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Article

Hydrogen-Powered Engines: A Study on Selected Technological and Emissions Issues

by
Katarzyna Markowska
1,
Kamil Wittek
1,
Patrycja Kabiesz
2,*,
Kinga Stecuła
2,*,
Barış Aydın
3,
Szymon Pawlak
4 and
Agata Markowska
5
1
Faculty of Transport and Aviation Engineering, Silesian University of Technology, 44-100 Gliwice, Poland
2
Faculty of Organization and Management, Silesian University of Technology, 44-100 Gliwice, Poland
3
Department of Industrial Engineering, Manisa Celal Bayar University, Manisa 45140, Türkiye
4
Faculty of Materials Engineering, Silesian University of Technology, 44-100 Gliwice, Poland
5
Faculty of Mechanical Engineering, Military University of Technology, 00-908 Warsaw, Poland
*
Authors to whom correspondence should be addressed.
Energies 2025, 18(7), 1675; https://doi.org/10.3390/en18071675
Submission received: 17 February 2025 / Revised: 22 March 2025 / Accepted: 25 March 2025 / Published: 27 March 2025
(This article belongs to the Section A5: Hydrogen Energy)
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Abstract

:
With the growing trend towards the electrification of transport, it is anticipated that internal combustion engines will continue to play an important role in the production of electricity for electricity systems or the direct propulsion of vehicles. However, these engines are under considerable pressure to achieve carbon neutrality, making zero-emission fuels a key solution. One solution is the use of hydrogen, which is an extremely clean and carbon-free fuel whose combustion product is only water. The paper also introduces the KEYOU concept, which involves switching from burning propellant oil to a supercharged, lean-burn, hydrogen-fueled ignition engine. The authors provide a study on the selected issues based on 113 reviewed literature sources and highlight the achievements and potential of hydrogen engines. Based on the achievements described, the paper provides a comprehensive overview of the impact of hydrogen engines in reducing emissions as well as supporting the sustainable development of transport systems. The literature research conducted highlights hydrogen as an important solution for decarbonizing internal combustion engines and moving towards an emission-free future.

