1. Thermal properties of heavy fuel oil (engineering focus)

• Lower heating value: typically in the $40\sim42\ \text{MJ/kg}$ range (affected by density, sulfur, water, and ash)
• High viscosity: high at room temperature; must be preheated to reduce viscosity for atomization. Engineering goal is often to control nozzle inlet viscosity in the atomization-suitable window (depends on grade and nozzle).
• Sulfur and corrosion: higher $S$ means higher $SO_2/SO_3$; low-temperature zones are prone to acid dew point corrosion; high-temperature zones combine with metal salts in ash to form deposits.
• Ash and vanadium/sodium: when heavy-oil ash contains $V,Na$, low-melting salts can form and aggressively attack refractories and high-temperature metal parts.
• Atomization and burnout: smaller droplets evaporate faster and burn out more fully; atomization quality is core to heavy-oil combustion efficiency and smoke control.

2. Burner (oil burner) classification

(A) Mechanical atomization (pressure type)
Oil pressure forces fuel through a small orifice to atomize; structure is relatively simple but sensitive to oil cleanliness, viscosity, and pressure stability.

(B) Pneumatic atomization (air/steam atomization)
High-speed air or steam shears the oil stream into fine mist; good atomization and wide adaptability, but requires compressed air/steam systems and higher auxiliary energy.

(C) Centrifugal atomization (rotary cup)
Oil forms a thin film on a high-speed rotating cup and is flung off to atomize; good for high-viscosity fuels with a wide turndown range, but higher complexity and maintenance.

Supplement: Industry also classifies burners by combustion organization (e.g., low $NO_x$ staged burners, internal/external swirl), but the atomization mechanism typically still falls into the three categories above.