Effect Of Hydrogen Enrichment Research Articles

Investigation into the Effect of H2-Enriched Conditions on the Structure and Stability of Flames in a Low-Swirl Combustor Derived from Aero-Engine Design

This study introduces an innovative approach involving the injection of hydrogen into a low-swirl, non-premixed flame, which operates with gaseous fuels derived from an air-blast atomizer designed for aero-engine applications. The aim is to characterize how hydrogen enrichment influences flame structures while maintaining a constant thermal output of 4.6 kW. Using high-speed chemiluminescence imaging, three fueling conditions were compared: the first involved pure methane/air, while the second and third conditions introduced varying levels of hydrogen to an air–methane mixture. The results reveal significant effects of hydrogen enrichment on flame characteristics, including a slightly shorter length and a wider angle attributed to heightened expansion within the Combustion Recirculation Zone. Moreover, the emission of UV light underwent considerable changes, resulting in a shifted luminosity zone and reduced variance. To delve deeper into the underlying mechanisms, the researchers employed Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD) analyses, showing coherent structures and energetic modes within the flames. Hydrogen enrichment led to the development of smaller structures near the nozzle exit, accompanied by longitudinal oscillations and vortex shedding phenomena. These findings contribute to an advanced understanding of hydrogen’s impact on flame characteristics, thereby propelling efforts toward improved flame stability. Additionally, these insights hold significance in the exploration of hydrogen as an alternative energy source with potential environmental benefits.

Effects of hydrogen enrichment on the heat generation and emission of natural gas turbulent premixed flame

The demand for clean energy and the decarbonisation targets set globally require researching and developing new solutions. An efficient computational approach was implemented to examine the effect of hydrogen enrichment on flame characteristics, flame temperature, heat generation, NOx and carbon emissions under varying stoichiometry of combustion. Results showed that hydrogen enrichment significantly reduces CO2 emissions but also has undesirable effects which include reducing the heat generation capability of flame and increasing NOx emissions. The level of impact on each of these characteristics was found to be different. Under a boiler-like condition and stoichiometry (Ф = 0.8), a 10 % decrease in CO2 emissions was observed when enriching the fuel with 20 % hydrogen. Concurrently, the heat flux generated from the flame is reduced by 6 % and NOx emission is increased by 2 %. The effect of hydrogen enrichment on these aspects becomes more prominent at a higher enrichment level. The study also finds that making combustion leaner is an effective strategy to combat the effect of hydrogen enrichment with respect to CO2 and NOx emission generation. Despite the leaner combustion producing less emissions for any given hydrogen enrichment level, it significantly decreases the heat transfer capacity of the flame. Alongside these flame characteristics, the significant role of hydrogen enrichment on increasing water vapour (H2O) production was examined.

Effects of Hydrogen Enrichment on Thermoacoustic and Helical Instabilities in Swirl Stabilised Partially Premixed Flames

The effects of hydrogen enrichment on flame and flow dynamics of a swirl-stabilised partially premixed methane-air flame are studied using large eddy simulation. The sub-grid reaction rate is modelled using unstrained premixed flamelets and a presumed joint probability density function approach. Two cases undergoing thermoacoustic oscillations at ambient conditions are studied. The addition of hydrogen modifies both thermoacoustic and fluid dynamical characteristics. The amplitude of the fundamental thermoacoustic mode increases with the addition of 20% hydrogen by volume. A second pressure mode associated with the chamber mode is also excited with the hydrogen addition. Intermittent single, double and triple helical instabilities are observed in the pure methane case, but are suppressed substantially with hydrogen addition. The results are analysed in detail to shed light on these observations. The feedback loop responsible for the thermoacoustic instability is driven by mixture fraction perturbations resulting from the unequal impedances of the fuel and air channels. It is shown that hydrogen addition increases the flame’s sensitivity to these perturbations, resulting in an increase in amplitude. This higher amplitude thermoacoustic oscillation, along with a higher local heat release rate in the presence of hydrogen, is shown to considerably modify the flow structures, leading to a suppression of the helical instabilities.

