jimmason

yes, that is the correct compression ratio.  

we advance the timing about 10degrees.  sadly we can't do this easily electronically, so we do it by redrilling the trigger ring on the flywheel to mechanically advance it to where we want it.

j

yes, please write to "jobs@allpowerlabs.org".  thanks for pointing this out.  i'll go add the info to the descriptions.

jim

actually, it is a feature that the ends are vertical.  this prevents pinch points at the corners.  if one builds a funnel as four flat sides, the angled joints create partially opposed motion of the flowing solid fuels.  this creates pressure points in the fuel, and thus increased bridging.  

this is why typical auger boots are done with two tapered walls and two vertical walls.  if you can't do this, the next best taper method is round to round, or a standard cone.  the worst method is the square to square method, or the taper square cone.  each joint here will be a bridging spot once there if fuel flowing downward.

these solid fuel handling realities are relevant whether building an auger boot or a hearth.  the hearths get a bit of a get out of jail free card as you have nozzle blast and thus a driver through the restriction.  nonetheless, a trough hearth like above will have better flow than a round cone hearth, like the gek uses.  but ease of flow is only one of many concerns we are balancing in hearth design, so one might choose to ignore this benefit to access competing benefits of other shapes.

either way, these solid material handling points are non-obvious to us kids.  the greybeards knew this way back in the day, and thus you find most ag equipment conforming to these principles, or violating them when the materials they are moving are easy to deal with (like grain).

j

you can use many different types of material to back fill around the hearth.  we typically use perlite.  but you can also use charcoal, ash, and yes, even sand.

i would encourage you to use one of the other three, but if they are not findable, sand is a not terrible stand in.

j

jerry, good to hear from you.

by wild chance, we are trying to arrange a workshop in maui later this summer or early fall.  the details continue to be negotiated, but something should be clear soon.

this will be at the Puu o Hoku ranch.  by chance do you know these folks?

they have a power pallet there already.  we'll likely be converting a tractor or vehicle at the workshop.

j