AB Förgasningsapparater - Genius Silent Burner

Now back again to the 'Genius' silent burner configuration.

Spent afternoon progressively modifying the riser set up for the UFO burner. Initially today's changes revolved around lowering the height at which the UFO top cap sits. This was done with 2 successive drops of 1mm each. The difference in flame quality is significant. This is now the light up situation after a strong pre-heat:


But with no improvement in relation to a tendency to flip to under-burn without any obvious provocation. Lowering the riser height one further millimetre reduced the under-burn tendency notably, but did not eliminate it:


The final change made was to remove the copper inner cap altogether. After the second 1mm drop, higher pressure performance had been further improved. And with the removal of the inner cap there was also some clearer indication of effective heat transfer to the main bell casting. The main burn now both looks and sounds really healthy:




But the annoying tendency to flip randomly into under-burn still persists, seemingly unaffected to any raising or lowering of tank pressure, or indeed any other obvious factor. Without that the burner would be performing equivalent to a decent No.4 burner.


@kerophile @Nicola Francesco Elia

 

Hi Ian, good improvements.

How do you control the height, internally to the ufo cap, of the central tube? Does it respect the radius internal height and distance from the top?

If the tube gets too close to the ufo top limiting the flow could be the cause of underburning.

Hope I am clear:

 

Quite the opposite in this case, the projection of the central riser tube sleeve section into the UFO cap is very small, only c.2mm at the most. I wonder if reducing the internal diameter of the riser by substituting thicker walled tubing might limit the capacity to blow back? I know some stoves can be more susceptible to under-burn than others, Primus no.10 for one, but the mechanism that leads to this?

 

@igh371 Ian, also a too small presence of the tube inside the cap could cause a wrong burning and underburning. The central tube inside the cap works like an inner cap on a regular burner. At the right distance from the internal top allows the vapor to move at the correct speed and to be well distributed towards the flame holes. I would consider, as first attempt, to respect the central tubing specs of a radius burner.

With a too small projection inside the cap I suspect an uncontrollable turbulence that causes the underburning.

Also the air mix would be affected by a too short inner tube.

Nicola

 

I have only done limited experiments with UFO caps (I have one complete burner with cap and can't risk damaging the cap!) however when trying to use the cap with another sort of burner I found it required a spigot like you have made, which had to be very close to the original in terms of diameter and length. It was also very sensitive to the distance between the bottom of the spigot and the jet, which also had to be close to the original.

This latter dimension would affect the fuel-air mixture to some extent and is likely also to affect the gas velocity.

 

Finally cracked it. 'Genius' burner now operating successfully, with small size Radius UFO silent cap behaving perfectly




So for those who have struggled through the saga so far, what made the difference? suddenly no overheating, no under-burn and steady burn?

More tweaks yesterday made minor improvements, but did not completely solve the problem of apparently random flips into under-burn. So today saw a more radical revision of everything achieved so far. And more careful observation of the nature of the under-burn flips. One thing stood out, in the lowered position, despite all of the benefits that had brought, the UFO cap did seem to gradually build up to an excessive temperature before the under-burn flips kicked in:


Thinking that this overheating of the cap could be due to it now being too low, too confined, in the cast Genius bell, I decided to rebuild the riser yet again. Was this now version 5 or version 6? Anyway the intended change was now to raise the whole cap approximately 1mm within the bell to see what effect that would have. At the same time the chance was taken to make a new inner sleeve too as the current one would now be too short anyway. OK, so not best scientific practice to change 2 variables at the same time.

The new inner sleeve was purposely cut too high i.e. too close to the inside of the cap top to support any decent flame at all. Then it was reduced in height, in the end by approx. 2mm, in steps, until a good flame was restored. And at full power this time, as seen above, now no overheating of the UFO cap, no under-burn flips, and still good heat transfer to the bell. Finally hit the 'sweet spot'. The crucial change in the end seems to have been that 1mm rise in the height the riser was holding the cap within the bell!

A further point is that the UFO cap always stood rather high relative to the standard leg and trivet heights. Now the gap between the burner cap top and a flat bottomed pan is barely 2mm, but it doesn't seem to affect performance. It would be very interesting indeed to be able to compare this trial-and-error make-do with how the original 'lighthouse' silent cap would have performed ...



@kerophile @Blackdog @Nicola Francesco Elia

 

Excellent!

Tony

 

Thanks Tony, its been a journey!


@Tony Press

 

Great work. Very impressive getting something as sensitive as a UFO cap to work in a set of different fixed dimensions!

 

Commendable determination.

 

@igh371 congratulations, all the effort was surely worthed. You spotted another key point for the under burning, the excessive heat surely can ignite the vapor before it goes out from the ufo cap, great job!

Nicola