Fuel cells as clean power sources are very attractive for the maritime sector, which is committed to sustainability and reducing greenhouse gas and atmospheric pollutant emissions from ships. This paper presents a technological review on fuel cell power systems for maritime applications from the past two decades. The available fuels including hydrogen, ammonia, renewable methane and methanol for fuel cells under the context of sustainable maritime transportation and their pre-processing technologies are analyzed. Proton exchange membrane, molten carbonate and solid oxide fuel cells are found to be the most promising options for maritime applications, once energy efficiency, power capacity and sensitivity to fuel impurities are considered. The types, layouts and characteristics of fuel cell modules are summarized based on the existing applications in particular industrial or residential sectors. The various research and demonstration projects of fuel cell power systems in the maritime industry are reviewed and the challenges with regard to power capacity, safety, reliability, durability, operability and costs are analyzed. Currently, power capacity, costs and lifetime of the fuel cell stack are the primary barriers. Coupling with batteries, modularization, mass production and optimized operating and control strategies are all important pathways to improve the performance of fuel cell power systems.

Accurate estimation of slip factor is of paramount importance to ensure centrifugal compressor work input is adequately predicted during the preliminary design process. However, variations in the flow field at impeller exit in both the pitchwise and spanwise directions complicate the evaluation procedure considerably. With the increasing implementation of engine downsizing technologies in the automotive sector, achieving a wide operating range has become a factor of prime importance for centrifugal compressors used in automotive turbocharging applications. As a result of the design features required to achieve this aim, modern impeller geometries have been shown to exhibit an approximately parabolic variation in slip factor across their respective operating maps. By comparison, traditional slip correlations typically exhibit a constant, or at best monotonic, relationship between slip factor and impeller exit flow coefficient. It is this lack of modeling fidelity which the current work seeks to address. In order to tackle these shortcomings, it is proposed that the impeller exit flow should be considered as being made up of three distinct regions: a region of recirculation next to the shroud providing aerodynamic blockage to the stage active flow, and a pitchwise subdivision of the active flow region into jet and wake components. It is illustrated that this hybrid approach in considering both spanwise and pitchwise stratification of the flow permits a better representation of slip factor to be achieved across the operating map. The factors influencing the relative extent of each of these three distinct regions of flow are numerous, requiring detailed investigations to successfully understand their sources and to characterize their extent. A combination of 3D computational fluid dynamics (CFD) data and gas stand test data for six automotive turbocharger compressor stages was employed to achieve this aim. Through application of the extensive interstage static pressure data gathered during gas stand testing at Queen's University Belfast, the results from the 3D CFD models were validated, thus permitting a more in-depth evaluation of the flow field in terms of locations and parameters that could not easily be measured under gas stand test conditions. Building on previous knowledge gained about the variation in shroud side recirculation with geometry and operating condition, the characteristic jet/wake flow structure emanating from the active flow region of the impeller was represented in terms of area and mass flow components. This knowledge allowed individual slip factor values for the jet and wake to be calculated and combined to give an accurate passage average value which exhibited the distinctive nonlinear variation in slip across the operating map which is frequently absent from existing modeling methods. Fundamental considerations of the flow phenomena in each region provided explanation of the results and permitted a modeling approach to be derived to replicate the trends observed in both the experimental data and the CFD simulations.

