In order to counteract the human-driven global warming, a wide variety of solutions is needed to reduce greenhouse gas emissions in all sectors. In the transport sector, the focus is particularly on CO2 emissions. To reduce this, an option is to renewably, synthetically produce fuels from hydrogen and CO2 separated e.g. from ambient air or from point sources by using renewable energy (eFuels). Waiving biogenic sources for the energy supply makes those eFuels to so-called RFNBOs (“Renewable Fuels of Non-Biologic Origin”). All of these can be integrated into the existing supply chain and infrastructure and can get used in conventional combustion engines. This means, that the current and the future existing fleet in particular could visionary be operated with significantly reduced CO2 emissions in the sense of a closed carbon cycle while the advantages of liquid energy storage remain.
Meanwhile, there are more and more plants worldwide producing eFuels via various synthesis paths. These include Fischer-Tropsch (FT) processes and Methanol-to-Gasoline (MtG) processes. In addition, further projects are already being planned. First supportive legislations now promote for this.
For example, the Swiss CO2 legislation as of January 1st, 2025 allows it car manufacturers to reduce their CO2 fleet emissions by purchasing so-called credits (respectively proofs of origin) from a renewable, synthetic fuel supplier introducing RFNBOs into the Swiss market. In case of Switzerland, the raw fuel (e.g. MtG) is blended into the fuel system at the tax warehouses. In the EU there are also efforts to blend RFNBOs in the fuel stock via quotas (via the renewable energy directive) and also possibly take the renewable content in a conventional (mainly fossil) fuel blend into account (“Carbon Correction Factor”). This is motivated by the renewable share leading to reduced CO2 emissions in the sense of a CO2 circular economy, since the CO2 formed during combustion was previously removed e.g. from ambient air or point sources. It is therefore not unlikely that in addition to offering pure eFuel at filling stations available quantities of eFuels will also be admixed to fossil fuels (“drop-in”).
The presentation will show the impact of admixing different proportions of renewable raw MtG, that does nearly meet all specifications of the EN228 on its own, to commercially available fuels of the Swiss market. The effects on their chemical and thermophysical properties such as density, RON, C-H-O ratio and vapor pressure will be presented. The predictive methods used for this purpose will be presented and validated. Additionally, it will be outlined what measures are possibly required to get the admixture of fossil fuel and raw MtG back in line with applicable standards. An outlook on the influence of admixtures on the engine behavior will be given.