Experimental assessment of the combustion performance of an oven burner operated on pipeline natural gas mixed with hydrogen

With the increasing need to reduce greenhouse gas emission and adopt sustainability in combustion systems, injection of renewable gases into the pipeline natural gas is of great interest. Due to high specific energy density and various potential sources, hydrogen is a competitive energy carrier and a promising gaseous fuel to replace natural gas in the future. To test the end use impact of hydrogen injection into the natural gas pipeline infrastructure, the present study has been carried out to evaluate the fuel interchangeability between hydrogen and natural gas in a residential commercial oven burner. Various combustion performance characteristics were evaluated, including flashback limits, ignition performance, flame characteristics, combustion noise, burner temperature and emissions (NO, NO₂, N₂O, CO, UHC, NH₃). Primary air entrainment process was also investigated. Several correlations for predicting air entrainment were compared and evaluated for accuracy based on the measured fuel/air concentration results in the burner. The results indicate that 25% (by volume) hydrogen can be added to natural gas without significant impacts. Above this amount, flashback in the burner tube is the limiting factor. Hydrogen addition has minimal impact on NO_X emission while expectedly decreasing CO emissions. As the amount of hydrogen increases in the fuel, the ability of the fuel to entrain primary air decreases.     

Assessment of the combustion performance of a room furnace operating on pipeline natural gas mixed with simulated biogas or hydrogen

With the inexorable depletion of fossil fuel and the increasing need to reduce greenhouse gas emissions, blending renewable fuels like biogas or renewable hydrogen into natural gas is of great interest. Due to various potential sources and low-carbon or even carbon-free properties, biogas and hydrogen are competitive energy carriers and promising gaseous fuels to replace pipeline natural gas in the future. From the perspective of end users and combustion device manufacturers, one of the major concerns is the influence of the renewable content on the combustion device performance. In addition, the upper limit of renewable gas content percentage in pipeline also interests policy makers and gas utility companies. Therefore, the present study is conducted to investigate the influence of renewable gas content on the operating performance of a residential room furnace. Evaluated combustion performance characteristics include ignition performance, blow-off/flashback limits, burner temperature and emissions (NO, NO₂, N₂O, CO, UHC, NH₃). The results show that 5% carbon dioxide and 15% (by volume) hydrogen can be added to natural gas separately without significant impacts. Above this amount, the risk of blow-off and flashback is the limiting factor. Generally speaking, carbon dioxide addition helps decrease NO_X emission but increases CO emission. However, hydrogen addition up to the amounts studied here in has minimal impact on NO_X and CO emissions.     

Influence of hydrogen addition to pipeline natural gas on the combustion performance of a cooktop burner

Displacing pipeline natural gas with renewable hydrogen is a promising way to reduce the emission of carbon dioxide, which is a major greenhouse gas. However, due to significantly differing characteristics of hydrogen and natural gas, such as flame speed, adiabatic flame temperature and stability limits, the combustion performance of hydrogen/natural gas mixture differs from pure natural gas. From the perspective of residential end users, a key question is: how much hydrogen can be injected into the pipeline natural gas without influencing the performance of the residential burners? A representative cooktop burner is selected to study the influence of hydrogen addition on the combustion and cooking performance. Flashback limits, ignition time, flame characteristics, cooking performance, combustion noise, burner temperature, and various emissions (NO, NO₂, N₂O, CO, unburned hydrocarbon (UHC), NH₃) are evaluated for different levels of hydrogen addition. According to the experimental results, the combustion performance of the cooktop burner is not significantly affected with up to about 15% hydrogen addition by volume, which shows the feasibility of utilizing hydrogen on existing cooking appliances without any modification. The experiment methodologies and results in this study will serve as a reference for future test and emission regulation standards on domestic burners.     

