Hydrogen Blends Research Articles

Experimental investigation of the characteristics of combustion in the full hydrogen blending range of methane-hydrogen mixtures in a MILD model combustor

MILD combustion technology is expected to enable safe and stable low-emission combustion of hydrogen-doped fuels, or pure hydrogen fuels, in gas turbines designed for zero-carbon emissions. To improve combustion stability at high hydrogen content while maintaining low NOx emissions, a MILD model combustor was modified, specifically the upstream fuel/air distribution and mixing method. And the combustion stability of the modified MILD combustor was significantly extended. Here, the combustion characteristics of the modified MILD combustor are experimentally investigated at 0–100% hydrogen contents. The investigation results demonstrate that unlike the combustion stability region at low hydrogen concentrations, a narrow thermoacoustic instability region occurs at 60% hydrogen content. As the hydrogen content increases, the instability region becomes narrower while shifting towards lower equivalence ratios. The change in hydrogen content is accompanied by a significant peak energy migration of the dynamic pressure. The OH* chemiluminescence images showed that the heat release zone became more concentrated with increasing hydrogen content. And the dominance of high-frequency peak energy correlates to lateral motion, whereas the dominance of low-frequency peak energy corresponds to axial motion. This transition in flame dynamics occurs not only for different hydrogen contents but also for different equivalence ratios of pure hydrogen combustion. In contrast, NOx emissions are not sensitive to hydrogen content. At the same time, the MILD model combustor produces low emissions, with NOx emissions of less than 10 ppm@15%O2 at adiabatic flame temperatures ranging from 1200 K to 2100 K. These results show that the MILD model combustor has favorable fuel suitability.

Numerical simulation on combustion characteristics of methane/hydrogen blended fuel for non-premixed conical bluff body burner

Blending hydrogen into methane impacts flame stability, morphology, and pollutant emissions. This study, set against the backdrop of hydrogen-enriched natural gas combustion technology, employs a non-premixed coaxial burner with conical bluff body to create recirculation zones for flame stabilization. Combining EDC and GRI-Mech 3.0, the research fills in the gap of effects of hydrogen blending ratio (0–100%) and equivalence ratio vary (0.4–1.4) within a wide range. Keeping equivalence ratio and fuel volume flow rate as constants, as increasing hydrogen blending ratio, the mean velocity in the chamber decreases, the size of vortex structure located in outer recirculation zones reduces, and the flame length is shortened, illustrating the reaction zone shifts to chamber inlet. Furthermore, when Ф = 1.4, average temperature and temperature uniformity are averagely larger 59.82% and 4.21% than that under Ф = 0.4. The CO2 emission at XH2 = 80% is 54.70% averagely lower than that at XH2 = 0%, but peak concentration of NO increases.

A numerical study on hydrogen blending in natural gas pipeline by a T-Pipe

In order to study the flow blending and transporting process of hydrogen that injects into the natural gas pipelines, a three-dimensional T-pipe blending model is established and the flow characteristics are investigated systematically by the large eddy simulation (LES). Firstly, the mathematical formulation of hydrogen-methane blending process is provided and the LES method is introduced and validated by a benchmark gas blending model having experimental data. Subsequently, the T-pipe blending model is presented, and the effects of key parameters, such as the velocity of main pipe, hydrogen blending ratio, diameter of hydrogen injection pipeline, diameter of main pipe and operating pressure on the hydrogen-methane blending process, are studied systematically. The results show that, under certain conditions, the gas mixture will be stratified downstream of the blending point, with hydrogen at the top of the pipeline and methane at the bottom of the pipeline. In the no-stratified scenario, the mixing distance increases at lower hydrogen mixing ratio and larger diameter of the hydrogen injection pipe or the main pipe. Finally, based on the numerical results, the underlying physics of the stratification phenomenon during the blending process are explored and an indicator for stratification is proposed using the ratio between the Reynolds numbers of the natural gas and hydrogen.

