Rationale

Incorporation of multiblends in ASTM D7566 There is no explicit recognition in ASTM D7566 that blends of synthetic kerosene and fossil kerosene may be anything other than binary blends. Only such blends are directly discussed, so there is no explicit basis to create a multiblend. The legal basis to create such a multi-blend could only be deduced from section 1.2.2, where reference is made to the fossil fuel used for blending as D1655 fuel (which may on the whole or in part have originated as D7566 fuel). This section recognizes that it is safe and permitted to blend bio kerosene with another bio kerosene, and in combination with section 1.2.1 and 1.2.3 constitutes a basis for aviation use of a multiblend. However, section 1.2.2 only refers to the case that first a binary blend is created of one synthetic kerosene and fossil kerosene, and a second synthetic component is then blended in afterwards, after the initially created blend has been certified according to ASTM D7566. This is not how one would normally blend several components especially not in the context of a future widespread use of renewable fuels for aviation purposes. Blenders may in the future want to create multiblends for commercial reasons, e.g. to increase the overall renewable kerosene content permitted by a given fossil kerosene, by using the properties of one kind of renewable kerosene to offset property weaknesses of another. For example, HEFA kerosene might be used to offset a ATJ-SPK with a low T50-T10. It is therefore recommended to explicitly recognize the possibility of multiblends, and to permit the simultaneous blending of all constituent fuels. A possible wording would be: If several different synthetic paraffinic kerosene blendstocks are blended with fossil kerosene in one batch, the blending of all synthetic components may occur simultaneously in one single blending processes. The resulting multiblend needs to meet the requirements of Table 1 of this specification (D7566)., to be inserted either as a last sentence in 1.2.1, or as a separate paragraph in section 1.2. In addition, in several passages in Annex X4.3.1 the term synthetic blending component should be changes to the plural form, i.e. synthetic blending components. This is the case for X4.3.1.8 Synthetic Content List the percentage of synthetic blending component in the finished fuel. X4.3.1.9 Synthetic type List the type of synthetic blending component from those specified in Annex A1, Annex A2 or Annex A3. In the latter case Annex A1, Annex A2 or Annex A3 should also be replaced by Annex A1 to Annex A5, to permit listing of more than one type of synthetic component and to include Annexes A4 and A5. The same change should also be made in Figure X4.1. As discussed, there is no explicit wording on the production of multiblends. In the absence of such wording, the procedures to follow have to be deduced. As far as maximum percentages are concerned, the relevant section is 6.1. However, section 6.1 only sets limits on the blend percentages for the individual synthetic components, but not on the maximum overall content of synthetic material. Given that the properties of one synthetic component can to some extent be used to balance out the properties of another synthetic component, ASTM D7566 can be interpreted to permit a total percentage of synthetic components that exceeds 50 % (v/v), as long as the individual percentage limits of section 6.1 are not exceeded. Therefore, it should be expressly clarified whether such a multiblend with synthetic components exceeding 50 % (v/v) would be covered by ASTM D7566 or not.