Overview
This lecture explains the indicator diagram, power card, and various methods of power calculation for marine engines.
Methods of Power Calculation
- There are five main methods to calculate the power of a marine engine.
- Brake power is obtained by the braking method (brake drum method).
- Torque method and indicator diagram method are also used.
- There is a difference between brake power and indicated power — brake power is the actual power available at the flywheel.
Introduction to Indicator Diagram
- The indicator diagram is a graph between pressure and volume inside the cylinder.
- Pressure inside the cylinder changes according to the movement of the piston, creating a PV diagram.
- Work and power are calculated based on the area.
How to Make an Indicator Diagram
- The indicator instrument consists of a piston, lever, spring, and connected drum.
- The up-down movement of the piston rotates the drum and creates a graph on paper.
- This diagram helps in calculating the indicated power.
Use of Planimeter
- A planimeter is an instrument used to measure the area of the indicator diagram.
- The planimeter is slowly rotated around the line from the start point to measure the area.
- The measured area and spring constant give the mean indicated pressure (MIP).
Terms Used in Power Calculation
- Indicated Power = Mean Indicated Pressure × Stroke Length × Area × Revolution/Cycle.
- Brake Power = Actual power available at the flywheel.
- Mechanical Efficiency = Brake Power/Indicated Power × 100 (%)
Key Terms & Definitions
- Indicated Power — Total power generated inside the cylinder.
- Brake Power — Power available at the engine output shaft/flywheel.
- Mean Indicated Pressure (MIP) — Average pressure in the cylinder.
- Indicator Diagram — Graph of pressure versus volume.
- Planimeter — Instrument for measuring the area of irregular shapes.
Action Items / Next Steps
- Create a chart of the working of the indicator diagram and planimeter.
- Prepare power card and compression card for the next lecture.