Hydrogen Engine Research Articles

Future Technological Directions for Hydrogen Internal Combustion Engines in Transport Applications

The paper discusses some of the requirements, drivers, and resulting technological paths for manufacturers to develop hydrogen combustion engines for use in two types of market application – on-road heavy- and light-duty. One of the main requirements is legislative certainty, and this has now been afforded – at least in the major market of Europe – by the European Union's recent adoption into law of tailpipe emissions limits specifically designed to encourage the uptake of hydrogen engines in heavy-duty vehicles, giving manufacturers the confidence they need to invest in productionized solutions to offer to customers.It then discusses combustion systems and boosting systems for the two market types, emphasizing that heavy-duty vehicles need best efficiency throughout their operating map while light-duty ones, since they are rarely operated at full load, will mainly primarily need efficiency in the part-load region. This difference will likely cause a divergence in solutions, with heavy-duty engines running very lean everywhere and light-duty ones likely operating at the stoichiometric air-fuel ratio, at least for most of the map. The impacts of the strategies on engine systems and vehicle integration are discussed.It is postulated that due to reasons of preignition avoidance and efficiency hydrogen engines will rapidly adopt direct injection and that the long-term heavy-duty types will migrate towards the typical current spark-ignition-type cylinder head architecture where tumble, rather than swirl, will ultimately be needed for air motion in the cylinder for these reasons. They may also adopt active pre-chamber technology to ignite extremely lean mixtures for maximum efficiency and minimum emissions of oxides of nitrogen.It is suggested that light-duty engines will evolve less from their current gasoline architectural norm since they already contain all of the necessary fundamentals for hydrogen combustion. However, since part-load efficiency will be important, some new strategies may become desirable. Developing dual-fuel light-duty engines could accelerate their uptake as the heavy-duty market simultaneously accelerates the creation of the fuel supply infrastructure.The likely technological evolution suggests that variable valve trains, and specifically cam profile switching technology, would be extremely useful for all types of hydrogen engine, especially since they are readily available in different gasoline engines now. New operating strategies afforded by variable valve trains would benefit both heavy- and light-duty engines, and these strategies will become more sophisticated. There will therefore likely be a convergence of technologies for the two markets, albeit with some key differences maintained due to their vehicle applications and their differing operation in the field.

Hydrogen-fueled PFI SI engine investigation for near-zero NOx emissions in de-throttled and supercharged ultra-lean burn conditions

This study investigates the efficiency and combustion characteristics of a hydrogen port fuel injection (PFI) spark ignition (SI) engine under various load levels, excess air ratios and intake pressures. Experiments were conducted on a single-cylinder research engine to evaluate the effects of throttle opening and supercharging on pumping work and combustion parameters. The key findings indicate that abnormal combustion events are more closely related to the relative air-fuel ratio (λ) than to load, further limiting load increases during de-throttled operation. Additionally, combustion variability compromised mixture enleanment in both naturally aspirated and supercharged conditions. The gross indicated efficiency was approximately 40.7% across the range of 2.2 < λ < 3.5 with minimal variation. Efficiency gains were linked to reduced heat transfer losses in lean conditions, as validated by computational heat transfer, thermodynamic and fluid dynamic models on Gamma Technologies GT-ISE software. Moreover, nitrogen oxides (NOx) emissions were nearly zero for all test conditions when λ was above 2.2. These findings provide crucial insights into optimizing hydrogen engine performance under various intake pressures, highlighting the potential for achieving high efficiency and low emissions.

Optimization of power performance and combustion stability of ultra-lean combustion in hydrogen fuel engines through combined turbulent jet ignition and variable valve timing

Although pure hydrogen engines can achieve zero carbon and extremely low NOx emissions under ultra-lean combustion conditions, there are limitations with combustion stability and power performance. This paper combines turbulent jet ignition (TJI) and variable valve timing (VVT) technology, which not only improves the power output of pure hydrogen engines under ultra-lean combustion conditions but also ensures the engine’s stable operation. Therefore, this research reveals the working characteristics of TJI engines under lean conditions through numerical methods and explores the optimization characteristics of VVT on engine power performance and stability through experiments. The results indicate that TJI utilizes strong turbulence and multiple-point ignition to improve the efficiency of the mixture and combustion speed, ensuring reliable ignition capability under ultra-lean operating and achieving a stable and effective combustion process. According to the experimental results, the combination of TJI with VVT technology can ensure engine cyclic-variability of less than 1.5 % and the maximum values of Brake mean effective pressure (BMEP) and Brake thermal efficiency (BTE) are 4.5 bar and 41.6 %, respectively. This innovative technology combination not only enables the efficient and eco-friendly development of the transportation industry but also holds significant importance for promoting carbon-free fuels and environmental protection in the future.