A compilation of operability and emissions performance of residential water heaters operated on blends of natural gas and hydrogen including consideration for reporting bases

The impact of hydrogen added to natural gas on the performance of commercial domestic water heating devices has been discussed in several recent papers in the literature. Much of the work focuses on performance at specific hydrogen levels (by volume) up to 20–30% as a near term blend target. In the current work, new data on several commercial devices have been obtained to help quantify upper limits based on flashback limits. In addition, results from 39 individual devices are compiled to help generalize observations regarding performance. The emphasis of this work is on emissions performance and especially NOx emissions. It is important to consider the reporting bases of the emissions numbers to avoid any unitended bias. For water heaters, the trends associated with both mass per fuel energy input and concentration-based representation are similar For carbon free fuels, bases such as 12% CO2 should be avoided. In general, the compiled data shows that NOx, NO, UHC, and CO levels decrease with increasing hydrogen percentage. The % decrease in NOx and NO is greater for low NOx devices (meaning certified to NOx <10 ng/J using premixing with excess air) compared to conventional devices (“pancake burners”, partial premixing). Further, low NOx devices appear to be able to accept greater amounts of hydrogen, above 70% hydrogen in some cases, without modification, while conventional water heaters appear limited to 40–50% hydrogen. Reporting emissions on a mass basis per unit fuel energy input is preferred to the typical dry concentration basis as the greater amount of water produced by hydrogen results in a perceived increase in NOx when hydrogen is used. While this effort summarizes emissions performance with added hydrogen, additional work is needed on transient operation, higher levels of hydrogen, system durability/reliability, and heating efficiency.     

Experimental study of the combustion of natural gas and high-hydrogen content syngases in a radiant porous media burner

The primary objective of this work is to study the blending of natural gas in equimolar proportions with three high hydrogen content syngases in a radiant porous media burner. We examined the effects of the composition of the syngases, the fuel-to-air ratio and the thermal input on the flame stability, the radiation efficiency and the pollutant emissions (CO and NOx). In this study, we emulated the syngases with H₂–CO mixtures, in which the H₂ to CO ratio was varied between 1.5 and 3. Additionally, pure natural gas was also used as a base fuel for comparison. The thermal inputs evaluated in this study correspond to two values (300 and 500 kW/m2) found in practical applications. The results indicate that the thermal input and the fuel-to-air ratio significantly influenced the temperature profile in the radiant porous media burner, the radiation efficiency, and the pollutant emissions. On the other hand, contrary to what was observed in other studies for lower hydrogen concentrations, we found that substituting natural gas with high hydrogen content syngases (up to 50%) affected the flame stability limits. Significant differences were also observed for the radiation efficiencies and pollutant emissions.     

Experimental investigation on performance of hydrogen additions in natural gas combustion combined with CO2

Natural gas with H₂ is widely used for lean-burn combustion, which leads to NO_x emission as the main problem for it. For decreasing NO_x emission and increasing thermal efficiency, the investigation on seeking the influence of H₂ fractions on the mixture of CH₄ and CO₂ was conducted. Firstly, the ignition timing was decided through thermal efficiency and brake mean effective pressure (BMEP) for CH₄ only. Then, combustion characteristics of CH₄, CH₄+CO₂ and CH₄+CO₂+H₂ were compared with volume percentage of H₂ changing from 5% to 30%. Finally, the H₂ injection strategy was checked between closed and open valve injections. Among these discussions, thermal efficiency, power output, BMEP and fuel consumption were evaluated. Results show that CO₂ addition decreases power output and BMEP, leading to much more fuel consumption and lower thermal efficiency. When H₂ is added, at the rich mixture conditions (λ＜1.0), power output and thermal efficiency decrease sharply as the mixture is enriched. However, at the lean-burn conditions (λ＞1.0), the decrease in flow rate of lower heating value (LHV) and increase in power output finally result in the higher efficiency with H₂ addition. Moreover, when λ＞1.0, both low fuel consumption and high efficiency can be obtained with H₂ addition to achieve the high BMEP. Furthermore, the open valve injection could obtain higher thermal efficiency, power output and BMEP with lower fuel consumption, suggesting that the H₂ injection strategy should be well controlled with the ignition timing.     

