Applications & Pathways

Recent targets have increased pressure for the maritime sector to accelerate the uptake of clean fuels. A potential future fuel for shipping is hydrogen however there is a common perception that the volume requirements for this fuel are too large for deep sea shipping. This study has developed a range of techniques to accurately simulate the fuel requirements of hydrogen for a case study vessel. Hydrogen can use fuel cells which achieve higher efficiencies than combustion methods but may require a battery hybrid system to meet changes in demand. A series of novel models for different fuel cell types and other technologies have been developed. The models have been used to run dynamic simulations for different energy system setups. Simulations tested against power profiles from real-world shipping data to establish the minimum viable setup capable of meeting all the power demand for the case study vessel to a higher degree of accuracy than previously achieved. Results showed that the minimum viable setup for hydrogen was with liquid storage a 105.6 MW PEM fuel cell stack and 6.9 MWh of batteries resulting in a total system size of 8934 m3 . Volume requirement results could then be compared to other concepts such as systems using ammonia and methanol 8970 m3 and 6033 m3 respectively.

Benchmark refrigerated systems in the road transportation sector are powered by diesel having operation costs of up to 6000 €/y. This paper presents the development of an alternative refrigeration system based on fuel cells with higher efficiency reduced costs and independent of diesel price fluctuations. Energy load profiles have been analyzed and the fuel cell stack and auxiliaries are being modeled in order to dimension and design a balance of plant and control algorithms that ensure a safe and easy utilization. Additionally a prototype shall be tested under different load profiles to validate the control strategies and to characterize the performance of the system.

The current political scenario and the concerns for global warming have pushed very harsh regulations on conventional propulsion systems based on the use of fossil fuels. New technologies are being promoted but their current technological status needs further research and development for them to become a competitive substitute for the ever-present internal combustion engine. Hydrogen-fueled internal combustion engines have demonstrated the potential of being a fast way to reach full decarbonization of the transport sector but they still have to face some limitations in terms of the operating range of the engine. For this reason the present work evaluates the potential of reaching full load operation on a conventional diesel engine assuming the minimum modifications required to make it work under H2 combustion. This study shows the methodology through which the combustion model was developed and then used to evaluate a multi-cylinder engine representative of the medium to high duty transport sector. The evaluation included different strategies of dilution to control the combustion performance and the results show that the utilization of EGR brings different benefits to engine operation in terms of efficiency improvement and emissions reduction. Nonetheless the requisites defined for the needed turbocharging system are harsher than expected and result in a potential non-conventional technical solution.

The aim of this article is to review hydrogen combustion applications within the energy transition framework. Hydrogen blends are also included from the well-known hydrogen enriched natural gas (HENG) to the hydrogen and ammonia blends whose chemical kinetics is still not clearly defined. Hydrogen and hydrogen blends combustion characteristics will be firstly summarized in terms of standard properties like the laminar flame speed and the adiabatic flame temperature but also evidencing the critical role of hydrogen preferential diffusion in burning rate enhancement and the drastic reduction in radiative emission with respect to natural gas flames. Then combustion applications in both thermo-electric power generation (based on internal combustion engines i.e. gas turbines and piston engines) and hard-to-abate industry (requiring high-temperature kilns and furnaces) sectors will be considered highlighting the main issues due to hydrogen addition related to safety pollutant emissions and potentially negative effects on industrial products (e.g. glass cement and ceramic).

This review presents state-of-the-art for representative sampling of hydrogen from hydrogen refueling stations. Documented sampling strategies are presented as well as examples of commercially available equipment for sampling at the hydrogen refueling nozzle. Filter media used for sampling is listed and the performance of some of the filters evaluated. It was found that the filtration efficiency of 0.2 and 5 mm filters were not significantly different when exposed to 200 and 300 nm particles. Several procedures for gravimetric analysis are presented and some of the challenges are identified to be filter degradation pinhole formation and conditioning of the filter prior to measurement. Lack of standardization of procedures was identified as a limitation for result comparison. Finally the review summarizes results including particulate concentration in hydrogen fuel quality data published. It was found that less than 10% of the samples were in violation with the tolerance limit.

