FuelEU WtW

Well-to-Wake intensity formulas, Annex II default factors, methane slip, and biofuel period dating.

src/lib/utils/fuelEUCalculator.ts implements EU Regulation 2023/1805 with Annex II default emission factors. This page documents the formulas and constants in use.

WtW = WtT + TtW

WtT (per fuel) = Annex II default value (gCO₂eq/MJ)
TtW (per gram of fuel) = ttW_CO₂ × GWP_CO₂ + ttW_CH₄ × GWP_CH₄ + ttW_N₂O × GWP_N₂O
TtW (per MJ)   = TtW per gram / LCV (MJ/g)
WtW            = WtT + TtW per MJ (gCO₂eq/MJ)

Global warming potentials use AR5 values:

Gas	GWP
CO₂	1
CH₄	28
N₂O	265

Annex II default factors

The platform supports 19 fuel types. Key conventional and alternative fuels:

Fuel	LCV (MJ/g)	WtT (gCO₂eq/MJ)	TtW CO₂ (g/g)	TtW CH₄ (g/g)	TtW N₂O (g/g)
HFO	0.0405	13.5	3.114	0.00005	0.00018
LFO	0.0410	13.2	3.151	0.00005	0.00018
MDO	0.0427	14.4	3.206	0.00006	0.00018
MGO	0.0427	14.4	3.206	0.00006	0.00018
LNG (Otto MS)	0.0491	18.5	2.750	0.031	0.00011
Methanol (fossil)	0.0199	31.3	1.375	0.00012	0.00002
LPG (Propane)	0.0461	7.5	3.030	0.00005	0.00018
LPG (Butane)	0.0455	8.4	3.030	0.00005	0.00018

Biofuels (TtW CO₂ counted as 0 — biogenic):

Fuel	LCV	WtT	Notes
FAME	0.037	21.0	Average across feedstocks
HVO	0.044	10.0	Certified sustainable
Bio-Methanol	0.0199	7.6	Waste-based pathway
Bio-LNG	0.0491	7.5	Waste/manure
Bio-Blend	0.040	18.0	Blended; partial biogenic content

E-fuels:

Fuel	LCV	WtT
E-Methanol (Green)	0.0199	3.0
E-LNG	0.0491	5.0

Ammonia and Hydrogen:

Fuel	LCV	WtT	TtW N₂O
Ammonia (Grey)	0.0186	121.0	0.008
Ammonia (Green)	0.0186	5.0	0.008
Hydrogen (Grey)	0.120	132.0	—
Hydrogen (Green)	0.120	5.0	—

LNG methane slip

For LNG and Bio-LNG, methane slip (ttW_CH₄) varies by engine:

Engine	Slip (Cslip)
Otto medium-speed	3.1% (default)
Otto slow-speed	1.7%
Diesel	0.2%
LBSI (lean-burn spark-ignition)	2.6%

The platform defaults to Otto medium-speed unless engine type is supplied.

Biofuel period dating

Bio-Blend bunkers are dated against the user’s certification records. Two periods exist with different certified WtW intensities:

Period	Cf (t CO₂ / t fuel)	WtW (gCO₂eq/MJ)
Pre-8-Aug-2025	2.331	9.2
Post-8-Aug-2025	2.502	10.8

Cutoff: 8 August 2025 (FIFO consumption assumption). Consumption before the cutoff uses the earlier bunker; after, the later one.

Fleet GHG intensity

Fleet GHG Intensity = Σ (Energy_i × WtW_i) / Σ Energy_i

Energy is computed per fuel as tonnes × 1,000,000 × LCV.

Targets and compliance

Target intensity (year)  = step function from {2020 baseline, 2025, 2030, ..., 2050}
Compliance Balance       = (Target − Actual) × Total Energy   (in gCO₂eq)
Compliance status        = COMPLIANT if Actual ≤ Target else NON_COMPLIANT
Penalty (€)              = |Balance| / Actual × (€2,400 / 41,000 MJ)

The penalty divides by Actual to convert the gCO₂eq gap into MJ of energy at the actual intensity, then values that energy at €2,400 per tonne of VLSFO equivalent (41,000 MJ).

Targets are step-wise: the 2025 target (89.34) applies through 2029, then drops at 2030. Years before 2025 use the baseline (91.16).

Implementation

src/lib/utils/fuelEUCalculator.ts — exports include calculateWtW, calculateFleetGHGIntensity, calculateFuelEUCompliance, calculateFuelEUComplianceWithBiofuelPeriods, and the FUEL_FACTORS, LNG_CSLIP, GWP, GHG_TARGETS, BIOFUEL_EMISSION_FACTORS constants.

Reference

• Regulation (EU) 2023/1805 — FuelEU Maritime
• Annex II default emission factors — WtT, TtW, LCV for every supported fuel
• IPCC AR5 GWP values — CH₄ = 28, N₂O = 265
• DNV — FuelEU Maritime
• CE Delft technical report
• Sustainable Ships — FuelEU penalty calculator