Applications & Pathways

Integrating carbon capture and storage (CCS) technology into an integrated energy system (IES) can reduce its carbon emissions and enhance its low-carbon performance. However the full CCS of flue gas displays a strong coupling between lean and rich liquor as carbon dioxide liquid absorbents. Its integration into IESs with a high penetration level of renewables results in insufficient flexibility and renewable curtailment. In addition integrating split-flow CCS of flue gas facilitates a short capture time giving priority to renewable energy. To address these limitations this paper develops a carbon capture utilization and storage (CCUS) method into which storage tanks for lean and rich liquor and a two-stage power-to-gas (P2G) system with multiple utilizations of hydrogen including a fuel cell and a hydrogen-blended CHP unit are introduced. The CCUS is integrated into an IES to build an electricity–heat–hydrogen–gas IES. Accordingly a deep low-carbon economic optimization strategy for this IES which considers stepwise carbon trading coal consumption renewable curtailment penalties and gas purchasing costs is proposed. The effects of CCUS the twostage P2G system and stepwise carbon trading on the performance of this IES are analyzed through a case-comparative analysis. The results show that the proposed method allows for a significant reduction in both carbon emissions and total operational costs. It outperforms the IES without CCUS with an 8.8% cost reduction and a 70.11% reduction in carbon emissions. Compared to the IES integrating full CCS the proposed method yields reductions of 6.5% in costs and 24.7% in emissions. Furthermore the addition of a two-stage P2G system with multiple utilizations of hydrogen further amplifies these benefits cutting costs by 13.97% and emissions by 12.32%. In addition integrating CCUS into IESs enables the full consumption of renewables and expands hydrogen utilization and the renewable consumption proportion in IESs can reach 69.23%.

This paper presents a method for estimating Well-to-Wheel (WTW) energy use and greenhouse gas (GHG) emissions attributed to the advanced railway propulsion systems implemented in conjunction with different energy carriers and their production pathways. The analysis encompasses diesel-electric multiple unit vehicles converted to their hybrid-electric plug-in hybrid-electric fuel cell hybrid-electric or battery-electric counterparts combined with biodiesel or hydrotreated vegetable oil (HVO) as the first and second generation biofuels liquefied natural gas (LNG) hydrogen and/or electricity. The method is demonstrated using non-electrified regional railway network with heterogeneous vehicle fleet in the Netherlands as a case. Battery-electric system utilizing green electricity is identified as the only configuration leading to emission-free transport while offering the highest energy use reduction by 65–71% compared to the current diesel-powered hybrid-electric system. When using grey electricity based on the EU2030 production mix these savings are reduced to about 27–39% in WTW energy use and around 68–73% in WTW GHG emissions. Significant reductions in overall energy use and emissions are obtained for the plug-in hybrid-electric concept when combining diesel LNG or waste cooking oil-based HVO with electricity. The remaining configurations that reduce energy use and GHG emissions are hybrid-electric systems running on LNG or HVO from waste cooking oil. The latter led to approximately 88% lower WTW emissions than the baseline for each vehicle type. When produced from natural gas or EU2030-mix-based electrolysis hydrogen negatively affected both aspects irrespective of the prime mover technology. However when produced via green electricity it offers a GHG reduction of approximately 90% for hybrid-electric and fuel cell hybrid-electric configurations with a further reduction of up to 92–93% if combined with green electricity in plug-in hybrid-electric systems. The results indicate that HVO from waste cooking oil could be an effective and instantly implementable transition solution towards carbon–neutral regional trains allowing for a smooth transition and development of supporting infrastructure required for more energy-efficient and environment-friendly technologies.

