return to How to Build and Run the GEK Gasifier
Here's a very simple method to make your first woodgas carburetor. More elaborate methods are always possible, but this will get you started quick and easy. The goal is simply to create a tee in the intake to the native engine carburetor, where you can vary the syngas/air mixture on the way to the engine.
All that is needed to do this is one variable valve on the air side of the tee. You do not need two valves. As you choke down on the air side, the engine will pull proportionally more syngas from the gasifier. You have to manually adjust the ball valve to get the correct mixture, and continue to adjust it as the engine load changes. It can be touchy, but you'll get the feel for it quickly.
I find the easiest way to do the start is to fill the open side with starter fluid, pull the cord, then fiddle with the valve as things choke to life.
The more fancy way to do the same thing is with a purpose made butterfly and servo to control it. This can then be controlled electronically, in relation to air/fuel mixture info fedback from the O2 sensor on the engine. This is how we did this in the Honda Accord. You could also start do the same with an obtainium throttle body from a fuel injection engine.
And yes, we covered the hole in the middle of the butterfly later. The butterfly was made from a fender washer, thus the hole needing covering.
More pictures of the Honda installation are in the Flickr set here: http://www.flickr.com/photos/allpowerlab/sets/72157611845184353/
How to size the air-gas mixer
(forum note from december, 2010 on sizing)
we're currently going round and round trying to get custom manufactured a small electronic throttle body for the automated mixing system on the power pallet. we currently make these ourselves using the method here: [url]http://gekgasifier.pbworks.com/w/page/28307181/Servo-Valve-Assembly[/url] while these work, a proper efi drive-by-wire throttle body would be better. they are sadly very rare at small sizes, thus we need to get it custom manufactured for us.
while doing this, i've reviewed what we've learned about air-syngas mixer sizing, and how this relates to the existing speed throttle already on the engine. i've been surprised to find we've ended up with essentially the same size for both.
i took apart the kubota throttle body tonight and found it to be a 26mm bore diameter. the 1" npt butterfly valve on the shop made servo valve is basically identical. chosing between, 1/2, 3/4, 1, and 1.25" npt tube/valve options, we found the 1" one to give us the best mixing range and butterfly movement for this engine size.
at first i thought this odd and that we were trying to oversize the air throttle body. the air throttle body is only seeing about half the volume of the engine throttle body, given the 1:1 syngas/fuel mix ratio.
but then i realized that the engine throttle and air mix throttles are working against very different vac sources. the engine throttle is controlling about 0-10"hg. the air mix is controlling 0-10"h2o. given that each inch of hg is about 14 inches of water, we have over an order of magnitude difference in force the two butterflies are needing to contend with.
calculating with some handwaving and anecdotal experience, it seems factors balance out so that about the same size of mixer is needed for these two very different tasks.
maybe this is a new rule of thumb: size your air mixer throttle/valve at the same diameter as the carburetor bore standard with your engine.
how does this relate to what others have experienced in sizing the mixer valve?
j