# Compatibility of Different Automotive Elastomers in Paraffinic Diesel Fuel
###### Abstract
The requirements for paraffinic diesel fuels are set out in the standard EN 15940, however, this standard does not supersede EN 590 [25]; therefore, these fuels, such as B30 and B100 can be used in a dedicated fleet (approved by vehicle manufacturers). The producers of synthetic components point to their normative and operating properties being equivalent to fossil fuel [26; 27]. However, it should be stressed that they are characterized by lower density, which does not fall within the diesel fuel range stipulated in EN 590. The studies conducted in terms of analyzing combustion and emission characteristics confirm that paraffinic fuels do not exhibit worse properties than fossil diesel fuel [28; 29]. Based on many years of experience of the automotive industry with fossil diesel, it is assumed that the materials found in fuel supply systems are compatible with it. However, the process of introducing new, alternative fuels and fuel components generates additional questions as to the direction of their impact on the materials used by a given manufacturer. The aviation industry has already introduced seven synthetic components into fuel in the amount of up to 50% (\(v/v\)). These fuels can power aircraft jet engines [30]. Furthermore, the aviation industry has also implemented the \"Standard practice for evaluation of new aviation turbine fuels and fuel additives\" procedure, which indicates the materials (metals and non-metals) that the new fuels can safely interact with, as well as the scope of required tests. With regard to non-metals, the test involves a 28-day immersion of the material in the fuel, followed by the determination of its properties, such as volume swell, tensile, elongation, hardness or resistivity [31]. The automotive industry has not yet developed such an industry-wide guidebook, rather vehicle manufacturers individually comment on the possibility of using paraffinic fuels in their engines. Given the constant growth of the interest in using alternative fuels, the market currently offers a wide range of biofuels, with new fuels or fuel components destined to appear. Materials commonly used in seals and O-rings in vehicles include ethylene-propylene-diene monomer (EPDM), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), fluoroelastomers (FKM), silicone rubber (SR) or polytetrafluoroethylene (PTFE). Please note that FKM is best suited for use as a seal in fuel supply systems of vehicles powered by diesel fuel and biodiesel [32]. However, due to the different hydrocarbon composition (its lower diversity), synthetic fuel may interact with various materials, including rubber, differently to petroleum products. Although the compatibility of fuel with the materials used in a fuel supply system is always a key issue, the source literature does not contain many publications in the field of synthetic fuel's impact on the elastomers used in the automotive industry (GTL [33] and HVO [34]). Most publications address the impact of fuels with a FAME additive [35; 36; 37; 38; 39]. Their authors select fossil fuel blends with methyl esters obtained from various raw materials, which are then exposed to selected rubbers. The obtained results are used as a base to develop ranking lists showing the elastomers most and least resistant to biofuels. The authors of [40] identified all vehicle components that contain rubbers. These are, among others, fuel pump seals, fuel gauge seals, in-tank seals, fuel filter seals, fuel injector O-rings, fuel hoses, canister seals, etc. As already mentioned, there is currently no standardized list of materials to be introduced, therefore the author of [41] selected elastomers and plastics (NBR, FKM, nylon and Teflon) and metal components (copper, zinc, mild steel, matt sheet metal, brass and aluminum) to be tested for the impact of new fuels on structural materials. In addition, he suggested blend concentrations, conditions of interaction between the fuel and material and also the test scope itself.