Fuel Valve:
Injector: Requirements:
1. Spray must be in atomized state, at all times, regardless of engine speed.
2. Pressure should be set at required value. [Too high – late injection: Too low – early injection].
3. Valve seat should not pass more than stated quantity of fuel, when testing, for a given period of time.
4. Valve lift should not be excessive. [Excessive valve lift can cause hammer action to valve seat, leading to permanent damage.]
5. There should be sufficient leak-off for lubrication.
6. Should be snap-seated and no dribbling.
2. Pressure should be set at required value. [Too high – late injection: Too low – early injection].
3. Valve seat should not pass more than stated quantity of fuel, when testing, for a given period of time.
4. Valve lift should not be excessive. [Excessive valve lift can cause hammer action to valve seat, leading to permanent damage.]
5. There should be sufficient leak-off for lubrication.
6. Should be snap-seated and no dribbling.
Excessive Atomisation:
1. Smaller oil particles have insufficient KE, to go through combustion chamber.
2. Dense compressed air has high resistance to the motion of oil particles.
3. Smaller particles tend to cluster around injector tip, and oxygen-starved during combustion.
4. Can cause after-burning.
1. Smaller oil particles have insufficient KE, to go through combustion chamber.
2. Dense compressed air has high resistance to the motion of oil particles.
3. Smaller particles tend to cluster around injector tip, and oxygen-starved during combustion.
4. Can cause after-burning.
Insufficient Atomisation:
1. Oil particles become larger and will have more KE and travel further into combustion chamber, and some may rest on cylinder liner and piston crown.
2. Carbon built-up around the top of cylinder and piston crown.
3. Lower rate of combustion and after burning.
1. Oil particles become larger and will have more KE and travel further into combustion chamber, and some may rest on cylinder liner and piston crown.
2. Carbon built-up around the top of cylinder and piston crown.
3. Lower rate of combustion and after burning.
Low Penetration:
1. Less intimate mixing of air and fuel particles in combustion chamber.
2. Fuel cluster around injector tip causing after burning.
1. Less intimate mixing of air and fuel particles in combustion chamber.
2. Fuel cluster around injector tip causing after burning.
High Penetration:
1. Fuel particles travel further into the combustion chamber and some may rest on the cylinder liner and piston crown.
2. Lower rate of combustion and after burning.
1. Fuel particles travel further into the combustion chamber and some may rest on the cylinder liner and piston crown.
2. Lower rate of combustion and after burning.
Needle Scores:
Causes:
1. Due to excessive valve lift. Normal valve lift is about 1.00mm.
2. Cat-fines carried over from purifier and filters can cause abrasion, and needle scores.
Causes:
1. Due to excessive valve lift. Normal valve lift is about 1.00mm.
2. Cat-fines carried over from purifier and filters can cause abrasion, and needle scores.
Effects:
1. Due to needle score, fuel leakage across the seat will occur during the cut-off period. (Originally, the angle of needle valve and its seat is cut in difference of about
1°~ 2° to achieve point contact, thus preventing dribbling.)
2. Carbon formation at nozzle tip interferes the spray pattern causing poor combustion, high exhaust temperature, and increased fuel consumption.
3. In excessive case, surface burning of piston crown, too much carbon deposits in combustion space will occur.
1. Due to needle score, fuel leakage across the seat will occur during the cut-off period. (Originally, the angle of needle valve and its seat is cut in difference of about
1°~ 2° to achieve point contact, thus preventing dribbling.)
2. Carbon formation at nozzle tip interferes the spray pattern causing poor combustion, high exhaust temperature, and increased fuel consumption.
3. In excessive case, surface burning of piston crown, too much carbon deposits in combustion space will occur.
Leak-off of a fuel valve:
1. Amount of fuel oil, which seep past the needle valve and nozzle body and it is used for lubrication.
2. Little Leak- off may seize needle in nozzle body.
3. Too high Leak-off reduce quantity of atomized fuel into combustion chamber.
2. Little Leak- off may seize needle in nozzle body.
3. Too high Leak-off reduce quantity of atomized fuel into combustion chamber.
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