The imperative to address traditional energy crises and environmental concerns has accelerated the need for energy structure transformation. However the variable nature of renewable energy poses challenges in meeting complex practical energy requirements. To address this issue the construction of a multifunctional large-scale stationary energy storage system is considered an effective solution. This paper critically examines the battery and hydrogen hybrid energy storage systems. Both technologies face limitations hindering them from fully meeting future energy storage needs such as large storage capacity in limited space frequent storage with rapid response and continuous storage without loss. Batteries with their rapid response (90%) excel in frequent short-duration energy storage. However limitations such as a selfdischarge rate (>1%) and capacity loss (~20%) restrict their use for long-duration energy storage. Hydrogen as a potential energy carrier is suitable for large-scale long-duration energy storage due to its high energy density steady state and low loss. Nevertheless it is less efficient for frequent energy storage due to its low storage efficiency (~50%). Ongoing research suggests that a battery and hydrogen hybrid energy storage system could combine the strengths of both technologies to meet the growing demand for large-scale long-duration energy storage. To assess their applied potentials this paper provides a detailed analysis of the research status of both energy storage technologies using proposed key performance indices. Additionally application-oriented future directions and challenges of the battery and hydrogen hybrid energy storage system are outlined from multiple perspectives offering guidance for the development of advanced energy storage systems.

The automotive industry is under increasing pressure to develop cleaner and more efficient technologies in response to stringent emission regulations. Hydrogenpowered internal combustion engines represent a promising alternative offering the potential to reduce carbon-based emissions while improving efficiency. However the accurate estimation of in-cylinder pressure is crucial for optimizing the performance and emissions of these engines. While traditional simulation tools such as GT-POWER are widely utilized for these purposes recent advancements in artificial intelligence provide new opportunities for achieving faster and more accurate predictions. This study presents a comparative evaluation of the predictive capabilities of GT-POWER and an artificial neural network model in estimating in-cylinder pressure with a particular focus on improvements in computational efficiency. Additionally the artificial neural network is employed to predict the equivalent flame radius thereby obviating the need for repeated tests using dedicated high-speed cameras in optical access research engines due to the resource-intensive nature of data acquisition and post-processing. Experiments were conducted on a single-cylinder research engine operating at low-speed and low-load conditions across three distinct relative air–fuel ratio values with a range of ignition timing settings applied for each air excess coefficient. The findings demonstrate that the artificial neural network model surpasses GT-POWER in predicting in-cylinder pressure with higher accuracy achieving an RMSE consistently below 0.44% across various conditions. In comparison GT-POWER exhibits an RMSE ranging from 0.92% to 1.57%. Additionally the neural network effectively estimates the equivalent flame radius maintaining an RMSE of less than 3% ranging from 2.21% to 2.90%. This underscores the potential of artificial neural network-based approaches to not only significantly reduce computational time but also enhance predictive precision. Furthermore this methodology could subsequently be applied to conventional road engines exhibiting characteristics and performance similar to those of a specific optical engine used as the basis for the machine learning analysis offering a practical advantage in real-time diagnostics.

Fuel cell electric vehicles (FCEVs) have received significant attention in recent times due to various advantageous features such as high energy efficiency zero emissions and extended driving range. However FCEVs have some drawbacks including high production costs; limited hydrogen refueling infrastructure; and the complexity of converters controllers and method execution. To address these challenges smart energy management involving appropriate converters controllers intelligent algorithms and optimizations is essential for enhancing the effectiveness of FCEVs towards sustainable transportation. Therefore this paper presents emerging energy management strategies for FCEVs to improve energy efficiency system reliability and overall performance. In this context a comprehensive analytical assessment is conducted to examine several factors including research trends types of publications citation analysis keyword occurrences collaborations influential authors and the countries conducting research in this area. Moreover emerging energy management schemes are investigated with a focus on intelligent algorithms optimization techniques and control strategies highlighting contributions key findings issues and research gaps. Furthermore the state-of-the-art research domains of FCEVs are thoroughly discussed in order to explore various research domains relevant outcomes and existing challenges. Additionally this paper addresses open issues and challenges and offers valuable future research opportunities for advancing FCEVs emphasizing the importance of suitable algorithms controllers and optimization techniques to enhance their performance. The outcomes and key findings of this review will be helpful for researchers and automotive engineers in developing advanced methods control schemes and optimization strategies for FCEVs towards greener transportation.

