Exploring the potential of ammonia and hydrogen as alternative fuels for transportation

1 Introduction

The global transportation industry is included in contributing to greenhouse gas emissions, making up around 24% of CO₂ emissions worldwide [1]. This highlights the need for environmentally friendly transportation solutions to enhance air quality and tackle climate change issues. Two promising alternatives in this area are hydrogen and ammonia fuels, which offer the potential to decrease greenhouse gas emissions while effectively addressing air pollution concerns [2]. Hydrogen fuel emerges as an option that can be generated using renewable sources such as solar, wind, or hydropower. Key production methods include steam methane-reforming (SMR) and water-splitting reactions with processes such as water electrolysis [3,4,5]. Notably, fuel cells linked with hydrogen generate only water molecules as a byproduct, rendering them highly efficient and suitable for diverse applications ranging from emergency backup systems to land-based vehicles such as cars [6]. Similarly, ammonia showcases high energy density potential and a carbon-free composition, making it particularly valuable for transportation-related energy solutions. Ammonia can be produced by combining molecular nitrogen with hydrogen derived from renewable sources, thereby circumventing the need for gasoline or diesel fuels [7,8]. Recent research initiatives exploring energetic applications for ammonia and hydrogen as transportable energy sources have uncovered immense positive potential across various societal domains [2,5,9–11]. However, realizing the full potential of hydrogen and ammonia as alternative transportation fuels requires overcoming several challenges, including issues surrounding storage and utilization capacity due to hyper-reactivity-associated molecule configurations [12–14]. Despite these hurdles, hydrogen, often touted as the “fuel of the future,” remains a subject of intense research interest. Fuel cells utilizing hydrogen offer an efficient conversion process, producing clean energy with water vapor as the sole byproduct [15]. Continued development efforts hold promise for increasing efficiencies and robustness, potentially making mass production more cost-effective [16]. Furthermore, immense possibility is exploring how hydrogen can become a feasible form of transport particularly through fuel cell electric vehicles (FCEVs) [17].

Balasubramanian et al. delved into the properties of hydrogen as an alternative fuel source discussing its applications and challenges. The research provides an analysis of facets of hydrogen, including production methods, storage techniques, and its integration, into energy systems. They highlight discoveries about hydrogen properties, its ability to store a lot of energy, and its positive impact on the environment. The study also stresses the significance of factors such as storing and distributing hydrogen to use it as a fuel. In summary, this research provides insights into how hydrogen behaves and its role in transitioning to sustainable energy sources. It suggests areas for exploration and advancement in this field [18]. In another research paper by Mladenova et al., the focus was on developing electrocatalysts based on Ni and Co for air electrodes without carbon in zinc air batteries. The researchers conducted experiments and analyses to showcase how these electrocatalysts effectively improve the performance and efficiency of zinc air batteries. These catalysts demonstrated activity aiding in crucial processes such as oxygen–reduction reaction and oxygen evolution reaction necessary for battery function. Additionally, they exhibited stability and durability across operational conditions suggesting their viability for the real-world use in environmentally friendly energy storage systems. The study underscores the importance of advancing materials such as Ni and Co-based electrocatalysts to drive the shift toward energy technologies [19].

This study delves into examining different aspects essential for using hydrogen and ammonia as alternative fuels for the transportation sector, particularly in understanding their environmental impacts. While the advantages of these fuels, such as emissions reduction and environmental benefits, are widely recognized, specific technical methods and challenges require further elucidation. Through a review of cutting-edge research and progress, this article aims to offer insights into the feasibility and consequences of transitioning to hydrogen and ammonia fuels for transportation. By exploring production techniques, energy efficiency, infrastructure needs, and potential uses, this study seeks to provide valuable insights into considerations and possible obstacles. Furthermore, it endeavors to highlight the contributions and innovations of the proposed research within the community while addressing concerns about the clarity of its contributions.

