Indicator power

Indicated power is the power developed inside the cylinder by gas pressure on the piston, before mechanical friction is subtracted. It is computed from the indicator diagram: indicated power equals indicated mean effective pressure times swept volume times the number of working strokes per second times the number of cylinders. Subtracting friction and the power to drive scavenge and lube pumps gives brake power at the coupling, so the ratio of brake to indicated power is the mechanical efficiency, typically 0.85 to 0.92 for large two-strokes. Indicated power is the figure used to compare cylinder-to-cylinder load balance and to verify an engine’s tuning against its shop-trial sheet.