Engine characteristics of emissions and performance using mixtures of natural gas and hydrogen

An evaluation was performed on the efficiency and emissions from an engine fuelled with compressed natural gas (CNG) and a mixture of natural gas and hydrogen, respectively. The mixtures of CNG and hydrogen were named HCNG.     

Combustion performance of low-NOx and conventional storage water heaters operated on hydrogen enriched natural gas

Adding renewable hydrogen into natural gas pipeline would bring down the net gas C/H ratio and hence the CO₂ emissions. Also, it can help stabilize electric grids and maximize the renewable output of intermittent energy sources (solar, wind, etc.) via power-to-gas pathway. However, hydrogen differs in its chemical and physical characteristics (flammability range, flame speed, density, adiabatic flame temperature, energy content, etc.) than natural gas. Before transitioning to hydrogen admixing into pipelines, a general agreement on maximum hydrogen tolerance pertaining to end use (residential appliances) operation needs to be established. Focusing on the combustion performance of two representative models of storage water heaters (conventional and low-NO_x) in California, this research addresses how much H₂ content in natural gas can be tolerated without loss of critical performance parameters with reliable operation. Characteristics like flashback, ignition delay, flame structure, and emissions (NO_x, NO, CO, CO₂, UHC, and NH₃) at different concentrations of H₂ admixed with natural gas is investigated. The present study shows <10% H₂ can be added to natural gas without any loss of efficiency for both the low-NO_x and conventional storage water heater. This work also aims to provide a brief review of burner configuration and emission regulation pertaining to water heating owing to a gap in the literature.     

Study on the stratification of the blended gas in the pipeline with hydrogen into natural gas

When blending hydrogen into existing natural gas pipelines, the non-uniform concentration distribution caused by the density difference between hydrogen and natural gas will result in the fluctuations of local hydrogen partial pressure, which may exceed the set one, leading to pipeline failure, leakage, measurement error, and terminal appliance. To solve the problem, the H₂–CH₄ stratification in the horizontal and undulated pipe was investigated experimentally and with numerical simulations. The results show that in the gas stagnant situation, hydrogen-methane blending process will cause an obvious stratification phenomenon. The relations between the elevation, pressure, hydrogen fraction, etc., and the gas stratification are figured out. Moreover, even when the blended gas flows at a low rate, the hydrogen-caused stratification should also be considered. Thereafter, the blended gas should be controlled into a situation with low pressure and high speed, which could help to set the pressure, speed, the fraction of H₂.     

The influences of hydrogen on the performance and emission characteristics of a heavy duty natural gas engine

Because blending hydrogen with natural gas can allow the mixture to burn leaner, reducing the emission of nitrogen oxide (NO_x), hydrogen blended with natural gas (HCNG) is a viable alternative to pure fossil fuels because of the effective reduction in total pollutant emissions and the increased engine efficiency.In this research, the performance and emission characteristics of an 11-L heavy duty lean burn engine using HCNG were examined, and an optimization strategy for the control of excess air ratio and of spark advance timing was assessed, in consideration of combustion stability. The thermal efficiency increased with the hydrogen addition, allowing stable combustion under leaner operating conditions. The efficiency of NO_x reduction is closely related to the excess air ratio of the mixture and to the spark advance timing. With the optimization of excess air ratio and spark advance timing, HCNG can effectively reduce NO_x as much as 80%.     

Effect of natural gas enrichment with hydrogen on combustion characteristics of a dual fuel diesel engine