1. Introduction

The increasing demand for energy around the world and the rising cost of energy have prompted the intensification of research efforts aimed at reducing fuel consumption and reducing emissions of harmful substances into the atmosphere [1]. Additionally, the rapid depletion of conventional fossil fuel resources [2,3] influences the development of engines capable of using alternative energy sources [4,5,6]. The negative environmental impacts of burning fossil fuels, especially in the transportation sector, highlight the need to address these challenges [7,8]. Environmental protection and the need to reduce fossil fuel emissions are becoming increasingly important global priorities [9].
Therefore, renewable alternative fuels such as biofuels [10,11], natural gas [12], and hydrogen [13] are increasingly being promoted. Nevertheless, most of the energy is still obtained from exhaustible fossil fuels (gas, oil, coal), which account for over 90% of global energy demand [14,15,16,17].
Nowadays, environmental protection is crucial, and scientists are investigating alternative energy sources that could partially or completely replace fossil fuels. Alternative energy sources include methanol [18,19], gas [20,21], biogas [22,23,24] biodiesel [23], and hydrogen [25,26,27,28].
Hydrogen is the lightest and most common element in the universe. Hydrogen mainly forms chemical compounds by reacting with other elements. It is also considered a universal fuel due to its versatility and potential to be used, among others, in transport, for electricity production, and in the chemical industry [29,30,31].
However, despite its promise, adopting hydrogen as a mainstream energy source faces several significant challenges. One of the primary obstacles is the current cost of hydrogen production, which is still relatively high compared to traditional fossil fuels [32,33]. To fully realize hydrogen’s potential as a clean energy source, advancements in green hydrogen production—where hydrogen is generated using renewable energy sources through electrolysis—are essential [34,35]. Green hydrogen has the advantage of being carbon-neutral, but its cost-effectiveness is still under active research and development [36]. In addition to production challenges, the storage and transportation of hydrogen also pose technical and economic obstacles [37,38]. Additionally, there are issues connected with infrastructure, which is currently not sufficiently developed [39]. On the other hand, in the literature, there are already some solutions aimed at solving this problem [40,41]. Addressing these challenges will require coordinated efforts between governments, industries, and research institutions to develop innovative technologies and establish supportive policies and regulations.
One of the barriers encountered during the deployment of hydrogen vehicles is the infrastructure necessary for refueling hydrogen-powered vehicles. The lack of a developed network of hydrogen-refueling stations is a significant problem in the large-scale deployment of these vehicles. Despite growing interest in the development of hydrogen-refueling stations, this infrastructure is not adequately developed. The main problem is the high cost of building hydrogen stations and the difficulty in ensuring safety during hydrogen storage and distribution at these stations [5]. In urban agglomerations and along expressways, a large number of filling stations need to be built, which involves considerable investment and technological innovation.
Another barrier to the deployment of hydrogen vehicles is the availability of hydrogen vehicles in confined spaces, including underground car parks and garages. Hydrogen is a flammable gas and poses a risk in confined spaces without a specialized ventilation system, leak detection system, and appropriate safety measures [21]. It is therefore essential to develop safety protocols for the storage and use of hydrogen in confined spaces.
Another important challenge to consider when building hydrogen vehicles is the cost of building a hydrogen-powered internal combustion engine. The high construction cost is due to both the use of safety components required for the engine and auxiliary systems, as well as the on-board storage of hydrogen. One solution for on-board hydrogen storage is high-pressure tanks for gaseous hydrogen and a cryogenic system for liquid hydrogen, which require a high level of engineering expertise and specialized materials to manufacture, increasing production and operating costs [20,25]. Each of the hydrogen storage methods has advantages and disadvantages in terms of energy density, safety, and feasibility of implementation in vehicles. High-pressure tanks are often used, but require reinforced materials and advanced safety mechanisms. Liquid hydrogen has a higher energy density, but requires very low temperatures that cause energy losses during storage. Metal hydrides, on the other hand, which are in solid form, offer a promising alternative for safer and more compact storage, but their mass and hydrogen release rates need further refinement [26]. In addition, additional explosion-proof components and leak detection systems and pressure regulators are required to ensure driver and passenger safety in hydrogen cars, which generate costs. All of these factors add to the costs associated with the production of hydrogen cars and make them significantly higher than their conventional fossil fuel counterparts, which is an additional barrier to their widespread deployment.
One of the key factors influencing the development of hydrogen vehicles is a comparative analysis of the costs of different fuels. The cost of hydrogen needs to be compared with traditional fuels such as petrol, diesel, LPG (Liquefied Petroleum Gas), and CNG (Compressed Natural Gas). Nowadays, petrol and diesel are the most commonly used fuels due to their low cost and well-developed infrastructure. LPD and CNG have some cost advantages, especially in regions with favorable tax policies, but their use is still limited compared to conventional fuels. Hydrogen, on the other hand, has a much higher cost per unit of energy associated with its production, storage, and distribution [23]. Despite ongoing work to develop green hydrogen [12], as well as to improve hydrogen-refueling infrastructure, the economic viability of hydrogen is still under investigation. Removing hydrogen’s cost differentials to fossil fuels is key to promoting it and providing an alternative to fossil fuels.
Given the increasing popularity of hydrogen as an alternative energy source and its significant potential to address environmental challenges, the authors have decided to conduct a study on this matter. This study is based on literature sources. Hydrogen, often promoted as the fuel of the future, presents promising opportunities due to its abundance and generality across various sectors like transportation, power generation, and industrial processes [42,43]. Its ability to produce energy without emitting harmful pollutants makes it attractive for reducing fossil fuel reliance and mitigating climate change impacts [44,45]. This paper analyzes the current state of the advances, environmental benefits, and safety measures associated with hydrogen-powered internal combustion engines. It aims to contribute to the growing body of knowledge on hydrogen energy and hydrogen engines, supporting informed decision-making for policymakers, researchers, and industry professionals.