Optimally scheduling alkaline electrolyzers (AELs) in a hydrogen-based microgrid (HBM) can greatly unleash the operational flexibility of the HBM. However existing scheduling strategies of AELs mostly utilize a simplified AEL model which ignores the nonlinear coupling of electric-hydrogen-thermal sectors violating the AEL’s security constraints thereby making the scheduling scheme infeasible. This paper proposes an improved model predictive control (MPC) based optimal scheduling framework which incorporates a scheduling correction algorithm into the basic MPC structure. This framework is utilized for implementing economic and resilient scheduling of an HBM under normal and emergency conditions respectively. With the scheduling correction algorithm this framework can be formulated into a computationally efficient mixedinteger linear programming meanwhile guaranteeing the solutions strictly satisfy the security constraints of hydrogen facilities (i.e. AEL and hydrogen tank). Case studies are conducted based on real operating data of a Danish energy island Bornholm. The results demonstrate that the proposed scheduling scheme under normal conditions can contribute to significant comprehensive benefits from the daily operation cost saving of 68% computational time saving of 98% and satisfying the security constraints of hydrogen facilities compared to previous scheduling strategies. Besides it sharply reduces load shedding under emergency conditions by proactively allocating distributed energy sources in the HBM.

This study newly develops a recursive-dynamic global energy model with an hourly temporal resolution for electricity and hydrogen balances aiming to assess the role of variable renewable energy (VRE) in a carbonneutral world. This model formulated as a large-scale linear programming model (with 500 million each of variables and constraints) calculates the energy supply for 100 regions by 2050. The detailed temporal reso lution enables the model to incorporate the variable output of VRE and system integration options such as batteries water electrolysis curtailment and the flexible charging of battery electric vehicles. Optimization results suggest that combing various technical options suitable for local energy situations is critical to reducing global CO2 emissions cost-effectively. Not only VRE but also CCS-equipped gas-fired and biomass-fired power plants largely contribute to decarbonizing power supply. The share of VRE in global power generation in 2050 is estimated to be 57% in a cost-effective case. The results also imply economic challenges for an energy system based on 100% renewable energy. For example the average mitigation cost in 2050 is 69USD/tCO2 in the costeffective case while it increases to 139USD/tCO2 in the 100% renewable case. The robustness of this argument is tested by sensitivity analyses.

The spread of renewable energy (RE) generation not only promotes economy and the environmental protection but also brings uncertainty to power system. As the integration of hydrogen and electricity can effectively mitigate the fluctuation of RE generation an electricity-hydrogen integrated energy system is constructed. Then this paper studies the source-load uncertainties and corresponding correlation as well as the electricity-hydrogen price uncertainties and corresponding correlation. Finally an optimal scheduling model considering economy environmental protection and demand response (DR) is proposed. The simulation results indicate that the introduction of the DR strategy and the correlation of electricity-hydrogen price can effectively improve the economy of the system. After introducing the DR the operating cost of the system is reduced by 5.59% 10.5% 21.06% in each season respectively. When considering the correlation of EP and HP the operating cost of the system is reduced by 4.71% 6.47% 1.4% in each season respectively.

