Ratio of brake to indicated power. A falling η_m at fixed IMEP is the earliest sign of rising friction (piston rings, bearings, seals).
Formula
$$ \eta_m = \frac{P_b}{P_i}, \quad P_f = P_i - P_b $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $P_b$ | Brake power | kW | shaft torsionmeter |
| $P_i$ | Indicated power | kW | indicator / IMEP |
| $\eta_m$ | Mechanical efficiency | - | result |
| $P_f$ | Friction power loss | kW | result |
Sources
- Pounder’s Marine Diesel Engines.