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Commercial medium and heavy-duty diesel vehicles in Europe are responsible for transporting an average of 73% of the total freight tonnage over distances up to 150 km as of 2021. These vehicles often operate on routes where no other form of transport is viable while still assuring fast deliveries. However, due to the nature of the journeys performed by the heavy-duty vehicles, which can span over several days or weeks depending on the mileage and the loading and unloading destinations, it becomes essential for the drivers to address the energy demands for heating and for the cabin accessory appliances during resting periods. As a rule, and especially in cold weather conditions, in order to prevent start-up problems, engine idling has traditionally been used. In order to mitigate the negative impact of increased fuel consumption and cut the harmful emissions from the engine's idling, the usage of a fuel cell auxiliary power unit (APU) is proposed. Fuel cells are more efficient than internal combustion engines and as an APU they could be sized appropriately to specifically power the cabin's accessories. There are two types of fuel cells that are applied for an APU in heavy-duty vehicles, namely, proton exchange membrane fuel cell (PEMFC) and solid oxide fuel cell (SOFC), each one imposing specific system topology requirements. A brief literary review on fuel cell APUs for heavy-duty vehicles is undertaken in the paper with emphasis being on the most recent advancements and on the advantages and disadvantages for the two possible systems. An estimation of the cabin power consumption during rest periods for European heavy-duty vehicles is presented. Some general suggestions and considerations are laid down, which may be of use when designing such a system, as there is not much information on the topic. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell systems are a novel concept for combined heat and power (CHP) generation with high total efficiency and low emissions of harmful gases. In order to successfully review the operational processes of such a system, thermodynamic analyses are normally employed. The aim of this paper is to propose a SOFC system topology based on a preselected SOFC and determine the heat transfer rates as well as the overall efficiency of the plant by means of a mathematical model. The results indicate a total system efficiency of 0.628 without evaluating the energy available from the combustion of the remaining anode off-gas (AOG). Analysis of the effects of the steam to carbon (S/C) ratio on the system's behavior and outcomes is also performed. The analysis reveals that increasing the S/C ratio of the system leads to a decrease in the electrical efficiency, while the total efficiency of the system experiences a slight increase. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells (SOFC) are an emerging technology for production of electricity through processing of different fuels such as contemporary diesel or gasoline fuel, natural gas (NG) and hydrogen. SOFC are advantageous over other fuel cells due to their high efficiency (up to 65%), the usage of a cheap catalysts and the low requirements towards the purity of the fuel when hydrogen is utilized. Additionally, SOFC can be combined with an internal combustion engine (ICE) or a gas turbine (GT) to work in combined cycles. The heat engine (HE) utilizes the residual anode-off hydrocarbon-containing gases of the SOFC to guarantee even better efficiencies and higher versatility of the power system over standalone-SOFC and standalone-ICE layouts. Such combined systems can successfully be applied in stationary power or combined heat and power (CHP) generation for remote regions, or where the electricity from the grid is too expensive. They are also a promising concept in the transportation sector, particularly for heavy-duty transport means such as trains, trucks and airplanes. One of the greatest advantages of hybrid cycle systems is that they generate very low amounts of harmful gases, which makes them viable in the context of contemporary strict emission regulations. Namely the basics of the SOFC technology, its possible applications, and the approaches and possible layouts for building a combined cycle with an ICE or a GT, are reviewed. In the publication it is emphasized on the models' results in order to compare the effectiveness and feasibility of such a setup. The main differences of the systems caused by employment of a particular HE – ICE or GT, are also highlighted. [ABSTRACT FROM AUTHOR]