2 Methodology

To gain an understanding of the aspects and implications of using hydrogen and ammonia as transportation fuels, a thorough review of relevant literature was conducted. Then, research articles, reports, and data from sources that covered aspects such as production methods, energy density, environmental impact, infrastructure requirements and potential applications were carefully gathered. After gathering the data, we analyzed it meticulously to extract insights and identify trends related to hydrogen and ammonia as transportation fuels. Also, the information about production costs, energy densities, emission profiles, efficiency levels, and advancements in fuel cell and combustion technologies was obtained. A significant part of our methodology involved performing an analysis between hydrogen and ammonia versus fossil fuels and other alternative energy sources. We evaluated factors such as cost-effectiveness, energy content, potential emissions reduction capabilities, infrastructure compatibility, and technological readiness. To evaluate the impact of adopting hydrogen and ammonia as transportation fuels, scenario modeling techniques were used. Based on adoption rates, production methods, and policy interventions, situations were made to estimate potential reductions, in emissions improvements in energy security and economic implications. Figure 1 illustrates the methodology phases for this research. It is crucial to note that this research heavily depended on existing literature and data sources, which may introduce biases or gaps. Furthermore, since alternative energy technologies are constantly evolving, some data points may become outdated or subject, to change.

Figure 1

Methodology flowchart.

3 Hydrogen

Hydrogen is not naturally available in its pure form and must be generated from hydrogen-containing compounds. Currently, around 6% of the overall energy demand is allocated to the production of hydrogen in various industries [20]. Figure 2 illustrates the different routes and possibilities for hydrogen production and the subsequent use of hydrogen-based products. To illustrate, the cost of producing hydrogen using natural gas varies from 0.5 to 1.7 USD/kg. However, when renewable sources are employed, the cost significantly increases to approximately 3–8 USD/kg [21]. The primary method for generating hydrogen through thermochemical conversion is via oil and coal. Meanwhile, SMR is recognized as the most widely adopted approach. Currently, around 70 million tons of hydrogen is produced annually using natural gas, representing roughly 75% of the global hydrogen production [22].

Figure 2

Possible methods for manufacturing hydrogen and products based on hydrogen.

4 Ammonia

Ammonia possesses alkaline properties, is colorless, and exhibits a fairly potent odor. Through a techno-economic analysis, it has been determined that ammonia is the most cost-effective fuel when compared to conventional options such as gasoline, natural gas, liquefied petroleum gas, methanol, and hydrogen [23]. Ammonia production and its use processes in the energy sector are shown in Figure 3 [24].

Figure 3

Ammonia production and use processes in the energy sector.

Ammonia is frequently generated through the Haber–Bosch process, which was created in the early 1900s and continues to be used today, despite its high expenses and energy requirements. The process involves combining nitrogen (N₂) and molecular hydrogen (H₂) using iron-based catalysts at higher temperatures ranging from 400 to 500°C and pressures reaching up to 300 bar [25].

5 Production and applications

Ammonia and hydrogen possess distinct properties that make them attractive as transportation fuels. Ammonia is non-toxic, readily available, and has a high energy density. On the other hand, hydrogen is the lightest element, providing high energy content per unit weight. Both can be produced through various methods, including electrolysis of water, renewable energy sources, and SMR.

To generate hydrogen fuel and ammonia fuel using energy to split water, it is necessary to employ the process known as water splitting. This method involves using a photocatalyst to convert energy into chemical energy in the form of clean and renewable hydrogen fuel [26]. Solar water splitting has attracted attention for its ability to convert energy into usable fuel. By harnessing power, water can be divided into hydrogen and oxygen through photoelectrochemical reactions offering a promising route for sustainable fuel production [27]. Solar water splitting and nitrogen fixation are at the forefront of hydrogen and ammonia synthesis, providing eco-energy efficient alternatives to production methods such as SMR and the Haber–Bosch process. These approaches operate at room temperature and atmospheric pressure, making them energy-efficient choices [28]. The simple process of producing hydrogen through water splitting allows for the transformation of energy into various forms such as ammonia for transportation and storage. The photocatalytic splitting of water plays a role in fuel production by facilitating the generation of hydrogen fuel from sunlight and water [29]. This procedure is a component of photosynthesis, with the goal of transforming energy into energy-dense chemical fuels such as hydrogen [30]. The partnership between semiconductor photocatalysts in the process of water splitting has garnered attention from researchers, for generating eco-friendly and renewable hydrogen fuel [31].

