Burner handling of heavy oils What is the typical maximum viscosity for tar/PCM/fuel oil to allow easy and efficient atomisation in a conventional pressure jet burner? (Approximate equivalence: 100 Redwood I seconds ≈ 25 cSt.)

Introduction / Context:
Heavy fuel oils must be heated to reduce viscosity for proper atomisation in burners. Excessive viscosity produces large droplets, poor mixing with air, incomplete combustion, and smoke/soot formation.

Given Data / Assumptions:

• Conventional pressure jet burner (not special twin-fluid/steam atomisers).
• Rule-of-thumb conversion: 100 Redwood I seconds ≈ 25 centistokes.
• We seek the practical viscosity ceiling for good atomisation.

Concept / Approach:
Industry practice targets a modest viscosity at the burner nozzle to balance spray quality and pump handling. A commonly taught benchmark is ~25 cSt (about 100 R1 s). Preheating lines and heaters are adjusted so the oil at the gun meets this condition.

Step-by-Step Solution:

Verification / Alternative check:
Combustion handbooks and burner manuals specify similar nozzle viscosity targets for heavy oils.

Why Other Options Are Wrong:

• 5 cSt: Very low; unnecessary and can hurt pump sealing.
• 50 / 100 cSt: Too viscous for clean atomisation in conventional burners.

Common Pitfalls:
Neglecting line temperature drop—measured viscosity should be at the nozzle, not only at the heater outlet.

Final Answer:
25 cSt