Study of activity stratification-controlled NH3–H2 combustion in a large-bore gas engine utilizing split-channel supercharge and fuel-air mixing technology

In this study, the split-channel supercharge and fuel-air mixing technology (SCS-FAM) is firstly proposed for large-bore ammonia (NH3)-hydrogen (H2) engine, which involves the separation of fuel and air intake ports to mitigate the risk of H2 backfire in intake system. We explored the activity stratification under different intake schemes and H2 blend ratios through simulation, as well as how it affects the NH3–H2 combined combustion characteristics including in-cylinder flow turbulence, temperature, concentration, and key intermediates distribution. The results show that in Scheme 2 when air entered the high swirl ratio intake 1 and fuel entered the low swirl ratio intake 2, a rich mixture was formed near the spark plug, accompanied by localized NH3 thermal reforming phenomena, which improved the activity distribution of H2. Additionally, the strong swirl promoted combustion in the squish zone and significantly shortened the post-combustion period. Scheme 2 achieved a higher indicated thermal efficiency (ITE) than Scheme 1 with a small amount of H2 addition, with the highest ITE of 42.1% obtained at 15 vol% H2 blend ratio. Notably, the addition of H2 promoted NH3 consumption and the generation of active radicals, resulting in reduced N2O emissions during the expansion stroke, but causing an increase in NO emissions.

Study on combustion and emission characteristics of hydrogen/air mixtures in a constant volume combustion bomb

Hydrogen is an environmentally-friendly fuel with the characteristics of low carbon, high calorific value, and extensive combustible range, making it an optimal alternative fuel for internal combustion engines. In this study, an experiment using a spherical constant volume combustion bomb (CVCB) was conducted to investigate the combustion and emission characteristics of hydrogen/air mixtures. The results shows that the flame propagation velocity of hydrogen laminar flow initially increases and then decreases with the excess air coefficient (λ), reaching peak at λ = 0.6, and the flame becomes unstable on the side of lean burning (λ > 1.0). Both the NOx emissions and the average temperature in the CVCB initially rise before eventually declining with the λ, the peak values for both NOx emission and mean temperature are reached at λ = 1.0. The dilution of N2 inhibits the laminar combustion and emission of hydrogen. As the dilution rate of N2 increases, little change occurs in the Markstein length, while flame propagation velocity, NOx emission, and average temperature all decrease. An increase in initial pressure hinders the development of the initial flame, while promoting the formation of cellular structure within the flame. Consequently, unstable combustion leads to a rapid increase in flame propagation speed during later stages. The average temperature inside the CVCB and the NOx emission increase by 6.6 % and 25.9 %, respectively, with the initial pressure increasing from 0.1 MPa to 0.5 MPa. On the other hand, an increase in initial temperature can facilitate flame development and results in an increased flame propagation speed. Especially, Markstein length is less sensitive to changes in initial temperature than to changes in initial pressure. The average temperature and NOx emission present a pattern of increasing first and decreasing then with the increase in initial temperature. These results have provided empirical evidence for optimizing the combustion and emission control of hydrogen engines.

Research Progress and Challenges of Hydrogen-Ammonia Hybrid Fuel Engines

In this paper, we review the research status of hydrogen and ammonia engines, and discuss the potential of the two fuels as clean energy sources and their challenges. Hydrogen fuel has attracted attention due to its high energy density and zero-emission characteristics, but hydrogen fuel engines have problems such as increased nitrogen oxide emissions, tempering and early ignition. Ammonia fuel, as a carbon-free alternative fuel, has the advantage of being easy to store, but it is inferior to traditional fuels in combustion performance. This paper further analyzes the research progress of hydrogen/ammonia hybrid fuel engines, highlighting specific challenges such as optimizing the fuel mixture ratio, addressing safety concerns related to hydrogen's flammability and ammonia's toxicity, and overcoming technical difficulties in combustion control, points out the combustion support effect of hydrogen and the influence of ammonia on combustion rate, and discusses the advantages of hybrid fuel engines in emission control. Finally, this paper summarizes the current development trend of hydrogen/ammonia fuel engine technology and puts forward suggestions for future research directions.

