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!!

 

[Lou Scannon]

How about giving us some details about the composition and properties of the fuel, and its production rate...

 

[malbeare]

chucksk (Bioengineer)

Have a look at

http://www.sixstroke.com/

a new head design,
cheers

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

http://www.sixstroke.com

 

[dcasto]

Malbeare, the sixstroke looks like a take off and maybe improvement of the submarine engine, cool.

http://www.fairbanksmorse.com/engine_opposed_piston_model_38.php?return=stationary_power.php

 

[mishar]

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.

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.

 

[chucksk]

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]

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]

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]

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]

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

 

[globi5]

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:

http://www.sunmachine.com/animation.htm

 

[ivymike]

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]

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]

dcasto,

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.

http://en.wikipedia.org/wiki/Wood_gas

 

[dcasto]

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]

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.

http://www.woodpower.ch/energie

 

[chucksk]

Wow, lots of responses!! )
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]

The wood gas generator of that mini power plant in Switzerland

http://www.ekz.ch/internet/ekz/de/g...03-File.File.FileRef.pdf/anlage_woodpower.pdf

was delivered by Dasagren:

http://www.dasagren.ch/index.asp

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:

http://www.man-engines.com/en/Industrial_engines/Stationary_engines/Gas_engines.jsp

http://www.man-engines.com/datapool/mediapool/800/MAN_diesel_and_gas_engine_genset_cp_2007-02.pdf

 

[MikeHalloran]

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]

I was mistaken in my previous post.
The wood gas power plant has a GE Jenbacher gas engine:

http://www.gepower.com/prod_serv/products/recip_engines/en/index.htm

Here's an English description of the project:

http://www.netprorenewable.com/NETPRO/Field_exp/swissProj/SWISSPROJ_MAIN.html