In the maritime domain hydrogen fuel cell propulsion and autonomous vessels are two important issues that are yet to be implemented together because of a few challenges. It is obvious that there are several individual safety studies on Maritime Autonomous Surface Ships and hydrogen storage as well as fuel cells based on various risk assessment tools but the combined safety studies that include hydrogen fuel cells on autonomous vessels with recent risk analysis methods are extremely limited. This research chooses the “System-Theoretic Process Analysis” (STPA) method which is a recent method for potential risk identification and mitigation. Both hydrogen and autonomous vessels are analyzed and assessed together with the STPA method. Results are not speculative but rather flexible compared to conventional systems. The study finds a total of 44 unsafe control actions (UCAs) evolved from human and central control unit controllers through STPA. Further the loss scenarios (LS) are identified that lead to those UCAs so that loss scenarios can be assessed and UCAs can be mitigated for safe operation. The objective of this study is to ensure adequate safety for hydrogen fuel cell propulsion on autonomous vessels.

In this work the Design and Operation of Integrated Technologies (DO-IT) framework is developed a comprehensive tool to support short- and long-term technology investment and operation decisions for integrated energy generation conversion and storage technologies in buildings. The novelty of this framework lies in two key aspects: firstly it integrates essential open-source modelling tools covering energy end uses in buildings technology performance and cost and energy system design optimisation into a unified and easily-reproducible framework. Secondly it introduces a novel optimisation tool with a concise and generic mathematical formulation capable of modelling multi-energy vector systems capturing interdependencies between different energy vectors and technologies. The model formulation which captures both short- and long-term energy storage facilitates the identification of smart design and operation strategies with low computational cost. Different building energy demand and price scenarios are investigated and the economic and energy benefits of using a holistic multi-energy-vector approach are quantified. Technology combinations under consideration include: (i) a photovoltaic-electric heat pump-battery system (ii) a photovoltaic-electric heat pump-battery-hot water cylinder system (iii) a photovoltaic-electrolyser‑hydrogen storage-fuel cell system and (iv) a system with all above technology options. Using a university building as a case study it is shown that the smart integration of electricity heating cooling and hydrogen generation and storage technologies results in a total system cost which is >25% lower than the scenario of only importing grid electricity and using a fuel oil boiler. The battery mitigates intra-day fluctuations in electricity demand and the hot-water cylinder allows for efficiently managing heat demand with a small heat pump. In order to avoid PV curtailment excess PV-generated electricity can also be stored in the form of green hydrogen providing a long-term energy storage solution spanning days weeks or even seasons. Results are useful for end-users investment decision makers and energy policy makers when selecting building-integrated low-carbon technologies and relevant policies.

There are a large number of applications in which hydrogen internal combustion engines represent a sensible alternative to battery electric propulsion systems and to fuel cell electric propulsion systems. The main advantages of combustion engines are their high degree of robustness and low manufacturing costs. No critical raw materials are required for production and there are highly developed production plants worldwide. A CO2-free operation is possible when using hydrogen as a fuel. The formation of nitrogen oxides during hydrogen combustion in the engine can be effectively mitigated by a lean-burn combustion process. However achieving low NOx raw emissions conflicts with achieving high power yields. In this work a series industrial diesel engine was converted for hydrogen operation and comprehensive engine tests were carried out. Various measures to improve the trade-off between NOx emissions and performance were investigated and evaluated. The rated power output and the maximum torque of the series diesel engine could be exceeded while maintaining an indicated specific NOx emission of 1 g/kWh along the entire full load curve. In the low-end-torque range however the gap to the full load curve of the series diesel engine could not be fully closed with the hardware used.

The increase in the overall global temperature and its subsequent impact on extreme weather events are the most critical consequences of human activity. In this scenario transportation plays a significant role in greenhouse gas (GHG) emissions which are the main drivers of climate change. The decline of non-renewable energy sources coupled with the aim of reducing GHG emissions from fossil fuels has forced a shift towards a net-zero emissions economy. As an example of this transition the European Union has set 2050 as the target for achieving carbon neutrality. Hydrogen (H2 ) is gaining increasing relevance as one of the most promising carbon-free energy vectors. If produced from renewable sources it facilitates the integration of various alternative energy sources for achieving a carbon-neutral economy. Recently interest in its application to the transportation sector has grown including different power plant concepts such as fuel cells or internal combustion engines. Despite exhibiting significant drawbacks such as low density combustion instabilities and incompatibilities with certain materials hydrogen is destined to become one of the future fuels. In this publication experimental activities are reported that were conducted on a sparkignition engine fueled with hydrogen at different operating points. The primary objective of this research is to gain a better understanding of the thermodynamic processes that control combustion and their effects on engine performance and pollutant emissions. The results show the emission levels performance and combustion characteristics under different conditions of dilution load and injection strategy and timing.