Experimental multiple parameters optimization of the injection strategies for a turbocharged direct injection hydrogen engine to achieve highly efficient and clean performance

Improving the brake thermal efficiency (BTE) and reducing NOx emissions are two main goals for hydrogen-powered internal combustion engines to achieve efficient and clean performance. This paper focuses on the multiple parameters optimization of injection and ignition both experimentally and numerically based on a 2.0L turbocharged direct injection hydrogen engine. Firstly, the effects of single and split injection on engine performance, in-cylinder mixing and combustion characteristics are investigated. Secondly, the single-factor effect of split injection parameters and spark timing on engine performance are obtained with different engine speeds. Significant interaction effects are detected between these factors. Thus, a multi-parameter optimization is conducted based on the response surface methodology method to analyze the co-relationship of factors (split injection control parameters and ignition) on responses (BTE, NOx emissions, and knock intensity) at high-load. Finally, a maximum BTE of 43.03% and a reduction in NOx emissions by 71.19% are achieved with the help of model prediction at 2500 rpm and a load of 1.40MPa. Further optimization of other engine speeds is conducted, and the boundary of high-efficiency region (BTE>40%) covers over 50% of the load map after optimization. These results can provide valuable support for the performance improvement of efficiency and clean hydrogen engines.

Effect of ignition timing and hydrogen injection phase on HDI engine combustion and NOx emissions

ABSTRACT In order to improve the ITE and reduce NOx emissions in direct-injected hydrogen (HDI) engines under at medium and high loads, the effects of IT and hydrogen injection phase on the combustion and NOx emission characteristics of the HDI engine at high rpm and medium load were investigated numerically. The base engine is a four-cylinder turbocharged direct-injected gasoline (GDI) engine, which is modified into a HDI engine with direct-injected hydrogen fuel. The simulation is performed using GT-Power software. The operating condition of HDI engine is set to 5500 rpm and 50% load. Firstly, IT is optimized, and then based on the IT optimization results, the hydrogen injection phase is optimized. The results show that as the IT is advanced, the maximum pressure rise rate (MPRR) shows a gradual increasing trend, while the combustion intensity and the indicated thermal efficiency (ITE) increases firstly and then decreases, and the former reaches a maximum value at 25° CA BTDC, while the latter reaches a maximum value of 40.5% at 18°CA BTDC. In addition, the nitrogen oxide (NOx) emissions decrease as the IT is delayed. Based on 18°CA BTDC of IT, the results indicated that the later the moment of hydrogen injection, the higher the MPRR, resulting in the greater the knock intensity. The ITE is less affected by the hydrogen injection phase. When the hydrogen injection phase is delayed, NOx emissions increase slightly.

Experimental analysis and optimization of the variable valve timing on attaining high efficiency with low NOx emission of a direct-injected hydrogen engine

The direct-injection hydrogen engine (DI-H2ICE) has demonstrated zero carbon emissions with high brake thermal efficiencies (BTE). Due to the high stoichiometric air–fuel ratio of hydrogen, with a lean burn strategy the gas exchange process of a hydrogen engine is different to a gasoline engine, and the valve timing controlling strategy requires reinvestigation. In this research, the optimal variable valve timing (VVT) is investigated in a 2.0 L DI H2ICE. The intake and exhaust valve timing controlling strategies are analyzed experimentally over the whole operating map. A multi-indicator decision-making method is applied to determine the entropy weight of BTE and NOx emissions. Results indicate that BTE greatly benefits from advanced intake valve timing, and exhaust valve timing affects BTE through pumping losses. Advanced intake and exhaust valve timings are employed in the hydrogen engine to enhance the BTE until the NOx emissions rise rapidly at high loads. The retarded exhaust valve timing helps reduce NOx emissions and avoid the risk of abnormal combustion at high loads. Therefore, earlier IVO and later EVC are applied simultaneously for DI-H2ICE compared to the gasoline engine. A maximum power of 124.8 kW at an engine speed of 4500 rpm and a BTE of 42.57 % is achieved with optimized VVT. Furthermore, NOx emissions are controlled to under 20 ppm over nearly half of the engine operating map. The conclusions are valuable in the development of high-performance H2ICEs, the numerical simulation studies, and hydrogen fuel applications.