Environmental benefits are one of the main motivations encouraging the use of natural gas as fuel for internal combustion engines. In addition to the better impact on pollution, natural gas is available in many areas. In this context, the present work investigates the effect of hydrogen addition to natural gas in dual fuel mode, on combustion characteristics improvement, in relation with engine performance. Various hydrogen fractions (10, 20 and 30 by v%) are examined. Results showed that natural gas enrichment with hydrogen leads in general to an improved gaseous fuel combustion, which corresponds to an enhanced heat release rate during gaseous fuel premixed phase, resulting in an increase in the in-cylinder peak pressure, especially at high engine load (4.1 bar at 70% load). The highest cumulative and rate of heat release correspond to 10% Hydrogen addition. The combustion duration of gaseous fuel combustion phase is reduced for all hydrogen blends. Moreover, this technique resulted in better combustion stability. For all hydrogen test blends, COV_IMEP does not exceed 10%. However, no major effect on combustion noise was noticed and the ignition delay was not affected significantly. Regarding performance, an important improvement in energy conversion was obtained with almost all hydrogen blends as a result of improved gaseous fuel combustion. A maximum thermal efficiency of 32.5%, almost similar to the one under diesel operation, and a minimum fuel consumption of 236 g/kWh, are achieved with 10% hydrogen enrichment at 70% engine load.     

An MILP model for the reformation of natural gas pipeline networks with hydrogen injection

A mixed integer linear programming (MILP) model is proposed for the reformation of natural gas pipelines. The model is based on the topology of existing pipelines, the load and pressure at each node and the design factors of the region and minimizes the annual substitution depreciation cost of pipelines, the annual construction depreciation cost of compressor stations and the operating cost of existing compressor stations. Considering the nonlinear pressure drop equations, the model is linearized by a piecewise method and solved by the Gurobi optimizer. Two cases of natural gas pipeline networks with hydrogen injection are presented. Several adjustments are applied to the original natural gas pipeline network to ensure that our design scheme can satisfy the safety and economic requirements of gas transportation. Thus, this work is likely to serve as a decision-support tool for the reformation of pipeline networks with hydrogen injection.     

Simulation of a hydrogen/natural gas engine and modelling of engine operating parameters

At the present work for improving the engine performance and decrease of emissions, a port injection gasoline engine is converted into direct injection. Engine performance behavior was investigated by AVL Fire software with adding hydrogen to natural gas from 0% up to 30%. Validation of the simulated model and experimental results show good confirmation. To determine the relationship between independent variables engine speed, ignition timing, injection timing and H₂% versus the dependent variables including engine performance parameters, specific fuel consumption, CO and statistical analysis models were used. Comparison between different errors models shows that Radial basis function model with training algorithm Bayesian regularization back propagation can estimate better engine performance variables. The results showed that adding hydrogen to natural gas cause the output power, torque, fuel consumption efficiency increase and specific fuel consumption drop. Also, CO decreases when ignition and injection timing be advanced and engine speed reaches to its largest.     

Investigations on performance and emission characteristics of an industrial low swirl burner while burning natural gas,methane, hydrogen-enriched natural gas and hydrogen as fuels

Although many detailed chemical reaction mechanisms, skeletal mechanisms and reduced mechanisms are available in the literature to modeling the natural gas, they are computational expensive, required high power computing especially for three dimensional complex geometries with intense meshes. For example, though the DRM19 reduced mechanism does not include NO and NO₂ species, it includes 19 species and 84 reactions. On the other hand, Eddy Dissipation combustion model in which the overall rate of reaction is mainly controlled by turbulent mixing can be utilized as a practical approach for fast burning and fast reaction fuels such as natural gas. Unlike fossil fuels, hydrogen is a renewable energy and quite clean in terms of carbon monoxide and carbon dioxide emissions. However, numerical and experimental studies on hydrogen combustion in burners are very restricted. In this study, the combustion of natural gas in an industrial low swirl burner–boiler system has been experimentally investigated. The results obtained from the experimental setup have been utilized as boundary conditions for CFD simulations. With the use of Eddy Dissipation method, methane-air-2-step reaction mechanism is used for modeling of natural gas as methane gas and the reaction mechanism has been modified for natural gas considering the natural gas properties to reveal the similarities and differences of both fuels in modeling. In addition, the combustion performances of natural gas with the use of full and periodic models, which are geometric models of the burner–boiler pair, are compared. Moreover, in order to reveal the effect of the hydrogen-enriched natural gas and pure hydrogen on the performance of low swirl burner–boiler considering the combustion emissions, four various gas contents (thermal load ratio: 75%NG + 25%H₂, 50%NG + 50%H₂, 25%NG + 75%H₂, 100%H₂) at the same thermal load have been investigated. The turbulent flames of the industrial low swirl burner have been studied numerically using ANSYS Fluent 16.0 for the solution of governing equations. The results obtained in this study show that with the utilizing Eddy Dissipation method, natural gas can be modeled as methane gas with well-known methane-air-2step reaction mechanism or as natural gas with modified methane-air-2step reaction mechanism with approximate results. Additionally, the use of periodic boundary condition, which enables studying with 1/4 of geometric model, gives satisfactory results with less number of meshes when compared to the full model. Furthermore, in the case of using hydrogen-enriched natural gas or pure hydrogen instead of natural gas as the fuel, the combustion emissions of the burner–boiler such as CO and CO₂ are remarkably decreasing compared to the natural gas. However, the NOx emissions are significantly increasing especially due to thermal NO.     