Power to gas technology is an innovative solution to promote the use of renewable energy technologies also including e-fuels. This work presents a techno-economic analysis of a novel concept of a renewable power to gas plant. A 2.4 MW solid oxide electrolyzer fed by a 3.1 MW photovoltaic field is coupled with a biomethane production unit to produce synthetic methane by means of a 2.4 MW methanation unit. The hydrogen produced by the electrolyzer is used for the methanation reaction aiming at producing natural gas at net zero carbon emissions. The CO2 is obtained as a byproduct of the membrane separation in a biogas upgrading unit. The methanation unit and the electrolyzer models are developed in MatLab and integrated in TRNSYS to perform a dynamic simulation of all the components and the system as a whole. Dynamic simulation results show a 42% increase in the production of natural gas from renewable energy sources. The thermoeconomic analysis shows a remarkable primary energy saving index of 176% and a total amount of 896 tons of CO2 equivalent emissions saved. As expected the critical point is the economic feasibility since the simple payback is 9 years in case local incentives and subsidies are considered. The parametric analysis on the photovoltaic capacity shows that the simple payback dramatically depends on such design parameter varying from 6 years in the best case scenario to 92 years in the worst case scenario.

With increasing concerns about environmental pollution the shipping industry has been considering various fuels as alternative power sources. This paper presents a study of the holistic environmental impacts of eco-friendly alternative ship fuels of marine gas oil (MGO) liquefied natural gas (LNG) and hydrogen across each of their life cycles from their production to the operation of the ship. The environmental impacts of the fuels were estimated by life-cycle assessment (LCA) analysis in the categories of well-to-tank tank-to-wake and well-to-wake phases. The LCA analysis was targeted for a 170 gross tonnage (GT) nearshore ferry operating in the ROK which was conceptually designed in the study to be equipped with the hydrogen fuel cell propulsion system. The environmental impact performance was presented with comparisons for the terms of global warming potential (GWP) acidification potential (AP) photochemical ozone creation potential (POCP) eutrophication potential (EP) and particulate matter (PM). The results showed that the hydrogen showed the highest GWP level during its life cycle due to the large amount of emissions in the hydrogen generation process through the steam methane reforming (SMR) method. The paper concludes with suggestions of an alternative fuel for the nearshore ferry and its production method based on the results of the study.

Hydrogen energy is regarded as an important way to achieve carbon emission reduction. This paper focuses on the combination of the design of the hydrogen supply chain network and the location of hydrogen refueling stations on the expressway. Based on the cost analysis of the hydrogen supply chain a multi-objective model is developed to determine the optimal scale and location of hydrogen refueling stations on the hydrogen expressway. The proposed model considers the hydrogen demand forecast hydrogen source selection hydrogen production and storage and transportation hydrogen station refueling mode etc. Taking Dalian City China as an example with offshore wind power as a reliable green hydrogen supply to select the location and capacity of hydrogen refueling stations for the hydrogen energy demonstration section of a certain expressway under multiple scenarios. The results of the case show that 4 and 5 stations are optimized on the expressway section respectively and the unit hydrogen cost is $14.3 /kg H2 and $11.8 /kg H2 respectively which are equal to the average hydrogen price in the international range. The optimization results verify the feasibility and effectiveness of the model.

This work addresses the energy efficiency of hydrogen refueling stations (HRS) using a first principles model and optimal control methods to find minimal entropy production operating paths. The HRS model shows good agreement with experimental data achieving maximum state of charge and temperature discrepancies of 1 and 7% respectively. Model solution and optimization is achieved at a relatively low computational time (40 s) when compared to models of the same degree of accuracy. The entropy production mapping indicates the flow control valve as the main source of irreversibility accounting for 85% of the total entropy production in the process. The minimal entropy production refueling path achieves energy savings from 20 to 27% with respect to the SAE J2601 protocol depending on the ambient temperature. Finally the proposed method under nearreversible refueling conditions shows a theoretical reduction of 43% in the energy demand with respect to the SAE J2601 protocol.

