Division 1.1.3 In the case of natural gas/biomethane fuelled engines, including dual-fuel engines, the manufacturer shall demonstrate the parent engines capability to adapt to any natural gas/biomethane composition that may occur across the market. This demonstration shall be carried out in accordance with this Section and, in the case of dual-fuel engines, also in accordance with the additional provisions regarding the fuel adaptation procedure set out in paragraph 6.4 of Annex 15 to UNECE Regulation No 49.F1

In the case of compressed natural gas/biomethane (CNG) there are generally two types of fuel, high calorific fuel (H-gas) and low calorific fuel (L-gas), but with a significant spread within both ranges; they differ significantly in their energy content expressed by the Wobbe Index and in their λ-shift factor (S _λ ). Natural gases with a λ-shift factor between 0,89 and 1,08 (0,89 ≤ S _λ ≤ 1,08) are considered to belong to H-range, while natural gases with a λ-shift factor between 1,08 and 1,19 (1,08 ≤ S _λ ≤ 1,19) are considered to belong to L-range. The composition of the reference fuels reflects the extreme variations of S _λ .

The parent engine shall meet the requirements of this Regulation on the reference fuels G _R (fuel 1) and G ₂₅ (fuel 2), as specified in Annex IX, without any manual readjustment to the engine fuelling system between the two tests (self-adaptation is required). One adaptation run over one WHTC hot cycle without measurement is permitted after the change of the fuel. After the adaptation run, the engine shall be cooled down in accordance with paragraph 7.6.1 of Annex 4 to UNECE Regulation No 49.

In the case of liquefied natural gas/biomethane (LNG) the parent engine shall meet the requirements of this Regulation on the reference fuels G _R (fuel 1) and G ₂₀ (fuel 2), as specified in Annex IX, without any manual readjustment to the engine fuelling system between the two tests (self-adaptation is required). One adaptation run over one WHTC hot cycle without measurement is permitted after the change of the fuel. After the adaptation run, the engine shall be cooled down in accordance with paragraph 7.6.1 of Annex 4 to UN/ECE Regulation No 49.