Investigations of hydrogen and hydrogen–hydrocarbon composite fuel combustion and emission characteristics in a model combustor (original) (raw)
Related papers
International Journal of Hydrogen Energy, 2005
In this paper, the numerical simulation of a turbulent non-premixed hydrogen (H 2 ) diffusion flame has been performed in a model combustor. CFD studies using Fluent code were carried out changing fuel composition from pure hydrogen to natural gas (100% H 2 , 70% H 2 + 30% CH 4 , 10% H 2 + 90% CH 4 , and 100% CH 4 ). The model prediction studies have been extended to combustion air staging. Air 25% was staged and introduced through the two tangential inlets. The predictions are validated and compared against the experimental results obtained in this study and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation and reaction equations governing the problem. The standard kmodel is used for modelling of turbulent flow as the model was far enough for the turbulence phenomena in the combustor. The chemical combustion reactions are described by seven species and three steps. A NO x post-processor has been used for predicting NO x emissions from the combustor. The temperature and major pollutant concentration (CO and NO x ) distributions are in good agreement with the experimental measurements. The overall flame temperature increases as hydrogen is added or decreases as methane is added to the fuel mixture. The addition of methane to hydrogen decreases the flame temperature and thus NO x emissions considerably. Air staging causes rich and lean combustion regions and thus lower NO x emissions through the combustor exit. ᭧
International Journal of Energy Research, 2005
The objective of this work is to investigate numerically the turbulent non-premixed hydrogen (H2) and hydrogen–hydrocarbon flames in a small burner. Numerical studies using Fluent code were carried out for air-staged and non-staged cases. The effects of fuel composition from pure hydrogen to natural gas (100%H2, 70%H2+30%CH4, 10%H2+90%CH4, and 100%CH4) were also investigated. The predictions are validated and compared against the experimental results previously obtained and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation equations and reaction equations governing the problem. Although, three different turbulence models were tested, the standard k–ε model was used for the modelling of the turbulence phenomena in the burner. The temperature and major pollutant concentrations (CO and NOx) distributions are in good agreement with the existing experimental results. Air staging causes rich and lean combustion regions thus lower NOx emissions through the combustor exit. Blending hydrogen with methane causes considerable reduction in temperature levels and thus NO emissions. Increasing the mixture ratio from stoichiometric to leaner mixtures also decreases the temperature and thus NO emissions. Hydrogen may be considered a good alternative fuel for burners, as its use reduces the emission of pollutants, and as it is a renewable synthetic fuel. Copyright © 2005 John Wiley & Sons, Ltd.
Numerical Investigation of Turbulent Hydrogen-Methane-Nitrogen Non-Premixed Jet Flame
Journal of Energy Technologies and Policy, 2016
In this work, the numerical investigation of the two-dimensional axisymmetric turbulent diffusion flame of a composite fuel was performed by using a computational fluid dynamics code to predict flame structure. The composite fuel was an H 2 /CH 4 /N 2 gas mixture. The amount of H 2 and N 2 in the fuel mixture varies under constant volumetric fuel flow rate. Fluent, which solves the governing and reaction equations using the finite volume method, was used as the computational fluid dynamics program. The non-premixed model was used for computation of the combustion. The standard k-ε model was used for modeling the turbulent flow. The interaction of the chemistry and turbulence was accounted for by the program with the probability density function model. This model was validated against the experimental data taken from literature. In general, the numerical results of the temperature, velocity, and CO 2 concentration distributions were in satisfactory agreement with the experimental results. The numerical results showed that adding H 2 to the fuel mixture decreases the flame length and generally increases the maximum temperature of the flame. On the other hand, adding N 2 to the mixture decreases both the flame length and maximum flame temperature. The flame length corresponds to the axial position of the peak flame temperature.
Hydrogen–hydrocarbon turbulent non-premixed flame structure
International Journal of Hydrogen Energy, 2009
Hydrogen-hydrocarbon blend flames have recently received increased attention as alternative fuels for terrestrial and aerospace power generation applications. The combustion modelling of these composite fuels flames is complex. In order to better understand turbulent flames if blend fuels, this study is carried out in which the flame structure and flow field modifications induced by hydrogen addition are investigated numerically in a co-flow axisymetric turbulent non-premixed flame. Experimental data of this flame configuration in the case of 100 % methane which correspond to the equivalence ration of 0.251 (Brookes and Moss, 1999a) are used for model validation. The hydrogen content is varied between 0 % and 50 % of the total volumetric fuel flow while the equivalence ratio is varied from 0.251 to 0.152.
Experimental analysis of the effects of hydrogen addition on methane combustion
International Journal of Energy Research, 2012
This paper presents gas emissions from turbulent chemical flow inside a model combustor, for different blending ratios of hydrogen-methane composite fuels. Gas emissions such as CO and O 2 from the combustion reaction were obtained using a gas analyzer. NOx emissions were measured with a NOx analyzer. The previously obtained flame temperature distributions were also presented. As the amount of hydrogen in the mixture increases, more hydrogen is involved in the combustion reaction, and more heat is released, and the higher temperature levels are resulted. The results have shown that the combustion efficiency increases and CO emission decreases when the hydrogen content is increased in blending fuel. It is also shown that the hydrogen-methane blending fuels are efficiently used without any important modification in the natural gas burner.