Numerical investigation on combustion regulation for a stoichiometric heavy-duty natural gas engine with hydrogen addition considering knock limitation

Aiming to further improve the thermal efficiency and reduce NO_x emissions in the stoichiometric hydrogen-enriched natural gas (NG) engine, a detailed 3-D simulation model of stoichiometric operation heavy-duty NG engine is built based on the actual boundary conditions from high load bench test. The superimposed methods for knock regulation, combustion and emission control, including Miller valve timing, hydrogen volume fraction and EGR rate were proposed and investigated comprehensively. It reveals that the typically bimodal characteristic of heat release rate (HRR) curve is caused by knock, which seriously restricts the performance improvement of stoichiometric NG engine under high load condition. To predict and control the occurrence of the second peak of HHR accurately, a new parameter BI is defined. Moreover, the Miller timing with 20°CA of the intake valve late closing shows better combustion performance within the knock limit, accompanied by a slight increase in NO_x emissions. Additionally, the 5% hydrogen blend, coupled with the Miller cycle, can further enhance the indicated thermal efficiency (ITE) of the NG engine due to the stronger effects on acceleration of laminar flame propagation velocity than the promotion of end-gas auto-ignition. Besides, the great potential of EGR rate for balancing NO_x and ITE is also confirmed in the heavy-duty hydrogen-enriched NG engine adopting Miller cycle. Compared to the original indexes, combing with the regulation strategies of intake valve late closing (20°CA), hydrogen addition (5%) and EGR (17%) are proved to increase the indicated thermal efficiency by 1.89% and reduce NO_x emissions by 11.47% within the knock limit.     

Optimization of hydrogen production by filtration combustion of natural gas by water addition

The effect of adding steam during filtration combustion of natural gas–air mixtures was studied with the aim to evaluate the optimization of hydrogen production. Temperature, velocity, chemical products of combustion waves, and conversion from fuel to H₂ and CO were evaluated in the range of equivalence ratio (φ) from stoichiometric (φ = 1.0) to φ = 3.0 and steam content in the mixture from 0% to 39%, at filtration velocities from 12 to 25 cm/s. Numerical simulation was carried out using GRI-MECH 3.0. Results suggest that H₂ and CO concentrations, dominant for rich and ultrarich combustion, are products from partial oxidation and steam natural gas reforming processes. Experimental and numerical results show that hydrogen yield increase with an increase of steam content in the natural gas–air mixtures.     

