Review of Potential CO₂-Neutral Fuels in Passenger Cars in Context of a Possible Future Hybrid Powertrain

To minimize the impact of global warming worldwide, net greenhouse-gas (GHG) emissions have to be reduced. The transportation sector is one main contributor to overall greenhouse gas emissions due to the fact that most of the current propulsion systems rely on fossil fuels. The gasoline engine powertrain is the most used system for passenger vehicles in the EU and worldwide. Besides emitting GHG, gasoline driven cars emit harmful pollutants, which can cause health issues for humans. Hybrid powertrains provide an available short-term solution to reduce fuel consumption and thus overall emissions. Therefore, an overview of the currently available technology and methodology of hybrid cars is provided in this paper as well as an overview of the performance of current HEV cars in real world testing. From the testing, it can be concluded that despite reducing harmful emissions, hybrid vehicles still emit pollutants and GHG when fueled with conventional gasoline. It is therefore questionable if hybrid vehicles can meet future emission standards such as Euro 7. To further minimize harmful emissions, engines can also utilize potential future fuels which are GHG-neutral over their lifecycle. Several of these synthetic fuels have a big potential to reduce pollutants as well. Two potential candidates with already proven field testing are hydrogen and methanol. Another candidate that could be used in today's car fleet is synthetically produced gasoline. One potential newer option is a mixture of dimethyl carbonate and methyl formate or mixtures of these with gasoline. The mentioned candidates/blends are reviewed here specifically regarding available engine test bench data. Based on the available data, the technological capability is discussed.