Effect of Hydrogen Enrichment on Transfer Matrices of Fully and Technically Premixed Swirled Flames

Abstract Knowledge of flame responses to acoustic perturbations is of utmost importance to predict thermoacoustic instabilities in gas turbine combustors. However, measuring transfer functions linking acoustic quantities upstream and downstream of flames are very challenging in practical systems and these measurements can significantly deviate from state-of-the-art models. Moreover, there is a lack of studies investigating the effect of hydrogen enrichment on the response of natural gas (NG) flames. In this work, measurements of flame transfer matrices (FTMs) of turbulent H2/NG flames in an atmospheric combustor featuring an axial swirler burner have been performed, allowing us to unravel the transition between FTM in fully premixed (FP) and in technically premixed (TP) conditions. Furthermore, imaging of OH* chemiluminescence and OH-planar laser induced fluorescence are obtained for characterizing the topology of the flame for varying H2 fraction and mixing conditions. Transfer matrices are measured using the multimicrophone method for H2 fractions ranging from 12% to 43% in power. Afterward, the flame transfer functions (FTFs), which linearly relate the coherent fluctuations of the heat release rate to the acoustic velocity oscillations, are obtained from the FTM by using the Rankine–Hugoniot jump conditions across the flame. Using the OH* chemiluminescence intensity as a surrogate for the heat release rate, the FTF based on this optical measurement is also extracted and compared to the one exclusively obtained with the multimicrophone method. As expected, the two different methods are in very good agreement for the FP case and significantly differ for the TP case. Indeed, chemiluminescence fluctuations cannot be directly linked to heat release rate fluctuations when the acoustic forcing induces equivalence ratio fluctuations at the flame, making the optical method unusable for TP configurations. We also show that the two methods agree in the high end of the explored excitation frequency range and we provide an explanation to this intriguing finding. Moreover, we investigate the sensitivity of the FTM measurement to the estimate of the speed of sound in the rig in FP conditions. Finally, the measured FTFs are fitted with FTF models based on multiple distributed time delays. This allows us to explain the frequency dependence and the hydrogen fraction dependence of the gain and the phase in FP and TP conditions.

The combined effect of hydrogen enrichment and exhaust gas recirculation on the combustion stability, performance and emissions of CI engine energized by algae biodiesel

The scarcity of fossil fuels, the rising cost of liquid fuels, and the wide pollution footprint of conventional fuels all motivate scientists to seek out new approaches. This experimental study aims to explore the performance and emissions of compression ignition (CI) engines by introducing hydrogen into a biodiesel blend derived from algae. According to this study, the superior thermal properties of hydrogen associated with algal biodiesel have a significant impact on the performance and emissions of dual-fuel engines. The effect of hydrogen substitution rates of 10.4, 21.6, 32.4, 43.2, and 54 g per hour (g/h) on pure algae biodiesel was investigated. In comparison to diesel, the algae biodiesel reduces unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions by 4.1% and 8.82%, respectively, while nitrogen oxide (NOx) emissions increase by 18%. Diesel was found to have increased brake thermal efficiency (BTE) and decreased brake specific energy consumption (BSEC) compared to biodiesel. With the addition of pure biodiesel, the 43.2 g/h H2 substitution rate produces a maximum thermal efficiency of 1.92% and a 9.5% decrease in brake-specific energy consumption compared to diesel at maximum load. Compared to diesel, the emission attributes of UHC, CO, and smoke opacity decreased by about 45%, 48%, and 41%, respectively. However, NOx emissions increase by about 36% compared to diesel due to the higher flame temperature and carbon-free fuel of hydrogen and oxygenated biodiesel. The induction of 15% exhaust gas with B100 + 43.2 g/h H2 reduces NOx by about 31% in comparison to B100 + 43.2 g/h H2 without exhaust gas recirculation (EGR). This is primarily attributable to the high oxygen dilution and specific heat capacity of burned gases, which result in a decrease in peak cycle temperature. Compared to diesel, B100 + 43.2 g/h H2 increased the cylinder pressure and heat release rate by about 1.86 and 4.29%, respectively. As a result of its high energy density, hydrogen improves overall energy utilization and engine performance. Hydrogen's rapid flame speed and wide flammability range contribute to the efficient and complete combustion of the algae fueling the CI engine. As well as showing outstanding performance, dual fuel CI engines have the potential to significantly contribute to lowering emissions. Finally, it was determined that using algae biodiesel and exhaust gas recirculation with hydrogen substitution in diesel engines can significantly reduce emissions while increasing efficiency.