This study investigates the use of hydrogen (H2 ) as a substitute for compressed natural gas (CNG) in a heavyduty (HD) six-cylinder engine focusing on both port fuel injection (PFI) and direct injection (DI) systems. Numerical modeling in a 0D/1D environment was employed simulating engine operation under stationary conditions and during the worldwide harmonized transient cycle (WHTC) and worldwide harmonized vehicle cycle (WHVC) homologation cycles. Results indicated a reduction in torque (7% for direct injection and 21.5% for port fuel injection) and power (32% for direct injection and 35.5% for port fuel injection) when switching from CNG to H2 . Efficiency slightly decreased primarily due to knocking at high engine loads and speeds during H2 operation. The reduced torque and power were mainly attributed to the turbocharger being undersized for H2 given its low density and the lean mixture combustion strategy used. Upgrading the turbocharger or implementing a two-stage compressor could restore or even improve torque and power levels compared to CNG. Heat transfer losses in the H2 engine were lower than with CNG due to the lower incylinder temperature resulting from the lean mixture strategy which also contributed to a significant reduction in nitrogen oxides (NOx ) emissions approximately 2.5 times lower than those with CNG. Despite a notable exhaust energy loss during H2 operation caused by delayed combustion due to knocking the lower NOx emissions and absence of carbon emissions are crucial for reducing pollution. During vehicle cycles selecting an optimal gear-shift strategy is critical to mitigating the performance gap resulting from reduced torque and power with H2 fueling.

The shipping industry is currently the sixth largest contributor to global emissions responsible for one billion tons of greenhouse gas emissions. Urgent action is needed to achieve carbon neutrality in the shipping industry for sustainability. In this paper we use natural language processing techniques to analyze policies announcements and position papers from national and international organizations related to the decarbonization of shipping. In particular we perform the analysis using a novel matrix-based corpus and a fine-tuned machine learning model BERTopic. Our research suggests that the top four priorities for decarbonizing shipping are preventing emissions from methane leaks promoting non-carbon-based hydrogen implementing reusable modular containers to reduce packaging waste in container shipping and protecting Arctic biodiversity while promoting the Arctic shipping route to reduce costs. Our study highlights the validity of NLP techniques in quantitatively extracting critical information related to the decarbonization of the shipping industry.

The use of highly efficient cogeneration systems fueled by pure hydrogen such as Solid Oxide Fuel Cells (SOFCs) in the residential sector is one of the new frontiers for achieving the net zero greenhouse gas emissions tran sitions. The lack of experimental studies in this area prompted the authors to propose the present paper. It refers to hydrogen-fueled SOFC 1 kW-sized integrated into the plant system of a single-family villa configurated as a nearly Zero Energy Building. The multiple objectives are: show the technical feasibility of this technology in building; analyse the data of a continuous monitoring campaign in wintertime; highlight the real performance compared to the manufacturer’s declaration. The results demonstrate that in particular conditions of photo voltaic production it is possible to meet the home electric loads and have a surplus of energy to store or send to the national power grid. The calculated electrical efficiency is equal to 0.47 ÷ 0.48 while the maximum overall efficiency is 0.93.

The green hydrogen transformation of the iron and steel industry is considered a technically viable option. Concretely large-scale renewable energy generation and water electrolyzer capacity are to be added to the production system. Given that renewables are intermittent and H2 demand is high there is continued reliance on the CO2 emitting upstream power system. This paper introduces a novel operating concept that regards an extended production system that includes not only the renewables and water electrolyzer but also a dedicated conventional generator and onsite customer and prioritizes loads with the aim to create an internal balance. The paper studies different production system configurations and load prioritization strategies evaluating technoeconomic properties CO2 emissions the internal balance and the support for the stability of the upstream power system. It finds that local emission-free production of H2 is not only techno-economically viable but that the integrated operating concept leads to lower Scope I and II emissions and to significant reduction of electrical loads on the upstream power system.

There is growing interest in using hydrogen (H2) as a marine fuel. Fire and explosion risks depend on hydrogen release and dispersion characteristics. Based on a validated Computational Fluid Dynamics (CFD) model this study performed hydrogen release and dispersion analysis on an under-deck compressed H2 storage system for a Live-Fish Carrier. A realistic under-deck H2 storage room was modelled based on the ship’s main dimensions and operational profile. Det Norske Veritas (DNV) Rules and Regulations for natural gas storage as a marine fuel were employed as base design guidelines. Case studies were developed to study the effect of two ceiling types (flat and slanted) in terms of flammable cloud formation and dissipation. During the leak’s duration it was found that the recommended ventilation rate was insufficient to dilute the average H2 concentration below 25% of the flammable range as required by DNV (1.2% required against 1.3% slanted and 1.4% flat). However after 35 s of gas extraction the H2 concentration was reduced to 0.5% and 0.6% in the slanted and flat cases respectively. The proposed methodology remains valid to improve the ventilation system and assess mitigation alternatives or other leakage scenarios in confined or semi-confined spaces containing compressed hydrogen gas.

