My observations and analysis:
I hope we can all agree that a blue flame is indicative of complete combustion which releases all the BTUs within the fuel. ** Yellow, orange, & red flame colors all indicate carbon or carbon compounds produced from the fuel that didn't fully oxidize and represent wasted, unrealized BTUs as well as atmospheric pollution. Therefore, adjusting the air-fuel mix to give the most blue flames will result in the best fuel efficiency.**
I would actually respectfully disagree with you, but I'll address that lower down.
On erosion, you hafta look at when you have. You have a forced air burner with very high flow rates.
Take two examples with the same color flame, one is a USA space shuttle main engine, the other is a methanol spirt lamp.
Both flames are similar in color and are blue with high IR signatures.
Both are so faint that they are invisible in daylight.
The shuttle hydrogen/oxygen engine flame is clearly going to erode anything you part in front of it.
The soft methanol flame is going to clearly not erode materials put above it, unless they are very fine like transformer wire but that's extending the metaphor beyond meaning.
You built a jet engine combustion can. You pretty much have an electric Thermojet.
You need to look at the flame as something harsh, turbulent and fast moving, not at all like a stove flame.
On the note of burner flame color; soot, smoke, flaming black snow flakes (that's sorta what droplets of unburnt fuel look like as they eject with the flame) and so on, are the indicators of incomplete combustion.
As I mentioned earlier, I have and it is possible to burn the same fuel air mixture with all those colors - which means they are not indicators of completion of combustion efficiency but flame front speed.
I betcha that given your fuel flow rate that you could make a less efficient burner and get a two foot long yellow soft flame sootless. You've taken that and made it a few cm.
That means that the energy intensity, both thermal, kinetic and chemical are highly focused.
Imagine that you are looking at two 100% efficiency fixed displament pumps. One moves 1714 gallons at 1 psi the other moves 1 gpm at 1714 psi, each take exactly 1 horse power.
Which will cut off your finger?
For you, "combustion efficiency" should mean both that you have complete combustion as measured at the exhaust (easy to determine with a Grove multi gas sensor) AND that you are spreading that flames heat out for the whole boiler to absorb, because a Hotspot could be catastrophic.
Going waaaaaaaay back to your surmise that poping a leak will mean a jet of nasty gas not an explosion; I would personally bet on damage to the refrigerating cause by a hot spot to form an autocataltic reaction that could cause a broad failure as tlarge sections of the boiler corrode internally vs a pin hole. Aka if the seals don't go first, you could have an actual explosion realesing stuff that is more toxic then cyanide.
The web is sadly a midden for "blue" flames.
I'm not trying to preach or put you down or anything. Your project is well beyond my machining and electronic abilities. You are very smart, and it's clear.
I am just giving my .02$ as someone who spent a lot of time working with flame chemistry and is worried you may get injured due to the web's poor info.
All the best.
-Troll