Parametric instability in propagating flames and the impact of hydrogen enrichment on the onset of secondary instability

A self-excited acoustic instability of laminar premixed flames propagating in an open-ended tube with a length of 700 mm and a radius of 10 mm was simulated by solving the reacting unsteady compressible Navier–Stokes equations, to understand the way of massive acoustic generation and its onset behaviors. Four fuel–air mixtures with an equivalence ratio of 1.2 were considered, namely, methane–air and methane–hydrogen–air mixtures, to identify the role of hydrogen in rich methane–air mixture. Parametric instability, which generated huge acoustic disturbance and violent flame pulsations, was observed only for a particular methane–hydrogen–air mixture with RH = 0.2, consistent with previously reported experimental observations. For the investigation of the reinforcement mechanism of acoustic instability under parametric instability, the flame surface area modulation was examined. It was found that violent subharmonic flame front pulsations could strongly modulate the flame surface area in the fundamental mode, resulting in a fluctuating heat release rate and increased thermoacoustic coupling. When hydrogen addition was small, attaining a higher level of primary instability, which is the precursor of the parametric instability, was more dominant than increasing the threshold level for the onset of the parametric instability. With larger hydrogen addition, the increase in the threshold level was more dominant than attaining a higher level of the primary instability. In particular, as the flame propagation time decreased, the level of the primary instability was saturated in larger hydrogen addition. This study elucidates the mechanism for the acoustic generation of propagating flames under the parametric instability, and the effects of hydrogen enrichment within rich methane–air mixtures.

Numerical Investigation of Combustion Instabilities in Swirling Flames with Hydrogen Enrichment

This work presents a numerical study on technically premixed, swirl-stabilised flames in the PRECCINSTA model combustor. The employed method, BOFFIN-LES, comprises a fully compressible formulation to study unsteady combustion with thermo-acoustic instabilities. To allow for this, the iso-thermal flows are first investigated, based on which three reacting cases are established. The investigation delves into various aspects including flame topology, flow characteristics, and the related thermo-acoustic and hydrodynamic instabilities are studied and results are benchmarked against available measurement data. The dominant feedback mechanism of the observed thermo-acoustic fluctuations is identified; the evolution of the helical vortex is discussed together with the related flame stabilisation process. Furthermore, the interplay of the thermo-acoustic oscillations, helical structure, and the flame stabilisation process is summarised in the end, with the potential effect of the wall-heat transfer on them discussed. This work establishes that the Large Eddy Simulation (LES) effectively captures the iso-thermal flow dynamics and the flame topology under various operating conditions, with a good prediction of the thermo-acoustic frequencies in all the cases. The dominant driving mechanism of the observed thermo-acoustic fluctuations was identified as a combined effect of equivalence ratio and velocity fluctuations in all the cases investigated. The effect of Hydrogen enrichment on modifying the flame topology and changing the thermo-acoustic instability features are well predicted by the simulations. Moreover, different modes of the helical vortex are detected, and their periodic excitement, evolution, and effect on flame stabilisation are discussed in great detail. To conclude, this LES-based investigation offers valuable insights into the complex interplay of unsteady combustion, acoustic fluctuations, flow dynamics, and solid boundaries within swirling flames subjected to unsteady conditions.

Erratum: “Dynamical Characterization of Thermoacoustic Oscillations in a Hydrogen-Enriched Partially Premixed Swirl-Stabilized Methane/Air Combustor” [ASME J. Eng. Gas Turbines Power, 143(12), p. 121022; DOI: 10.1115/1.4052091

Abstract In this study, we systematically analyze the effects of hydrogen enrichment in the well-known PRECCINSTA burner, a partially premixed swirl-stabilized methane/air combustor. Keeping the equivalence ratio and thermal power constant, we vary the hydrogen percentage in the fuel. Successive increments in hydrogen fuel fraction increase the adiabatic flame temperature and also shift the dominant frequencies of acoustic pressure fluctuations to higher values. Under hydrogen enrichment, we observe the emergence of periodicity in the combustor resulting from the interaction between acoustic modes. As a result of the interaction between these modes, the combustor exhibits a variety of dynamical states, including period-1 limit cycle oscillations (LCO), period-2 LCO, chaotic oscillations, and intermittency. The flame and flow behavior is found to be significantly different for each dynamical state. Analyzing the coupled behavior of the acoustic pressure and the heat release rate oscillations during the states of thermoacoustic instability, we report the occurrence of 2:1 frequency-locking during period-2 LCO, where two cycles of acoustic pressure lock with one cycle of the heat release rate. During period-1 LCO, we notice 1:1 frequency-locking, where both acoustic pressure and heat release rate repeat their behavior in every cycle.

