Indicator diagrams indicates, simultaneously , the pressures and the relative position of the piston for a particular engine cylinder. They are taken for every voyage, both in loaded and ballast condition. It is a practice to take indicator cards after every major overhauls.
- To calculate indicated power of the engine
- To determine peak pressures and compression pressures
- To evaluate the process of combustion inside the engine
- To evaluate scavenging and exhausting conditions
- Check whether the spring fitted on the indicated instrument will meet the peak pressure (maximum combustion pressure) to be expected
- Stretch diagram paper firmly over the drum.
- Before taking diagram, open indicator cock, allow two or three firing strokes, to blow out soot and combustion residues in the cock.
- After drawing atmospheric pressure line, hook the cord to indicator drive, open indicator cock, take power card and shut off the cock.
- Make sure that the instrument is not exposed to high temperature for long time. This may affect its accuracy.
- Remove the hook, turn the drum by hand to a place clear from the power diagram, take compression pressure line with the fuel cut off.
- After taking indicator cards from all the cylinders, open the instrument and clean all the parts, and lubricate the same.
Types of Indicator Diagrams
Calculate Indicated Power
Evaluation of Indicator Diagrams
- To calculate indicated power, also gives peak pressure.
Out of Phase Diagram
- Required for accurate determination of the compression pressure.
- To evaluate peak pressure (more accurately), compression pressure and ignition delay period.
- It shows combustion process (early or late combustion).
- To evaluate injection, fuel quality, ignition delay, combustion, loss of compression, expansion, fuel pump timing and after burning.
Troubleshooting with Indicator Diagrams
Precautions While Taking Indicator Cards
- Always lubricate indicator instrument parts to prevent seizure at high temperatures.
- Tightness of the indicator piston inside the cylinder to be checked. It should be a free sliding fit.
- The cock to be free from accumulated carbon particles.
- Do not apply much pressure on the stylus while taking the diagram.
- Allow sufficient cooling time for the instrument after taking diagrams from each units.
“Reference of Marine Engineering Knowledge for MOT 2nd Class Part B (Oral)” by Min Zar Tar