Yanche wrote:What size nozzle and cone angle did you use? How did you decide what to use? I've never understood how to choose. Did you do anything to the combustion chamber material?
Though not addressed to me I think I can give you the answers you want.
The size of the nozzle determines the firing rate in gallons per hour, and is selected to match the rated output of the boiler or furnace. My inclination is always to use slightly smaller than recommended to obtain longer run times which are more efficient than shorter times since there is less loss getting up to heat. The ideal of course would be to run steadily which would obviate any standby and start up heat loss. Not practical though except in commercial applications.
The correct angle and whether hollow or solid spray is determined by the air pattern of the burner which in modern burners is specified by the maker. For my boiler it would be for a Beckett, 1 gallon per hour and 80 degree A which means a hollow spray. For Carlin burner it would be 1gallon 60B which is a solid spray pattern, and for Riello it would be .90 60 degree B. The .90 figure for the Riello burner may be because it uses a higher pump pressure than the standard which is 100 pounds.
Looking at the above there is an 80 degree air pattern and two 60 degree patterns. The 80 degree would be ideal for a round combustion chamber and the 60 degree for somewhat longer than wide chamber, so the selection of the burner should also be determined by the shape of the boiler and possible shape of the chamber. If I had a long narrow boiler then none of these burners would be ideal.
The air pattern of these burners is strong and precise and by matching the pattern of the oil spray to more exactly match the air pattern less excess air is needed for clean combustion resulting in higher efficiency. The burners are so good that manufacturers often use a minimal combustion chamber, sometimes just a target wall of refractory. A good chamber though will always be better.
The Shell oil company pioneered the first flame retention head about 60 years ago. These new burners are all patterned after it. The Babcock and Wilcox company made a firebrick of Kaolin clay and mixed sawdust with the clay before firing. After firing the brick had a mass of air pockets where the sawdust had been. You can hold one of these insulating firebricks in your hand and play a blowtorch on one side which will be incandescent and not burn yourself. Using a Shell head burner and chamber of this brick the highest burner efficiencies ever achieved has resulted.
Hope this helps,