessitate fuel flexibility not only for various liquid fuels (e.g. bio-ethanol, neat plant/animal oils, trans-esterified fatty-acids, etc.) but also bio-gas and solid biomass, I've nixed-off the choice ICEs for Sterling.

 

[malbeare]

"mishar (Automotive) 27 Oct 07 0:01
While I am waiting for a type of fuel chucksk using, I tried to find those two additional strokes malbeare recommended. No luck.

Sliding and rotational valves are older than anybody on this forum, but unfortunately they do not work any longer than few tests and they are leaking in the mean time."

mishar,
The rotary disk and reed valves are not subjected to cylinder pressure as the upper piston takes care of this . the rotary valves only have to cope with low pressure to seperate exhaust from intake. minor leakage is not a problem . The valves do not actually touch anything so ware and lubrication doesnt happen.






A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare

http://www.sixstroke.com