Design of optimal alternative fuels and their production processes

To reduce emissions in the transport sector, renewable sustainable energy carriers and efficient propulsion technologies are needed. The associated raw material, process, fuel, and engine technology aspects line up to a fuel value chain that needs to be designed with respect to cost, resource, and emission efficiency. This thesis aims at optimizing the different aspects of the fuel value chain for cost and environmental criteria by using and advancing methods for an (integrated) process and fuel design. Starting with the choice of raw materials and processes, screening methods for bio based processes are advanced to make them applicable for other raw material resources and associated processing pathways. This enables production comparisons of bio- and electricity based fuel species regarding cost and environmental criteria. The analysis of optimized production processes shows that bio-based processes generally lead to lower overall costs due to lower raw material costs compared to electricity-based production. However, conversion of biomass is often associated to higher carbon losses and energy-intensive separations, whereas electricity-based production can be achieved with low material losses and often facile liquid-gas separations. Furthermore, feedstock combinations can result in synergies, e.g., by upgrading CO2 from bioethanol production with electricity-based H2. The results of the screening thus provide a first understanding of optimal application areas and possibilities for combining raw materials in renewable fuel production. One step further in the fuel value chain, optimization of production aspects does often not suffice to design a technically viable (multi-species) fuel. Instead, fuel requirements posed by the engine application must also be taken into account. To identify cost- and emission-optimal fuel production processes while ensuring fuel compositions feasible in an engine, a new method for simultaneous process and product design is developed. In contrast to previous integrated methods, this approach accounts for the energy requirement of the production processes and thus enables cost and emission optimization. The new method is demonstrated for the design of biofuels for ultra-high efficiency engines (UHEEs).Finally, the analysis is expanded to the last step of the fuel value chain, i.e., the use of the fuel in the engine. To this end, the fuel requirements are employed as the link between the integrated process/fuel design and the engine application to determine cost and emission optimized engine/fuel combinations. The analysis considers three types of spark-ignition engines, a variety of selective, renewable processing routes, and fossil gasoline that is provided as an additional blending option. By running the new integrated design problem separately for each of the three engine types, optimal fuel production designs and associated fuel compositions are determined that are suitable for the considered engine type. The comparison of these optimal engine/fuel combinations indicates that fuels for advanced engines, i.e., UHEEs and flexible fuel vehicle engines, show a better cost/emission Pareto performance than fuels for conventional engines, which advocates a future technological change away from today’s gasoline engines