The maritime transport and the port-logistic industry are key drivers of economic growth although they represent major contributors to climate change. In particular maritime port facilities are typically located near cities or residential areas thus having a significant direct environmental impact in terms of air and water quality as well as noise. The majority of the pollutant emissions in ports comes from cargo ships and from all the related ports activities carried out by road vehicles. Therefore a progressive reduction of the use of fossil fuels as a primary energy source for these vehicles and the promotion of cleaner powertrain alternatives is in order. The present study deals with the design of a new propulsion system for a heavy-duty vehicle for port applications. Specifically this work aims at laying the foundations for the development of a benchmark industrial cargo–handling hydrogen-fueled vehicle to be used in real port operations. To this purpose an on-field measurement campaign has been conducted to analyze the duty cycle of a commercial Diesel-engine yard truck currently used for terminal ports operations. The vehicle dynamics has been numerically modeled and validated against the acquired data and the energy and power requirements for a plug-in fuel cell/battery hybrid powertrain replacing the Diesel powertrain on the same vehicle have been evaluated. Finally a preliminary design of the new powertrain and a rule-based energy management strategy have been proposed and the electric energy and hydrogen consumptions required to achieve the target driving range for roll-on and roll-off operations have been estimated. The results are promising showing that the hybrid electric vehicle is capable of achieving excellent energy performances by means of an efficient use of the fuel cell. An overall amount of roughly 12 kg of hydrogen is estimated to be required to accomplish the most demanding port operation and meet the target of 6 h of continuous operation. Also the vehicle powertrain ensures an adequate all-electric range which is between approximately 1 and 2 h depending on the specific port operation. Potentially the hydrogen-fueled yard truck is expected to lead to several benefits such as local zero emissions powertrain noise elimination reduction of the vehicle maintenance costs improving of the energy management and increasing of operational efficiency.

In this novel conceptual fuel cell vehicle (FCV) an on-board CH4 steam reforming (MSR) membrane reformer (MR) is considered to generate pure H2 for supplying a Fuel Cell (FC) system as an alternative to the conventional automobile engines. Two on-board tanks are forecast to store CH4 and water useful for feeding both a combustion chamber (designed to provide the heat required by the system) and a multi tubes Pd-Ag MR useful to generate pure H2 via methane steam reforming (MSR) reaction. The pure H2 stream is hence supplied to the FC. The flue gas stream coming out from the combustion chamber is used to preheat the MR feed stream by two heat exchangers and one evaporator. Then this theoretical work demonstrates by a 1-D model the feasibility of the MR based system in order to generate 5 kg/day of pure H2 required by the FC system for cruising a vehicle for around 500 km. The calculated CH4 and water consumptions were 50 and 70 kg respectively per 1 kg of pure H2. The on-board MR based FCV presents lower CO2 emission rates than a conventional gasoline-powered vehicle also resulting in a more environmentally friendly solution.

The concerns regarding the consumption of traditional fuels such as oil and coal have driven the proposals for several cleaner alternatives in recent years. Hydrogen energy is one of the most attractive alternatives for the currently used fossil fuels with several superiorities such as zero-emission and high energy content. Hydrogen has numerous advantages compared to conventional fuels and as such has been employed in gas turbines (GTs) in recent years. The main benefit of using hydrogen in power generation with the GT is the considerably lower emission of greenhouse gases. The performance of the GTs using hydrogen as a fuel is influenced by several factors including the performance of the components the operating condition ambient condition etc. These factors have been investigated by several scholars and scientists in this field. In this article studies on hydrogen-fired GTs are reviewed and their results are discussed. Furthermore some recommendations are proposed for the upcoming works in this field.

Turquoise hydrogen from natural gas pyrolysis has recently emerged as a promising alternative for low-carbon hydrogen production with a high-value pure carbon by-product. However the implications of this technology on the broader energy system are not well understood at present. To close this literature gap this study presents an assessment of the integration of natural gas pyrolysis into a simplified European energy system. The energy system model minimizes the cost by optimizing investment and hourly dispatch of a broad range of electricity and fuel production transmission and storage technologies as well as imports/exports on the global market. Norway is included as a major natural gas producer and Germany as a major energy importer. Results reveal that pyrolysis is economically attractive at modest market shares where the carbon by-product can be sold into highvalue markets for 400 €/ton. However pyrolysis-dominated scenarios that employ methane as a hydrogen carrier also hold promise as they facilitate deep decarbonization without the need for vast expansions of international electricity hydrogen and CO2 transmission networks. The simplicity and security benefits of such pyrolysis-led decarbonization pathways justify the modest 11 % cost premium involved for an energy system where natural gas is the only energy trade vector. In conclusion there is a strong case for turquoise hydrogen in future energy systems and further efforts for commercialization of natural gas pyrolysis are recommended.