2. Materials and Methods

This paper aimed to gather important information on the design of hydrogen-powered engines. Based on the information collected, it was possible to describe the current state of knowledge about hydrogen engines. A historical and logical methodology was used to develop this publication, allowing the description of knowledge in the field of hydrogen engine construction through a logical sequencing of the development of hydrogen-powered engine structures.
The authors reviewed 113 sources which were scientific papers, conference proceedings, and also websites including new information about hydrogen technology and related issues. The authors analyzed publications indexed by Scopus and Google Scholar. The papers were searched for, based on several keywords, including the following: “hydrogen engine”, “hydrogen vehicles”, “hydrogen-powered engine”, “hydrogen-powered vehicles” and “hydrogen-fueled engine”. In this paper, the authors extensively searched for literature related to hydrogen energy used for vehicles, drawing on academic journals and conference proceedings. During the review process, the authors identified common themes, perspectives, and challenges emerging from the literature. The gathered material was then organized into thematic sections, such as characteristics of hydrogen-powered engines, selected hydrogen-powered engines used in commercial vehicles, KEYOU’s concept which involves switching from diesel combustion to a supercharged and lean-burn spark-ignition engine, emissions of exhaust constituents of hydrogen-fueled internal combustion engines, and safety measures related to the use of hydrogen as a fuel, to provide structure to the narrative. Figure 1 shows a research map that provides information on the links between the sources of information, methodologies used, and technological features of hydrogen-fueled engines.
The main objective of this paper is to provide an overview of the advances, environmental benefits, and safety measures associated with hydrogen-powered internal combustion engines.
The additional objectives of the paper include the following:
  • Examination of recent innovations in hydrogen-powered internal combustion engine technology, such as advanced injection systems and turbocharging techniques;
  • Analysis of the reduction in harmful emissions and the potential of hydrogen engines to meet stringent environmental standards;
  • Investigation of the unique properties of hydrogen fuel and the safety strategies required to mitigate the risks associated with its use.
The novelty and contribution of this paper are connected to the fact that this work provides a study of hydrogen engines, particularly their potential in emissions reduction and developing sustainable transportation systems. This study categorizes 113 sources and suggests a thematic analysis based on a structured approach, including hydrogen engine development, emissions reduction, and safety. Among the key new contributions is the lengthy discussion of the KEYOU concept, which deals with the transition from diesel to hydrogen-fueled internal combustion engines, demonstrating a viable pathway to the decarbonization of internal combustion engines. The article also offers an evaluation of the technological and economic challenges of hydrogen adoption, with significant implications for policymakers, researchers, and industry stakeholders. By including both opportunities and challenges, this paper integrates the understanding of hydrogen-fueled engines and their potential in future energy transitions. It is worth noting that using 113 literature sources provides unbiased and complex insights into the topic of hydrogen vehicles and the related issues.

3. Characteristics of Hydrogen-Powered Engine

Hydrogen engines are distinguished by a number of unique properties in relation to internal combustion engines. The properties that characterize hydrogen and commonly used hydrocarbon fuels are shown in Table 1.
The following properties are important with respect to the use of hydrogen as a fuel to power internal combustion engines [47,48,49,50]:
  • Wide flammability range;
  • Low ignition energy;
  • Short flame extinction distance at the wall;
  • High auto-ignition temperature;
  • High flame speed at stoichiometric ratio;
  • High diffusivity;
  • Very low density.
Hydrogen has a wide flammability range, which ranges from 4% to 75% by volume of fuel in air under standard conditions. We can distinguish the following types of hydrogen, presented in Figure 2.
Using hydrogen (H2) as a fuel, it is possible to increase the efficiency of internal combustion engines while reducing emissions to almost zero [52,53]. The use of hydrogen in combustion engines is itself a proven technology. Various car manufacturers (e.g., BMW, MAN, Ford, Mazda) have continuously explored the potential of hydrogen combustion until the last decade. However, due to various technical limitations, development in recent years has focused on combustion control and neglected the potential of efficiency and power density [54,55].
The method of ignition of the hydrogen–air mixture is a key differentiating factor for hydrogen-fueled internal combustion engines, as shown in Figure 3. Combustion initiation techniques in engines with an external power source mainly involve the use of an electrically induced spark, piloted diesel injection to initiate combustion, or achieving self-ignition through homogeneous compression ignition (HCCI) [56]. Where hydrogen is supplied directly to the combustion chamber, ignition is initiated by a glow plug, spark plug, or by piloted diesel injection [47,48].