Thermodynamic and environmental analyses of a hydrogen-enriched natural gas oxy-fuel combustion power plant

Hydrogen-enriched natural gas is regarded as a promising low-carbon fuel in clean energy field. A hydrogen-enriched natural gas oxy-fuel combustion power plant is established to study the effect of hydrogen content on system thermodynamic performance. Three different diluents including recycled flue gas (RFG), H2O, and CO2 are used to moderate the high combustion temperature. The transcritical CO2 cycle is adopted to efficiently utilize flue gas waste heat. As the hydrogen blending ratio increases from 0 to 0.5, the efficiency of the O2/RFG system, O2/H2O system and O2/CO2 system increases by 1.45%, 1.13% and 1.16%, respectively. The RFG system is preferable to realize high efficiency that can reach 50.23%. In the proposed systems, the carbon capture rate (CCR) decreases while specific CO2 emission (SECO2) increases with the hydrogen addition. In O2/RFG system, the CCR reaches a minimum of 99.09% when SECO2 is 3.81. The study results can have a positive influence on the utilization of hydrogen energy.

Development of a modified gas turbine-based sustainable power generation and water treatment system; Economical/environmental considerations and data-driven optimization

Developing environmentally friendly solutions that optimize existing power plants while considering economic factors is crucial for ensuring sustainable energy production and mitigating environmental impact. This study promotes a gas turbine-based power plant design that prioritizes environmental concerns and underscores its versatility. The proposed setup is composed of various components, including a gas turbine, a Rankine cycle (RC), an organic Rankine cycle (ORC), a reverse osmosis (RO) desalination unit, a proton exchange membrane electrolyzer (PEME), and a hydrogen blending module. This system engenders the simultaneous generation of hydrogen, electrical power, and desalinated water. Additionally, the direct utilization of produced hydrogen in the proposed system offers improved technical performance and serves as an effective means to mitigate greenhouse gas emissions. A resilient programming code is formulated to systematically evaluate the system through the lenses of techno-economic and environmental considerations. Incorporating innovative modifications into the existing system resulted in an 8% cost reduction, a 1.2% decrease in carbon dioxide emissions, and a 5% enhancement in exergy efficiency. To attain optimal performance of the system, a data-driven and machine learning methodology is employed, wherein two distinct optimization scenarios are used to define the conditions that yield the utmost system performance. In the first scenario, the optimal values for cost, exergy efficiency, and normalized CO2 emissions have been computed as 39%, 5963 $/h, and 367.4 kg/MWh, respectively. In the subsequent scenario, the optimized system demonstrates the capability to generate a fresh water flow rate of 840.4 kg/s. Concurrently, the cost rate for the system equates to 7054.5 $/h.

Effect of hydrogen ratio on leakage and explosion characteristics of hydrogen-blended natural gas in utility tunnels

Based on computational fluid dynamics technology, the effect of hydrogen blending ratio (HBR) on the concentration distribution of leaked gas diffusion in utility tunnels was investigated, and based on this, the explosion characteristics of hydrogen-blended natural gas (HBNG) were studied in an inhomogeneous concentration field. The results showed that the concentration field of HBNG gradually stabilized in the downstream of the leak site, and the peak concentration increased linearly with HBR. When HBR≤5%, a high concentration region above the upper explosive limit is formed inside the gas cloud. This characteristic of the distribution induces secondary combustion in utility tunnels. The maximum flame velocity and steady acceleration distance increase with the increase of HBR. The flame shape is significantly affected by the concentration field distribution. The explosion overpressure induced by the real concentration field created multiple peak structures that exacerbated the explosion disaster complexity. The first overpressure peak at the ends was formed by the superposition of the precursor shock wave and its reflected wave, and those at other locations are caused by the shock waves. However, all maximum overpressure peaks are formed by the superposition of multiple reflections of the explosion wave. The maximum peak overpressure at both ends of the tunnel is higher than that in the middle. The explosion overpressure induced by the inhomogeneous gas cloud is lower than that caused by homogeneous gas cloud under the same volume. The research results can provide an effective reference for the anti-explosion design and risk assessment of utility tunnel.

