According to recent legislation pure renewable fuels (reFuels) will be a valid option for CO2-neutral mobility in Europe from 2035 onwards. This decision on the EU level takes into account that the legacy vehicle fleet has great impact on the overall CO2-emissions of transport and especially that the EU climate targets can only be reached by converting the internal combustion engine driven vehicle fleet to CO2-neutrality using fossil-free fuels. In order to end up with pure reFuels in 2035 it is essential to increase the renewable portion of fuels from todays 10% (i.e. RON95 E10) step by step to higher renewable shares. Following this route, it is crucial on the one hand to keep all future fuels fully compatible with the existent vehicles (drop-in fuels) and on the other hand to find improvements in fuel quality, especially concerning engine emissions. Future fuel composition has to generate CO2 savings but must also help to decrease the contribution of mobility to air pollution. In this context particulate number (PN) and gaseous emissions like (NOx, CO, HC) of the engines play a central role. Thus, in this study a 4-cylinder series engine from Audi is taken as an object of study to evaluate the bandwidth of engine emissions induced by the different fuel properties of some predominantly fossil fuels in comparison to a set of fuels with increased renewable content. The renewable potential of these fuels varies from 20 to 80 percent by volume and can be achieved using renewable components like ethanol, ether, high value paraffinic components, bio-naphtha, MTG or ETG.