The effect of hydrogen enrichment on thermoacoustic instabilities in laminar conical premixed methane/air flames

We perform a conceptual study about the linear stability of a hydrogen-enriched methane-air premixed laminar flame inside a cylindrical duct with both ends open. The flame and acoustic subsystems are coupled using the Flame Transfer Function (FTF). The power output is set to a constant value and the hydrogen molar fraction of the fuel mixture is varied. We show that adding hydrogen reduces the flame length and impacts the FTF in two ways: (i) gain drop-off shifts towards higher frequencies and (ii) phase lag reduces. Then, we compute the eigenvalues of the thermoacoustic system varying the hydrogen molar fraction. We show that adding hydrogen to the fuel mixture can stabilise linearly unstable systems and vice versa, depending on the duct natural frequencies. The results show that the hydrogen molar fraction can be a tunable parameter for controlling thermoacoustic instabilities.

Effect of hydrogen enrichment and TiO2 nanoparticles on waste cooking palm biodiesel run CRDI engine

In this study, we deal with the production and utilization of waste-cooking palm biodiesel (WCB) and.evaluated the influence of the addition of titanium dioxide (TiO2) nanoparticles in hydrogen-enriched single-cylinder CRDI diesel engine. XRD, SEM, and EDX decide the structure and morphology of TiO2 nanoparticles. The TiO2 nanoparticles were dispersed in the tested fuels at a dosage of 50–75 ppm with the aid of ultra-sonication. Based on the oxidation stability study, the B20 + 75 ppm (TiO2) fuel blend is the pilot fuel for the engine test. Further, the engine is enriched with a hydrogen (H2) flow of 10 lpm. Results revealed that the performance parameters were improved with the addition of H2 enrichment and TiO2 nanoparticles compared to D. The brake thermal efficiency of the engine was improved by 8.21%. In comparison, brake-specific fuel consumption decreased by 42.86%. Furthermore, adding nanoparticles also reduced CO and HC emissions by 74% and 27.27%, respectively, whereas the NOx emission was slightly increased. Thus, the findings demonstrated that hydrogen-enriched nanoparticles added to biodiesel might be considered a substitute for fossil fuels and report a positive impact on diesel engine performance without requiring significant modifications.

Investigation of the effect of hydrogen enrichment on the performance, emission, and combustion characteristics of a diesel engine

Abstract: With an aim to partially replace conventional diesel fuel, this work investigated the impact of injecting hydrogen into an intake manifold of a diesel engine on its performance. Due to the benefits of hydrogen fuel, such as its high calorific value and flame velocity, it can be used in a dual-fuel mode of operation with diesel. The experiment was carried out for various engine loads with engine speed maintained constant at 1500. By using a digital volume flow metre, hydrogen was injected at three different volume flow rates, namely 3, 6, and 9 lpm. Engine combustion, emission, and performance parameters were evaluated for different hydrogen flow rates and compared to sole diesel. The result revealed that the brake thermal efficiency of the engine increased, whereas the brake-specific fuel consumption decreased due to hydrogen enrichment. The hydrocarbon and carbon monoxide emissions were lower in dual fuel mode when compared to sole diesel operation under all load situations. On the other hand, Oxides of Nitrogen (NOx) emission increased with hydrogen flow rate and resulted in higher NOx than diesel. Furthermore, hydrogen enrichment increased the values of the peak heat release rate and cylinder pressure by a significant margin from the corresponding values given by diesel fuel. Among the evaluated H2 flow rates, 9 lpm is found to be the best, demonstrating enhanced engine characteristics background: Due to the benefits of hydrogen fuel, such as its high calorific value and flame velocity, it can be used in a dual fuel mode of operation with diesel. The experiment was carried out for various engine loads with engine speed maintained constant at 1500. objective: By using a digital volume flow metre, hydrogen was injected at three different volume flow rates, namely 3, 6, and 9 lpm. Engine combustion, emission, and performance parameters were evaluated for different hydrogen flow rates and compared to sole diesel. method: The result revealed that brake thermal efficiency of the engine increased, whereas the brake specific fuel consumption decreased due to hydrogen enrichment. The hydrocarbon and carbon monoxide emissions were lower in dual fuel mode when compared to sole diesel operation under all load situations. conclusion: Among the evaluated H2 flow rates, 9 lpm is found to be the best, demonstrated enhanced engine characteristics.

