Interest in hydrogen-powered rail vehicles has gradually increased worldwide over recent decades due to the global pressure on reduction in greenhouse gas emissions, technology availability, and multiple options of power supply. In the past, research and development have been primarily focusing on light rail and regional trains, but the interest in hydrogen-powered freight and heavy haul trains is also growing. The review shows that some technical feasibility has been demonstrated from the research and experiments on proof-of-concept designs. Several rail vehicles powered by hydrogen either are currently operating or are the subject of experimental programmes. The paper identifies that fuel cell technology is well developed and has obvious application in providing electrical traction power, while hydrogen combustion in traditional IC engines and gas turbines is not yet well developed. The need for on-board energy storage is discussed along with the benefits of energy management and control systems.

The central aim of this paper is to provide an up-to-date snapshot of hybrid and hydrogen technology-related developments and activities in the North American heavy haul railway setting, placed in the context of the transportation industry more broadly. An overview of relevant alternative propulsion technologies is provided, including a discussion of applicability to the transportation sector in general and heavy haul freight rail specifically. This is followed by a discussion of current developments and research in alternative and blended fuels, discussed again in both general and specific settings. Key factors and technical considerations for heavy haul applications are reviewed, followed by a discussion of non-technical and human factors that motivate a move toward clean energy in North American Heavy Haul systems. Finally, current project activities are described to provide a clear understanding of both the status and trajectory of hybrid and hydrogen technologies in the established context.

In October 2018, Porterbrook and the University of Birmingham announced the HydroFLEX project, to demonstrate a hydrogen-hybrid modified train at Rail Live 2019. The concept of modifying a Class 319 Electric Multiple Unit was developed, with equipment including a fuel cell stack, traction battery, 24 V control system and hydrogen storage elements to be mounted inside one of the carriages. This was followed by procurement of a fuel cell stack, traction batteries, and control equipment, which was then installed inside the train, being fixed to the seat rails. One substantial change from the concept was the provision of considerably more hydrogen storage than the minimum necessary, providing the train with more potential to be further modified to allow for higher speed mainline testing. After the Rail Live exhibition where HydroFLEX was demonstrated, numerous modifications were performed to increase the reliability and power of the HydroFLEX train, primarily concerned with modifying the base train logic, with the aim of a successful mainline test. Supporting this effort was a multitude of documentation concerning safety, operations, and approvals to gain approvals from the relevant approvals bodies. The project demonstrated the feasibility of using hydrogen fuel cells as an autonomous fuel for railway propulsion systems, which has the potential for full decarbonisation.

Diesel fuel combustion results in exhaust containing air pollutants and greenhouse gas emissions. Many railway vehicles use diesel fuel as their energy source. Exhaust emissions, as well as concerns about economical, alternative power supply, have driven efforts to move to hydrogen motive power. Hydrogen fuel cell technology applied to railways offers the opportunity to eliminate harmful exhaust emissions and the potential for a low- or zero-emission energy supply chain. Currently, only multiple-unit trains with hydrail technology operate commercially. Development of an Integrated Hybrid Train Simulator for intercity railway is presented. The proposed tool incorporates the effect of powertrain components during the wheel-to-tank process. Compared to its predecessors, the proposed reconfigurable tool provides high fidelity with medium requirements and minimum computation time. Single train simulation and the federal government’s Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET^®) model are used in combination to evaluate the feasibility of various train and powertrain configurations. The Piedmont intercity service operating in North Carolina is used as a case study. The study includes six train configurations and powertrain options as well as nine hydrogen supply options in addition to the diesel supply. The results show that a hydrail option is not only feasible, but a low- or zero-carbon hydrogen supply chain could be possible.