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

The rapid growth in fossil fuels has resulted in climate change that needs to be controlled in the near future. Several methods have been proposed to control climate change including the development of efficient energy conversion devices. Fuel cells are environmentally friendly energy conversion devices that can be fuelled by green hydrogen with only water as a by-product or by using different biofuels such as biomass in wastewater urea in wastewater biogas from municipal and agricultural wastes syngas from agriculture wastes and waste carbon. This editorial discusses the fundamentals of the operation of the fuel cell and their application in various sectors such as residential transportation and power generation.

Increasing penetrations of renewable-based generation have led to a decrease in the bulk power system inertia and an increase in intermittency and uncertainty in generation. Energy storage is considered to be an important factor to help manage renewable energy generation at greater penetrations. Hydrogen is a viable long-term storage alternative. This paper analyzes and presents use cases for leveraging electrolyzer-based power-to-gas systems for electric grid support. The paper also discusses some grid services that may favor the use of hydrogenbased storage over other forms such as battery energy storage. Real-time controls are developed implemented and demonstrated using a power-hardware-in-the-loop(PHIL) setup with a 225-kW proton-exchange-membrane electrolyzer stack. These controls demonstrate frequency and voltage support for the grid for different levels of renewable penetration (0% 25% and 50%). A comparison of the results shows the changes in respective frequencies and voltages as seen as different buses as a result of support from the electrolyzers and notes the impact on hydrogen production as a result of grid support. Finally the paper discusses the practical nuances of implementing the tests with physical hardware such as inverter/electrolyzer efficiency as well as the related constraints and opportunities.

The H2-ICE project aims at developing through numerical simulation a new generation of hybrid powertrains featuring a hydrogen-fueled Internal Combustion Engine (ICE) suitable for 12 m urban buses in order to provide a reliable and cost-effective solution for the abatement of both CO2 and criteria pollutant emissions. The full exploitation of the potential of such a traction system requires a substantial enhancement of the state of the art since several issues have to be addressed. In particular the choice of a more suitable fuel injection system and the control of the combustion process are extremely challenging. Firstly a high-fidelity 3D-CFD model will be exploited to analyze the in-cylinder H2 fuel injection through supersonic flows. Then after the optimization of the injection and combustion process a 1D model of the whole engine system will be built and calibrated allowing the identification of a “sweet spot” in the ultra-lean combustion region characterized by extremely low NOx emissions and at the same time high combustion efficiencies. Moreover to further enhance the engine efficiency well above 40% different Waste Heat Recovery (WHR) systems will be carefully scrutinized including both Organic Rankine Cycle (ORC)-based recovery units as well as electric turbo-compounding. A Selective Catalytic Reduction (SCR) aftertreatment system will be developed to further reduce NOx emissions to near-zero levels. Finally a dedicated torque-based control strategy for the ICE coupled with the Energy Management Systems (EMSs) of the hybrid powertrain both optimized by exploiting Vehicle-To-Everything (V2X) connection allows targeting H2 consumption of 0.1 kg/km. Technologies developed in the H2-ICE project will enhance the know-how necessary to design and build engines and aftertreatment systems for the efficient exploitation of H2 as a fuel as well as for their integration into hybrid powertrains.

The average temperature of the Earth has risen due to the accumulation of greenhouse gases emitted from the usage of fossil fuels. The consequential climate changes have caused various problems fueling the growing demand for environmentally friendly energy sources that can replace fossil fuels. Batteries and hydrogen have thus been utilized as substitute energy sources for automobiles to reduce fossil fuel consumption. Consequently the number of hydrogen refueling stations is increasing due to an increase in the number of hydrogen-powered vehicles. However several incidents have been reported in the United States of America and Japan where hydrogen refueling stations have been operating for a long time. A risk assessment of hydrogen refueling stations operating in urban areas was performed in this study by calculating the risk effect range using a process hazard analysis tool (PHAST) v8.7 from DNV-GL and a hydrogen risk assessment model (HyRAM) from Sandia National Laboratories (SNL). The societal risk was assessed through a probit model based on the calculation results. The assessment results showed that the risk caused by jet fire and overpressure in an incident is lower than the ‘as low as reasonably practicable’ (ALARP) level.