4. Selected Hydrogen-Powered Engines Used in Commercial Vehicles

The first hydrogen-powered engine for use in city buses was the YCK16 hydrogen-powered engine with direct ejaculation launched in December 2021 [57]. Yuchai successfully launched China’s first hydrogen-powered engine for use in city buses and other lighter applications, the YCK05H. Following the completion of this engine platform, Yuchai began work on the YCK16H, a heavy-duty direct-injection hydrogen-powered engine. According to China Yuchai, this hydrogen-powered YCK16H engine was successfully operated in late June in Yulin, Guangxi. The YCK16H engine, with a capacity of 15.93 L and a maximum power of 560 horsepower, is said to be the largest hydrogen-powered engine in China in terms of capacity and power [58]. In December 2021, Yuchai launched China’s first hydrogen-powered engine, the YCK16H, characterized by the following:
  • A high-pressure common-rail direct-injection system into the cylinder combined with dual-channel turbocharging technology to achieve both homogeneous and stratified combustion;
  • A platform that is highly adaptable to different levels of fuel purity and can run on fuels prepared from gray hydrogen, green hydrogen, hydrogen produced from methanol, and other means;
  • The low power consumption per liter of hydrogen-powered engines, using a platform in the YC16H hydrogen-powered engine that has a particularly high power-to-weight ratio in its class when powered by diesel;
  • An engine control system and a high-performance air handling system that can achieve both equivalent stoichiometric combustion and lean combustion and can adjust fuel injection pressure and air intake volume for different fuels.
AVL Racetech, the motorsports division of AVL, has unveiled a hydrogen-powered internal combustion engine prototype of AVL concept cars.
The proposed hydrogen-powered internal combustion engine prototype features are as follows [59,60,61,62]:
  • It has a 2 L turbocharged engine;
  • It is equipped with what the company calls intelligent water injection, enabling high levels of performance;
  • The prototype is the first racing engine that AVL Racetech has developed and built in-house;
  • AVL’s racing engine uses only low poor combustion and achieves performance levels of around 150 kW per liter, unlike other hydrogen internal combustion engines, which tend to operate at high levels of excess air (low poor combustion), meaning they generate relatively less performance.
It should be noted that to achieve the engine’s high performance, AVL opted for water injection, a technique that was first used in improved aircraft engines during World War II. The injector shoots additional water into the intake stream, increasing the density of the charge. In addition, the water evaporates, providing a significant cooling effect in the combustion chamber. AVL notes that designing the necessary injectors and valves required a thorough understanding of the overall behavior of the system at all air, fuel, and exhaust flows, for which the company used its well-proven simulation models and 3D flow calculations [59,60,61,62]. Figure 4 shows hydrogen-powered engines, according to the KEYOU concept, for various applications.
KEYOU’s concept is to switch from diesel combustion to a supercharged and lean-burn spark-ignition engine. The uniqueness of H2 as a fuel enables efficient engine operation for air/fuel ratios as low as—λ = 5. KEYOU takes advantage of the unique combustion properties of hydrogen and proposes engine operation over the entire operating range, with excess air—λ > 1. Figure 2 shows NOx formation as a function of the air/fuel ratio. It can be seen that NOx formation (orange curve) approaches zero at λ > 2 for lean combustion. This propulsion strategy results in very low nitrogen oxide emissions (≤0.046 g/kWh), which are already well below the strict Euro 6 emission limits without an extensive aftertreatment system (Figure 5). This combustion, combined with innovative EGR control, efficiently prevents NOx formation [64].
Figure 5 is an illustration showing the various applications of hydrogen internal combustion engines (H2-ICE) in different types of vehicles and machines. This emphasizes the various applications of this type of vehicle. The purpose of presenting this figure is to raise awareness as usually the literature presents passenger cars powered by hydrogen. Hence, the figure is presented to raise the readers’ awareness about the multiple applications of hydrogen in vehicles. It is worth adding that H2-ICE engines require fine-tuning of all the systems, ensuring the best performance. It is necessary to perform precise calibration of the fuel injection systems, ignition timing, and air/fuel ratio control in order to maximize efficiency and minimize emissions.
Tuning all systems to ensure the best performance in hydrogen-fueled engines leads to the following [65,66,67,68,69]:
  • Radiator and valve: High performance of the radiator and precise control of the EGR stage.
  • Injection system: pressure and injectors: optimized H2 injection process for good mixture homogenization throughout the operating range.
  • Engine map strategy: controlling the quality and quantity of H2 dosage throughout the operating range along with EGR strategy.
  • H2 pressure control system: electronically adjustable pressure valve: accurate and fast flow control changes throughout the operating range.
  • Ignition system: ignition module and plugs: ignition voltage and energy adjusted according to ignition conditions.
  • Timing system: valves and valve seats made of special materials for maximum durability, because H2 has no lubricating properties.
  • Piston junction system: piston and rings to ensure high mixture homogenization and avoid abnormal combustion and low lubricating oil penetration.
  • Supercharging system: turbocharger: special requirements due to the low enthalpy of the exhaust gas for high supercharging and high torque; + E-supercharging.
  • Exhaust aftertreatment system: simple (SCR), efficient, low cost.
Beyond road transport, hydrogen can also be treated as an important fuel in other key transportation sectors, such as marine, railway, and aviation sectors. In the marine industry, hydrogen fuel cells and ammonia–hydrogen blends are being explored as sustainable alternatives to traditional marine fuels (which are a major source of carbon emissions). Some projects, such as the development of hydrogen-powered ferries in Norway [70,71,72], Denmark [73], Sweden [74], and Japan [75], highlight the potential for clean maritime transport. However, there are still many challenges, such as hydrogen storage, infrastructure development, and fuel supply chains. These are critical areas for further research.
Similarly, hydrogen trains are already being deployed in countries like Germany and France, where fuel-cell-powered locomotives provide a zero-emission alternative to diesel trains on non-electrified railways. This is particularly relevant for Poland and other countries with extensive railway networks that are still partially reliant on fossil fuels. Germany will eliminate diesel trains by 2038 [76] and the United Kingdom by 2040 [77]. Research into hydrogen-refueling stations, cost-effective fuel cell systems, and operational efficiency will be crucial to scaling up hydrogen rail transport.
In the aviation sector, hydrogen is also being considered for next-generation aircraft propulsion, with companies like Airbus actively developing hydrogen-powered airplane concepts [78]. While technological advancements in hydrogen storage and combustion are needed, this could change long-distance and cargo flights by significantly reducing aviation emissions.