A Comprehensive Analysis of Hydrogen–Gasoline Blends in SI Engine Performance and Emissions

This study investigates the influence of adding hydrogen as an additive to gasoline in a four-stroke engine, utilizing comprehensive thermodynamic comparative analysis conducted with self-developed engine model. This research aims to assess the performance, emissions, and efficiency of the engine when using gasoline–hydrogen blends, and to provide insights into the potential benefits of this approach. First, the engine performance and emissions under different hydrogen blending levels were examined. A range of different air/fuel ratios (rich to lean) and varying percentages of hydrogen were considered. This systematic variation allowed for a detailed evaluation of the influence of hydrogen content on combustion efficiency, power output, and emissions characteristics. The analysis results included key parameters such as indicated specific fuel consumption and mean effective pressure. Additionally, the study focused on the range prediction of nitrogen oxide (NOx) emissions, which are a critical environmental concern associated with internal combustion engines. The analysis of pressure and temperature profiles throughout the engine cycle shed light on the combustion characteristics and efficiency improvements associated with hydrogen addition. In terms of emissions, the study projected that all emissions were reduced except NOx, which is highly dependent on hydrogen percentage, and might be reduced in some cases, but with the higher temperatures and pressures associated with hydrogen addition, in most cases, there is actually a NOx increase, especially at higher engine loads.

Ammonia/hydrogen laminar flame speed measurements at elevated temperatures

Laminar flame speeds of ammonia/hydrogen blends diluted in a mixture of 79% Ar and 21% O2 (referred to as “airgon”) were measured for the first time at high temperatures exceeding 500 K and atmospheric pressure using the shock tube flame speed method. Lean (ϕ = 0.8), stoichiometric (ϕ = 1) and rich (ϕ = 1.2) mixtures, with hydrogen fuel fractions xH2 = 0.2, 0.4, and 0.6 were studied in the temperature range of 500–820 K behind reflected shock waves. A significant enhancement in flame speeds and improved flame morphology was observed with increasing concentrations of hydrogen. Equivalent fuel/air data were computed from fuel/airgon measurements using a mixture-scaling approach and compared against available literature data. Although current data do not overlap with the temperatures of data in the literature, the full 300–800 temperature range of experimental data remain consistent with a non-Arrhenius correlation, while a power-law fit does not capture the full data trend. 1-D flame speed simulations were conducted using five recent chemical kinetic models of ammonia combustion available in the literature. Large disagreement was found among the models, with the model by Zhou et al. agreeing well with experiments at all conditions studied in this work. Sensitivity analyses were performed, and the most relevant reactions involved in the computation of flame speed, according to the models, were identified. Overall, the experimental data and modeling demonstrate the value of using blends of ammonia and hydrogen to improve the combustion characteristics of ammonia as a carbon-free fuel.

Investigation of Hydrogen-Blended Natural Gas Pipelines in Utility Tunnel Leakage and Development of an Accident Ventilation Strategy for the Worst Leakage Conditions

The development of hydrogen-blended natural gas (HBNG) increases the risk of gas transportation and presents challenges for pipeline security in utility tunnels. The objective of this study is to investigate the diffusion properties of HBNG in utility tunnels and evaluate the effectiveness of various ventilation mechanisms. The numerical simulation software Fluent 2023 R1 is applied to simulate and analyze the leakage of small holes in a HBNG pipeline in the natural gas compartment. By examining the leaking behavior of HBNG through small holes in different circumstances, we aimed to identify the most unfavorable operational situation for leakage. Subsequently, we analyzed the ventilation strategy for sub-high-pressure pipes at various pressure levels in this unfavorable condition. This study’s findings demonstrate that blending hydrogen improves the gas diffusion capacity and increases the likelihood of explosion. The primary factors that influence the pattern of leakage are the size of the leaking holes and the pressure of the pipeline. The gas compartment experiences the most unfavorable working conditions for natural gas pipeline leaks when there are higher pressures, wider leak openings, higher hydrogen blending ratios (HBRs), and leaks in close proximity to an air inlet. When the HBR is 20%, the minimum accident ventilation rates for pressures of 0.4 MPa and 0.8 MPa are 15 air changes per hour and 21 air changes per hour, respectively. The maximum allowable wind speed for accident ventilation is 5 m/s, as regulated by China’s national standard, GB 50838-2015. This regulation makes it difficult to minimize the risk of leakage in a 1.6 MPa gas pipeline. It is recommended to install a safety interlock device to quickly shut off the pipeline in the event of a leak in order to facilitate the dispersion of the substance.