Nowadays, the interest in hybrid vehicles is constantly increasing, not only in the automotive sector, but also in other transportation systems, to reduce pollution and emissions and to improve the overall efficiency of the vehicles. Although railway vehicles are typically the most eco-friendly transportation system, since commonly their primary energy source is electricity, they can still gain benefits from hybrid technologies, as many lines worldwide are not electrified. In fact, hybrid solutions allow ICE-powered (internal combustion engine) railway vehicles, such as diesel multiple units (DMUs), to operate in full-electric mode even when the track lacks electrification. The possibility to switch to full electric mode is of paramount importance when the vehicle runs on urban or underground track sections, where low or zero emission levels are required. We conduct the feasibility study of hybridization of an existing DMU vehicle, designed by Blue Engineering S.r.l., running on the Aosta–Torino Italian railway line, which includes a non-electrified urban track section and an electrified underground section. The hybridization is obtained by replacing one of the diesel generators installed on the original vehicle with a battery pack, which ensures the vehicle to operate in full-electric mode to complete its mission profile. The hybridization is also exploited to implement a regenerative braking strategy, which allows an increase in the energetical efficiency of the vehicle up to 18%. This work shows the sizing of the battery pack based on dynamic simulations performed on the Turin underground track section, and the results demonstrate the feasibility of the hybridization process.

Hybrid locomotive concepts have been considered as a step towards converting the railway industry into a green transport mode. One of the challenges in integrating a hybrid locomotive in the train consist is that the battery pack in the locomotive needs to be recharged during a long-haul trip which requires stopping of the train. A typical battery pack requires about 1 h to recharge which is unacceptable. With the improvement in the charging system, it is now possible that the same capacity battery pack could be recharged in 10–12 min which can be a competitive option for the railway companies. This paper proposes a method based on simulation to evaluate the positioning of charging stations on a train network. A typical example of a heavy haul train operation hauled by diesel-electric and hybrid locomotives is used to demonstrate the method by using simulation softwares. The result of the simulation study show that the method developed in this paper can be used to evaluate the state of charge (SoC) status of a hybrid locomotive along the track. It is also shown that the SoC status obtained by the simulation method can be further used to assess the positions of charging stations along the track at the design stage.

This paper proposes an energy management strategy for a fuel cell (FC) hybrid power system based on dynamic programming and state machine strategy, which takes into account the durability of the FC and the hydrogen consumption of the system. The strategy first uses the principle of dynamic programming to solve the optimal power distribution between the FC and supercapacitor (SC), and then uses the optimization results of dynamic programming to update the threshold values in each state of the finite state machine to realize real-time management of the output power of the FC and SC. An FC/SC hybrid tramway simulation platform is established based on RT-LAB real-time simulator. The compared results verify that the proposed EMS can improve the durability of the FC, increase its working time in the high-efficiency range, effectively reduce the hydrogen consumption, and keep the state of charge in an ideal range.

A near-term strategy to reduce emissions from rail vehicles, as a path to full electrification for maximal decarbonisation, is to partially electrify a route, with the remainder of the route requiring an additional self-powered traction option. These rail vehicles are usually powered by a diesel engine when not operating on electrified track and are referred to as bi-mode vehicles. This paper analyses the benefits of discontinuous electrification compared to continuous electrification using the CO₂ estimates from a validated high-fidelity bi-mode (diesel-electric) rail vehicle model. This analysis shows that 50% discontinuous electrification provides a maximum of 54% reduction in operational CO₂ emissions when compared to the same length of continuously electrified track. The highest emissions savings occurred when leaving train stations where vehicles must accelerate quickly to line speed. These results were used to develop a linear regression model for fast estimation of CO₂ emissions from diesel running and electrification benefits. This model was able to estimate the CO₂ emissions from a route to within 10% of that given by the high-fidelity model. Finally, additional considerations such as cost and the embodied CO₂ in electrification infrastructure were analysed to provide a comparison between continuous and discontinuous electrification. Discontinuous electrification can cost up to 56% less per reduction in lifetime emissions than continuous electrification and can save up to 2.3 times more lifetime CO₂ per distance electrified.