CNG, Methane, LP? The Metha-Cycle?

Propane powered Honda GL1200 via

Propane powered Honda GL1200 via

This is something I’ve been working on.  How hard would it be to run a bike on methane?  Would you even want to?  Why?

Let’s start at the beginning.  Methane is a byproduct of virtually every landfill, cow, chicken, pig and whatever-farm in the land, as well as wastewater treatment facilty and composting.  Though not as much composting, because good composting is aerobic, whereas methane comes from anerobic breakdown.  It’s not a great gas, greenhouse-wise, being about ten times more greenhousey-bad than CO2.  And I’ve heard about people converting gas motors to burn it.  Burning methane, instead of gasoline, is something like 20 times cleaner. I started getting this mental image of a moped with a little gas cylinder on it running off of horse manure from my buddy’s farm.

Methane, coming out of a typical cow-poop-methane-“digester” is called “biogas”.  Biogas can be burned as-is, and has a mix of methane and CO2.  A lot of places incorporate a digester with an electrical generator, which will supply the facility as well as sell it back to the grid.  If you’re going to use the stuff for running vehicles, it has to be refined, and will be converted to CNG, or “compressed natural gas”, which is what a lot of city vehicles like buses here in Boston run.  CNG is purer methane, and highly compressed to 3000psi or so.  The definitive source for information on biogas is the Alternative Fuels Data Center’s Biomethane page, with a bunch of links and resources.


Then there’s propane, or “LP”, and the funny thing is gasoline, LP and CNG all can power a gas motor with very little difference.  Apparently LP is pretty close to gas in energy, where CNG is a little less volatile.  Interestingly, CNG has an octane rating of around 110 or something, so it’s better for a high-compression motor.  Just store that away in your head for now.

There are a ton of how-to pages out there for building your own methane digester, and it’s pretty simple, though it seems like a lot of tending-to to keep it at the right temperature for a small-batch rig, kind of smelly, and it doesn’t really yield a lot of usable gas.  You have the containment, compression problem too.  For the purpose of this maybe-a-project, I’d probably not do it that way, unless I wanted to make a science fair project out of it, and just pull CNG from a local facility.

If you poke around the internet enough you’ll find tons of videos showing various levels of “conversion” to propane, and most of them claim to be “tri-fuel”, including CNG and gasoline, ranging from a kid doing nothing more than hooking up a propane tank to his lawnmower through the gas line, to some $200 or so kits that include regulators and fittings.  The key issue seems to be regulating the fuel, since you don’t have your float valve and a liquid fuel anymore.  Here’s a good one, from a good supplier, US Carburetion.  They have a product called the Motor Snorkel.

So, is it going to be slow?  Check these boys out.  Roush’s drag-racing propane Mustangs.  Yeah.  No.  The funny part is, switching my head back to gas-motor high performance thinking, all that stuff you do to build motors for gasoline applies to CNG or LP too.  High compression, breathing, blowers, nitrous injection – you can do all that, and you’ll get similar increases in performance.  Remember what I said about the octane rating?  This is starting to feel kind of comfortable and familiar.

What about the tanks?  That’s where we run into trouble.


There are four basic classes of CNG tanks that range from steel to exotic carbon-fiber composite to try to keep weight down.  A standard steel tank, rated at 4 or 5 GGE (gasoline gallon equivalent) is going to cost you around $500, but they weigh around 140lbs.  It’s also almost 48″ long, at a 10″ diameter.  The cool ones, with a rubber membrane liner, carbon fiber wrapped and epoxy coated aren’t really available in smaller sizes.  You can’t afford them anyway.  The Type 3 tanks, which have an aluminum core, will run you around $2000, and for a 6.6gge tank that measures 16″ diam x 35″, it’s going to weigh in at around 80lbs.  Remember.  3000psi of stuff that will blow the hell up.

Oh.  Wait.  Remember this? I still can’t figure out why that one guy got out and left his car sitting there, but whatever.

Ummm.  OK, kind of losing interest in this project.  I can see converting your little gas generator to propane, since you can just fill one of those grill or RV tanks up almost anywhere and it gives you the choice of fuels.  I could see running your generator on methane or propane and using it to charge up your electric motorcycle.  I can see converting a car, where you have room and weight carrying capacity for a 300lb high pressure tank that can be mounted out of harm’s way.  But strapping a 3000psi, 4 foot long tank of methane between my legs on a moped?  …or even a big bike?  Nah, ain’t gonna happen.  Using low-pressure methane in a mouse-rig propane tank or something, or even using propane like the madman at the top of the page?  Besides the fact that I’d have a range of about nothing, my momma raised me smarter’n that.

Damn.  I had such high hopes.  Even registered




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