Combination of G-Equation and Detailed Chemistry: An application to 3D-CFD hydrogen combustion simulations to predict NOx emissions in reciprocating internal combustion engines

In the recent years, the growing pressure by the European Union to phase out the internal combustion engines has raised the quest for alternative solutions for low-environmental-impact mobility. Nevertheless, concerns on the life-cycle emissions of battery electric vehicles and perplexities on the socio-economic sustainability of the ecological transition suggest that maintaining the interest in internal combustion engines can be strategic, provided that carbon-neutral fuels are adopted. On the basis of the technological neutrality principle, relying on already existing and well-established technologies requires less effort and cost to convert the whole road transport. Moreover, the adoption of bio- or e-fuels obtained from renewable sources widely spread across the globe is not of secondary importance. In fact, cost reduction and worldwide diffusion of the resources are both main promoters of socio-economic sustainability.In this scenario, green hydrogen represents one of the main solutions for the survival of reciprocating engines. Since the production is solely based on renewable energy sources, it is not simply characterized by zero CO2 emissions at the tailpipe, but it can be considered overall carbon neutral. A technical drawback in the use of hydrogen is represented by emissions of nitrogen oxides (NOx), due to the ever-present high temperature combustion process. For this reason, an ad-hoc design is mandatory to minimize NOx production, and CFD can be a valid tool to reduce cost and time to market for the development of hydrogen engines.In this regard, the current work proposes a 3D-CFD numerical methodology, based on the combination of G-Equation and Detailed Chemistry models, for NOx prediction in in-cylinder simulations of reciprocating internal combustion engines fueled with hydrogen. Although the combination of level-set method and chemical kinetics is not a novelty in literature, it is the first time that it is applied to evaluate NOx emissions in H2 engines. The proposed approach is validated against experimental data on a direct injection, spark ignition, hydrogen engine. The methodology is able to properly predict NOx emissions at different mixture qualities, revving speeds and spark times. The total number of investigated cases is 17, which is a large set of simulations compared to the existing literature. Considering the best chemical mechanism (i.e. the one providing the best results among the tested ones), the error in the NOx prediction is always lower than 25% for all the simulations.Once the methodology is validated, the effect of spark and injection timings on NOx is discussed. Such a deepening is useful to emphasize the potential of the CFD to investigate phenomena leading to emission formation and, thus, to optimize engine parameters for NOx reduction.

Hydrogen Engine Development toward Performance Parity with Conventional Fuel-Type Engines While Ensuring Ultralow Tailpipe Emissions

Hydrogen Engine Development toward Performance Parity with Conventional Fuel-Type Engines While Ensuring Ultralow Tailpipe Emissions

The Effect of Injection Strategy on the Mixture Formation and Combustion in a Direct Injection Hydrogen Engine

The Effect of Injection Strategy on the Mixture Formation and Combustion in a Direct Injection Hydrogen Engine

Developments in world motor vehicle production and the future of hydrogen use in the automotive industry

This article provides an overview of World motor vehicle production and hydrogen utilization technologies for current and future use in the Automotive Industry. Hydrogen is the simplest and most abundant element in the Universe; however it is always combined with other elements. Still, the costs of hydrogen production from its combined elements remain high compared to other energy sources; it is extremely difficult to store onboard, the use of natural gas as a feedstock emits CO2, and there are many technical challenges to overcome with these systems. Many years of research and development, as well as changes to the energy infrastructure, may be required before hydrogen can have a significant impact on Earth energy use. In the very long term, electricity and hydrogen are likely to become the preferred complementary energy vectors. Hydrogen and the fuel cell are complementary and each enables the other. Nowadays, due to their low production costs, hydrogen engines are becoming more and more advantageous over fuel cells and are be-coming more widespread. Ammonia has the potential to be used as a hydrogen carrier, mainly due to its high hydrogen capacity. A significant effort would be needed to develop onboard ammonia cracker systems or direct ammonia fuel cells for vehicles.

Optimizing hydrogen spark-ignition engine performance and pollutants by combining VVT and EGR strategies through numerical simulation

Hydrogen combustion engines are considered one of the leading solutions for decarbonizing road transport, mainly due to the possibility of adapting current engines for hydrogen operation with minor changes. This research extensively analyzes the effect of combined EGR (exhaust gas recirculation) and VVT (variable valve timing) strategies on the performance and emissions of a commercial turbocharged SI engine fueled with hydrogen. To this end, a 1D model of the said engine, widely validated for gasoline operation, was adapted to simulate the engine's behavior with hydrogen. This adaptation involved hardware changes and the implementation of a predictive hydrogen combustion submodel, previously calibrated using experimental data from a single-cylinder engine of similar geometry. Firstly, 400 hydrogen engine simulations without EGR were conducted to optimize the VVT system for fuel efficiency over a wide operating range. A detailed explanation of the causality of varying valve overlap on pumping losses, in-cylinder gas composition, and combustion is provided from these simulations. Then, a series of EGR sweeps were simulated to study its impact on performance and NOx at various degrees of load; concluding that diluting with EGR, rather than air, leads to reduced NOx emissions in exchange for slightly increased fuel consumption.