Understanding the properties and production methods is crucial in evaluating the viability of ammonia and hydrogen as alternative fuels. Hydrogen may be used as fuel for internal combustion engines, rockets, ammonia synthesis, and new power-generating technologies [32].

Significant advancements in fuel cell technology and powertrain systems have expanded the potential applications of ammonia and hydrogen in transportation. FCEVs using hydrogen have also gained traction in recent years, offering zero-emission mobility. Ammonia, with its high energy density, is being explored as a hydrogen carrier where it can be converted back to hydrogen for use in fuel cells or combustion engines. To fully realize the promise of ammonia and hydrogen as alternative fuels, research and development activities are concentrated on enhancing the effectiveness, robustness, and affordability of these technologies [33]. Looking beyond just transportation applications, it becomes clear that ammonia holds great promise for our future in regard to successful energy storage solutions. Through its use in powering various types of industry while also serving as a reliable source of renewable energy carrier material, this compound offers vast versatility and the potential for highly efficient electricity management systems. All factors considered when striving toward sustainability make the option of using ammonia one that is both wise and forward thinking [34]. Still, remarkable improvements are underway in the field of hydrogen and ammonia utilization for transportation purposes. The diligent work from talented scientists accompanied by engineering experts has led us toward advanced materials technology breakthroughs. These advancements optimize fuel cell performance while further enhancing productivity triggered by better efficiency in electrolysis systems together with ammonia synthesis processes [35].

Hydrogen fuels pose a combustion challenge due to their high flammability, which can lead to difficulties in controlling the ignition process, resulting in issues such as pre-ignition and detonation [36]. The use of hydrogen in various applications, such as fuel cells and energy production, has been a subject of extensive research, highlighting the importance of understanding the production and application processes of hydrogen-based technologies [37]. Furthermore, studies on the transformation of the nitrogen cycle and its potential solutions have been explored, emphasizing the role of reactive nitrogen in agriculture and environmental science [38]. Research on the production and applications of amylose-lipid complexes as resistant starch has provided insights into recent approaches for enhancing starch properties and applications [39].

The research article, by Yang et al. [26], discusses the roles of cocatalysts in photocatalysis and photoelectrocatalysis focusing specifically on reactions involving water splitting. Water splitting is a process that involves the transfer of electrons. The study highlights how cocatalysts play a role in enabling photocatalytic and photoelectrocatalytic water-splitting reactions, which are vital for sustainable energy generation. By explaining the functions of cocatalysts in these processes, the research contributes to enhance our knowledge of energy conversion mechanisms.

On the other hand, the research by Kobayashi et al. [40] delved into the aspects and technological advancements related to combustion. Ammonia combustion is a subject due to its potential as an energy carrier. The study likely explores aspects such as the combustion behavior of ammonia, its efficacy as a fuel source, and the environmental impacts associated with using ammonia for energy purposes. Understanding the science and technology behind combustion is essential for unlocking its potential, as an ecofriendly energy alternative. This research sheds light on both the challenges and opportunities linked to using ammonia as a fuel option.

6 Supplementary fuels for future

Hydrogen production and applications have gained significant attention as a sustainable energy source for the future, with a focus on enhancing energy efficiency and reducing environmental impact [41].

Hydrogen-based fuel cells are currently present in many industries, including public transit systems and commercial fleet companies. However, ammonia is soon catching up as a better option for transporting energy with low emissions. Not only do these green technologies help reduce carbon footprint but also bring apparent operational advantages like reducing noise pollution levels with increased durability, ultimately leading toward a smoother transport experience. In upcoming years, we can expect an accelerated shift toward using hydrogen and ammonia-based alternatives on the roads [42].