Facing global warming and recent bans on the use of diesel in vehicles there is a growing need to develop vehicles powered by renewable energy sources to mitigate greenhouse gas and pollutant emissions. Among the various forms of non-fossil energy for vehicles hydrogen fuel is emerging as a promising way to combat global warming. To date most studies on vehicle carbon emissions have focused on diesel and electric vehicles (EVs). Emission assessment methodologies are usually developed for fast-moving consumer goods (FMCG) which are non-durable household goods such as packaged foods beverages and toiletries instead of vehicle products. There is an increase in the number of articles addressing the product carbon footprint (PCF) of hydrogen fuel cell vehicles in the recent years while relatively little research focuses on both vehicle PCF and fuel cycle. Zero-emission vehicles initiative has also brought the importance of investigating the emission throughout the fuel cycle of hydrogen fuel cell and its environmental impact. To address these gaps this study uses the life-cycle assessment (LCA) process of GREET (greenhouse gases regulated emissions and energy use in transportation) to compare the PCF of an EV (Tesla Model 3) and a hydrogen fuel cell car (Toyota MIRAI). According to the GREET results the fuel cycle contributes significantly to the PCF of both vehicles. The findings also reveal the need for greater transparency in the disclosure of relevant information on the PCF methodology adopted by vehicle manufacturers to enable comparison of their vehicles’ emissions. Future work will include examining the best practices of PCF reporting for vehicles powered by renewable energy sources as well as examining the carbon footprints of hydrogen production technologies based on different methodologies.

This paper uses a whole-system approach to examine different strategies related to the future role of the gas grid in a low-carbon heat system. A novel model of integrated gas electricity and heat systems HEGIT is used to investigate four key sets of scenarios for the future of the gas grid using the UK as a case study: (a) complete electrification of heating; (b) conversion of the existing gas grid to deliver hydrogen; (c) a hybrid heat pump system; and (d) a greener gas grid. Our results indicate that although the infrastructure requirements the fuel or resource mix and the breakdown of costs vary significantly over the complete electrification to complete conversion of the gas grid to hydrogen spectrum the total system transition cost is relatively similar. This reduces the significance of total system cost as a guiding factor in policy decisions on the future of the gas grid. Furthermore we show that determining the roles of low-carbon gases and electrification for decarbonising heating is better guided by the trade-offs between short- and long-term energy security risks in the system as well as trade-offs between consumer investment in fuel switching and infrastructure requirements for decarbonising heating. Our analysis of these trade-offs indicates that although electrification of heating using heat pumps is not the cheapest option to decarbonise heat it has clear co-benefits as it reduces fuel security risks and dependency on carbon capture and storage infrastructure. Combining different strategies such as grid integration of heat pumps with increased thermal storage capacity and installing hybrid heat pumps with gas boilers on the consumer side are demonstrated to effectively moderate the infrastructure requirements consumer costs and reliability risks of widespread electrification. Further reducing demand on the electricity grid can be accomplished by complementary options at the system level such as partial carbon offsetting using negative emission technologies and partially converting the gas grid to hydrogen.

Hydrogen addition affects the composition of exhaust gases in vehicles. However the effects of hydrogen addition to compression ignition engines in running vehicles have not been evaluated. Hydrogen‑mixed air was introduced into the air intake of a truck equipped with a direct‑ injection diesel engine and running on a chassis dynamometer to investigate the effect of hydrogen addition on fuel consumption and exhaust gas components. The reduction in diesel consumption and the increase in hydrogen energy share (HES) showed almost linear dependence where the percentage decrease in diesel consumption is approximately 0.6 × HES. The percentage reduction of CO2 showed a one‑to‑one relationship to the reduction in diesel consumption. The reduction in emissions of CO PM and hydrocarbons (except for ethylene) had one to one or a larger correlation with the reduction of diesel consumption. On the other hand it was observed that NOx emissions increased and the percentage increase of NOx was 1.5~2.0 times that of HES. The requirement for total energy supply was more when hydrogen was added than for diesel alone. In the actual running mode only 50% of the energy of added hydrogen was used to power the truck. As no adjustments were made to the engine in this experiment a possible disadvantage that could be improved by adjusting the combustion conditions.