Zukünftige Biokraftstoffe für fortschrittliche Brennverfahren
- Future biofuels for advanced combustion systems
Heuser, Benedikt; Pischinger, Stefan (Thesis advisor); Heufer, Karl Alexander (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020
Against the background of the climate protection convention of Paris, also CO2 emissions from transport must significantly be reduced. In Germany, the emissions of the transport sector shall be reduced by 40 to 42% by 2030 compared to the reference year 1990. The aim of this thesis was to assess the suitability of 1-octanol and di-butyl ether as representatives of future tailor-made biofuels for self-igniting combustion processes by means of experimental investigations. Optical measurements showed that the mixture formation with both the biofuel candidates is significantly different compared to diesel. Detailed emission characterization showed that both future biofuels feature significantly reduced soot emissions due to different mixture formation processes and especially due to molecular structure. Not only the particle mass but also the particle number is up to 93% lower than with fossil fuels. By means of model-based optimization of the engine calibration, the efficiency with both the biofuels could be increased by about 1%-point compared to diesel. Similar improvements could be achieved by increasing the geometric compression ratio, but the particle emissions were slightly negatively influenced by this at high partial load. In order to achieve further increases in efficiency and even lower raw emissions, dual-fuel combustion processes were investigated in the second part of the thesis. In addition to fossil diesel, di-butyl ether was also used as an ignition fuel. A conventional RON95 E10 fuel, ethanol, and the highly knock resistant biofuel candidate 2-butanone, were introduced into the combustion chamber via the intake manifold. Since the fuel has a significant influence on combustion control, efficiency, and emissions, the fuel mixture ratio, pairings of different fuel reactivities and times of fuel introduction were in the focus of the investigations. Due to the very homogeneous mixture in dual fuel operation, soot emissions were minimized close to the detection limit in all considered partial load tests – independent of the fuel pairing. However, the hydrocarbon and carbon monoxide emissions increased significantly. In the reactivity-controlled combustion process with di-butyl ether and 2-butanone, nitrogen oxide emissions were also reduced by over 90% compared to the classic diesel process due to lower peak temperatures. At the same time, the efficiency was increased to almost 46%. Due to the very good mixture formation and high reactivity, di-n-butyl ether is preferable to fossil diesel as an ignition fuel in dual-fuel operation. Due to its higher efficiency, a conventional mono-fuel combustion process is superior to a dual-fuel process in the very low part load regime when using tailor-made fuels such as dibutyl ether. In the range of low to high part load, the reactivity-controlled process offers efficiency advantages. At full load, the ignition jet process is beneficial compared to the reactivity-controlled process due to its good combustion control. Within this thesis, the use of tailor-made biofuels enabled in all investigated combustion processes higher efficiencies and lower emissions when compared to fossil fuels. Hence, it is possible to achieve both CO2-neutrality and lowest pollutant emissions in transport with the use of future biofuels.