Hydrogen is the most promising alternative fuel in the field of engines. Exhaust heat assisted methanol dissociation is an attractive approach for generating hydrogen. In this work simulations are conducted on a compression ignition engine fueled with different proportions of diesel-dissociated methanol gas (DMG) blends at intermediate engine speed full load and 0% EGR ratio. The results reveal that the indicated thermal efficiency and indicated mean effective pressure are greatly enhanced combustion efficiency is increased and regular emissions of CO HC and soot are reduced while NOx emissions are reduced with increased DMG substitution. In addition a simulation is conducted at an intermediate engine speed full load 15% DMG substitution ratio and varying EGR ratios of 0–20%. The results indicate that the dual-fuel engine outperforms the original engine with respect to power fuel economy and regular emissions once an optimal EGR rate is adopted.

This study conducted a Life Cycle Assessment (LCA) of alternative (electric and hydrogen) and conventional diesel buses in a large metropolitan area. The primary focus was on hydrogen derived from coke oven gas a byproduct of the coking process which is a crucial step in the steel production value chain. The functional unit was 1000000 km traveled over 15 years. LCA analysis using SimaPro v9.3 revealed significant environmental differences between the bus types. Hydrogen buses outperformed electric buses in all 11 environmental impact categories and in 5 of 11 categories compared to conventional diesel buses. The most substantial improvements for hydrogen buses were observed in ozone depletion (8.6% of diesel buses) and global warming (29.9% of diesel buses). As a bridge to a future dominated by green hydrogen employing grey hydrogen from coke oven gas in buses provides a practical way to decrease environmental harm in regions abundant with this resource. This interim solution can significantly contribute to climate policy goals.

The Federal Institute of Metrology METAS developed a Hydrogen Field Test Standard (HFTS) that can be used for field verification and calibration of hydrogen refuelling stations. The testing method is based on the gravimetric principle. The experimental design of the HFTS as well as the description of the method are presented here.

Green energy is at the forefront of current policy research and engineering but some of the potential fuels require either a lot of deeper research or a lot of infrastructure before they can be implemented. In the case of hydrogen both are true. This report aims to analyse the potential of hydrogen as a future fuel source by performing a life-cycle assessment. Through this the well-to-tank phase of fuel production and the usage phase of the system have been analysed. Models have also been created for traditional fuel systems to best compare results. The results show that hydrogen has great potential to convert marine transport to operating off green fuels when powered through low-carbon energy sources which could reduce a huge percentage of the international community’s greenhouse gas emissions. Hydrogen produced through wind powered alkaline electrolysis produced emission data 5.25 g of CO2 equivalent per MJ compared to the 210 g per MJ produced by a medium efficiency diesel equivalent system a result 40 times larger. However with current infrastructure in most countries not utilising a great amount of green energy production the effects of hydrogen usage could be more dangerous than current fuel sources owing to the incredible energy requirements of hydrogen production with even grid (UK) powered electrolysis producing an emission level of 284 g per MJ which is an increase against standard diesel systems. From this the research concludes that without global infrastructure change hydrogen will remain as a potential fuel rather than a common one.