5. KEYOU’s Concept—Switching from Diesel Combustion to a Supercharged and Lean-Burn Spark-Ignition Engine

With an innovative proprietary technology concept that is suitable for commercial vehicle engines, this technology is also applicable to passenger car engines. The aforementioned concept involves the use of intelligent lean combustion with exhaust gas recirculation (EGR), turbocharging, and efficient injection; KEYOU is once again turning its attention to the hydrogen combustion engine and showing how powerful, efficient, and clean engines of the future can be [64].
The hydrogen engine concept offers many economic and environmental advantages over other propulsion technologies [79,80,81,82,83]:
  • In line with the CO2 emission limit for commercial vehicles, the European Union has classified the hydrogen-powered internal combustion engine as a “zero-emission vehicle”. This enables manufacturers of traditional engines and existing technologies in the existing production infrastructure to meet the new stringent CO2 emission requirements and toxic component standards for the commercial vehicle sector, providing an attractive alternative to electric vehicles and fuel cells.
  • In hydrogen-powered engines, exhaust aftertreatment systems are less extensive than in conventional internal combustion engines. The smaller number of components leads to a significant reduction in the cost of the end product.
  • Supercharged hydrogen-fueled engines achieve higher power and torque compared to conventional spark-ignition and compression-ignition engines.
  • The environmental performance of hydrogen-fueled internal combustion engines is greater than that of other types of propulsion. The technology is also sustainable and clean, as it does not consume rare earth elements, and above all, far fewer (toxic) raw materials are required for production.