Numerical Investigation of the Combustion Characteristics of a Hydrogen-Fueled Engine with Water Injection

The quest for clean, efficient engine technologies is imperative in reducing transportation’s environmental impact. Hydrogen, as a zero-emission fuel, offers significant potential for internal combustion engines but faces challenges such as optimizing engine performance and longevity. Water injection is proposed as a solution, yet its effects on engine performance require thorough investigation. This study bridges the knowledge gap by examining various water injection ratios (WIRs) and their impact on engine performance, focusing on the balance between power output and engine longevity. We identified the existence of an optimum WIR (e.g., 10% in this study), which provides peak performance with minimal adverse effects on engine performance and health. Computational simulations of a single-cylinder engine revealed how WIRs influence in-cylinder temperature, pressure, and IMEP, emphasizing the nuanced benefits of water injection. Additionally, our analysis of turbulence, through TKE and dissipation rate, deepens the understanding of combustion and fuel efficiency in hydrogen engines. This research provides valuable guidance for optimizing engine operations and paves the way for advanced water injection systems in hydrogen engines, marking a significant step towards cleaner engine technology.

Optimizing heat transfer predictions in HCNG engines: A novel model validation and comparative study via quasi-dimensional combustion modeling and artificial neural networks

Heat transfer from the walls of engine has a significant role on engine combustion, performance and emission characteristics. The study objectives to showcase the efficacy of the new model through an analysis by comparison with existing heat transfer models. New model is based on woschni model in which pressure and temperature is replaced by other fluid properties like density, thermal conductivity and dynamic viscosity. A series of experiments were conducted on a compressed natural gas internal combustion engine across varying hydrogen fractions, EGR ratios, engine speeds and different loads under stoichiometric conditions. The study demonstrates the efficacy of the proposed model by constantly achieving high prediction quality across a wide range of engine calibration coefficients by using Quasi-dimensional Combustion Model (QDCM) on MATLAB. Comparative analyses of new model with different heat transfer models were undertaken to validate the heat transfer rates with experimental results across a broad spectrum of operational conditions. It is observed that heat transfer rate is increased by increasing the engine load as 25%, 50%, 75% and 100% as 90.57J/deg, 130.12J/deg, 200.02J/deg, and 260.26J/deg with new model correspondingly. Heat transfer rate reduced by rise in engine speed with 1100 rpm, 1200 rpm, 1500 rpm and 1700 rpm is as 32.91 kW, 32.16 kW, 25.36 kW and 18.03 kW by new heat transfer model respectively. Artificial neural network (ANN) popular backpropagation algorithm is adopted to predict the heat transfer rate of HCNG engine, the five-input and one-output network structure are used. The values of correlation coefficient (R) and mean square error (MSE) were 0.99957 and 0.22667, 0.99998 and 0.010776, 0.99253 and 4.4762, 0.9961 and 1.2329, 0.99994 and 0.025108 for Woschni, New_Model, Chang, Sitkei and experimental respectively. This research work offers that ANN is a wise option for conventional modeling systems. In this way, the heat transfer rate of hydrogen-added CNG engines may be precisely predicted using ANN modeling.

Combustion characteristics analysis and performance evaluation of a hydrogen engine under direct injection plus lean burn mode

Direct injection plus lean burn technology can effectively control combustion processes and reduce carbon emissions of hydrogen engines. Hence, hydrogen direct injection strategy optimization is a key means to improve engine performance and achieve low emissions. Thus, a three-dimensional transient calculation model coupled chemical reaction mechanism is established, and its reliability and accuracy are systematically evaluated using experimental data. Then, the effects of hydrogen direct injection strategies on the hydrogen-air mixing and combustion process are investigated. The results indicate that the ideal mixture stratification law is that the gas fuel concentration is gradually stratified from the ignition center to the periphery region. The maximum indicated work is obtained for the B-60° scheme which its injection position is near the intake side and 7.5 mm from the cylinder center on the X-axis. The optimal hydrogen injection angles vary with different injection positions by evaluating engine performance, specifically, 60° is optimal for injection position B, while 30° is best for injection position C which is between intake and exhaust and 40 mm from the cylinder center on the Y-axis. Finally, the achieved maximum thermal efficiencies of 41% and indicated power of 4.29 kW for the B-60° scheme, and its nitric oxide can meet the Europe V emission standards (7.5 g/kWh). This research can offer theoretical guidance for designing and optimizing fuel injection strategies for hydrogen energy engines, and it is relevant for promoting carbon neutrality and cleaner production.