Characteristics of direct injection combustion fuelled by natural gas–hydrogen mixtures using a constant volume vessel

The effects of hydrogen addition and turbulence intensity on the natural gas–air turbulent combustion were studied experimentally using a constant volume vessel. Turbulence was generated by injecting the high-pressure fuel into the vessel. Flame propagation images and combustion characteristics via pressure-derived parameters were analyzed at various hydrogen volumetric fractions (from 0% to 40%) and the overall equivalence ratios of 0.6, 0.8 and 1.0. The results showed that the turbulent combustion rate increased remarkably with the increase of hydrogen fraction in fuel blends when hydrogen fraction is over 11%. Combustion rate was increased remarkably with the introduction of turbulence in the bomb and decreased with the decrease of turbulence intensity. The lean flammability limit of natural gas–air turbulent combustion can be extended with increasing hydrogen fraction addition. Maximum pressure and maximum rate of pressure rise increased while combustion duration decreased monotonically with the increase of hydrogen fraction in fuel blends. The sensitivity of natural gas/hydrogen hybrid fuel to the variation of turbulence intensity was decreased while increasing the hydrogen addition. Maximum pressure and maximum rate of pressure rise increased while combustion duration decreased with the increase of turbulent intensity at stoichiometric and lean-burn conditions. However, slight influence on combustion characteristics was presented with variation of hydrogen fraction at the stoichiometric equivalence ratio with and without the turbulence in the bomb.     

Research on the dynamic characteristics of natural gas pipeline network with hydrogen injection considering line-pack influence

Hydrogen energy has the advantages of renewable, clean and high energy density, which is considered as the most potential secondary energy in the 21st century. But transportation is a major constraint on development of hydrogen. A possible solution is to inject hydrogen into natural gas network for transport. Due to the obvious differences in the properties of natural gas and hydrogen, it is necessary to establish natural gas pipeline model with hydrogen injection to explore the influence of hydrogen on pipeline. The line-pack of natural gas network can improve the flexibility of the system to deal with uncertainties, and the line-pack has a significant impact on the dynamic characteristics of the natural gas network under the change of external conditions. When hydrogen is injected into the natural gas network, the line-pack is affected by both pressure and hydrogen mixture ratio, and the line-pack influence on the dynamic characteristics of the network is more complicated. In this paper, a natural pipe network with hydrogen injection is established based on the finite difference method, and simulation is carried out under different situations to explore the influence of different line-pack on the dynamic characteristics of the natural gas network. The results show that the response speed of hydrogen mixture ratio is faster under the condition of low line-pack, which is conducive to reducing the risk of hydrogen embrittlement when the hydrogen mixture ratio surges for a short time. However, the pressure loss caused by the increase of flow can be reduced in the high line-pack state.     

A multi-objective model for optimizing hydrogen injected-high pressure natural gas pipeline networks

The paper develops a statistical model for optimizing the Hydrogen-injected Natural gas (H-NG) high-pressure pipeline network. Gas hydrodynamic principles are utilized to construct the pipeline and compressor station model. The model developed is implemented on a pipeline grid that is supposed to carry Hydrogen as an energy carrier in a natural gas-carrying pipeline. The paper aims to optimize different objectives using ant colony optimization (ACO). The first objective includes a single objective optimization problem that evaluates the maximum permissible hydrogen amounts blended with natural gas (NG) for a set of pipeline constraints. We also evaluated the variations in operational variables on injecting Hydrogen into the natural gas pipeline networks at varying fractions. The study further develops a multi-objective optimization model that includes bi-objective and tri-objective problems and is optimized using ACO. Traditional studies have focused on single-objective optimization with minimal bi-objective issues. In addition, none of the earlier research has shown the effect of introducing Hydrogen to the NG network using tri-objective function evaluations. The bi-objective and tri-objective functions help evaluate the effect of injecting Hydrogen on different operational parameters. The study further attempts to fill the gap by detailing the modelling equations implemented through a bi-objective and tri-objective function for the H-NG pipeline network and optimized through ACO. Pareto fronts that show the tradeoff between the different objectives for the multi-objective problem have been generated. The primary objective of the bi-objective and tri-objective optimization problems is maximizing hydrogen mole percent in natural gas. The other objective chosen is minimizing compressor fuel consumption and maximizing delivery pressure, throughput, and power delivered at the delivery station. The findings will serve as a roadmap for pipeline operators interested in repurposing natural gas pipeline networks to transport hydrogen and natural gas blend (H-NG) and seeking to reduce carbon intensity per unit of energy-delivered fuel.