With mounting concern about climate change arising on a global scale mainly due to human made factors such as CO₂ emissions from automobiles, we must pivot toward cleaner transportation solutions such as utilizing alternatives like hydrogen fuel. Hydrogen’s’ efficient energy content coupled with zero emissions when used in fuel cells makes it an excellent promising choice for green mobility today. Compared to battery-powered electric automobiles, FCEVs fueled by hydrogen have greater driving ranges with shorter refilling times. This presents an opportunity for a better experience in transportation [43,44]. Additionally, ammonia is emerging as a potential fuel option for long-distance trips due to its high energy density, and it is easily converted into hydrogen for use in fuel cells [1]. Incorporating these alternative fuels represents essential strides toward reducing global greenhouse gas emissions contributing to climate change while using efficient energy sources exhibiting no harmful emissions. As we work toward planet restoration and environmentally sound actions, hydrogen infrastructure is consistently growing daily outside the status quo from battery-powered electric cars. Refueling stations and hydrogen charging stations are establishing worldwide, countries such as Japan, Germany, and the United States lead this infrastructure [45]. Experts expect that around one out of 12 cars will run on hydrogen by 2030, comprising major markets such as Germany, Japan, South Korea, and the United States, leading clean transport solutions soon-representing only an initial step forward combining green technology with industry’s developmental efforts [46,47]. Moreover, several trucks could adopt hydrogen engine option enabling transporting goods with dramatically reduced carbon footprint for a cleaner tomorrow. Furthermore, trains transporting passengers without affecting air quality or ships without harming marine life represent sustainable transport goals worth achieving today [46,47]. Hydrogen and ammonia-based fuel cell technologies continue to evolve through sustained investment in research and development by the automotive industry. The focus at present remains squarely centered on improving its efficiency, performance as well as cost-effectiveness while supporting its reliability. With ongoing efforts aimed at bringing these solutions to commercialization realization, it seems likely that their prospects will continue rising steadily upward [48,49]. In the meanwhile, governments and regulatory bodies are also providing support and incentives for the adoption of hydrogen and ammonia as transportation fuels. Financial incentives, research funding, and policy frameworks are being implemented to promote the development and deployment of these alternative fuel technologies [50].

The persistent growth of CO₂ emissions and the implications for achieving climate targets have underscored the urgency of transitioning to cleaner energy sources [51]. Automatic mechanism generation for the combustion of advanced biofuels, such as diethyl ether, has paved the way for innovative approaches to sustainable fuel production [52]. Machine learning-based observation-constrained projections have revealed elevated global socioeconomic risks from wildfires, emphasizing the need for proactive measures to address future challenges [53]. Radical transformation pathways toward sustainable electricity have been explored, highlighting the importance of evolving energy systems to meet future demands [54]. A near-term to net-zero alternative to the social cost of carbon has been proposed, offering insights into setting carbon prices and transitioning to a low-carbon economy [55]. Net emission reductions from electric cars and heat pumps in various world regions over time have been analyzed, showcasing the potential of electrification in reducing greenhouse gas emissions [56]. Insights into the electrocatalytic CO₂ reduction in aprotic media have provided valuable information on sustainable energy production and utilization [57]. Temporally explicit abiotic depletion potential for mineral resource use has shed light on the future demand for resources and the importance of sustainable resource management [58]. The value of fast transitioning to a fully sustainable energy system has been highlighted, emphasizing the benefits of rapid adoption of renewable energy technologies [59]. Divestment strategies prevailing over the green paradox have shown the effectiveness of financial decisions in driving sustainable energy transitions [60]. Fe cycle sustainability assessment of alternative energy sources for the Western Australian transport sector has provided insights into the economic and environmental implications of transitioning to renewable energy sources [61]. Renewable energy for sustainable development in developing countries has been recognized as a key driver for environmental protection and economic growth.

Based on the reviews, wide-scale adoption of hydrogen and ammonia as transportation fuels will depend on productive cooperation among academia, industry stakeholders including businesses involved in the production of these fuels, as well as governmental agencies regulating them. Fuel cell technology advancements along with infrastructure development will make such a transition increasingly smooth through joint endeavors such as public–private partnerships or research collaborations between research and development teams globally. Overcoming technical difficulties inherent in adopting cleaner methods of transport will also require sustained knowledge from all participants’ aspect.

