Compatibility screening for two marine residual fuels before co-mingling on board. Combines a Calculated Carbon Aromaticity Index (CCAI) mass-weighted mix with the CCAI difference as a proxy for ASTM D4740 Spot-test risk.
Formula
$$ \text{CCAI} = \rho_{15} - 81 - 141 \log_{10}(\log_{10}(\nu_{50} + 0.85)) $$
$$ \text{CCAI}_\text{mix} = \frac{m_A \cdot \text{CCAI}_A + m_B \cdot \text{CCAI}_B}{m_A + m_B} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\rho_{15}$ | Density at 15 °C | kg / m³ | BDN certificate |
| $\nu_{50}$ | Kinematic viscosity at 50 °C | cSt | BDN certificate |
| $\text{CCAI}$ | Calculated Carbon Aromaticity Index | - | Exxon / Shell standard |
| $m_A, m_B$ | Mass of fuels A and B to blend | t | bunker plan |
| $\text{CCAI}_\text{mix}$ | Mass-weighted blend CCAI | - | result |
Risk bands (ΔCCAI between fuels)
| $|\Delta\text{CCAI}|$ | Interpretation | |—|—| | < 8 | Likely compatible - blend with confidence | | 8 – 20 | Lab ASTM D4740 Spot test recommended before co-mingling | | > 20 | High asphaltene-instability risk - segregate the two fuels |
CCAI alone cannot prove compatibility, but a Spot test (D4740) on a small sample before large-scale co-mingling is standard practice whenever |ΔCCAI| > 8.
Sources
- ASTM D4740 - standard test for compatibility of residual fuels.
- ISO 8217 Annex F - stability & compatibility guidance.