While it may not be great for vehicles, it's still one of the most promising choices for stationary power production. Plants are self replicating solar power fuel sources, and by converting them to syngas you can produce electricity, heated water and air, and biochar. The biochar is wonderful for the soil when properly used, and locks away carbon that used to be in the air.
There are any number of cogeneration plants that use waste wood chips to run their kilns and produce electricity. All Power Labs (www.allpowerlabs.com) produces small scale (10-20kWh) generators that fit on a 4' pallet and thus can be transported to a fuel source.
This is really interesting. I'm fortunate enough to live in a city that collects yard waste and composts it. I've never considered that it could be used as an energy source, much less a carbon negative one. I doubt I could produce a usable amount of electricity by myself with something like this, but I'd be curious to see how much energy a city of 900,000 could produce with yard waste.
Edit: From the feedstocks page (http://www.allpowerlabs.com/support/support-feedstock) it looks like this works best with wood and woodlike fuels. I'd still be curious if grass clippings could be processed in a way to make them work similarly.
Grass clippings and a variety of waste streams can be pelletized to produce a fuel that can be gasified. Although it's generally not recommended to leave pelletized fuel in a gasifier during shut down, as any residual moisture will cause the pellets to decompose into their powdered form and thus clog up the reactor. Solid fuel handling is more difficult than liquid or gas fuels as you have to use augers and gravity. There is a tendency for "bridging" and compacting where the space between the solid components become either too large or too small. Different reactor designs can accommodate different fuel sources but there is no one size fits all for all fuel types.
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While composting is great, it does produce a significant amount of methane, which is a much worse greenhouse gas than carbon dioxide (~84 CO2e). Ideally this would be captured and put to use.
The 'bridging' problem is one area where vehicular applications have less of a problem given the fact that the generator is constantly being shaken, especially when used on tractors or other similar equipment (e.g. old-style bone-rattler pickup trucks). A modified diesel engine in which the injectors have been swapped for long-necked spark plugs can run on gengas and has a higher efficiency and relative power output than a petrol engine which is fed with the same fuel. On this type of application the extra bulk for the generator and fuel doesn't matter as much either.
Adding a spark plug (and the timing circuitry) is definitely possible. You can often find diesel engine blocks that have been converted to propane or natural gas that are essentially this arrangement.
You can also run a diesel engine on duel fuel, where the (bio)diesel injection provides the flame front to ignite the woodgas and air mixture. In this case no modification is necessary. Only the bare minimum, equivalent to just idling on diesel is necessary. This is a robust system where the governor for the diesel engine can compensate for lower woodgas fuel content when need be.
The gas going into the engine ideally is broken down to hydrogen and carbon monoxide, with some methane. This is also scrubbed of all tars and ash for the safety of your engine. Within the pistons of your generator's engine it is combusted to water and carbon dioxide. Unlike gasoline and diesel which needs to pyrolysis within the engine's cylinders or fuel rail, the syngas has already been broken down to its bare combustable components...so emissions are usually much lower.
That being said, there is a variety in the solid fuels used, and operational and engineering problems to overcome for some waste streams. There are backyard versions that use water to scrub the woodgas, leaving behind large ponds of toxic waste full of PAHs (Poly Aromatic Hydrocarbons) and other carcinogens. But the exhaust from the motors is generally better than that of a gas or diesel engine. (Source, I used to work for All Power Labs, where we did a variety of tests on our fuel, exhaust and ash production)
Apparently North Korea still has a lot of those[1], and as recent as 30 years ago they were quite popular on Vietnam's streets. I have heard of people died from the heat or suffocation riding on them.
Wood gas is mainly hydrogen and carbon monoxide. Even a small leak into the passenger compartment could be deadly, especially if it was filtered well enough to be odourless and the occupants don't notice quickly.
There are any number of cogeneration plants that use waste wood chips to run their kilns and produce electricity. All Power Labs (www.allpowerlabs.com) produces small scale (10-20kWh) generators that fit on a 4' pallet and thus can be transported to a fuel source.