6. Emissions of Exhaust Constituents of Hydrogen-Fueled Internal Combustion Engines

Unlike hydrocarbon fuel engines, hydrogen engines do not release significant amounts of compounds such as carbon monoxide (CO), hydrocarbons (HC), carbon dioxide (CO2), and sulfur oxide (SOx) into the atmosphere [84]. A hydrogen-powered engine mainly emits water vapor as a result of total combustion, resulting from a reaction that synthesizes hydrogen and oxygen from the atmosphere delivered to the combustion chamber [85,86]. Exhaust from hydrogen engines may also include trace amounts of hydrocarbons and carbon oxides, resulting from the combustion of lubricating oil in the combustion chamber [87,88].
However, in a well-engineered hydrogen-fueled engine, only a small fraction of the oil layer is combusted. The exhaust gas composition, under specific conditions, may include slight amounts of hydrogen peroxide or molecular hydrogen not involved in the combustion process. Nonetheless, hydrogen molecules on their own do not demonstrate toxic properties nor contribute to pollution; hence, H2 does not significantly pose any issue within the overall framework of environmental degradation [89]. The release of NOx emissions resulting from the combustion process is influenced by various factors, with λ being the predominant one [90,91]. The stratification of the hydrogen and air mixture significantly affects the characteristics of NOx emissions. Therefore, a necessary condition for establishing a fundamental correlation between λ and NOx emissions is the presence of an external hydrogen fuel injection system (PFI), which creates a homogeneous mixture [92]. The excess air ratio λ is crucial for NOx emissions, as it increases the propagation velocity and flame temperature during combustion of the hydrogen–air mixture. NOx emissions are virtually absent at λ greater than about 2 and show a mild increase in the range 1.8 < λ < 2, but increase sharply below these values, reaching a maximum value at excess air ratios in the range λ = 1.1 to 1.3 [91,92,93]. When a hydrogen engine is fueled with a rich mixture, minimal amounts of NOx are still present in the exhaust gas, even at near-zero oxygen levels in the combustion chamber, due to inhomogeneities in mixture composition and temperature distribution. NOx emissions decrease with a decrease in λ [82]. The compression ratio and speed of the hydrogen engine also affect NOx emissions [94]. With poor mixtures above the NOx threshold (λ > ~2.2), there is no need for any exhaust aftertreatment method. The use of appropriate operating strategies and exhaust aftertreatment systems, while maintaining high energy efficiency, enables the hydrogen engine to operate with minimal emissions over the entire load and speed range [85].
Another important issue that must be discussed is the control of the combustion rate. This significantly affects efficiency, performance, and emissions [95]. Hydrogen’s high flame speed can lead to premature ignition and knocking which needs advanced control strategies [96]. The use of hydrogen blends, such as hydrogen–ammonia mixtures [97,98], has been proposed to moderate combustion rates and improve engine stability. Further research is needed to explore optimal fuel blends, injection timing adjustments, and innovative ignition systems to ensure safe and efficient hydrogen engine operation. Analyzing and facing these aspects will be crucial for the adoption of hydrogen as a sustainable fuel.

7. Safety Measures Related to the Use of Hydrogen as a Fuel

The use of hydrogen as a fuel for internal combustion engines only poses a potential risk if not properly supervised or used incorrectly. However, due to its unique properties, which differ significantly from traditional hydrocarbon fuels, hydrogen can be seen as a potentially safer fuel unless exceptional circumstances arise [99,100]. The risks associated with the use of hydrogen are essentially due to the properties of this fuel and therefore require an appropriate approach when developing a safety strategy. In the event of a potential leak, hydrogen, due to its low molecular weight compared to air, diffuses rapidly into the environment [101,102]. Additionally, when a leak occurs, hydrogen, due to its lightness in relation to air, spreads quickly, making it difficult to detect and control. To prevent this and reduce the risk of fire or explosion, it is necessary to use specialized equipment and safety procedures [103].
Although the hydrogen–air mixture has a wide flammability range, its practical importance is marginal. The key factor for the risk of ignition in a hydrogen leak is the lower flammability limit. The risk of hydrogen deflagration, despite the low energy required for ignition, depends on a number of factors, such as fuel concentration, temperature, as well as the shape and characteristics of the space in which the hydrogen is contained. At the same time, hydrogen leaks into the environment have a minimal chance of detonation [104]. The lower flammability limit for hydrogen is 18.3% by volume, which means that for deflagration to occur, concentrations higher than this value are necessary once an ignition source has occurred, which is a relatively rare occurrence [105]. In practice, it is difficult to prevent every potential ignition source from occurring when using a hydrogen vehicle, so to increase safety, hydrogen sensors have been used to detect hydrogen leaks and reduce hydrogen concentration [80,105,106].
Additionally, advancements in technology and safety protocols are continuously improving the safety of hydrogen-powered engines. Modern hydrogen storage systems are designed with robust materials and are rigorously tested to withstand extreme conditions, significantly reducing the risk of leaks [107,108]. Furthermore, ongoing research focuses on developing more efficient hydrogen detection systems [109,110] and improving ventilation in storage and usage areas [111] to swiftly disperse any leaked hydrogen. These advancements, coupled with comprehensive safety training for personnel handling hydrogen, contribute to creating a safer environment for the deployment of hydrogen as a fuel in internal combustion engines. The integration of these safety measures ensures that hydrogen can be utilized effectively and securely, paving the way for its broader adoption as a sustainable and clean energy source.