A Numerical Investigation on Effects of Hydrogen Enrichment and Turbulence on NO Formation Pathways in Premixed Ammonia/Air Flames

ABSTRACT NO x emission reduction is one of the major challenges when using ammonia/hydrogen blends as an alternative fuel for carbon-free combustion. In this study, chemical reaction pathways of NO formation in planar premixed flames of stoichiometric ammonia/hydrogen/air at atmospheric pressure and reactants temperature of 298 K are investigated under laminar and decaying turbulent conditions using quasi-DNS with detailed chemistry and the mixture-averaged transport model. The sweep parameter, , is the volumetric ratio of hydrogen to the ammonia/hydrogen mixture. Here, for unstrained laminar conditions, = 0, 0.4, and 0.6 and for turbulent condition, = 0.4 within the thin reaction zones region ( 34.2) are studied. Under 1D laminar conditions, increasing enhances NO formation drastically, around 3 times when comparing = 0 and 0.6. At different , despite the high activity of the reactions which belong to the Zeldovich pathway, the contribution of this pathway is insignificant in NO formation. However, HNO and N2O pathways have the most significant roles. For instance, at = 0.4, R85 (NH+NO N2O+H) in the N2O pathway and R144 (HNO+H NO+H2) in the HNO pathway have major roles in NO formation. Higher NO formation at larger is found to be due to the increased H and O radicals within the reaction zone as well as the increased reaction rates because of the higher flame temperature. Under the 3D turbulent condition ( = 0.4), it is observed that turbulence does not switch the pathways trends across the flame brush compared to the laminar condition. In the reaction zone, however, it is observed that NO formation is lower (higher) in the regions convex (concave) toward the reactants. The underlying reason for this effect is the preferential diffusion of H2 to the regions of the flame front convex toward the reactants, which consumes NO and also depletes O and OH radicals, which are necessary for NO formation.

Effects of hydrogen enrichment on diesel engine fueled with Afzelia Africana biodiesel – TiO2 blends

Effects of hydrogen enrichment on diesel engine fueled with Afzelia Africana biodiesel – TiO2 blends

Numerical Study of Combustion and Emission Characteristics for Hydrogen Mixed Fuel in the Methane-Fueled Gas Turbine Combustor

The aeroderivative gas turbine is widely used as it demonstrates many advantages. Adding hydrogen to natural gas fuels can improve the performance of combustion. Following this, the effects of hydrogen enrichment on combustion characteristics were analyzed in an aeroderivative gas turbine combustor using CFD simulations. The numerical model was validated with experimental results. The conditions of the constant mass flow rate and the constant energy input were studied. The results indicate that adding hydrogen reduced the fuel residues significantly (fuel mass at the combustion chamber outlet was reduced up to 60.9%). In addition, the discharge of C2H2 and other pollutants was reduced. Increasing the volume fraction of hydrogen in the fuel also reduced CO emissions at the constant energy input while increasing CO emissions at the constant fuel mass flow rate. An excess in the volume fraction of added hydrogen changed the combustion mode in the combustion chamber, resulting in fuel-rich combustion (at constant mass flow rate) and diffusion combustion (at constant input power). Hydrogen addition increased the pattern factor and NOx emissions at the outlet of the combustion chamber.

Effect of hydrogen enrichment on exhaust gas temperature and emission of a dual fuel diesel engine

Rapid and irregulated use of fossil fuels to meet the energy requirements caused fast draining of stocks. Also, the use of these conventional resources emits harmful pollutants and gases in the atmosphere which is a major concern as of now. To protect these resources for future needs, alternate energy sources must be identified. Many researchers contributed their effort to find the optimum solutions of energy requirement and emission control. The present study revealed the effect of enrichment of gaseous hydrogen on the emission and exhaust gas temperature of the engine. For experimental study, a conventional modified diesel engine was operated in dual fuel approach, could produce a power of 3.5 kw at a fixed speed of 1500 rpm, compression ignition, four stroke, direct injection, single cylinder, model Kirlosker TV1 was used. The experimental results revealed that induction of hydrogen as a gaseous fuel exhaust gas temperature was increased in comparison with neat diesel. The exhaust gas temperature was incremented by hydrogen enrichment upto 30 % after that it increased again. The NOx formation was increased by increasing the hydrogen substitution compared with diesel. Again, the formation of carbon mono-oxide and carbon di-oxide was reduced by increasing the hydrogen enrichment compared with neat diesel.

