A First Principles Model-Based Study of Fuel Cell Gas Turbine Hybrid Power Sources for Transport Applications

Abstract

There are multiple types of power sources that can contribute to decarbonising transport including the adoption of battery electric vehicles (BEVs), fuel cell electric vehicles (FCEVs), hybrid FC-battery systems, hybrid gas turbine (GT)-battery systems, and Fuel Cell-Gas Turbine (FC-GT) hybrid systems. Each option has its advantages and challenges. Battery-only systems can provide zero emissions at the point of use but are limited by battery weight, energy density, and charging infrastructure. Fuel Cell-only systems can deliver clean energy with quick refuelling but may face challenges with hydrogen storage and infrastructure. Hybrid FC-Battery systems combine the benefits of both technologies, providing improved range and efficiency, but have very low power and energy density. GT-Battery systems can offer high power density but have lower efficiency than FC systems. Fuel Cell-Gas Turbine (FC-GT) systems combine the high efficiency of fuel cells with high power density and load following ability of gas turbines, making them suitable for applications where long range and high power are required. This study presents a First Principles Model-Based analysis FC-GT Hybrid Power Sources for Transport Applications, aiming to address the urgent need for sustainable energy solutions in the transportation sector. The research focuses on Proton Exchange Membrane Fuel Cells (PEMFC) and Solid Oxide Fuel Cells (SOFC), exploring their potential integration with gas turbines to enhance electrical efficiency and reduce carbon emissions. PEMFCs, known for their operation below boiling point and high power density, have great potential as propulsive and auxiliary power sources in road and air transport. The electrical efficiency of a PEMFC can be improved by pressurising its air stream. Typically, this is done by a motor-driven compressor which draws power from the PEMFC and therefore reduces its usable power output. This parasitic loss can be reduced by the addition of a turbine at the PEMFC outlet that is driven by the fuel cell’s exhaust gases and assists the compressor motor. Such a system is called a “Turbocharged PEMFC”. SOFCs, which operate at high temperatures (500°C to 900°C) and high efficiency, are examined for their suitability in creating highly efficient propulsive power sources in marine and rail transport, as well as long-endurance air transport. The SOFC can be added to a Brayton cycle between the compression and combustion stages where fuel cell receives pressurised air from the compressor and the unutilised fuel from the SOFC is burned in the combustor. FC-GT systems show good potential in various transport applications: • Aviation: Both PEMFCs and SOFCs are considered for auxiliary power units (APUs) and potentially for primary propulsion in long endurance UAVs. • Road Transport: PEMFCs are considered for use in passenger vehicles, buses, and trucks, where their high power density and quick refuelling capabilities provide significant advantages. • Marine: SOFCs are explored for use in ships, where their high efficiency and ability to utilise various fuels such as methanol and ammonia can significantly reduce emissions. • Rail: SOFCs are also considered for trains, offering a cleaner alternative to diesel engines, especially for long-distance routes. Beyond transport applications, FC-GT systems can also be used for stationary power generation for residential and industrial power generation, with SOFC-GT systems showing especially great potential in combined heat and power generation. However, the design considerations for stationary power and transport applications are different. For stationary applications, efficiency, longevity, and integration with existing infrastructure get the most emphasis and they can be larger and heavier. Transport applications require greater focus on factors like weight, volume, fuel storage, and dynamic load-following capabilities. These systems must be robust, reliable, and capable of operating under varying conditions. The design and development FC-GT system for transport applications is therefore more challenging as there are more design constraints and performance targets to meet. Modelling and simulation-based design plays an important role in making this challenging process quicker and more cost-effective. The document details the development of agile, fast-solving models for simulating these hybrid systems in various transport applications. It begins with a literature review to identify optimal system configurations and proceeds with the design and implementation of these models. The performance of turbocharged PEMFC and SOFC-GT systems is analysed, demonstrating their potential to significantly contribute to the decarbonisation of the energy and transport sectors. The study also delves into the challenges associated with hybrid system development, including thermal management, system integration, and the optimisation of operating parameters. These challenges can be tackled through analytical models based on first principles. Through analytical modelling and simulation studies, the research offers insights into the capabilities of FC-GT systems, providing recommendations for future work in the field. This project sets a foundational step towards establishing an FC-GT research lab at the University of Hertfordshire, aiming to propel the design and optimisation of concepts and operating strategies for sustainable transport solutions. By addressing both technical and environmental challenges, the research underscores the potential of FC-GT hybrid systems in revolutionising power sources for transportation and other sectors, aligning with global decarbonisation goals.