Oil Burners and Combustion
This domain tests high-pressure gun burners: nozzle selection, atomization, ignition, flame shape, and the adjustments that keep combustion clean. Questions cover nozzle ratings, electrode settings, pump pressure, air settings, and the primary control's flame-sensing circuit.
Nozzle and spray
- Nozzles are rated in gph at 100 psi; flow varies with the square root of pressure, so 140 psi increases flow by about 18%.
- Pattern (solid, hollow, semi-solid) and angle (typically 70–90°) must match the combustion chamber; a wide angle in a shallow chamber wets the walls.
- Electrode gap and position follow the manufacturer's spec - commonly a gap near 1/8 in., with tips slightly ahead of the nozzle face. A wide gap makes the transformer strain to strike the arc.
Ignition and flame
- The transformer steps 120 V up to roughly 10,000 V at the electrodes. A cracked insulator or carbon track shorts the spark to ground.
- The retention head stabilizes the flame; the air shutter and damper set excess air. Too much air lifts the flame; too little makes smoke.
Worked example
A 0.85 gph nozzle is rated at 100 psi, but the pump is set to 140 psi. New flow = 0.85 × √(140/100) = 0.85 × 1.183 = 1.006 gph. Input = 1.006 × 140,000 = about 140,800 Btu/hr, not the 119,000 Btu/hr implied at 100 psi. That extra 22,000 Btu/hr needs more combustion air and can soot a chamber sized for the original rate.
Traps
- Never set pump pressure by ear; use a gauge.
- Angle and pattern are separate choices; matching angle alone can still wet the chamber.
- A cad cell detects light, not heat, and a dirty lens mimics no flame.
- Delayed ignition - fuel first, spark second - causes puffback; check electrode position and pump cut-off.