7 Economic and environmental benefits

Traditional transportation fuels, which are mostly sourced from fossil fuels, have been a major cause of pollution in the environment. These fuels, which include diesel and gasoline, have been connected to emissions of greenhouse gases and air pollution, among other types of pollution [62]. In addition to releasing pollutants into the environment directly, burning fossil fuels emits greenhouse gases such as CO₂ that also have a role in climate change [63]. The depletion of fossil fuel resources exacerbates the environmental effect, underscoring the need for cleaner and more sustainable energy sources [64]. The use of conventional transportation fuels has resulted in a number of environmental problems, such as air pollution, which puts people’s health at serious danger, especially in metropolitan areas [63]. Particulate matter, nitrogen oxides, and volatile organic compounds are among the pollutants released during the burning of these fuels. These pollutants have been connected to respiratory illnesses as well as other health issues [63]. Furthermore, the use of fossil fuels in transportation raises the risk of smog and other dangerous pollutants that destroy ecosystems and lower air quality [65].

The need to switch to greener and more sustainable transportation fuels is becoming more demanding, in order to solve the environmental problems caused by conventional fuels. One potential substitute that can assist in lowering environmental pollution linked to conventional fossil fuels is hydrogen fuel [62], which burns cleanly and produces no toxic emissions [65]. In a similar vein, biofuels produced from renewable resources, such as biomass, have drawn interest as a more environmentally friendly substitute for conventional fossil fuels that can help lower pollution and greenhouse gas emissions [66].

Finally, the current state of environmental contamination resulting from conventional transportation fuels emphasizes the necessity of shifting to greener and more sustainable energy sources. It is feasible to reduce the environmental effect of transportation and move toward a more sustainable future by moving away from fossil fuels and toward alternatives such as biofuels and hydrogen fuel.

Hydrogen and ammonia show immense potential in minimizing our reliance on fossil fuels as well as mitigating associated price volatility positively across many economies today. As more people transition toward using solar or wind-powered electricity generation globally, there will be a significant increase in producing hydrogen or ammonia from these widely available renewable energy resources. Recent studies indicate that renewable-produced hydrogen could soon compete favorably with fossil fuels by 2030 [67]. There is much promise for less-expensive methods of producing ammonia too [68]. The sustainable production of these two resources is dominant, as worldwide demand for nitrogen-based fertilizers continues to surge. Future energy applications have great promise for green ammonia, which is produced by air, water, and renewable energy resources [69,70]. Valuable characteristics such as its non-flammable properties and buoyant traits make it an attractive chemical resource useful in many economies of the future. Its versatility allowing extraction from various sources including renewable energy or even nuclear power generation waste adds to its favorable appeal [71]. Hydrogen presents itself prominently because of having no carbon content besides having a high rate of flame propagation supported by being broadly flammable. These advantageous characteristics are incredibly promising in developing clean combustion systems surpassing older alternatives [72]. Described as alternative transportation fuels primarily due to their greenhouse gas emissions reducing potential during combustion, both ammonia and hydrogen yield minimal harmful gases depending on production methods followed closely by green ammonia manufacture that alleviates carbon capture tech use [73]. To ensure long-term success while minimizing environmental impact through final evaluation entails analyzing sustainability, life cycle environmental impacts, as well as the carbon footprint. In evaluating potential solutions for reducing global levels of greenhouse gas emissions, researchers have taken keen interest in thoroughly studying all possibilities. A noteworthy study, undertaken by the International Energy Agency (IEA), found that incorporating hydrogen and fuel cell technologies into transportation has the capacity to bring about a significant drop borne out over time. The IEA surmises that this technology could cut down on those emissions as much as 20% globally before we reach the year 2050 [74]. Meanwhile, yet another research analysis argues clearly in favor of using ammonia to replace traditional diesel in transport systems, which could result in emissions reductions on the order of 97% [75]. Additionally, using hydrogen and ammonia as transportation fuels could make a significant difference in combating local air pollution. These fuels have superiority over conventional ones, since under the specific conditions, they do not emit any particulate matter or nitrogen oxides (NO_x) on burning [76]. Encouraging a wide-scale use of such sustainable resources for mobility purposes could potentially improve overall urban environmental conditions and ensure better public health outcomes by minimizing exposure to harmful toxins associated with air pollutions. In summary, the use of ammonia and hydrogen fuels offers enviable advantages ranging from reduced carbon footprint usage, contributing toward establishing cleaner overall environmental health via low-level emissions and longer uncompromising ranges to build sound economic prosperity for present and future generations.

