Bio-methane ignition
LoopyByteloose
Posts: 12,537
In May of 2010 I visited friends in Thailand with a pig farm and was quite excited to see their cooling via bio-methane running a 1600cc automotive engine. But the project has consistently hit snags with ignition of the methane.
Problems include the low pressure, about 2 PSI feed of the bio-methane, the low BTU content of bio-methane as opposed to pure methane due to a mixture of CO2 and methane, and conventional compression ratio of the engine.
I did a lot of research and it does seem that a turbo-charger is about the best way to optimize a bio-methane engine, but I also wonder if creation of a hotter ignition is a useful alternative. Can any one make suggestions about how to get a hotter spark into the engine?
Problems include the low pressure, about 2 PSI feed of the bio-methane, the low BTU content of bio-methane as opposed to pure methane due to a mixture of CO2 and methane, and conventional compression ratio of the engine.
I did a lot of research and it does seem that a turbo-charger is about the best way to optimize a bio-methane engine, but I also wonder if creation of a hotter ignition is a useful alternative. Can any one make suggestions about how to get a hotter spark into the engine?
Comments
Is the problem in starting it or keeping it running?
Rich H
The LP or propane as it's called here in the u.s. requires a higher compression engine than what would be used for gas.
As an example, the Nissan (Over head valve) industrial engines I used to work on, the gasoline engine used a thicker head gasket which means it had lower compression than the LP version which used a thinner head gasket for higher compression.
In the case of a OHV you could remove the cylinder head and have a machine shop mill off about 0.004" or 0.005" to gain a little more compression.
If the engine is an OHC over head cam then things get complicated.
http://www.impcotechnologies.com/
http://www.zenithfuelsystems.com/
-dan
Reading through that document, it appears there can be a lot of water in there, as well as CO2. Neither are going to help combustion.
Scrubbing CO2 takes huge amounts of water and is not realistic at this scale. That is the heart of the conflict. Bigger engines and a larger scale have more solutions, but this engine at this scale is at the bottom margin of economic productivity. (One can buy a bio-methane engine completely tested and configured at about three times the displacement, but even that really wants a higher feed pressure than 2 psi.) BTU content is reduced by as much as 50% due to the CO2 content.
I am trying to sort out what exactly can be done with a hotter spark and just burning the CO2 as it is. HS is scrubbed as that is rather easily done and damages the engine.
Yes, the engine is roughly 8.0-8.5 compression ratio and bio-methane would operate better as 10.5 compression ratio.
At this point, the biggest problem is starting and the engine spark is being heavily advanced (roughly 50-45 degrees).
I had hopes to help out with a microcontroller and RTC for automatic daily start and stop with thermostatic and humidity monitoring, but they can't get it reliably to start. After starting, it indeed runs rough.
Yes they have considered diesel engines, but they would need to double or triple the number of pigs to fuel a more costly diesel engine and in any case, the diesel engine either must run a mix of bio-methane and diesel or be adapted to lower compression and a spark ignition. Once they get all that running, they are then producing more power than they need locally and must consider putting power on to the grid. That will require a much more concise speed control for electrical generation.
Overall, it seems like there are serious constraints in every direction, but it would be best to make the current scale of operation work as it would be of greater benefit to small farmers throughout the 3rd world. Larger and more sophisticated equipment are harder to come by. The Thai's buy a lot of used Nissan engines from scrap out of Japan.
One might think it is an odd oversight, but the fuel line is very low pressure due to the gas being accumulated in a large neoprene bladder (about 2 psi) and as a result they are using a 2 inch line for gas supply. Everybody just assumed that it could not get blocked, but finally a local farm mechanic went through the basics once again -- just to be sure.
And so, now I have the opportunity to add sensors and a RTC to the basic set up (fans and an evaporative water wall for cooling the pigs in hot weather).
If it is water, and you are running refrig aircon, I wonder if you could use the refrig to also do some condensing of the water? I found somd documents that go through some of the maths involved - how much of the energy in the gas you devote to cooling and hence condensing, and important things like the dew point.
It is a pig shed about 200 feet long on a sloped hill side. At the top of the hill, there is a water wall that is the 'intake point' and at the bottom of the hill is a bank of fans driven by the automotive engine.
I wouldn't exactly call this refrigeration, more accurately is 'evaporative cooling'. When the weather changes to high humidity conditions, the cooling effect no longer functions and becomes a waste of water.
I have seen similar cooling used in local production green houses for orchids.
All they really need to do is to have their fuel line consistently slope back into the bio-digester. It seems that they didn't notice that they were trapping water in a low point (sloppy construction). With the bio-digester (a big tub of pig sh*t and water), this system is always going to run somewhat wet. Since the fuel line is about 30 feet long, just getting it properly slopped will work well.
It is always more efficient to exploit a passive solution rather than an active one. The additional energy has to come from somewhere.
If it is as simple as keeping a constant slope on a pipe and that is good enough then that sounds great. I too like solutions that you can do 'with a bit of fencing wire'.
Anyway, I do appreciate your suggestions. I was thinking that a hotter spark or a primative turbo charger might get this resolved (even my 125cc Yamaha is turbo-charged these days). But it just seems that they were rather inattentive about the fuel line. I can't believe this has been going on since May. They even had the engine completely rebuilt. They may have had new pistons or the head shaved for higher compression, but I couldn't get a clear answer.
A few years back I looked into running engines off wood gas (I think it was done in the UK in WW2. Big gas bladders on cars.) but there are all sorts of issues with tar forming and gumming up the engine. Methane seems cleaner.
I'm surrounded by paddocks with cows, but I think I'll get better value using the manure on my veggie garden. But I did read another article about how you can digest anything really - especially plant matter. Just need to keep the temperature right for the methanogens.
Here is a thought - will they be producing any electricity at all? Hmm - they might already be if they are using a car engine with presumably an alternator and battery.
If so, I wonder if you could spare 60W to run a peltier? Put a small length eg 10cm of metal two inch galv pipe in the gas pipe. Angle grinder to grind a flat bit. Strap on the peltier with some heat conducting paste. Big heatsink on the hot side of the peltier. Lag the metal pipe so it stays cold.
Maybe it would work, maybe not? Just basing this on my scientific observation that in the tropics, a cold can of beer collects moisture very quickly.