Impeller recirculation is a loss which has long been considered in one-dimensional (1D) modeling; however, the full extent of its impact on stage performance has not been analyzed. Recirculation has traditionally been considered purely as a parasitic (or external) loss, i.e., one which absorbs work but does not contribute to total pressure rise across the stage. Having extensively analyzed the impact of recirculation on the impeller exit flow field, it was possible to show that it has far-reaching consequences beyond that of increasing total temperature. The overall aim of this package of work is to apply a much more physical treatment to the impact of impeller exit recirculation (and the aerodynamic blockage associated with it) and hence realize an improvement in the 1D stage performance prediction of a number of turbocharger centrifugal compressors. The factors influencing the presence and extent of this recirculation are numerous, requiring detailed investigations to successfully understand its sources and to characterize its extent. A combination of validated three-dimensional computational fluid dynamics (CFD) data and gas stand test data for six automotive turbocharger compressor stages was employed to achieve this aim. In order to capture the variation of the blockage presented to the flow with both geometry and operating condition, an approach involving the impeller outlet to inlet area ratio and a novel flow coefficient term were employed. The resulting data permitted the generation of a single equation to represent the impeller exit blockage levels for the entire operating map of all the six compressor stages under investigation. With an understanding of the extent of the region of recirculating flow realized and the key drivers leading to its creation identified, it was necessary to comprehend how the resulting blockage influenced compressor performance. Consideration was given to the impact on impeller work input through modification of the impeller exit velocity triangle, incorporating the introduction of the concept of an “aerodynamic meanline” to account for the reduction in the size of the active flow region due to the presence of blockage. The sensitivity of the stage to this change was then related back to the level of backsweep applied to the impeller. As a result of this analysis, the improvement in the 1D performance prediction of the six compressor stages is demonstrated. In addition, a number of design recommendations are presented to ensure that the detrimental effects associated with the presence of impeller exit recirculation can be minimized.

Fuel economy has become an important consideration in forklift truck design, particularly in Europe. A simulation of the fuel consumption and performance of a forklift truck has been developed, validated and subsequently used to determine the energy consumed by individual powertrain components during drive cycles.The truck used in this study has a rated lifting capacity of 2500kg, and is powered by a 2.6 litre naturally aspirated diesel engine with a fuel pump containing a mechanical variable-speed governor. The drivetrain consisted of a torque convertor, hydraulic clutch and single speed transmission.AVL Cruise was used to simulate the vehicle powertrain, with coupled Mathworks Simulink models used to simulate the hydraulic and control systems and governor. The vehicle has been simulated on several performance and fuel consumption drive cycles with the main focus being the VDI 2198 fuel consumption drive cycle.To validate the model, a truck was instrumented and measurements taken to compare the performance and instantaneous fuel consumption to simulated values. The fuel injector pump was modified and calibrated to enable instantaneous fuel flow to be measured.The model has been validated to within acceptable limits and has been used to investigate the effect four different torque converters have on the fuel consumption and performance of the forklift truck. The study demonstrates how the model can be used to compare the fuel consumption and performance trade-offs when selecting drivetrain components.

The implementation of increasingly stringent emissions and efficiency targets has seen engine downsizing and other complementary technologies increase in prevalence throughout the automotive sector. In order to facilitate ongoing improvements associated with the use of these strategies, delivering enhancements to the performance and stability of the turbocharger compressor when operating at low mass flow rates is of paramount importance. In spite of this, a few concepts (either active or passive) targeting such aims have successfully transitioned into use in automotive turbochargers, due primarily to the requirement for a very wide compressor-operating range. In order to overcome the operational limitations associated with existing pre-swirl generation devices such as inlet guide vanes, this study developed a concept comprising of an electrically driven axial fan mounted upstream of a standard automotive turbocharger centrifugal compressor. Rather than targeting a direct contribution to compressor boost pressure, the fan was designed to act as a variable pre-swirl generation device capable of being operated completely independently of the centrifugal impeller. It was envisioned that this architecture would allow efficient generation of the large pre-swirl angles needed for compressor surge margin extension and efficiency enhancement at low mass flow rate-operating points, while also facilitating the delivery of zero pre-swirl at higher mass flow rates to ensure no detrimental impact on performance at the rated power point of the engine. Having progressed through 1-D and 3-D aerodynamic modelling phases to understand the potential of the system, detailed component design and hardware manufacture were completed to enable an extensive experimental test campaign to be conducted. The experimental results were scrutinized to validate the numerical findings and to test the surge margin extension potential of the device. Compressor efficiency improvements of up to 3.0% pts were witnessed at the target-operating conditions.