Essential reading: SPINČIĆ, A., PRITCHARD, B., An English Textbook For Marine Engineers 2, Pomorski fakultet, Rijeka LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog jezika za pomorce, Pomorski fakultet, Rijeka Tomislav Skračić, MA Undergraduate English Course for MARINE ENGINEERS 5th Semester

LESSON 11 FUEL OIL SYSTEMS

1.FUEL OILS 1.H.F.O. Heavy fuel oil (residual, blends & crudes); 2.D.F.O. Diesel fuel oil or M.D.O. Marine Diesel oil or light fuel oil ( in restricted sense ) Residuals are residues from various rafinery processes; Blends are fuel oil mixtures of different viscosity to obtain a product of desired viscosity and density Crudes: natural mixtures consisting of hydrocarbons + sulphur, nitrogen and / or oxygen derivatives of hydrocarbons.

2. FUEL VISCOSITY Viscosity is the 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 5.1 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) A purifier eliminates contaminants and a clarifier eliminates high density impurities). 5.4 Then it is admitted into a service tank.

5. FROM THE DOUBLE BOTTOM TO THE ENGINE 5.5 From the service tank the oil is passed through a heated buffer tank to the booster pumps (or fuel delivery pump) 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.

B. Pritchard, J. Luzer, M. Borucinsky, A. Spinčić

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

B. Pritchard, J. Luzer, M. Borucinsky, A. Spinčić

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 discharge and that of the compressed air in the combustion chamber.

B. Pritchard, J. Luzer, M. Borucinsky, A. Spinčić

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. 8.4 TURBULENCE Is the movement of the compressed air and fuel within a combustion space before combustion occurs.

B. Pritchard, J. Luzer, M. Borucinsky, A. Spinčić

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 (symmetrical fuel spray) or in other way depending upon the position of exhaust valves.

B. Pritchard, J. Luzer, M. Borucinsky, A. Spinčić

9. FUEL INJECTORS 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 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 Opening pressure  Usually about 600 bar (for medium speed diesel engines) Types  Multi orifice type.  The disposition of holes and their number depend upon the combustion chamber design.

Fuel injector and some examples of nozzles

Internal combustion engine procedure The fuel oil system for a diesel engine can be considered in two parts – the fuel supply and the fuel __________ systems. Fuel supply deals with the __________ of fuel oil suitable for use by the injection system. A slow-speed two-stroke diesel is usually arranged to operate continuously on __________ and have available a diesel oil supply for __________ conditions. Exercise 1 – Supply the missing terms heavy fuel injection manoeuvring provision

The oil is stored in tanks in the __________ from which it is pumped to a __________ tank and heated. After passing through centrifuges the cleaned, heated oil is pumped to a daily __________ tank. From this tank the oil flows through a three-way __________ to a mixing tank. A flow meter is fitted into the system to indicate fuel consumption. __________ are used to pump the oil through heaters and a viscosity __________ to the engine-driven fuel pumps. These pumps will discharge high- pressure fuel to their respective __________. valve injectors settling booster pumps double bottom regulator service Exercise 1 – Supply the missing terms

The viscosity regulator controls the fuel oil __________ in order to provide the correct viscosity for combustion. A pressure regulating valve ensures a constant-pressure supply to the engine- driven pumps, and a __________ bypass is used to heat up the fuel before starting the engine. A diesel oil daily service tank may be installed and is connected to the system via a __________. temperature pre-warming three-way valve Exercise 1 – Supply the missing terms

The engine can be started ________ and manoeuvred ________diesel oil or even a blend of diesel and heavy fuel oil. The mixing tank is used to collect recirculated oil and also acts ________ a buffer or reserve tank as it will supply fuel when the daily service tank is empty. The system includes various safety devices such ________ low-level alarms and remotely operated tank outlet valves which can be closed ________ the event of a fire. Exercise 1 – Supply the missing terms as on in up

Delivering right amount of fuel The function ______ the fuel injection system is to provide the right amount of fuel ______ the right moment and in a suitable condition ______ the combustion process. There must therefore be some form of measured fuel supply, a means ______ timing the delivery and the atomisation of the fuel. The injection of the fuel is achieved ______ the location of cams ______ a camshaft. This camshaft rotates at engine speed for a two-stroke engine and ______ half engine speed for a four-stroke. Exercise 1 – Supply the missing terms at by for of on

A typical fuel injector ________ two basic parts, the nozzle and the nozzle holder or body. The high-pressure fuel enters and ________ down a passage in the body and then into a passage in the nozzle, ________ finally in a chamber surrounding the needle valve. The needle valve ________ closed on a mitred seat by an intermediate spindle and a spring in the injector body. The spring pressure, and hence the injector opening pressure, ________ by a compression nut which acts on the spring. The nozzle and injector body are manufactured as a matching pair and are accurately ground to ________ a good oil seal. The two ________ by a nozzle nut. Exercise 1 – Supply the missing terms are joined can be set ending has give is held travels

The __________ valve will open when the fuel pressure acting on the needle valve tapered face exerts a sufficient __________ to overcome the spring compression. The fuel then flows into a lower __________ and is forced out through a series of tiny holes. The small holes are sized and arranged to atomise, or break into tiny __________, all of the fuel oil, which will then readily burn. Once the injector pump or timing __________ cuts off the high pressure fuel supply the needle valve will shut quickly under the spring __________ force. chamber compression drops force needle valve Exercise 1 – Supply the missing terms

Exercise 2 – Describe the fuel oil system and the passage of fuel oil from the DB tank to the engine