Experimental and computational study on the enhancement of engine characteristics by hydrogen enrichment in a biogas fuelled spark ignition engine

Limitations on the upgradation of biogas to biomethane in terms of cost effectiveness and technology maturity levels for stationary power generation purpose in rural applications have redirected the research focus towards possibilities for enhancement of biogas fuel quality by blending with superior quality fuels. In this work, the effect of hydrogen enrichment on performance, combustion and emission characteristics of a single-cylinder, four-stroke, water-cooled, biogas fuelled spark-ignition engine operated at the compression ratio of 10:1 and 1500 rpm has been evaluated using experimental and computational (CFD) studies. The percentage share of hydrogen in the inducted biogas fuel mixture was increased from 0 to 30%, and engine characteristics with pure methane fuel was considered as a baseline for comparative analysis. The CFD model is developed in Converge CFD software for a better understanding on combustion phenomenon and is validated with experimental data. In addition, the percentage share of hydrogen enrichment which would serve as a compromise between biogas upgradation cost and engine characteristics is also identified. The results of study indicated an enhancement in combustion characteristics (peak in-cylinder pressure increased; COVIMEP reduced from 9.87% to 1.66%; flame initiation and combustion durations reduced) and emission characteristics (hydrocarbon emissions reduced, and NOx emissions increased but still lower than pure methane) with increase in hydrogen share from 0 to 30% in biogas fuelled SI engine. Flame propagation speed increased and combustion duration reduced with hydrogen supplementation and the same was evident from the results of the CFD model. Performance of the engine increased with increase in hydrogen share up to 20% and further increment in hydrogen share degraded the performance, owing to heat losses and the enhancement in combustion characteristics were relatively small. Overall, it was found that 20% blending of hydrogen in the inducted biogas fuel mixture will be effective in enhancing the engine characteristics of biogas fuelled engines for stationary power generation applications and it holds a good compromise between biogas upgradation cost and engine performance.

Application of line pipe and hot induction bends in hydrogen gas

For the upcoming hydrogen economy, transport pipelines for hydrogen gas and gas mixtures of hydrogen and natural gas are one of the important components. For the application of steel in hydrogen gas it is necessary to handle the risk of hydrogen embrittlement by adapting the right knowledge. Compared to existing hydrogen pipelines, which are safely running since decades, higher gas pressures and steel strength levels are in discussion. For a safe operation and limited resource consumption it is necessary to clarify the product requirements. The semi-finished products medium and large line pipes and bends are regarded over the production chain: pre-material, hot rolled strip, welded pipes, and induction bent pipes. The interaction of hydrogen with steel is investigated since decades. For hydrogen gas, the surface reaction with steel is considerably reduced compared to other corrosion reactions i.e. with sour gas. This results in a much lower amount of introduced hydrogen atoms within the material. Results of lab trials of different materials after storage in pressured hydrogen gas will be shown to clarify this point. Furthermore, results of tests of applicability of commonly used flow coats in hydrogen atmosphere are shown. For a possible failure scenario of a hydrogen transport line the investigations must be focused on local effects of hydrogen enrichment in conjunction with mechanical loads. There are different laboratory tests possible to evaluate these material reactions. They are shown and discussed in the view of the following aspects: product qualification, further product and specification development and suitable approval tests.

The effect of hydrogen enrichment, flame-flame interaction, confinement, and asymmetry on the acoustic response of a model can combustor

