- Verify that the indicator instruments (including the indicator, its connecting lines, and the planimeter used for area measurement) are in good working order. Lubricate all moving parts as needed to ensure smooth operation and prevent damage. Check that the spring fitted to the indicator is appropriate for the expected peak pressure.
- Confirm that the ship is at even keel and that the propeller is fully submerged to avoid variations in engine load and pressure readings due to the ship's motion. Ideal conditions involve calm weather (minimal rolling, pitching, and wind) to minimize external influences.
- Verify past records for various engine parameters and the RPM at which indicator diagrams were previously taken to establish a baseline for comparison.
- Notify the duty officer on the bridge about the planned RPM and duration for the procedure. Ensure the ship’s route is not altered during this time.
- Increase the engine RPM gradually and stabilize the load before beginning.
- Open the indicator cocks while the engine is running and blow through them to ensure they are clear of any obstructions.
- Securely connect the indicator instruments to the engine and prepare to take diagrams.
- Allow the instruments sufficient cooling time after taking diagrams from each cylinder.
1. Power Card: This card shows the pressure-volume relationship throughout the power stroke of the engine. The area enclosed represents the work done per cycle. The indicator drum rotates in phase with the piston movement
Procedure:
- Fix a diagram paper on the indicator drum.
- Draw an atmospheric pressure line.
- Connect the cable to the indicator cam and open the indicator cock.
- Press the stylus on the paper to obtain the power card.
From the above sketch,
- 1-2 piston is moving upwards, scavenging the cylinder
- 2-3 Scavenging ports are shut, exhaust closing
- 3-4 Compression
- 4-5 Fuel injection and combustion cause rapid rise in pressure
- 5-6 Expansion: Piston forced down by expanding gases
- 6-7 Exhaust opens, cylinder blowdown, rapid pressure drop
- 7-1 Scavenge ports open, scavenging commences
2. Draw Card: Also known as an “Out of phase card”, this card provides a detailed representation of the entire combustion process, including compression, injection, ignition, maximum pressure (Pmax), and expansion. The indicator drum rotates 90° out of phase with the piston stroke.
Procedure:
- Fix a diagram paper on the indicator drum.
- Open the indicator cock and press the stylus on the paper while manually pulling the wire to rotate the drum and obtain the draw card.
3. Compression Card: Taken with fuel supply cut off, this card illustrates the compression pressure within the cylinder. It helps detect problems like worn cylinder liners, faulty piston rings, or leaking exhaust valves.
Procedure:
- Shut off the fuel supply to the cylinder.
- Replace the paper and follow the same steps as for the draw card to record the compression card.
4. Light Spring Diagram: This card uses a weaker spring to record the pressure variations during the exhaust and scavenging phases. It aids in detecting issues with these processes.
Procedure:
The procedure is similar to a power card, but with a light spring and a different phase movement during compression.
- Engine RPM
- Scavenge air pressure
- Fuel pump index
- Jacket cooling water (JCW) temperature
- Variable Injection Timing (VIT) settings
- Injection timing
- Lubricating oil (L.O.) temperatures and pressures
- Fuel temperature
- Exhaust temperature
- Air cooler pressure drop
- Wind force and direction
- Load Index
- Peak pressure is obtained (Pmax) & Pcomp is obtained.
- Indicated power is calculated.
- The combustion process is determined by evaluating injection, ignition, compression & expansion.
- Scavenge & exhaust defects are evaluated.
Calculating Cylinder Power:
Formula:
$$Indicated\:power\:=\:PLAN$$
- P: Mean Indicated Pressure (MIP) obtained from the power card
- A: Area of the piston
- L: Stroke length
- N: Number of power strokes per second
Mean Indicated Pressure (MIP):
- Use a planimeter to measure the area of the power card diagram.
- Divide the area by the diagram's length and multiply it by the spring constant.
Use the measured MIP along with the cylinder dimensions and engine RPM to calculate the power developed in each cylinder.