Fuel and CO₂ impact of running a Power Take-Off (PTO) shaft generator instead of an auxiliary engine.
Formula
$$ F_\text{saved} = \frac{P_\text{PTO} \cdot h \cdot \text{SFOC}_\text{AE}}{10^6} $$$$ F_\text{extra} = \frac{P_\text{PTO} \cdot h \cdot \text{SFOC}_\text{ME}}{10^6} $$$$ \Delta \text{CO}_2 = F_\text{saved} \cdot C_{f,\text{AE}} - F_\text{extra} \cdot C_{f,\text{ME}} $$Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $P_\text{PTO}$ | Electrical output produced by the shaft generator | kW | PTO-maker data |
| $h$ | PTO running hours | h | operating profile |
| $\text{SFOC}_\text{AE}$ | SFOC of the aux engine that would otherwise run | g / kWh | NOx Technical File |
| $\text{SFOC}_\text{ME}$ | SFOC of the main engine supplying the PTO | g / kWh | NOx Technical File |
| $F_\text{saved}$ | Aux fuel displaced | t | result |
| $F_\text{extra}$ | Extra ME fuel burned to cover the PTO load | t | result |
| $C_{f,\text{AE}}, C_{f,\text{ME}}$ | CO₂ factors for the aux and ME fuels | t CO₂ / t fuel | MEPC.364(79) |
Net saving comes from $\text{SFOC}_\text{AE} > \text{SFOC}_\text{ME}$ and potentially from the fuel-Cf gap if the ME burns HFO/VLSFO and the aux burns MGO.
Sources
- IMO MEPC.1/Circ.815 - innovative energy-efficient technologies.
- MAN Energy Solutions - Shaft Generator Packages.