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designing long-life engines for home biomass energy systemsHelpful Member!(3) 

chucksk (Bioengineer) (OP)
26 Oct 07 13:46
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!!

hemi (Automotive)
26 Oct 07 14:38
How about giving us some details about the composition and properties of the fuel, and its production rate...
Helpful Member!  malbeare (Automotive)
26 Oct 07 16:24
chucksk (Bioengineer)

Have a look at

a new head design,

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

dcasto (Chemical)
26 Oct 07 16:37
Malbeare, the sixstroke looks like a take off and maybe improvement of the submarine engine, cool.
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. sad

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.

Claims about efficiency and torque sound too good to be true.

I do not see any advantage of opposite piston engine dcasto linked. Two stroke turbo Diesel works just like that and has standard valves and camshaft mechanism instead of half of that engine. May be I am missing something. Never been on a working submarine. smile
chucksk (Bioengineer) (OP)
27 Oct 07 3:04
Thanks Hemi, Malbeare, Dcasto, and Mishar!
  Fuel composition : ( % by volume): 19%CO, 14%CO2, 17% H2, 2% CH4, and 48%N2.  Basically, a mixture of carbon monoxide and hydrogen, with a little methane, and a lot of filler!
  Production rate is dependent on gassifier size, and since the engine vacuum "pulls" the fuel from the gassifier, it varies according to engine vacuum, but can be induced with a blower.  
  I'll check out the new head design - that's one of the problems!  Where there's no lube, there's the wear..
  Hmm.. not since the Knight engine do I recall sliding valves!  But how well did they work back then??  Willys used them for quite a few years, so they must have been fairly descent..
  Anyhow, I did take a look at stellite valves (supopsedly the best) some time ago. RE valve shape - good old Henry Ford at one time had his valves ground in a special shape (mushroom bottomed) - claimed to last longer, but were more expensive. Was this really better?
  I did look at balanced engine designs on Wikipedia - I like the opposed cylinder design, as it is (according to the article, at least) perfectly balanced in a flat 6-cylinder arrangement.  I like that!  In-line 6 & others do as well, too..
  Hmm!! Been a few years since Diesel Subs!! Probably some of the best engines, I would imagine (wouldn't want one to fail wayy out in the ocean!).  
  I like the Scuderi engine design - producer gas (this CO/H2 mix) has a very high octane, and works very well at higher (ie - Diesel) compression ratios.  It would be nice to optimize compression for maximum efficiency, and with the split-cycle, one could design for the best performance.
  Thanks for all your help!!  I'll keep searching..
dicer (Automotive)
27 Oct 07 10:57
In other words you have a flu gas engine set-up?
What you need is good filtration, and some hard materials.
If it is a reciprocating engine there will always be a maintenance aspect, as it is not going to run forever with out some maintenance. To reduce wear, keep out abrasives, hard wear resitant materials, lots of lubrication.
Maybe a closed cycle stirling engine is what you need, using external combustion of the gasifier components.
chucksk (Bioengineer) (OP)
28 Oct 07 2:01
Hello Dicer!
Flue gas - well, more like reconstituted flue gas, I suppose!  The gas coming off the hot wood is run through the red-hot coals, and gets broken down into Carbon Monoxide and Hydrogen, plus some other gases.  Definitely, good filtration is a must!!  
  Yes, some maintenance - I agree.  I just had in mind something that runs a long, long time between service intervals, and lasts as long as is practical.  If this system were to compete with conventional heating systems, it needs to be comparable in service interval (or fewer customers would be interested in one..)
  Is it better to use hard wear-resistant materials in the head, or cast-iron, which has graphite particles to help lubricate?  (hmm.. I'd better go look at that article..)
  I did look some time ago at closed sterling-type systems currently being offered in New Zealand and England (made to operate on natural gas).  Some question about whether the bearings would hold up based on the design, and the efficiency would be much lower..  Perhaps the better choice, if these systems prove durable?  My thought is: since electricity is a high-end product (takes a lot of inputs to get a little out of the wall sockets, and it's pricey), I would like to maximize electricity production at the destination point.  I did look into other methods as well - peltier junctions, brayton-cycle engines, turbines, etc., but the standard otto-cycle engine, with miller-effect, looked to be the best.
  If the truckers I know can get 1-2 million miles out of their engines, I figured the same should be possible with stationary units, given optimal lubrication and filtering.  With a 50% duty cycle per 6-month heating season, this would translate to about a 10-year engine lifespan, between rebuilds - acceptable for home systems as a start point.
  Anyhow, I'll check out harder materials for bearing surfaces - curious about those newer head designs!
dicer (Automotive)
28 Oct 07 2:31
I think your best and most inexpensive route is to just use some off the shelf engine, and experiment with it. Run it for a month or so then check it out, see what kind of wear it has gone through. From what I've seen in the past many farmers where using flue gas for fuel during WWII
to power their tractors, since petro was difficult to obtain. A good filtration system is the key to longevity.
I have though about doing what you are as well.
Good luck keep us posted on your results.
MikeHalloran (Mechanical)
28 Oct 07 15:51
Another way to get longevity is with sturdy construction and low rpm.  

There was a big ol' six running in the shop last week.  It sounded nice.  I asked how old it was.  Nobody knew for sure, but the consensus was that it was originally built around 1935.  It got a new set of cylinder liners, and a new warranty.  

I'm told that such monsters (Waukesha) are popular in the oil patch because they run on gas that would otherwise be flared off, and they don't break easily.

