main engine performance and how to maintain it?

Indicator Diagrams:

Taken at every month and every major O/H.

Power card: In phase with piston movement, with fuel on, to determine:
IP (Indicated Power)
Pmax (Between Atmospheric line and highest point)
Operational faults.

Draw card: 90° out of phase with piston movement, with fuel on, to determine:
Pmax
Pcom (more accurately)
Nature of expansion curve.
To evaluate injection, ignition delay, fuel quality, combustion, loss of
compression, expansion process, fuel pump timing, and after-burning.

Compression card: In phase and fuel cut-off, to determine:
Compression pressure
Cylinder tightness.

Light spring : In phase, using light spring, with fuel on, to determine:
Pressure variation during Exhausting and Scavenging periods.

How to maintain good Performance:

1. Maintain good power output per cylinder.
2. Take Power Card, to check Power Output / Cylinder.
3. Take Compression Card, to check for cylinder tightness.
4. Check ratio of Absolute Compression Pressure to Absolute Scavenging Pressure.
5. If the ratio is same as that during Sea Trial, Piston rings and exhaust valves are sufficiently tight. (With B&W engine, this ratio is about 30.)
6. If Absolute Pressure Ratio is less, check for cylinder tightness, charge air cooler,
scavenge air ports, scavenge valves, piston rings, exhaust valves, TC, etc.
7. Light Spring Diagram is taken if necessary.
8. Check Exhaust Temperatures, exhaust smoke, Load Indicator and engine running parameters.
9. Check fuel, CLO & LO consumption.
10. Regular maintenance works and repairs.

Absolute Pressure = Gauge Pressure (of Manometer) + Atmospheric Pressure (15 psi or 30″ Mercury)

If Compression Pressure is low:

1. Carry out Unit O/H and renew liner, piston and rings.
2. TC checked, clean and overhauled, to have efficient operation.
3. Check Scavenge air line, charge air cooler, for insufficient scavenge air condition.
4. Check Inlet and Exhaust valves may be leaking.
5. Clean Scavenge Ports, Scavenge Valves, if 2/S engine.

Early combustion:
Causes:
1. Cetane no: of fuel higher than normal.
2. Fuel pump plunger set too high.
3. Incorrect adjustment of fuel cam on camshaft. Fuel valve ē low-pressure setting.
Effects:
1. High Pmax.
2. Low expansion line.
3. Less S.F.O.C.
4. Low exhaust temperature.
5. Heavy shock load to bearings.
6. Knocking.

Late combustion:
Causes:
1. Cetane no. of fuel lower than normal.
2. Plunger set too low.
3. Incorrect adjustment of fuel cam on camshaft.
4. Leaky fuel valves or high-pressure setting.
Effects:
1. Loss of power.
2. High expansion line.
3. Increased S.F.O.C.
4. High exhaust temperature.
5. Overheating
6. Lubrication difficulty.

Cetane Number:
1. A measure of ignition quality of fuel.
2. The higher the Cetane Number the shorter the time between fuel injection and rapid combustion.
3. The higher the Cetane No. the better the ignition quality.
4. Considered as poor fuel, if C  37 . Usual range is 30 – 45.

High Cetane no: Effects:
1. Shorter delay period
2. Early combustion
3. Increased power
4. Knocking

Low Cetane no: Effects:
1. Longer delay period
2. Late combustion
3. Decreased power
4. After burning
5. High exhaust temperature and smoke.

Diesel Knock:
– Violent knocks produced by high rate of pressure rise, RPR, during combustion, as delay period is longer than normal.
Causes:
1. Too low working temperature.
2. Cold start.
3. Too early fuel injection.