Fuel oils h. F. O. Heavy fuel oil ( residual, blends & crudes )



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  • FUEL OILS
    • H.F.O. Heavy fuel oil ( residual, blends & crudes );
    • D.F.O. Diesel fuel oil or M.D.O. Marine Diesel oil or light fuel oil ( in restricted sense )
      • 1.1.1 Residuals are residues from various rafinery processes;
      • 1.1.2 Blends are fuel oil mixtures of different viscosity to obtain a product of desired viscosity and density.
      • 1.1.3 Crudes: natural mixtures consisting of hydrocarbons + sulphur, nitrogen and / or oxygen derivatives of hydrocarbons.
  • FUEL OILS
    • H.F.O. Heavy fuel oil ( residual, blends & crudes );
    • D.F.O. Diesel fuel oil or M.D.O. Marine Diesel oil or light fuel oil ( in restricted sense )
      • 1.1.1 Residuals are residues from various rafinery processes;
      • 1.1.2 Blends are fuel oil mixtures of different viscosity to obtain a product of desired viscosity and density.
      • 1.1.3 Crudes: natural mixtures consisting of hydrocarbons + sulphur, nitrogen and / or oxygen derivatives of hydrocarbons.
  • 2. FUEL VISCOSITY
  • Internal resistance of a fluid to relative movement. Oil is more viscous when cold. Viscosity is measured in Redwood Universal, Saybolt Universal, Saybolt Furol and Engler, but most commonly in kinematic cSt.
  • 3. PURPOSE OF THE FUEL OIL SYSTEM
  • To store, transfer & clean the oil prior to injection.
  • 4. SEPARATE FUEL OIL SYSTEMS
  • 4.1 H.F.O. Heavy fuel oil → in navigation;
  • 4.2 D.F.O. Diesel fuel oil / or M.D.O. Marine Diesel oil / or light fuel oil → in manuvering.
  • 5. FROM THE DOUBLE BOTTOM TO THE ENGINE
  • 5. FROM THE DOUBLE BOTTOM TO THE ENGINE
  • 5.1 Oil is taken from the double bottom tanks and pumped into a settling tank.
  • 5.2 Then it is heated in the settling tank ( the sediment and the water are drawn off. )
  • 5.3 Next, the fuel is purified in a centrifuge ( a centrifuge is a unit usually consisting of a purifier and a clarifier.)
  • 5.3.1. A purifier eliminates contaminants and a clarifier eliminates high density impurities).
  • 5.4 Then it is admitted into a service tank.
  • 5.5 From the service tank the oil is passed through a heated buffer tank to the booster pumps ( or fuel delivery pump ).
  • 5.5.1 Buffer tank or a mixing tank:
  • a) H.F.O. and M.D.O. are mixed in it;
  • b) it recives a surplus fuel not consumed by engine
  • 5.6 Eventualy it is discharged into injection system through a fuel heater, viscosity regulator and a fine filter.
  • 6. SAFETY DEVICES
  • 6.1 Low tank level alarm signals that a level in the tank is too low.
  • 6.2 Pressure loss alarm indicates a pressure drop below permissible limits.
  • 6.3 Viscosity regulator* controls fuel oil temperature, i.e. viscosity)
  • 6. SAFETY DEVICES
  • 6.1 Low tank level alarm signals that a level in the tank is too low.
  • 6.2 Pressure loss alarm indicates a pressure drop below permissible limits.
  • 6.3 Viscosity regulator* controls fuel oil temperature, i.e. viscosity)
  • 6.4 Pressure regulating valve ensures constant pressure at the fuel main;
  • 6.5 Quick close valves are valves having collapsable briage and may be closed from outside machinery space.
  • 6.6 Emergency remote cut-out switches fitted to the pumps and actuated in case of emergency.
  • Gear pump rotates at about 40 rpm
  • Fuel inlet / supply is close to the heater discharge
  • The fuel is discharged through a capillary tube
  • The pressure diference between each end of the tube is directly proportional to the viscosity of oil flowing through it.
  • Pressures are measured with Bourdon tubes and compared to read as viscosity.
  • Pressures are fed to a differential presure transmitter which can automatically operate the heater control to maintain fuel viscosity within close limits
  • 7. COMBUSTION
  • 8. FACTORS LEADING TO GOOD COMBUSTION
  • 8.1 VISCOSITY
  • It must be low enough to ensure correct atomisation at the fuel injection. When fuel oil is heated its viscosity is reduced.
  • 8. FACTORS LEADING TO GOOD COMBUSTION
  • 8.1 VISCOSITY
  • It must be low enough to ensure correct atomisation at the fuel injection. When fuel oil is heated its viscosity is reduced.