Mike Halloran
Pembroke Pines, FL, USA

Helpful Member!  globi5 (Mechanical)
29 Oct 07 4:32
Since power density (weight) is not critical in this application, you might as well consider a closed engine without valves at all.

e.g. such as this wood pellet driven stirling engine:
Helpful Member!  ivymike (Mechanical)
29 Oct 07 9:19
stirling engines are a good candidate for flexible-fueling power gen applications...  if you have the space for them, and a cold climate to run them in.  I wouldn't mind having a wood fired one at my place - that'd be a great backup in case of a prolonged power outage.
dcasto (Chemical)
29 Oct 07 16:56
The lowest BTU/CF I remeber being burned in an IC engine was about 600 BTU/cf.  This stuff is under 150 BTU/cf.  I believe Solar turbines got down to 250 or so.  They only way to burn this stuff is add enough propane or natural gas to get to 600 BTU/cf.
globi5 (Mechanical)
31 Oct 07 4:05

I'm not sure what you're refering to, but stirling engines are no IC engines and depend on an external heat source so BTU/cf has little relevance.

Besides, even IC engines can essentially run on wood with the help of a wood gas generator.
dcasto (Chemical)
31 Oct 07 10:00
I was speaking of IC.  In any case, I don't believe the stuff will sustain itself to burn without addition of more fuel, its very close and the OP needs to understand problems with it.  Also, there are other gases that will form solids and coat the sterling engine and drop the heat transfer.
globi5 (Mechanical)
31 Oct 07 13:54
There's is a small 350 kW (electricity) pure wood gas power plant with a 12 cylinder IC engine not far from Zurich (Switzerland).

They process and dry waste wood. The partially sell dried wood chips directly and partially produce and sell electricity and heat with the rest.
chucksk (Bioengineer) (OP)
1 Nov 07 0:50
Wow, lots of responses!! smile)
Thanks everyone!!

Sterling or IC Engines?  I'm leaning more towards internal combustion engines, as the efficiency of conversions is greater.  Perhaps Sterling Cycle would be better due to reduced maintenance, but I'm hopeful that, here in 2007, we have the technology to get a reasonably long interval between servicing IC engines.  Slower RPM's generally means longer engine life, so a reasonable engine size might be larger, even though this adds cost (but hey, who wants the headaches!) Waukesha made engines for the oil patch from the 30's - hmm!  No doubt they were built to last!  But back then it was low compression tech., and lubrication wasn't quite as good as it is today.  I did look at a newer Kohler engine, and liked the design (balanced very well, and built for long-life).  Perhaps I should obtain an auto engine (flat sixes are still being used), and revamp the unit for long-life (pre-lube systems, extra filters, etc.)?  I'm wondering how hard it would be to modify an engine, and turn one into a spit-cycle unit?  Seems do-able?!
  Yes, the fuel value is low, but quite sufficient to run an IC engine on.  Filtering is definitely a must; wood chips can be used as an excellent pre-filter, eliminating much of the need to dispose of gummed-up tarry filters! (since yesterday's chips become tomorrow's fuel stock).  The remaining char-ash (in the gassifier) is a bit of an issue, but since it contains sufficient carbon to burn, it could be used in a separate boiler system..  
  The biggest obstacle toward obtaining a reliable system, are the engine reliability issues, as far as my research indicates.  What do the best current practices indicate as far as this goes??  
  Thanks again for all the great comments, and I'll take a look at those sites being suggested!!  (12 cylinders in Switzerland sounds quite interesting!!)
globi5 (Mechanical)
1 Nov 07 7:15
The wood gas generator of that mini power plant in Switzerland
was delivered by Dasagren:
The Technology came from the Indian Institute of Science. All the components of the wood gas generator were produced in India.

I don't have any more details about the engine other than it has 12 cylinders (1500 rpm). But my guess is, that it is a MAN-gas-engine:
MikeHalloran (Mechanical)
1 Nov 07 17:43
You've got half a chance of making a successful home biomass cogeneration system.

You've got less than half a chance of making an engine more durable than what's in production now.

You've got zero chance of doing both.  Any project that has to clear more than one major technological hurdle is doomed.

Buy a crate engine and be done with it.  When it dies, buy another.  They're cheap.

Mike Halloran
Pembroke Pines, FL, USA

globi5 (Mechanical)
3 Nov 07 10:46
I was mistaken in my previous post.
The wood gas power plant has a GE Jenbacher gas engine:

Here's an English description of the project:
chucksk (Bioengineer) (OP)
4 Nov 07 1:00
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 (Mechanical)
4 Nov 07 10:09
At least the engines mentioned all have a turbocharger, so this 'pop' is already partially muffled.
mishar (Automotive)
4 Nov 07 12:34
I would focus on refining that fuel rather than on special engine.
chucksk (Bioengineer) (OP)
5 Nov 07 13:51
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!
mishar (Automotive)
6 Nov 07 1:19
I meant getting rid of CO2 and N2.
chucksk (Bioengineer) (OP)
1 Dec 07 22:13
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 (Automotive)
3 Dec 07 4:06
"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 (Electrical)
3 Dec 07 9:16
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.

globi5 (Mechanical)
3 Dec 07 14:55
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 (Bioengineer) (OP)
3 Dec 07 23:06
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 (Mechanical)
5 Dec 07 16:01
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:

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

(no moving parts, little complexity, no wood logging etc.).
chucksk (Bioengineer) (OP)
14 Mar 08 21:59
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 (Mechanical)
15 Mar 08 7:00
Actually, this house is also above the 45th parallel and generates enough heat and hot water just with the area available on the roof.

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 (Automotive)
16 Mar 08 8:52
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 (Automotive)
18 Mar 08 16:14

"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."

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

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