One of the first things you learn when you get an engine running on wood gas is that every time the fuel pile drops or shifts in the gasifier, it changes the fuel bed porosity, the gas flow, and the fuel/air ratio going to the engine. This means that the mixture valve needs to be constantly adjusted to keep the engine operating properly. One way to fix this issue is to install an oxygen sensor in the exhaust pipe and a model airplane servo to adjust a mixture valve. My hat goes off to All Power Labs for coming up with this method.
Here is the fuel/air mixture controller that I built:
and here is how I mounted the oxygen sensor on my sacrificial GX200 clone generator:
The engine only had a flanged exhaust interface so I had to make an NPT threaded exhaust manifold. These will be available under the “Get Hardware” tab at the top of the page. I was able to weld an O2 sensor bung from Carquest over a 3/4 tee, screw in a close nipple, the tee, and screw on a universal muffler. There are also custom brackets which go down to the generator frame to support the overhung load.
The O2 sensor threads seem to be universal at 18mm.
Here is the servo valve mounted on the Gas Station carburetor:
The manual valve allows the engine to warm up the O2 sensor and the servo valve takes care of the variability. This arrangement works well for larger engines over 390cc, for smaller engines the mixer should be closer to the engine so there is less time for the gas to get to the engine.
December 26, 2014
Progress on this project is picking up now that it is cold in my shop. During the winter I like to do electronics projects so I can stay in where it is warm. Here is my latest step toward a mass producible automixer:
(Click to enlarge)
It is a true custom Arduino shield which uses an automotive oxygen sensor and can run on 12-24V. It also has three channels of power sinks hooked to pulse width modulation pins. In English that means it has three power circuits which can make variable voltages for things like driving variable speed DC fans.
(Click to enlarge)
Here is the automixer running a bench test:
Here she is running her 4kW:
Since shooting that video I have refined the software so that the amplitude of the arm 0scillation is only about .06″/1.5mm.
The automixer is available for sale under the “Get Hardware” tab