A study of the effect of hydrogen on methane deflagration characteristics in a square confined space

Macroscopic and microscopic explosion kinetic properties of H2/CH4/air mixtures are investigated. The explosion characteristics of CH4/air mixtures with different hydrogen blending ratios(0–25%) are investigated experimentally. It is found that the increase of hydrogen blending ratios has almost no effect on the peak overpressure of the methane gas explosion, but the rate of maximum pressure rise, the explosion index and the flame propagation velocity increase significantly. The effect of hydrogen blending ratios on the chemical kinetics of CH4-air mixtures is analyzed based on the CHEMKIN software. The concentration of key radicals, which play a major role in the reaction, does not change much as the hydrogen blending ratio increases. A prediction model of explosion overpressure in a square confined space is established using the segmentation method, and it is verified that the relative errors between the model calculation results and experimental results are less than 10%.

Effect of hydrogen blending on the accuracy of smart gas meters

The exploitation of green hydrogen blending with natural gas (NG) is expected to contribute in lowering greenhouse gas emissions and fostering the share of renewable energy sources (RES). The NG infrastructure, in fact, can act as a storage facility for green hydrogen produced from excess RES, also providing flexibility to the electric system. However, the unbalance of the networks and the raise of protection issues for consumers may occur as a consequence of the potential decay of the metrological performance of gas meters operating with natural gas and hydrogen blends. In this paper, the authors present the results of an experimental campaign aimed at analysing the effect of hydrogen blending on the accuracy of smart domestic gas meters. Experimental tests were performed in the laboratory using air, natural gas and gas-hydrogen blends up to 23%vol. The results show no criticalities occur for diaphragm and ultrasonic gas meters, regardless of the hydrogen content. On the other hand, thermal mass gas meters show good reliability when hydrogen blends are within 2%vol, whereas for higher hydrogen contents, reliability is demonstrated only when they are equipped with a specific new design routine capable to address the gas quality changes.

Combustion and emission characteristics of ammonia-hydrogen fueled SI engine with high compression ratio

Ammonia combustion offers the advantage of zero carbon emissions. However, its high ignition energy requirement and slow flame propagation limit its use as an engine fuel. Employing a technological approach that combines a high compression ratio with spark ignition can be beneficial for enhancing ammonia combustion, and this approach warrants further in-depth research. This study investigates the combustion of ammonia within a spark-ignition engine with a compression ratio of 15:1. It enhances combustion by introducing hydrogen as a reactivity-enhancing fuel. Both ammonia and hydrogen are introduced into the engine's intake port. The findings suggest that efficient pure ammonia combustion occurs at low engine speeds (1000 r/min) and high brake mean effective pressure (BMEP exceeding 0.6 MPa). Pure ammonia combustion achieves a brake thermal efficiency of 33.7% at a BMEP of 0.94 MPa. Introducing hydrogen at an energy ratio of 2–16% expands the engine's load range. With hydrogen blending, the efficiency rises to 35.8% at a BMEP of 0.63 MPa. The research on NOx emissions reveals that, under specific operating conditions, there is a reduction reaction between unburned ammonia and NOx, leading to a decrease in NOx emissions as BMEP increases. This study can offer support for the application of ammonia engines.

Low carbon economic dispatch of integrated energy systems considering utilization of hydrogen and oxygen energy

Power-to-gas (P2G) facilities use surplus electricity to convert to natural gas in integrated energy systems (IES), increasing the capacity of wind power to be consumed. However, the capacity limitation of P2G and the anti-peaking characteristic of wind power make the wind abandonment problem still exist. Meanwhile, the oxygen generated by P2G electrolysis is not fully utilized. Therefore, this study proposes a low-carbon economic dispatch model considering the utilization of hydrogen and oxygen energy. First, the two-stage reaction model of P2G is established, and the energy utilization paths of hydrogen blending and oxygen-rich deep peaking are proposed. Specifically, hydrogen energy is blended into the gas grid to supply gas-fired units, and oxygen assists oxygen-rich units into deep peaking. Subsequently, the stochastic optimization is used to deal with the uncertainty of the system, and the objective function and constraints of the IES are given to establish a low-carbon dispatch model under the energy utilization model. Finally, the effectiveness of the proposed method is verified based on the modified IEEE 39-node electric network, 20-node gas network and 6-node heat network models.

