Application of E-Fuels to the Existing Gasoline Engine Fleet — Test Methods and Potential
Beside the direct electrification of traffic with plug-in hybrids and battery electric vehicles, also the indirect electrification by using E-fuels from renewable electric energy and CO2 is gaining importance, when reducing global CO2 emissions. To make efficient use of the CO2 reduction potential, E-fuels should be compatible with the existing vehicle fleet and also a drop-in should be possible. Beside the positive effect E-fuels will have on the CO2 emissions in a tank-to-wheel scenario, it is also the target to reduce the limited emissions like hydrocarbons, NOX and especially particulate mass and number emissions.
In this paper an E-fuel for gasoline engines with fuel components, which could be synthesized by future power-to-X (PtX) methods, has been tested. The test fuel has been developed by Porsche AG as one in a series of test fuels to gain experience on the effect different fuel compositions will have on the fuel consumption and emissions of vehicles in the existing fleet. In detail, the following groups of hydrocarbons are blended to a fuel with the intention to meet all requirements necessary to be operated with a current spark ignition engine technology: light Iso-Paraffins 12%, medium Iso-Paraffins 22%, heavy Iso-Paraffins 21%, Cycloalkane 30% and Ether 15%.
Since the mixture is fulfilling the existing European fuel standard, blending with standard crude oil-based fuel as well as the pure application is possible. However, the European fuel standard does not regulate some physical parameters, which are important to guarantee, that the fuel preparation does work for an engine, which is already on the market and thus not reflecting the technical standard, which could be optimized for a new fuel definition. Especially density, viscosity and surface tension are parameters, which are influencing the spray quality and mixture preparation. Since it is the target to find a fuel definition, which will work in the existing fleet without adjusting the software calibration of the engine, detailed investigations are necessary to understand how the infield vehicle fleet does work with the new fuel in an application as drop-in or 100%.
To do so, the fuel has been tested for physical parameters necessary for spray formation and also high-speed camera recording of the spray has been conducted in the laboratories of the University of Applied Sciences Darmstadt. In a second step, the fuel consumption as well as the emissions was measured on the engine test bench under stationary and dynamic conditions. To clarify whether the hydrocarbons emitted by the engine with this test fuel may convert differently in a standard Three-Way-Catalyst, the hydrocarbon spectrum has been measured with an FTIR analyser. With the help of a spark plug, which was prepared with a piezo pressure sensor, the in-cylinder pressure was recorded. In a final step, the fuel was tested in a vehicle with a direct injection turbocharged engine.
At the Porsche test facilities vehicle tests have been performed with a Porsche test car and the test fuel in a 100% concentration as well as a drop-in with different concentrations in a crude oil-based fuel.
The results demonstrate the performance of a modern fuel definition with regard to fuel consumption and emissions in application to the existing fleet. Especially the particle emissions could be reduced significantly. The vehicle tests demonstrate that a reduction of the particulate number emissions of more than 60% is realistic.
However, it has been found, that in critical areas of the engine map, where the engine calibration with regard to injection and ignition timing has been optimized to the current crude oil-based fuel standard, the beneficial effects of the test fuel are less pronounced. Here, the adjustment of the engine parameters might be interesting to improve the mixture preparation and combustion characteristics in order to optimize the full potential of the fuel.