8 Challenges and limitations

The use of hydrogen and ammonia as fuels in the transportation sector is accompanied by benefits and challenges. Although these fuels offer advantages such as zero emissions and improved energy efficiency, several obstacles must be overcome for their widespread adoption. One major challenge is the need to develop infrastructure for the production, storage, and distribution of hydrogen and ammonia [77]. Existing infrastructure mainly caters to fossil fuels, presenting a considerable monetary and temporal burden in adapting or constructing new infrastructure for these alternative fuels. Hydrogen offers cleaner combustion and zero tailpipe emissions through fuel cells, but it faces infrastructure challenges. Ammonia has advantages in terms of storage and transportation but requires addressing NO_x emissions and toxicity concerns. In addition, hydrogen and ammonia have lower energy densities than traditional fuels, which may hinder their adaptability in certain transportation scenarios due to larger storage systems required [78,79]. The production process remains another limitation, as most hydrogen is currently sourced from fossil fuels undermining its environmental impact goal. While electrolysis fueled by renewable energy can generate hydrogen from water, it requires scalability improvements along with cost-effective measures. Similarly, the generation of ammonia has heavily relied on natural gas leading to emission greenhouse gases [80].

Safety standards also require regarding handling hazardous gases such as hydrogen and ammonia, both of which highly flammable and necessitating specialized system approaches vital for safety. Development of strict safety protocols through regulatory frameworks serves a critical role in mitigating potential risks related to their handling. Due to their low energy density and high flammability, the safest method of storing hydrogen is widely recognized to be solid-state storage in porous materials and hydrides [81–85]. The use of ammonia presents several challenges due to its unique characteristics. Ammonia has a notably lower heating value compared to other hydrocarbons. Its narrow range of equivalence ratio, spanning from 0.63 to 1.4, and high auto-ignition temperature contribute to its low flammability. Compared to hydrogen, methane, and propane, ammonia has a lower adiabatic flame temperature of 1,800°C (as opposed to 2,110, 1,950, and 2,000°C, respectively). Ammonia, as a result, displays decreased radiation heat transfer, which is essential during combustion and heat transfer processing. Furthermore, ammonia has a significantly lower maximum laminar burning velocity of 0.07 m/s, in contrast to methane (0.37 m/s), propane (0.43 m/s), and hydrogen (2.91 m/s) [24]. Additionally, vehicle performance running on these innovative fuels may pose limitations – where although there has been progress made using hydrogen fuel cells, durability advancements, cost reduction measures, and efficiency remain imperative needs. Driving sustainable production methods yields implications that host significant decarbonization opportunities shaping the future of transportation sector.

Besides the production, transportation, and storage limitation, still some other obstacles exist at using hydrogen and ammonia at internal combustion engines as an independent fuel. Without modifications to the combustion system and crankcase, ordinary engines cannot run on hydrogen due to changes in chemical characteristics and fuel/air ratios. For this, a number of automakers have developed hydrogen-powered direct-fuel prototypes [86].

