Civil aviation provides an essential transportation network that connects the world and supports global economic growth. To maintain these benefits while meeting environmental goals, next-generation aircraft must have drastically reduced climate impacts. Hydrogen-powered aircraft have the potential to fly existing routes with no carbon emissions and reduce or eliminate other emissions. This paper is a comprehensive guide to hydrogen-powered aircraft that explains the fundamental physics and reviews current technologies. We discuss the impact of these technologies on aircraft design, cost, certification, and environment. In the long term, hydrogen aircraft appear to be the most compelling alternative to today’s kerosene-powered aircraft. Using hydrogen also enables novel technologies, such as fuel cells and superconducting electronics, which could lead to aircraft concepts that are not feasible with kerosene. Hydrogen-powered aircraft are technologically feasible but require significant research and development. Lightweight liquid hydrogen tanks and their integration with the airframe is one of the critical technologies. Fuel cells can eliminate in-flight emissions but must become lighter, more powerful, and more durable to make large, fuel cell-powered transport aircraft feasible. Hydrogen turbofans already have these desirable characteristics but produce some emissions, albeit much less damaging than kerosene turbofans. Beyond airframe and propulsion technologies, the viability of hydrogen aircraft hinges on low-cost green hydrogen production, which requires massive investments in the energy infrastructure. 

Hydrogen-powered aircraft: Fundamental concepts, key technologies, and environmental impacts

Evidence of an emerging focus on the role of farmer knowledge in developed countries is highlighted by the debate on the nature of local and scientific knowledge. Less attention has been paid to the interaction of different ways of knowing for sustainable capital-intensive agriculture. This paper explores the relationship between local and scientific knowledge in managing temperate pasture and grazing systems in Australia. The nature of farmer knowledge is firstly examined by describing the experiences of farm families in managing native and introduced perennial grasses in upland areas of the Murray-Darling Basin. The building of knowledge and skills through social learning was explored in group case studies and interviews with stakeholders involved in pasture research and development. The interchange of local and scientific knowledge in groups was shown to have a synergistic effect, whereby local knowledge was broadened and strengthened, and scientific knowledge adapted and molded to specific situations. The effectiveness of social learning was greatest in collaborative programs based on small, local groups involved in monitoring and evaluation of whole farm pasture and grazing systems.

Challenging the boundaries of local and scientific knowledge in Australia: Opportunities for social learning in managing temperate upland pastures

Sustainable aviation is a key part of achieving Net Zero by 2050, and is arguably one of the most challenging sectors to decarbonise. Hydrogen has gained unprecedented attention as a future fuel for aviation, for use within fuel cell or hydrogen gas turbine propulsion systems. This paper presents a survey of the literature and industrial projects on hydrogen aircraft and associated enabling technologies. The current and predicted technology capabilities are analysed to identify important trends and to assess the feasibility of hydrogen propulsion. Several key enabling technologies are discussed in detail and gaps in knowledge are identified. It is evident that hydrogen propelled aircraft are technologically viable by 2050. However, convergence of a number of critical factors is required, namely: the extent of industrial collaboration, the understanding of environmental science and contrails, green hydrogen production and its availability at the point of use, and the safety and certification of the aircraft and supporting infrastructure. 

A review of liquid hydrogen aircraft and propulsion technologies

of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy TECHNOLOGY DISSEMINATION AMONG SMALL-SCALE FARMERS IN MERU CENTRAL DISTRICT OF KENYA: IMPACT OF GROUP PARTICIPATION By Kristin Elizabeth Davis August 2004 Chair: Nick Place Cochair: Peter Hildebrand Major Department: Agricultural Education and Communication The goal of this study was to examine the role of farmer groups in technology dissemination, and to assess what factors make groups effective in extending technologies among small-scale dairy-goat farmers in Meru Central District of Kenya. The theoretical framework for the study included insight from agricultural extension theory, farming systems research and extension, social capital, and group theory. A mixed-methods, multiple-stage approach was used to obtain data. Research techniques included participant observation, documentary analysis, semi-structured interviews, social mapping, group timelines, and structured questionnaires. Dairy-goat farmer groups (n = 46) and individual farmers (n = 88) were interviewed during the study. Qualitative data provided baseline information, and helped in the formation of research questions. Quantitative data were entered into the Statistical Package for Social

http://ipcc-wg2.gov/njlite_download.php?id=5484

Technology dissemination among small-scale farmers in meru central district of kenya: impact of group participation