8. Conclusions

This paper presents the results of the study on the topic of hydrogen-powered engines. It examines the growing research efforts aimed at reducing fuel consumption and harmful emissions, driven by the rapid depletion of conventional fossil fuel resources and the negative environmental impacts associated with their combustion. Renewable alternative fuels such as biofuels, natural gas, and hydrogen are increasingly promoted, although fossil fuels still dominate global energy demand. Among these alternatives, hydrogen stands out due to its unique properties and potential applications in various sectors, including transportation, electricity production, and the chemical industry.
Internal combustion engines, powered by conventional hydrocarbon fuels, are now a key source of propulsion in the areas of transportation and industry. Equally significant amounts of energy are consumed on the propulsion of motor vehicles or machinery, which globally are almost exclusively dependent on fossil fuels. As a result, GHGs are emitted into the atmosphere. GHGs have negative effects on the environment and human health. However, due to the increasing temperature due to anthropogenic impact on global warming, air pollution, and overexploited hydrocarbon fuel deposits, there is an increased need to search for an alternative, ecological, and sustainable means of energy source, especially as the demand for hydrocarbon fuels is steadily increasing alongside economic development [81,112,113]. In the current decade, hydrogen-based technologies will be increasingly used not only in road transport, but also in other transport sectors. The use of hydrogen as an energy source does not necessarily imply the end of the age of the internal combustion engine, allowing a transition period for this type of propulsion. Continued research into hydrogen-fueled reciprocating engines could lead to their widespread use in industry.
The paper also highlights recent advancements in hydrogen-powered engines, such as the YCK16H engine in China, which showcases high adaptability to different fuel purities and innovative technologies like dual-channel turbocharging and high-pressure direct injection. Additionally, AVL Racetech has developed a hydrogen-powered internal combustion engine prototype featuring intelligent water injection to enhance performance. KEYOU’s approach involves transitioning from diesel to a supercharged and lean-burn spark-ignition engine, leveraging hydrogen’s unique combustion properties to achieve low nitrogen oxide emissions and high efficiency.
Hydrogen-powered engines offer numerous economic and environmental advantages over traditional technologies. They are classified as “zero-emission vehicles” by the European Union, reducing the need for extensive exhaust aftertreatment systems and lowering production costs. Furthermore, hydrogen engines emit mainly water vapor, significantly reducing the release of harmful pollutants compared to hydrocarbon fuel engines.
The paper also addresses safety measures related to hydrogen use, emphasizing the need for specialized equipment and procedures to manage potential risks such as leaks and ignition. Hydrogen’s rapid diffusion and low flammability limits contribute to its relatively safe profile when properly managed.
However, despite the great potential for the deployment of hydrogen cars, there are many challenges to the widespread implementation of the technology. One of the main problems is the lack of refueling infrastructure, which is critical for the large-scale introduction of hydrogen cars. The current number of hydrogen-refueling stations is severely limited, and a large amount of investment is required to expand the global infrastructure that will support hydrogen cars in cities and along highways. In addition, hydrogen distribution and storage infrastructure, which is linked to the development of safe and efficient systems for transporting hydrogen to refueling stations, is a key challenge.
Furthermore, the use of hydrogen cars in confined spaces such as underground car parks and garages is limited. Hydrogen is flammable and specialized safety measures, including ventilation systems and leak detection technologies, are required to ensure the safe use of hydrogen cars in closed environments. The development of these technologies and the implementation of safety standards are key to the adoption of hydrogen cars.
The topic of hydrogen engines has numerous research directions for the future. Research should be conducted not only in the theoretical sphere but, above all, in the practical and implementation sphere as hydrogen creates opportunities towards sustainable development and contributes to a cleaner environment. Further research should be focused on the increase in the efficiency of hydrogen engines by optimizing combustion processes and reducing emissions. Advanced ignition systems and adaptive fuel injection techniques, as well as hybridization with electric systems, are also important research topics that can significantly improve performance and benefit the environment. What is more, one key topic for future research will be the development of cost-effective methods for producing and storing hydrogen, such as green hydrogen from renewable sources.
In conclusion, hydrogen-powered internal combustion engines present a viable and sustainable alternative to traditional fossil fuels, offering significant environmental benefits and aligning with global priorities for reducing emissions and protecting the environment. The continued development and optimization of hydrogen technologies are crucial for achieving cleaner and more efficient energy solutions in the future.