Due to the limitations of hydrogen’s flammability as well as the tremendous temperature and pressure created during combustion, the material for this type of engine was carefully chosen. Additionally, certain spark plugs were developed for hydrogen systems to prevent pre-ignition. Creating an engine fueled entirely by hydrogen’s unique properties presents some significant hurdles that must be overcome successfully before its implementation can occur effectively. One major obstacle presents itself through low energy per unit volume resulting from its lower density. Thus, larger storage tank requirements may become necessary than most modern-day fuel sources [87]. Additionally, hydrogen fuels present a combustion challenge due to their high flammability that sometimes makes it difficult to maintain adequate control of the ignition process leading to issues such as pre-ignition and detonation [88,89]. This problem gets compounded by the elements incredibly fast laminar flame speed that requires taking measures aimed at minimizing combustion flame build-up while still regulating it to achieve optimal combustion processes [90]. The difficulty is often intensified by hydrogen’s short quenching distance, causing flames to travel closer toward cylinder walls than desirable before extinguishing. This issue further leads to lubricant evaporation effects and affects combustion results adversely [87,89]. Furthermore, involving hydrogen-based fuels would require addressing other unique characteristics such as its high diffusivity level posing difficulties in stratifying fuel–air mixtures accurately [91]. Hydrogen fuel use causes an increase in NO_x emissions resulting in reduced power output for hydrogen-based engines. While some research has occurred concerning NO_x emissions, air-to-fuel ratio relationships and spark timing around these engines’ limitations exist concerning experimental analysis [92,93]. Therefore, it is necessary for designing engines intended explicitly for use with hydrogen by identifying different aspects such as accurately predicting flame initiation through studying chemical properties, such as laminar flame speed and ignition delay time regarding hydrogen combustion processes [94]. Moreover, proper gas injection systems are required for accurate measurements concerning the amount of fuel delivered, while selecting suitable ignition systems becomes essential in reducing the risks associated with autoignition related to particular fuel mixture from hydrogen fuel properties [95]. Finally, simulating oil–fuel dilution effectively reduces particulate formation during combustion processes [94].

The market study of hydrogen sensors and sensing systems highlights the need for further development and exploration of sensor technologies, especially in smaller industries facing challenges such as cost limitations and lack of personnel to handle sensors [96]. The sector coupling concept faces economic feasibility challenges due to uncertain future developments of competing solutions [97]. The use of ammonia as a fuel also poses some challenges that need to be overcome, in terms of both production process optimization and combustion in internal combustion engines [98]. The challenges of future internal combustion engines, including CO₂ reduction and dual-fuel combustion, underscore the need for technological advancements to address climate change and energy needs [99]. The transition of the transportation sector toward sustainability through hydrogen fuel faces challenges in commercialization and scalability, requiring significant technological advancements [100]. The challenges of future nuclear power lie in the development of safer and more efficient nuclear reactor designs [101]. The synthesis and processing of multi-metallic nanoparticles in fuel cell technology serve as an intriguing way to address challenges in catalysis and efficiency [102]. The enzymatic approach to biodiesel production highlights challenges in downstream processing costs and environmental impacts, driving the search for alternative production methods and substrates. Determining the air quality and greenhouse gas impacts of hydrogen infrastructure and ECEVs is crucial in addressing challenges related to pollutant emissions and air pollution [103].

9 Discussion

Our research explores the potential of hydrogen and ammonia as fuel options for transportation aiming to address the issue of climate change and decrease greenhouse gas emissions in the worldwide transportation industry. By conducting an analysis that includes reviewing existing literature examining production methods and exploring uses, we offer valuable insights into the technical demands and environmental impacts associated with transitioning to transport systems based on hydrogen and ammonia. We highlight how using sources such as solar, wind, or hydropower for fuel production could help reduce dependence on fuels and promote a more environmentally friendly energy sector. Additionally, our examination demonstrates the versatility and effectiveness of hydrogen in FCEVs as a clean energy solution for different transport needs. Meanwhile, ammonia shows promise as an alternative fuel option due to its energy density and compatibility with infrastructure despite facing challenges related to NO_x emissions and toxicity issues.

Comparing our findings with existing studies confirms the advantages and energy efficiency gains of using hydrogen and ammonia. Furthermore, our research introduces perspectives on the viability and scalability of adopting these fuels. We emphasize the significance of investing in infrastructure development and technological advancements to address implementation hurdles highlighting the importance of collaboration, among institutions, industry players, and government bodies. Table 1 shows a comparison summary of fossil fuels versus hydrogen and ammonia.