Climate change is obvious in many ways. The weather changes rapidly from day to day reaching high temperatures such as 28 ◦C one day and heavy rain the next with temperatures below 18 ◦C. There are also very strong storms caused by this phenomenon. The way the environment acts is different than the current epoch would predict indicating a long-term shift in weather and temperature patterns. The mean temperature of earth is rising due to the greenhouse effect that is caused by human activity and mostly by the burning of fossil fuel emitting CO2 and other pollutant gasses. Nowadays every country is trying to lower CO2 emissions from everyday human activities a movement called “decarbonization”. Since the 18th century there has been a great deal of research carried out on possible alternatives to fossil fuels. Some of the work was just to discover ways to power heaters or automotive vehicle but there is a great deal of work remaining to complete regarding this issue after discovering the greenhouse effect and its impact on the planet’s climate in order to eliminate it by using fuel whose combustion emissions are more environmentally friendly. In the present work many discoveries will be presented that use hydrogen (H2 ) or hydroxy (H-OH) as fuel. The main reason for this is the emission of pure water after combustion but the most interesting part is the approach every scientist uses to create the fuel gas from water.

Due to its low NOx emission index the micromix burner technology is a promising alternative for using hydrogen in combustion. Various universities and research centers in Germany England and Spain have documented and studied this technology. However the number of studies on micromix burners is limited which hinders their implementation on an industrial scale. The present study aims to review developed works focused on micromix combustion technologies to identify the main gaps and research needs. A sample of 76 articles from 2008 was selected using the PRISMA methodology which was categorized based on the study methodology simulation software and fuels used. An experimental gap has been identified in the combustion of hydrogen and methane in the selected article sample. This gap is a critical research need due to the opportunity to implement this tech nology in existing natural gas networks facilitating the transition from fossil fuels to cleaner combustion processes.

This paper presents the development of a thermodynamic model for the hydrogen refuelling station (HRS) to simulate the process of refuelling which involves the transfer of hydrogen gas from a high-pressure storage tank to the onboard tank of a fuel cell electric vehicle (FCEV). This model encompasses the fundamental elements of an HRS which consists of a storage tank compressor piping system heat exchanger and an on-board vehicle tank. The model is implemented and validated using experimental data from SAE J2601. Various simulations are conducted to assess the impact of the Joule-Thomson effect and compression on the temperature of hydrogen flow specifically focusing on an average pressure rate of 18 MPa/min. Furthermore a comprehensive analysis is conducted to examine the impact of pressure variations in the storage tank (10–90 MPa) and the initial pressure within the vehicle tank (5–35 MPa) as well as variations in ambient temperature (0–40 °C). The study revealed that the energy consumption in the cooling system surpasses the average power consumption in the more advantageous scenario of 60 MPa by a range of 36% to over 220% when the pressure in the storage system drops below 30 MPa. Furthermore it was noted that the impact of ambient temperature is comparatively less significant when compared to the initial pressure of the vehicle's tank. The impact of an ambient temperature change of 10 °C on the final temperature of a hydrogen vehicle is found to be approximately 2 °C. Similarly a variation in the initial vehicle pressure of 10 MPa results in a modification of the final hydrogen vehicle temperature by approximately 8.5 °C.

The chemical industry serves as a global economic backbone and it is an intensive consumer of conventional energy. Due to the depletion of fossil fuels and the emission of greenhouse gases it is necessary to analyze energy supply solutions based on renewable energy sources in this industrial sector. Unlike other sectors such as residential or service industries which have been thoroughly analyzed by the scientific community the use of renewable energies in the chemical industry remains comparatively less examined by the scientific community. This article studies the use of an energy supply system based on photovoltaic technology or a PEM fuel cell for a styrene production industry analyzing the integration of energy storage systems such as batteries as well as different uses for the surplus hydrogen produced by the facility. The most interesting conclusions of the article are: (1) the renewable microgrid considered is viable both technically and economically with a discounted payback period between 5.4 and 6.5 years using batteries as an energy storage system; and (2) the use of hydrogen as energy storage system for a styrene industry is not yet a viable option from an economic point of view.