To maximise power density practical gas turbine combustion systems have several injectors which can lead to complex interactions between flames. However, our knowledge about the effect of flame-flame interactions on the flame response, the essential element to predict the stability of a combustor, is still limited. The present study investigates the effect of hydrogen enrichment, flame-flame interaction, confinement, and asymmetries on the linear and non-linear acoustic response of three premixed flames in a simple can combustor. A parametric study of the linear response, characterised by the flame transfer function (FTF), is performed for swirling and non-swirling flames. Flame-flame interactions were achieved by changing the injector spacing and the level of hydrogen enrichment by power from 10 to 50%. It was found that the latter had the most significant effect on the flame response. Asymmetry effects were investigated by changing one of the flames by using a different bluff-body to alter both the flame shape and flow field. The global flame response showed that the asymmetric cases can be reconstructed using a superposition of the two symmetric cases where all three bluff-bodies and flames are the same. Overall, the linear response characterised by the flame transfer function (FTF) showed that the effect of increasing the level of hydrogen enrichment is more pronounced than the effect of the injector spacing. Increasing hydrogen enrichment results in more compact flames which minimises flame-flame interactions. More compact flames increase the cut-off frequency which can lead to self-excited modes at higher frequencies. Finally, the non-linear response was characterised by measuring the flame describing function (FDF) at a frequency close to a self-excited mode of the combustor for different injector spacings and levels of hydrogen enrichment. It is shown that increasing the hydrogen enrichment leads to higher saturation amplitude whereas the effect of injector spacing has a comparably smaller effect.

Effects of hydrogen enrichment and turbulence intensity on the combustion mode in locally stratified dual-fuel mixtures of n-dodecane/methane

In dual-fuel (DF) engines, a high-reactivity fuel (HRF) ignites a low-reactivity fuel (LRF) premixed with air. Identification of the combustion mode after autoignition in DF engines with different fuel combinations and under various mixture stratification levels is of crucial importance since the combustion mode may affect the engine performance and emissions levels. However, to avoid expensive computational or experimental tests for different fuel combinations under various initial conditions, an analytical diagnostics tool can help identify the modes of combustion. Recently, we developed an a-priori tool (β-curve), which separates between the deflagration and spontaneous combustion modes in transient problems based on two parameters: HRF stratification amplitude and wavelength. However, the developed analysis was only evaluated for a single fuel combination and under 2D turbulent conditions. The present study extends our previous work by (1) evaluating the 1D β-curve analysis for more common fuel combinations including hydrogen, and (2) extending the combustion mode analysis to 3D turbulent combustion. First, using 1D numerical simulations, the combustion mode for a new DF combination of n-dodecane (HRF) and methane (LRF) with and without hydrogen enrichment in the LRF blend is investigated. Although hydrogen enrichment shortens the combustion duration, its role in changing the combustion mode remains subtle. Therefore, only n-dodecane/methane (no hydrogen enrichment) is considered in the 3D simulations to avoid highly expensive 3D numerical simulations with hydrogen enrichment. Second, using flame-resolved 3D numerical simulations, variations of the combustion mode for DF n-dodecane/methane mixtures at three different turbulence intensities are studied. It is observed that high turbulence levels can switch the combustion mode from deflagration to autoignition. For the first time, the diagnostic tool is evaluated compared to 3D turbulent numerical simulations and a correction factor is proposed in the β-curve equation.

Numerical modeling and analysis of hydrogen blast furnace ironmaking process

Hydrogen use in the blast furnace (BF) ironmaking process promises to mitigate the carbon footprint substantially. This paper presents a numerical study on the effects of hydrogen enrichment on the inner states and overall performance of a 380-m3 industrial BF. This is done using a recently developed three-dimensional process BF model. The model is validated under different conditions. A case of 40-degree pure hydrogen being injected into the hearth tuyeres is considered. The hydrogen content in the bosh gas varies from 3% to 49.5%, while the hot metal temperature, bosh gas volume, and flame temperature are fixed. The numerical results reveal that with increasing hydrogen enrichment, the coke rate decreases initially to a minimum, then increases; however, the productivity increases and subsequently slows down. Therefore, an optimum hydrogen enrichment is identified according to the minimum coke rate. The flow and thermochemical behaviors are analyzed in detail. It shows that as the hydrogen enrichment intensifies, the cohesive zone has a narrower horizontal width and a shorter total length, contributing to a reduced tuyere pressure. The relative importance of chemical reactions at different hydrogen enrichments is also analyzed. It shows that the intensified hydrogen enrichment enhances the H2 indirect reduction and impedes the carbon solution reaction. However, it also decreases the CO indirect reduction rate that is more significant than the H2 indirect reduction rate under the conditions considered. In addition, hydrogen enrichment requires extra coke combustion to compensate for the sensible heat of the reduced hot blast rate. Overall, hydrogen enrichment improves the energy efficiency of BF.