Post by peterberg on Dec 16, 2020 3:42:16 GMT -8
OK, you are right, it's time for an update. Luckily, there's some progress to report and also a change of target users but I'll come to that later.
Since the Testo was sent away for calibration I couldn't measure anymore. So it looked like a good moment to leave the slowly desintegrating ceramic fibre board in the top box and the far too massive 5 cm (2") cast refractory walls of the firebox behind.
I opted for firebrick slabs of 30 mm (1.18") thickness for all of the core, because of the relatively low mass. It wasn't cheap, since I had to order it through a webshop and had it shipped to me on a 1/2 pallet. I had to hire a wet saw in order to cut it accurately enough and in the course of a couple of days it was done.
As I probably mentioned earlier, during cold startup the top window tended to get dark brown and burned clean during the rest of the burn. With the higher mass of the top box this was much more pronounced, it didn't look good at all. About some struggle and a week later I decided the way forward should be lowering of the mass. The obvious solution seems to be by using hard firbrick(ish) material that is much thinner. By browsing the internet I stumbled across refractory slabs of just 10 mm (0.394"), used for stacking pottery in a ceramic kiln. Those are available in the Netherlands and while ordering through a webshop I discovered this shop has an outlet about half an hour drive from where I live.
Suffice to say, I cancelled the order and drove there to pick it up in person. Initially just for the shelf and the support of it, being the parts that are receiving the greatest heat stress. Those plates are specified as 1300 ºC (2370 ºF) and uptil now there's no sign of degrading or visable hairline cracks. Running it like that seemed to improve things but I couldn't measure since the Testo wasn't returned yet. What I got was a quotation for replacing the aging CO cell and minor reparations together with the yearly calibration. Needless to say, it would cost me an arm and a leg to have it usable and up to date again.
While I was pondering the possibility of giving up real testing altogether something else came along. In the shape of a friend who's selling as a one-man-band the Bulgarian Gamera rocket heaters in the Netherlands. He wanted to know what the new experiment was about and asked to see it working. Suffice to say he was really impressed with the sight of it, seeing the double vortex spinning through the glass. Some days later he phoned and asked whether it could be turned into a commercial appliance, of course complete with European certification. I honestly think it could and I told him that. This might be a commercial adventure, costing a lot of money (and time!) up front with the potential to generate a profit through a couple of years or not at all. The guy from rocketstove.store won't be able to cough up that kind of money on his own but when doing it together it might be doable.
So now the goal is different: not a simple do-it-yourself heater but one that is a sellable appliance, initially without any mass at all. Actually, a core that can be built without too much fuss and a bell-like housing about the size of one and a half barrel, specifically non-circular. Preferably easily serviceable, working right out of the box, dry build-up, possibility to add mass later and last but not least: released under the same CC license as the original batch box rocket.
Two weeks ago the Testo arrived accompanied by a hefty bill and I started to run test burns again. By this time all of the top box was built differently: two slabs of 10 mm with 12 mm Superwool in between. Simply put: all walls and ceilings are sandwiched, even the support of the shelf is. I switched the shelf from kiln plate to Neoceram glass which is holding up well so far. The stumbler or block in the top box is skipped for now, space above the shelf is about the same as in the afterburner area. And last week I experimented with secondary air in different guises, ruling out air intruduced into the sides of the port itself. Six different configurations and none of those were like hitting the pot of gold.
More on all this later.