no, it was not my idea. Max Gasman suggested this in the Seat thread of Kristijan more than three years ago:
(See this post and the ones following)
Anyway, I think no one really tested it this way.
I just try to absorb all good ideas “as a sponge” and then try to combine it. I hope that I can control the internal temp with this, as the water-air-mixture should be more or less constant at the generator inlet for different loads instead of a water drip.
Advatages of a central nozzle:
Easier to built and if the Lighting port is directly above (as in my scetch) easy to look directly into the burning hearth of the gasifier. -> Easier to check reaction temp (white glowing char or orange glowing)
Easier to replace or try a different design/material of the nozzle.
For the reaction there should be no big difference. With a central nozzle, the danger of a channel is burned down through the char to the grate (bridging) could be higher. Also the reaction zone could be more centralised and longer (more space between nozzle and grate needed). A design like Krisitjans last one can be more compact.
I thought about this, too. Gary Gilmore is doing this according to the colour of the reaction zone in his simple-fire-gasifiers: White glowing char = too hot, red glowing char = too cool, organge glow is about right.
In numbers: About 900 °C (centigrade) is the optimum point for EGR or added steam: With this temp, the best equilibrium of the reaction is reached: Most of the added EGR or steam is cracked and there is not much CO2 in the gas. With lower temps in the reaction, the amount of CO2 in the gas raises, with hihger temps you waste the surplus heat of the reaction.
Note: the hotter the primary air plus steam, the more steam can be added and the richer the gas.