A Comparative Analysis of Friction and Energy Losses in Hydrogen and CNG Fueled Engines: Implications on the Top Compression Ring Design Using Steel, Cast Iron, and Silicon Nitride Materials.

Optimizing the design of the top compression ring holds immense importance in reducing friction across both traditional Internal Combustion (IC) engines and hybrid power systems. This study investigates the impact of alternative fuels, specifically hydrogen and CNG, on the behavior of top piston rings within internal combustion (IC) engines. The goal of this approach is to understand the complex interplay between blow-by, fuel type, material behavior, and their effects on ring friction, energy losses, and resulting ring strength. Two types of IC engines were analyzed, taking into account flow conditions derived from in-cylinder pressures and piston geometry. Following ISO 6622-2:2013 guidelines, thick top compression rings made from varying materials (steel, cast iron, and silicon nitride) were investigated and compared. Through a quasi-static ring model within Computational Fluid Dynamics (CFD), critical tribological parameters such as the minimum film and ring friction were simulated, revealing that lighter hydrogen-powered engines with higher combustion pressures could potentially experience approximately 34.7% greater power losses compared to their heavier CNG counterparts. By delving into the interaction among the fuel delivery system, gas blow-by, and material properties, this study unveils valuable insights into the tribological and structural behavior of the top piston ring conjunction. Notably, the silicon nitride material demonstrates promising strength improvements, while the adoption of Direct Injection (DI) is associated with approximately 10.1% higher energy losses compared to PFI. Such findings carry significant implications for enhancing engine efficiency and promoting sustainable energy utilization.

Effect of injection strategy on the hydrogen mixture distribution and combustion of the hydrogen-fueled engine with passive pre-chamber ignition under lean burn condition

Turbulent jet ignition (TJI) effectively achieves lean and stable combustion in hydrogen engines. However, research on injection strategies for TJI hydrogen engines is still lacking. In this study, experimental methods investigated the effects of single and split injection strategies on the combustion and emissions of TJI hydrogen engines under medium loads. The numerical simulation reveals the operational characteristics of fuel distribution, ignition capability, and energy conversion in the pre-chamber at different injection times in a single injection strategy. This work is conducted at 1600 rpm with a manifold absolute pressure of 70 kPa. The experimental results indicate that the delay of the start of injection (SOI) can enhance the performance of the TJI hydrogen engine. However, as SOI approaches TDC, emissions worsen, and combustion stability decreases. When SOI is 90°CA BTDC, the brake mean effective pressure (BMEP) and brake thermal efficiency (BTE) can achieve 3.1 bar and 32.9 %, with the coefficient of variation of the IMEP (COVIMEP) of 1.6 % and lower emissions. For the split injection strategy, delaying the secondary end of injection (SEOI) can increase BMEP and BTE. As SEOI gradually delays the TDC, emissions deteriorate sharply. Under the split injection strategy, COVIMEP is higher, which is unfavorable for hydrogen engine applications.

An investigation on the H2O, unburned H2 and NO emission characteristics from a direct injection hydrogen engine

Hydrogen engines show great potential as a power source with good combustion performance, zero carbon emissions, and diverse sources. However, the exhaust emission characteristics with high water vapor (H2O) content have not yet been clarified. This study presents the exhaust emissions of a heavy-duty direct-injection hydrogen engine under various operational parameters, with a focus on the H2O content. The results reveal important exhaust emissions characteristics of the hydrogen engine, including lower exhaust temperature (200 °C–400 °C), higher unburned H2 emissions (up to 17100 ppm), less nitrogen oxide (NO) generation (<1000 ppm), and higher H2O content (6%–40%). Additionally, unburned H2 rises, and NO and H2O decrease as the excess air ratio (λ) increases. When λ is greater than 3, NO levels fall sharply to below 100 ppm. Optimal emissions performance is achieved with a 5 °CA BTDC ignition timing where low levels of H2, H2O, and NO are maintained. Increasing hydrogen injection pressure decreases H2 but raises exhaust temperature, H2O, and NO emissions. Excessively delaying hydrogen injection timing adversely affects the concentration gradient in the cylinder, increasing unburned H2 emissions. The best emissions performance is observed at a hydrogen injection timing of 110 °CA BTDC.