Lifecycle boundaries#

Note

Engine source: src/engine/lifecycle-boundaries.ts (DL-162, programme Unlock Full Per-Carrier Emission Scope Controls). Every chart, selector and label consumes this one module; the UI never re-derives boundary arithmetic. Validation: tests/lifecycle-boundaries.spec.ts (21 tests) inside the full regression suite.

Definitions#

Every aviation energy carrier can be evaluated at any of four boundaries:

Well-to-Wake (WTW)

The full chain — extraction/feedstock, processing, logistics and combustion. WTW values come from the engine’s existing carbon-intensity sources unchanged.

Tank-to-Wake (TTW)

Fossil combustion CO₂ only. Biogenic (HEFA/FT/ATJ, biomethane) and atmospheric-carbon (PtL e-SAF, e-methane) combustion counts zero — the CORSIA/EU convention that the carbon was drawn down upstream. Hydrogen and electricity emit no carbon in the wake. LCAF is fossil crude-derived: its TTW equals Jet-A combustion (≈ 73.15 gCO₂e/MJ), so its WTT is negative — the pathway’s claim is lower-carbon extraction.

Well-to-Tank (WTT)

Upstream only, defined as WTW − TTW so the identity WTW = WTT + TTW holds by construction for every carrier (test-locked at 10⁻⁹).

Custom

A per-stage boundary: the sum of exactly the stages the user includes (see below). With the default stage set (all CO₂ stages) Custom equals WTW; combustion-only equals TTW; all-CO₂-stages-minus-combustion equals WTT — all three equivalences are test-locked.

Carriers#

Thirteen carriers, each with an independent selector: Conventional Jet-A, HEFA SAF, FT SAF, ATJ SAF, PtL e-SAF, LCAF (liquid fuels); LH₂ aircraft, GH₂ feedstock (hydrogen); fossil LNG, biomethane, synthetic methane (methane); grid electricity, dedicated renewable electricity.

Worked examples (2035, engine defaults): Jet-A WTW 89 / TTW ≈ 73.15; LH₂ WTW > 0 (production + liquefaction + boil-off + distribution) / TTW 0; biomethane TTW 0; fossil LNG TTW ≈ 54.87 (CH₄ combustion CO₂). A carbon intensity is never displayed without its boundary and functional unit (gCO₂e/MJ) — UI rule, enforced in the settings cards and the lifecycle-comparison chart.

Per-stage Custom boundary#

carrierStagesAt() decomposes each carrier into the engine’s own published terms — the aggregate functions delegate to term-level exports (deliveredLH2CITermsAtYear, ptlStoichCITerms, ciCh4PtgTermsAt, ch4LossTermsAt), so stage sums equal WTW by construction, not by re-derivation. Canonical stages: extraction, feedstock, transport/leakage, processing/production, liquefaction, compression, storage/boil-off, airport distribution, aircraft transfer, combustion, non-CO₂ effects.

Two disclosure rules govern the decomposition:

  • Grouped aggregates. Where a source publishes only an aggregate — the CORSIA static SAF pathway CIs (feedstock + processing + logistics), the [F]-graded LH₂ distribution+airport bracket (which includes aircraft transfer), the CORSIA fossil-LNG constant — the whole aggregate sits in one stage and carries a grouped provenance flag. Nothing is invented apart; toggling a sibling stage of a grouped term is a no-op by design.

  • Non-CO₂ is not an additive CO₂ term. Including the non-CO₂ stage applies the engine’s ERF-style multiplier (nonco2.ts) as an add-on: (central − 1) × WTW for the four fuel families the engine defines. First-order screening only — the §11 finding stands: the envelopes overlap and fuel rankings can compress or invert, so non-CO₂ must never be collapsed to a single number.

Presets#

CASCADE Compatibility (default)

Reproduces the historical behaviour bit-identically: the conventional fuel follows the user-selectable global scope; every alternative fuel is locked to its CASCADE-methodology WTW value. This is the parity mode for CASCADE-derived scenarios.

Full Lifecycle / Tank-to-Wake / Custom

All-WTW (editable) / all-TTW (propulsion comparison) / unrestricted.

Regulatory presets (scope-selection aids)

Five presets load the per-carrier boundary implied by each instrument’s stated accounting basis: ICAO LTAG (WTW — life-cycle fuel basis), CORSIA (WTW — life-cycle values against the 89 gCO₂e/MJ fossil baseline), EU ETS (TTW — combustion accounting; compliant biofuel/RFNBO combustion zero-rated, matching the engine’s TTW convention), FuelEU (WTW), ReFuelEU Aviation (WTW — RED life-cycle methodology). They are not compliance calculators: no baselines, eligibility rules, ILUC factors or credit mechanics are modelled, and the UI displays that disclaimer whenever one is active.

Mixed boundaries#

When carriers sit at different boundaries the UI shows a Mixed lifecycle boundaries warning naming the boundaries in play, with one-click Normalize-to-WTW / Normalize-to-TTW actions.

Serialisation and API#

Flat scope_<carrier> keys plus scope_preset travel through the standard URL codec, so legacy URLs (no scope keys ⇒ CASCADE behaviour), CASCADE URLs (global scope translated through the CASCADE preset) and new per-carrier URLs coexist without ambiguity. The Custom stage set serialises as compact two-letter codes in custom_stages (full stage names also parse). carrierScopesJSON() provides the explicit carrier-field API object; CSV exports carry scope_preset, the full carrier-scope object, custom_stages, engine/basis, model, functional units and the export date.

Boundary of validity#

Per-carrier boundaries drive CI-space views, comparisons and labels. The wedge/net accounting keeps the engine basis plus the global display scope (the v10 convention), so CASCADE parity is preserved bit-identically; per-carrier boundaries inside the NET accounting are a registered follow-up (V14), not a shipped claim.