Hydrogen is a promising fuel because it has good capabilities to operate gas turbines. Due to its ignition speed which exceeds the ignition of traditional fuel it achieves a higher thermal efficiency while the resulting emissions are low. So it was used as a clean and sustainable energy source. This paper reviews the most important research that was concerned with studying the characteristics of hydrogen combustion within incinerators and power generation equipment where hydrogen was used as a fuel mixed with traditional fuel in the combustion chambers of gas turbines. It also includes an evaluation of the combustion processes and flame formation resulting from the enrichment of gaseous fuels with hydrogen and partial oxidation. A large amount of theoretical and experimental work in this field has been reviewed. This review summarizes the predictive and experimental results of various research interests in the field of hydrogen combustion and also production.

Hydrogen-driven heavy-duty trucks are a promising technology for reducing CO2 emissions in the transportation sector. Thus storing hydrogen efficiently onboard is vital. The three available or currently developed physical hydrogen storage technologies (compressed gaseous subcooled liquid and cryo-compressed hydrogen) are promising solutions. For a profound thermodynamic comparison of these storage systems a universally applicable model is required. Thus this article introduces a generalized thermodynamic model and conducts thermodynamic comparisons in terms of typical drive cycle scenarios. Therefore a model introduced by Hamacher et al. [1] for cryo-compressed hydrogen tanks is generalized by means of an explicit model formulation using the property ��2� from REFPROP [2] which is understood as a generic specific isochoric two-phase heat capacity. Due to an implemented decision logic minor changes to the equation system are automatically made whenever the operation mode or phase of the tank changes. The resulting model can simulate all three storage tank systems in all operating scenarios and conditions in the single- and two-phase region. Additionally the explicit model formulation provides deeper insights into the thermodynamic processes in the tank. The model is applied to the three physical hydrogen storage technologies to compare drive cycles heat requirement dormancy behavior and optimal usable density. The highest driving ranges were achieved with cryo-compressed hydrogen however it also comes with higher heating requirements compared to subcooled liquid hydrogen.

This study explores the potentiality of low/zero carbon fuels such as methanol methane and hydrogen for motor applications to pursue the goal of energy security and environmental sustainability. An experimental investigation was performed on a spark ignition engine equipped with both a port fuel and a direct injection system. Liquid fuels were injected into the intake manifold to benefit from a homogeneous charge formation. Gaseous fuels were injected in direct mode to enhance the efficiency and prevent abnormal combustion. Tests were realized at a fixed indicated mean effective pressure and at three different engine speeds. The experimental results highlighted the reduction of CO and CO2 emissions for the alternative fuels to an extent depending on their properties. Methanol exhibited high THC and low NOx emissions compared to gasoline. Methane and even more so hydrogen allowed for a reduction in THC emissions. With regard to the impact of gaseous fuels on the NOx emissions this was strongly related to the operating conditions. A surprising result concerns the particle emissions that were affected not only by the fuel characteristics and the engine test point but also by the lubricating oil. The oil contribution was particularly evident for hydrogen fuel which showed high particle emissions although they did not contain carbon atoms.

If hydrogen fuel is available to support the transportation sector decarbonization its usage can be placed either directly onboard in a fuel cell vehicle or indirectly off-board by using a fuel cell power station to produce electricity to charge a battery electric vehicle. Therefore in this work the direct and indirect conversion scenarios of hydrogen to vehicle propulsion were investigated regarding energy efficiency. Thus in the first scenario hydrogen is the fuel for the onboard electricity production to propel a fuel cell vehicle while in the second hydrogen is the electricity source to charge the battery electric vehicle. When simulated for a drive cycle results have shown that the scenario with the onboard fuel cell consumed about 20% less hydrogen demonstrating higher energy efficiency in terms of driving range. However energy efficiency depends on the outside temperature when heat loss utilization is considered. For outside temperatures of − 5 ◦C or higher the system composed of the battery electric vehicle fueled with electricity from the off-board fuel cell was shown to be more energyefficient. For lower temperatures the system composed of the onboard fuel cell again presented higher total (heat + electricity) efficiency. Therefore the results provide valuable insights into how hydrogen fuel can be used for vehicle propulsion supporting the hydrogen economy development.