The paper investigates the multi-actor processes of knowledge co-production in the implementation of research-based on-farm demonstration with a focus on collaboration arrangements and areas of con...

https://www.tandfonline.com/doi/pdf/10.1080/1389224X.2021.1953551

Knowledge production and communication in on-farm demonstrations: putting farmer participatory research and extension into practice

A fuel cell—gas turbine hybrid propulsion concept is introduced and initially assessed. The concept uses the water mass flow produced by a hydrogen fuel cell in order to improve the efficiency and power output of the gas turbine engine through burner steam injection. Therefore, the fuel cell product water is conditioned through a process of condensation, pressurization and re-vaporization. The vaporization uses the waste heat of the gas turbine exhaust. The functional principles of the system concept are introduced and discussed, and appropriate methodology for an initial concept evaluation is formulated. Essential technology fields are surveyed in brief. The impact of burner steam injection on gas turbine efficiency and sizing is parametrically modelled. Simplified parametric models of the fuel cell system and key components of the water treatment process are presented. Fuel cell stack efficiency and specific power levels are methodically derived from latest experimental studies at the laboratory scale. The overall concept is assessed for a liquid hydrogen fueled short-/medium range aircraft application. Block fuel savings of up to 7.1% are found for an optimum design case based on solid oxide fuel cell technology. The optimum design features a gas turbine water-to-air ratio of 6.1% in cruise and 62% reduced high-level NOx emissions.

https://www.mdpi.com/2226-4310/9/2/68/pdf?version=1644313190

Initial Assessment of a Fuel Cell—Gas Turbine Hybrid Propulsion Concept

It is argued that the transfer-of-technology model of research and development is not sufficient to bring about the most effective relationship between stakeholders in agricultural and environmental matters in Australia. An alternative approach is described and trialed which involves changing the process of extension and research by introducing new thinking and a qualitative methodology called Rapid Rural Appraisal (RRA). The paper describes the process of training a multi-disciplinary team to conduct an RRA with irrigated horticulture farmers. Some results of both the RRA survey and an evaluation exercise conducted on the research team's experience and learning outcomes are presented.

Changing paradigms for farmer-researcher-extensionist relationships: exploring methods and theories of farmer participation in research

In order to achieve aviation’s ambitious emission reduction targets specified by ACARE [1] radical changes in propulsion system concepts will be necessary. To fulfill the goal of carbon dioxide emission neutrality in 2050 and beyond, plenty propulsion system concepts are currently under investigations, mainly focusing on batteries and hydrogen as energy source. Especially for long range aircraft applications, hydrogen might by favorable due to its outstanding specific gravimetric energy density. Therefore, the Composite Cycle Engine (CCE) concept should be evaluated for hydrogen combustion. In a first step, the applied time resolved 0D piston engine performance simulation model of the CCE is adapted for hydrogen combustion. For example, the heat transfer and combustion characteristics of kerosene and hydrogen combustion differ significantly and require specific modeling approaches. The current publication illustrates the piston engine performance simulation model and the modifications needed to account for hydrogen combustion. Furthermore, results of validation case calculations as well as initial sensitivity studies of the hydrogen fueled piston engines model are presented and discussed in the CCE context. For example, sizing effects and the influence of valve timing on piston engine performance will be evaluated.

Piston Engine Modelling for Hydrogen Fueled Composite Cycle Engines

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Initial Assessment of a Fuel Cell—Gas Turbine Hybrid Propulsion Concept

Changing paradigms for farmer-researcher-extensionist relationships: exploring methods and theories of farmer participation in research

Piston Engine Modelling for Hydrogen Fueled Composite Cycle Engines