  • 8.2 ATOMISATION
  • Is splitting up the fuel into very small droplets. The size of a droplet depends upon:
  • a) the atomizer holes;
  • b) pressure difference between the fuel pump
  • c) discharge and that of the compressed air in the combustion chamber.
  • 8.3 PENETRATION
  • Is the distance the oil droplets travel into combustion space before mixing with air and igniting.
  • Penetration depends upon:
  • a) atomisation;
  • b) velocity leaving the injector
  • c) conditions within the combustion chamber
  • It is desirable that the fuel penetrates into the whole combustion space but it should not impinge on the internal surface before burning.
  • Penetration depends upon:
  • a) atomisation;
  • b) velocity leaving the injector
  • c) conditions within the combustion chamber
  • It is desirable that the fuel penetrates into the whole combustion space but it should not impinge on the internal surface before burning.
  • 8.4 TURBULENCE
  • Is the movement of the compressed air and fuel within a combustion space before combustion occurs.
  • Turbulence is caused by :
  • a) swirl, which is impared due to the air entry at scavange ports
  • b) fuel spray pattern
  • c) piston crown shape
  • Turbulence improves fuel and air mixing for effective and rapid combustion.
  • 9. FUEL INJECTORS
  • They are inserted into fuel valve pocket of the engine cylinder.
  • Injectors can be fitted centrally ( simetrical fuel spray ) or in other way depending upon the position of exhaust valves.
  • 9. FUEL INJECTORS
  • They are inserted into fuel valve pocket of the engine cylinder.
  • Injectors can be fitted centrally ( simetrical fuel spray ) or in other way depending upon the position of exhaust valves.
  • Defects:
  • a) choking due to dirt;
  • b) inadeqate cooling ( high t. → carbon building up on the atomiser;)
  • ( low t. → external corrosion )
  • Testing:
  • Fuel injectors must be regulary overhauled;
  • After assembly an injector is tested with a test pump ( operating pressure and fuel spray );
  • There should be no leakages.
  • 9.1 COOLING
      • By circulating water or oil through cooling passages.
      • Heavy fuel injectors are fitted with water cooled nozzles.
      • If there were no cooling, the nozzles would become too hot and liable to carbon deposits.
  • 9.2 VALVE BODY OR NOZZLE HOLDER CONTAINS
      • spring,
      • compression nut,
      • intermediate spindle,
      • fuel oil passages,
      • cooling passages
  • 9.2 VALVE BODY OR NOZZLE HOLDER CONTAINS
      • spring,
      • compression nut,
      • intermediate spindle,
      • fuel oil passages,
      • cooling passages
  • The body of an injector has a hardened surface.
  • The nozzle or atomiser is secured by a compression nut / retaining nut / spring adjusting nut.
  • A dowel is fitted to ensure that fuel oil passages and cooling water passages are aligned.
  • The needle valve and the atomiser are kept as one unit.
  • 9.3 FUEL INJECTOR NEEDLE VALVE
      • Spring loaded non-return needle valve ( 1 ) is lapped in a bore of an atomiser ( 2 ).
      • The pump supplies fuel oil through the oil fuel passage ( 6 ).
      • The upper chamber ( 3 ) is charged with fuel and sealed by needle valve ( 1 ).
      • The lower chamber ( 5 ) is sealed with mitre seat ( 4 ), also making an effective oil seal.
      • Atomiser holes ( 7 ) are used for discharging the fuel through them at a high pressure.
  • 9.4 NOZZLES
  • 9.4.1. Purpose
          • The fuel is injected at high velocity through small holes in the injector nozzle and the fine spray penetrates throughout the combustion chamber.
          • the injection must be sharp to avoid deterioration of spray into a dribble or jets.
  • 9.4 NOZZLES
  • 9.4.1. Purpose
          • The fuel is injected at high velocity through small holes in the injector nozzle and the fine spray penetrates throughout the combustion chamber.
          • the injection must be sharp to avoid deterioration of spray into a dribble or jets.
  • 9.4.2. Opening pressure
          • Usually about 600 bar ( for medium speed diesel engines)
  • 9.4 NOZZLES
  • 9.4.1. Purpose
          • The fuel is injected at high velocity through small holes in the injector nozzle and the fine spray penetrates throughout the combustion chamber.
          • the injection must be sharp to avoid deterioration of spray into a dribble or jets.
  • 9.4.2. Opening pressure
          • Usually about 600 bar ( for medium speed diesel engines)
          • 9.4.3 Types
          • Multi orifice type.
          • The disposition of holes & their number depend upon the combustion chamber design.

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