Author Contributions

Conceptualization, K.M., K.W., P.K., K.S., B.A. and A.M.; methodology, K.M., K.W., P.K., K.S., S.P. and A.M.; software, K.M., K.W., P.K., K.S. and A.M.; validation, K.M., P.K. and K.S.; formal analysis, K.M., K.W. and K.S.; investigation, K.M., K.W., P.K., K.S. and S.P.; resources, K.M., K.W., P.K. and K.S.; data curation, K.M.; writing—original draft preparation, K.W., P.K., K.S. and B.A.; writing—review and editing, K.W., P.K., K.S. and B.A.; visualization, K.M., K.W., P.K., K.S. and S.P.; supervision, K.M.; project administration, K.M.; funding acquisition, K.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding. The publication of this paper was financed by Silesian University of Technology.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Research map of the hydrogen engine review.
Figure 1. Research map of the hydrogen engine review.
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Figure 2. Types of hydrogen. Source: authors’ own work based on [51].
Figure 2. Types of hydrogen. Source: authors’ own work based on [51].
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Figure 3. Overview of ignition methods for hydrogen–air mixtures. Source: authors’ own work based on [47,48].
Figure 3. Overview of ignition methods for hydrogen–air mixtures. Source: authors’ own work based on [47,48].
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Figure 4. Hydrogen-powered engines, by KEYOU concept, for various applications. Own work based on [63].
Figure 4. Hydrogen-powered engines, by KEYOU concept, for various applications. Own work based on [63].
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Energies 18 01675 g005
Figure 5. Hydrogen-powered engines for various applications. Source: authors’ own work.
Figure 5. Hydrogen-powered engines for various applications. Source: authors’ own work.
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Table 1. Summary of properties that characterize fuels for internal combustion engines [46].
Table 1. Summary of properties that characterize fuels for internal combustion engines [46].
PropertiesH2CH4C8H18C8H20
Carbon content [wt%]0758486
Calorific value [MJ/kg]119.745.843.942.5
Density (1 bar, 273 K) [kg/m3]0.0890.72730–780830
Volumetric energy content (1 bar, 273 K) [MJ/m3]10.73333,00035,000
Molecular weight [g/mol]2.01616.043~110~170
Boiling point [K]20111298–488453–633
Minimum ignition energy in air (1 bar, stoichiometric mixture) [mJ].0.020.290.240.24
Stoichiometric fuel/air mass ratio [wt.]34.4:117.2:114.7:114.5:1
Flame extinction distance at the wall (1 bar, 298 K, stoichiometric mixture) [mm]0.642.1~2–
Propagation velocity of laminar flame in air (1 bar, 298 K, stoichiometric mixture) [m/s]1.850.380.37–0.430.37–0.43
Diffusion coefficient in air (1 bar, 273 K) [m2/s]8.5 × 10−61.9 × 10−6––
Flammability limits in air [vol%]4–765.3–151–7.60.6–5.5
Adiabatic flame temperature (1 bar, 298 K, stoichiometric mixture) [K]248022142580~2300
Octane number (RON)130+120+86–94–
Cetane number––13–1740–55
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Markowska, K.; Wittek, K.; Kabiesz, P.; Stecuła, K.; Aydın, B.; Pawlak, S.; Markowska, A. Hydrogen-Powered Engines: A Study on Selected Technological and Emissions Issues. Energies 2025, 18, 1675. https://doi.org/10.3390/en18071675

AMA Style

Markowska K, Wittek K, Kabiesz P, Stecuła K, Aydın B, Pawlak S, Markowska A. Hydrogen-Powered Engines: A Study on Selected Technological and Emissions Issues. Energies. 2025; 18(7):1675. https://doi.org/10.3390/en18071675

Chicago/Turabian Style

Markowska, Katarzyna, Kamil Wittek, Patrycja Kabiesz, Kinga Stecuła, Barış Aydın, Szymon Pawlak, and Agata Markowska. 2025. "Hydrogen-Powered Engines: A Study on Selected Technological and Emissions Issues" Energies 18, no. 7: 1675. https://doi.org/10.3390/en18071675

APA Style

Markowska, K., Wittek, K., Kabiesz, P., Stecuła, K., Aydın, B., Pawlak, S., & Markowska, A. (2025). Hydrogen-Powered Engines: A Study on Selected Technological and Emissions Issues. Energies, 18(7), 1675. https://doi.org/10.3390/en18071675

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