Effect of hydrogen on hydrogen–methane turbulent non-premixed flame under MILD condition
International Journal of Hydrogen Energy, 2010
Energy crises and the preservation of the global environment are placed man in a dilemma. To deal with these problems, finding new sources of fuel and developing efficient and environmentally friendly energy utilization technologies are essential. Hydrogen containing fuels and combustion under condition of the moderate or intense low-oxygen dilution (MILD) are good choices to replace the traditional ones. In this numerical study, the turbulent non-premixed CH 4 þH 2 jet flame issuing into a hot and diluted co-flow air is considered to emulate the combustion of hydrogen containing fuels under MILD conditions. This flame is related to the experimental condition of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147e1154]. In general, the modelling is carried out using the EDC model, to describe turbulenceechemistry interaction, and the DRM-22 reduced mechanism and the GRI2.11 full mechanism to represent the chemical reactions of H 2 /methane jet flame. The effect of hydrogen content of fuel on flame structure for two co-flow oxygen levels is studied by considering three fuel mixtures, 5%H 2 þ95%CH 4 , 10%H 2 þ90%CH 4 and 20% H 2 þ80%CH 4 (by mass). In this study, distribution of species concentrations, mixture fraction, strain rate, flame entrainment, turbulent kinetic energy decay and temperature are investigated. Results show that the hydrogen addition to methane leads to improve mixing, increase in turbulent kinetic energy decay along the flame axis, increase in flame entrainment, higher reaction intensities and increase in mixture ignitability and rate of heat release.
Investigation of a Burner Function with Methane-Air Fuel Mixture
A computer model has been developed for the analysis of confined, axis-symmetric, turbulent diffusion flames in a burner element due to high temperature and velocity gradients in the combustion chamber. The conservation equations of mass, momentum, species and energy in the turbulent flow field were solved in conjunction with the RNG k–ε turbulence model. In this case, the standard eddy dissipation is used as the turbulent combustion model and for subsequent nitrogen oxide predictions. A post-processing NO formation model was used to predict the concentration of thermal and prompt NO. The combustion model is based on reactions limited by mixing rate local chemical equilibrium. A model is presented for the rate of combustion which takes into account the intermittent appearance of reacting species in turbulent flames. This model relates the rate of combustion to the rate of dissipation of eddies and expresses the rate of reaction by the mean concentration of reacting specie, the turbulent kinetic energy and the rate of dissipation of this energy. The effects of equivalence ratio (φ) and oxygen percentage (γ) in the combustion air and NO formation are investigated for different values of φ and γ.
International Journal of Hydrogen Energy, 2009
Hydrogen Combustion model Kinetic mechanism NO x Computational fluid dynamics a b s t r a c t An experimental and computational investigation of a lab-scale burner, which can operate in both flame and MILD combustion conditions and is fed with methane and a methane/ hydrogen mixture (hydrogen content of 60% by vol.), is carried out. The modelling results indicate the need of a proper turbulence/chemistry interaction treatment and rather detailed kinetic mechanisms to capture MILD combustion features, especially in presence of hydrogen. Despite these difficulties, Computational Fluid Dynamics results to be very useful, as for instance it allows evaluating the internal recirculation degree in the burner, a parameter which is otherwise difficult to be determined. Moreover the model helps interpreting experimental evidences: for instance the modelling results indicate that in presence of hydrogen the NNH and N 2 O intermediate routes are the dominant formation pathways for the MILD combustion conditions investigated.
Numerical study of the effect of hydrogen addition on methane–air mixtures combustion
International Journal of Hydrogen Energy, 2009
Hydrogen Laminar premixed flame Chemical kinetics a b s t r a c t The stoichiometric methane-hydrogen-air freely propagated laminar premixed flames at normal temperature and pressure were calculated by using PREMIX code of CHEMKIN II program with GRI-Mech 3.0 mechanism. The mole fraction profiles and the rate of production of the dominant reactions contributing to the major species and some selected intermediate species in the flames of methane-hydrogen-air were obtained. The rate of production analysis was conducted and the effect of hydrogen addition on the reactions of methane-air mixtures combustion was analyzed by the dominant elementary reactions for specific species. The results showed that the mole fractions of major species CH 4 , CO and CO 2 were decreased while their normalized values were increased as hydrogen is added. The rate of production of the dominant reactions contributing to CH 4 , CO and CO 2 shows a remarkable increase as hydrogen is added. The role of H 2 in the flame will change from an intermediate species to a reactant when hydrogen fraction in the blends exceeds 20%. The enhancement of combustion with hydrogen addition can be ascribed to the significant increase of H, O and OH in the flame as hydrogen is presented. The decrease of the mole fractions of CH 2 O and CH 3 CHO with hydrogen addition suggests a potential in the reduction of aldehydes emissions of methane combustion as hydrogen is added. The methane oxidation reaction pathways will move toward the lower carbon reaction pathways when hydrogen is available and this has the potential in reducing the soot formation. Chemical kinetics effect of hydrogen addition has a little influence on NO formation for methane combustion with hydrogen addition.