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 NO X emissions.

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The use of modern biofuels in mobile applications has an enormous potential to reduce greenhouse gases as well as engine pollutant emissions, such as soot or nitrogen oxides. This beneficial effect is directly related to the molecular structure of the biofuel as a product of an optimized production process. To understand the influence and emission reduction potential of the large variety of different fuel properties, this study aims to identify desirable fuel characteristics and define optimized biofuel components. In a first step, a literature survey is carried out, focusing on the impact of the cetane number, boiling characteristics, and aromatic and oxygen contents on the diesel combustion process. The incorporated investigations that analyze the combustion behavior, engine efficiency, and emission performance underline the potential of tailoring fuels to desired properties. From this foundation, a modelbased analysis of desired fuel properties was conducted, using a large database with 32 different fuels (single molecules and fuel mixtures). With multiple correlation methods, different fuel properties can be used to predict the emission performance of the engine. The following fuel optimization based on emission performance and engine efficiency results in ideal fuel properties for diesel engine combustion. As it turns out, a blend of 2-methyltetrahydrofurane (2-MTHF) (which can be derived from cellulose) blended with di-n-butylether complies with the desired fuel properties, which were defined before. In combination with an improved homogeneous low-temperature combustion process and an increased ignition delay, a nearly soot-free diesel combustion over a wide load range is realized. The oxygenated fuel enables increased exhaust gas recirculation (EGR) rates while maintaining the high engine efficiency of the diesel process.

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ElsevierGarcía Martínez, A.; Monsalve Serrano, J.; Heuser, B.; Jakob, M.; Pichinger, S. (2016). Influence of fuel properties on fundamental spray characteristics and soot emissions using different tailor-made fuels from biomass. Energy Conversion and Management. 108:243-254. doi:10.1016/j.enconman.2015.11.010.Influence of fuel properties on fundamental spray characteristics and soot emissions using different tailor-made fuels from biomass Energy Conversion and Management, Volume 108, 15 January 2016, Pages 243-254. http://dx.doi.org/10.1016/j.enconman.2015 Antonio García AbstractThis work evaluates the potential of some new biomass-derived fuels as candidates for compression ignition operation. Thus, fundamental spray characteristics related to fuel vaporization and fuel/air mixing process for 2-Methyltetrahydrofuran, Di-n-butyl ether and 1-octanol has been studied and compared with conventional EN590 Diesel fuel. For this purpose, OH* chemiluminescence and shadowgraphy measurements in a high pressure chamber as well as 1D simulations with a spray model have been carried out at different operating conditions representative of the NEDC driving cycle. Finally, measured soot emissions in the singlecylinder engine were presented and discussed.Results from the high pressure chamber presented very good agreement in terms of liquid length and vapor penetration with simulation results. Thus, some analytical expressions related to macroscopic spray characteristics have been proposed and validated experimentally for all four fuels. Finally, the single-cylinder engine results confirmed the relevant role of soot formation on final emissions for 1-octanol and 2-MTHF. In addition, DNBE showed greater soot oxidation potential than diesel and other TMFB candidates.