Hydrogen diffusion simulation of the X80 pipeline steel girth weld zone considering the synergistic effect of the structure–stress–concentration field

Hydrogen embrittlement failure, caused by hydrogen permeation and diffusion in the girth weld zone of pipelines, is the main obstacle to large-scale hydrogen blending transportation. Accordingly, a three-dimensional model of the girth weld zone of X80 pipeline steel was established. Considering the influence of structural inhomogeneity in the weld zone, multi-field sequential coupling simulation technology was used to analyze the diffusion process of hydrogen under the combined action of the residual stress and hydrogen concentration fields. A synergistic mechanism between hydrogen enrichment, structural characteristics, and residual stress in the weld zone was revealed. The results indicated that the structural inhomogeneity in the girth weld zone and residual stress field significantly influenced the hydrogen concentration distribution. Moreover, for the hydrogen diffusion process at the grain boundaries, the impact of the residual stress was greater than that of the structural inhomogeneity. This study further clarifies the spatial distribution of hydrogen atoms induced by multi-field coupling in the weld zone and provides a reference for the safety assessment of girth weld layers from an engineering perspective.

Study on the Influence of Hydrogen Blended Transportation on the Safety of Existing X70 Steel in Gas Distribution Pipeline Network

Coal to gas is one of the natural gas sources utilized in Beijing, with a hydrogen blend concentration range from 1% to 3% and reaching up to 5% in specific cases. In order to evaluate the safety of transporting hydrogen blended natural gas with X70 pipeline steel in distribution pipelines, this study first conducted the slow strain rate tensile tests under a total pressure of 4 MPa in hydrogen environment. The results show that X70 steel exhibits highly sensitive to a hydrogen blending ratio of 5%. Subsequently, four types of hydrogen compatibility tests were conducted in the above sensitive hydrogen partial pressure include the impact toughness test, fracture toughness test, fatigue crack growth test, and fastening disk pressure test. The findings demonstrated that hydrogen blended natural gas has virtual no effect on the impact and fracture toughness, with only 10% reduction in fatigue crack growth threshold. Finally, based on fatigue life analysis by fracture mechanics evaluation, it can be concluded that the existing natural gas pipe of X70 steel is capable to operate safely over 40 years under a total pressure of 4 MPa with a hydrogen blend concentration of 5%.

Study on the Physical Properties of Hydrogen-Doped Natural Gas Based on Equation of State

As a zero-emission green clean energy, hydrogen energy is an important means to achieve the strategic goal of carbon neutrality and an important part of the energy Internet. Hydrogen-doped natural gas transportation is an economical and feasible scheme to realize long-distance transportation of hydrogen by using the existing natural gas pipeline network. However, the addition of hydrogen to natural gas will cause obvious changes in the physical properties of the transport medium, which will have a certain impact on the transport characteristics and flow measurement of the pipeline. The main problem is that we need to understand the changes of physical properties after natural gas mixed with hydrogen to ensure the safe operation of natural gas pipe network mixed with hydrogen. Based on this situation, this paper takes BWRS equation as the theoretical basis, selects typical natural gas temperament, calculates and solves the physical parameters of natural gas under different hydrogen blending ratios, and compares them with the standard physical reference values. After verification, the results are used to explore the physical properties of hydrogen-doped natural gas with hydrogen blending ratio, temperature and pressure as variables. The relative average absolute value error (RAAD) of the calculated physical properties of hydrogen-doped natural gas in this paper is less than 2% compared with the reference value of standard physical properties, which can provide theoretical data basis for studying hydrogen-doped pipeline transportation, ensuring pipeline transportation safety and hydrogen-doped natural gas metering.

An approach to coupling the gas flow dynamics and thermodynamics of hydrogen solubility in L485ME steel grade for estimation of fracture toughness

The paper presents the problem of coupling the gas flow dynamics in pipelines with the thermodynamics of hydrogen solubility in steel for the estimation of the fracture toughness. In particular, the influence of hydrogen blended natural gas transmission on hydrogen solubility and, consequently, on fracture toughness is investigated with a focus on the L485ME low-alloy steel grade. Hydraulic simulations are conducted to obtain the pressure and temperature conditions in the pipeline. The hydrogen content is calculated from Sievert’s law and, as a consequence, the fracture toughness of the base metal and heat-affected zone is estimated. Experimental data is used to define hydrogen-assisted crack size propagation in steel as well as to a plane strain fracture toughness. The simulations are conducted for a real natural gas transmission system and compared against the threshold stress intensity factor. The results showed that the computed fracture toughness for the heat-affected zone significantly decreases for all natural gas and hydrogen blends. The applied methodology allows for identification of the hydrogen-induced embrittlement susceptibility of pipelines constructed from thermomechanically rolled tubes worldwide most commonly used for gas transmission networks in the last few decades.

