Fabian Hoppe

Water injection for gasoline engines: Potentials, challenges, and solutions:

Further significant CO2 emission reduction beyond 2020 is mandatory in the United States and might also become mandatory in Europe, depending on the passenger car CO2 legislation, which is to be enacted. Hybrid and plug-in hybrid vehicles might account for a big portion of these CO2 reductions as a consequence of the favourable current legislative treatment which does not associate CO2 emissions from electric power generation with vehicle CO2 emissions. Nevertheless, these powertrains benefit from a highly efficient combustion engine. Exhaust heat recovery poses new synergetic possibilities for technologies to mitigate knock like cooled external exhaust gas recirculation and condensed water injection. The condensed water injection concept, which is proposed in this article, demonstrates a potential for efficiency increase of 3.3% – 3.8% in the region of the minimum specific fuel consumption on a stoichiometric combustion concept with Miller cycle and cooled external exhaust gas recirculation. Further improvement of the efficiency of up to 16% is possible at full-load operation. If water injection is used in addition to homogeneous lean combustion, an efficiency gain of 4.5% in the region of the minimum specific fuel consumption is achieved.

Tailor-made fuels for future engine concepts

Increasing carbon dioxide accumulation in earth’s atmosphere and the depletion of fossil resources pose huge challenges for our society and, in particular, for all stakeholders in the transportation sector. The Cluster of Excellence ‘Tailor-Made Fuels from Biomass’ at RWTH Aachen University establishes innovative and sustainable processes for the conversion of whole plants into molecularly well-defined fuels exhibiting tailored properties for low-temperature combustion engine processes, enabling high efficiency and low pollutant emissions. The concept of fuel design, that is, considering fuel’s molecular structure to be a design degree of freedom, aims for the simultaneous optimisation of fuel production and combustion systems. In the present contribution, three examples of tailor-made biofuels are presented. For spark ignition engines, both 2-methylfuran and 2-butanone show increased knock resistance compared to RON95 gasoline, thus enabling a higher compression ratio and an efficiency gain of up to 20% at full-load operation. Moreover, both fuels comprise a good mixture formation superior to the one of ethanol, especially under difficult boundary conditions. For compression ignition engines, 1-octanol enables a remarkable reduction in engine-out soot emissions compared to standard diesel fuel due to the high oxygen content and lower reactivity. This advantage is achieved without sacrificing the high indicated efficiency and low NOX emissions.

Hot surface pre-ignition in direct injection spark ignition engines investigations with tailor-made fuels from biomass

Two promising alternative fuel candidates for spark-ignition engines, 2-butanone and 2-methylfuran, have been identified in the context of the Cluster for Excellence ‘Tailor-Made Fuels from Biomass’. To further explore the potential of these fuels for spark-ignition engine application, experimental and numerical investigations into the occurrence of the abnormal combustion phenomenon of hot surface–induced pre-ignition have been conducted, with pure ethanol, RON97 E10, and pure iso-octane as reference fuels. For the experimental investigations, a single-cylinder engine with a compression ratio of 11, equipped with a glow-plug to create a hot spot in the cylinder, was operated at 1500 r/min and 1500 mbar charge pressure. Each fuel was tested with several glow-plug temperatures until a minimum pre-ignition frequency of 2% was observed. The results show that 2-methylfuran reaches its 2% pre-ignition frequency at a glow-plug temperature of 880 °C, which is 16 °C higher than the 2% pre-ignition frequency of ethanol at 864 °C and 10 °C less than RON97 E10 with 890 °C. Iso-octane showed the lowest pre-ignition resistance with a 2% pre-ignition frequency at a glow-plug temperature of 853 °C, and 2-butanone was most resistant against pre-ignition in this study with a 2% pre-ignition frequency at 932 °C. Further numerical investigations, including zero-dimensional ignition delay time calculations and three-dimensional computational fluid dynamics simulations, revealed a clear connection between the surface ignition frequency of these fuels and their reaction kinetics.