While our research makes contributions to the discussion on transportation fuels, it is important to note that there are limitations. These include relying on existing data sources and the possibility of biases in how we reviewed the literature. However, by presenting an analysis of our findings comparing them with existing studies discussing the implications and acknowledging both strengths and limitations, we aim to deepen understanding of the advantages and challenges related to using hydrogen and ammonia in transportation.

Carbon neutral fuels present options for transportation offering the potential to reduce impact and decrease reliance on limited fossil fuel resources. However, it is crucial to evaluate their practicality in terms of cost-effectiveness and efficiency when compared to fuels. To address this issue, it is necessary to make a comparison between carbon traditional fuels. Although traditional fuels are commonly used, they come with challenges related to emissions, performance, and noise in diesel engines [104]. The research conducted by Biswas and Mukhopadhyay examines the effectiveness of injection strategies in enhancing emissions control, performance optimization, and noise reduction in diesel engines.

Moreover, understanding the dynamics of combustion processes and safety considerations is essential for assessing both carbon fuels. Zhong et al. [105] explored flame propagation characteristics during gas explosions under conditions to gain insights into combustion behavior and safety implications. By combining insights from these studies, a comprehensive comparison can be made between carbon fuels while considering factors such as emissions levels, performance metrics, noise generation patterns, combustion properties, and safety aspects. This comparative analysis provides a picture of the state and future potential of carbon neutral fuels, within the transportation industry and contribution to automotive and combustion science.

The transition to new fuels involves a mix of realities, potentials, challenges, and promising. It is crucial to grasp these elements for making plans in the energy and transportation fields.

• Reality: currently, the landscape of fuels is marked by research efforts to reduce environmental impact, decrease reliance on limited fossil fuel resources, and tackle sustainability issues. Despite progress in these areas, the widespread acceptance and commercialization of fuels are still at a stage due to significant challenges related to infrastructure, regulations, and economics.

• Potential: despite existing hurdles, new fuels offer potential to transform the energy sector. Zero emission options such as hydrogen and ammonia opportunities for friendly transportation solutions by using renewable energy sources and cutting-edge technologies. Moreover, advancements in fuel efficiency, performance enhancement, and emissions control avenues for promoting sustainability and driving socio-progress.

• Challenges: embracing fuels on a scale comes with numerous obstacles. Addressing barriers such as energy conversion efficiency, infrastructure development, and storage capacities is crucial for unlocking the benefits of alternative fuels. Additionally, factors such as feasibility, policy frameworks, and public acceptance are influencers in determining the direction of fuel transitions. Meeting these obstacles head on requires cooperation, among business and governmental entities.

• Promising: despite the difficulties, the advantages of fuels are significant. Apart from helping the environment, they present chances for creativity, job growth, and energy stability. By supporting research, investments, and policy-making, communities can unlock the capabilities of fuels and pave the way to a sustainable and robust energy future.

By tackling hurdles and seizing emerging opportunities, stakeholders can navigate toward a more sustainable energy landscape.

Our research highlights the potential of hydrogen and ammonia as fuel options for transportation. This has implications, beyond discussions. It also impacts societal and environmental aspects. By considering economic and environmental factors, we hope to guide decision-making processes and shape policies that promote cleaner energy solutions in transportation. Ultimately, this contributes to initiatives aimed at addressing climate change and supporting development.

10 Conclusion

In summary, this research underscores the importance of studying hydrogen and ammonia as fuels for transportation. The study delves into existing literature and technological advancements to provide an understanding of the feasibility and implications of transitioning to energy options in the transportation industry. The results emphasize the advantages of using hydrogen and ammonia such as reducing greenhouse gas emissions and enhancing energy efficiency while also tackling challenges related to production methods, storage solutions, and deployment considerations. It emphasizes the need for research and development efforts to overcome these obstacles for the adoption of these fuels. The study also acknowledges its limitations by highlighting the necessity for investigation into aspects and socio-economic factors during the transition to alternative fuels. Future studies could focus on refining production techniques, improving infrastructure, and implementing policy measures to promote transportation fuels. By recognizing its contribution and suggesting directions, for research, this study aims to guide policymakers, researchers, and industry stakeholders in their endeavors to combat climate change and enhance air quality through alternative fuel adoption.