Experimental investigation on combustion and emission characteristics of non-premixed ammonia/hydrogen flame

The use of ammonia and hydrogen as fuels to decarbonise the heavy transport industry has attracted worldwide attention. In this work, a swirl-enhanced combustion test rig has been built to investigate the combustion and emission characteristics of non-premixed ammonia/hydrogen flames. The blowoff limits were first examined to ensure that a range of stable flames could be achieved. Emissions containing nitric oxide (NO), nitrous oxide (NO2), ammonia slip (NH3) and unburnt hydrogen (H2) were then measured with a variety of global equivalence ratios, hydrogen blending ratios, inlet gas temperature, swirl numbers and combustion chamber insulation conditions. The structure of non-premixed ammonia/hydrogen flames and the relationship between excited hydroxyl radicals (OH*) and NO emission were revealed using OH* chemiluminescence profiles. The stable non-premixed ammonia/hydrogen flames were achieved when the hydrogen blending ratio was greater than 20%. The optimal emission performance was achieved under stoichiometric conditions, as determined by combustion efficiency. The insulation conditions of the combustor wall played a key role in the emission results, as significant growth of NO and NO2 as well as a reduction of ammonia slip were found. Although a lower swirl number improved the flame stability range, the increases in NO and NO2 emissions were observed.

Analysis of the effect of the number of injector nozzles on the pressure and heat transfer coefficient in a hydrogen-diesel mixture diesel engine

In reciprocating internal combustion engines, the calculation of the heat transfer coefficient (HTC) is essential to estimate the heat transfer during combustion in the combustion chamber. The HTC calculation takes into account fluid flow and combustion processes and varies as a function of crank angle and location within the chamber. The mean HTC value is commonly used to calculate the thermo-mechanical analysis of various combustion chamber components. In this study, dynamic grids for the intake port, exhaust port and chamber are created in the chamber modelling section of the AVL-Fire software. The intake and combustion processes are then simulated and the calculated pressure data are compared with experimental data at 2800 rpm with 1, 3 and 6 hole injectors. Finally, the distribution of HTC over the chamber walls was evaluated using a time step method. The research also included verification of the HTC results with theoretical data obtained by Woschni and Hohenberg. In addition, with the decreasing availability of fossil fuels and the need for lower exhaust emissions from diesel engines, the use of blends of diesel and hydrogen fuel has become widespread. In this engine, a mixture of 10 % hydrogen and 90 % diesel fuel is used. The final results show that the heat transfer coefficient increases by approximately 1.72 % when hydrogen is added to diesel fuel due to the number of collisions between hydrogen and other fuel components.

Numerical Simulation of Hydrogen–Coal Blending Combustion in a 660 MW Tangential Boiler

With the adjustment of energy structure, the utilization of hydrogen energy has been widely attended. China’s carbon neutrality targets make it urgent to change traditional coal-fired power generation. The paper investigates the combustion of pulverized coal blended with hydrogen to reduce carbon emissions. In terms of calorific value, the pulverized coal combustion with hydrogen at 1%, 5%, and 10% blending ratios is investigated. The results show that there is a significant reduction in CO2 concentration after hydrogen blending. The CO2 concentration (mole fraction) decreased from 15.6% to 13.6% for the 10% hydrogen blending condition compared to the non-hydrogen blending condition. The rapid combustion of hydrogen produces large amounts of heat in a short period, which helps the ignition of pulverized coal. However, as the proportion of hydrogen blending increases, the production of large amounts of H2O gives an overall lower temperature. On the other hand, the temperature distribution is more uniform. The concentrations of O2 and CO in the upper part of the furnace increased. The current air distribution pattern cannot satisfy the adequate combustion of the fuel after hydrogen blending.