Numerical study on the combustion characteristics in a porous-free flame burner for lean mixtures

2019 ◽  
Vol 234 (4) ◽  
pp. 935-945 ◽  
Author(s):  
Seyed Amin Ghorashi ◽  
Seyed Mohammad Hashemi ◽  
Seyed Abdolmehdi Hashemi ◽  
Mahdi Mollamahdi
Keyword(s):  
Porous Medium ◽  
Numerical Study ◽  
Combustion Process ◽  
Experimental Tests ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Numerical Results ◽  
Flame Stability ◽  
Porous Burner ◽  
Flame Burner

The present work implements a numerical simulation to investigate the combustion process in a porous-free flame burner. The non-equilibrium thermal condition is performed, and discretization and solving of the governing equations are conducted in a two-dimensional axisymmetric model. In order to simulate the combustion process, a reduced chemical kinetic mechanism of GRI 3.0, which includes 16 species and 41 reactions, is used. In order to prove the precision of the numerical method, some experimental tests are carried out and the numerical results are in a good agreement with the experimental measurements. The numerical results demonstrate that the porous-free flame burner has a higher flame stability compared to the conventional porous burner and the radiative efficiency of the porous-free flame burner is less than the porous burner. In addition, an increase in thermal conduction of the porous medium leads to an extension in the flame stability. In addition, the results show that with decreasing the pore density of porous medium, the flame stability is extended.

Investigation of the premixed methane–air combustion through the combined porous-free flame burner by numerical simulation

2019 ◽  
Vol 233 (6) ◽  
pp. 773-785 ◽  
Author(s):  
Seyed Mohammad Hashemi ◽  
Seyed Abdolmehdi Hashemi
Keyword(s):  
Porous Medium ◽  
Thermal Efficiency ◽  
Combustion Process ◽  
Stability Limit ◽  
Flame Stability ◽  
The Novel ◽  
Flame Thickness ◽  
Porous Burner ◽  
Flame Burner ◽  
Stability Limits

Combustion process of the premixed methane–air in a novel combined porous-free flame burner was investigated numerically. Two-dimensional model considering nonequilibrium thermal condition between the gas and solid phases was used and the combustion was simulated using reduced GRI 3.0 multistep chemical kinetics mechanism. To examine the validity of the implemented numerical model, the burner was manufactured and tested. Good agreement between the numerical results and experimental data were observed. Thermal flame thickness, flame stability limit, and thermal efficiency were discussed. Multimode heat transfer in the porous medium including convection, radiation, and conduction were quantified and perused. Results showed that the thermal thickness of laminar free flame established in the perforated portion of the burner was considerably less than thickness of submerged flame stabilized in the porous medium. Predicted results suggested that the flame stability limit was augmented in the combined burner compared to the burner with full porous foam. Analyses of the heat balance showed that the thermal efficiency of the combined porous-free flame burner was less than thermal efficiency of the full porous burner. Comparison of the full porous burner with the novel combined porous-free flame burner demonstrated that the combined burner caused higher stability limits and lower thermal efficiencies.

Numerical study of the flame stability of premixed methane–air combustion in a combined porous-free flame burner

2018 ◽  
Vol 233 (4) ◽  
pp. 530-544 ◽  
Author(s):  
Seyed Mohammad Hashemi ◽  
Seyed Abdolmehdi Hashemi
Keyword(s):  
Equivalence Ratio ◽  
Numerical Study ◽  
Flame Stabilization ◽  
Pollutant Emissions ◽  
Pollutant Emission ◽  
Flame Stability ◽  
Emission Analysis ◽  
Porous Burner ◽  
Flame Burner ◽  
Stability Limits

Premixed methane–air combustion process within a combined porous-free flame burner was investigated numerically in the present study. The burner consisted of a perforated porous ceramic pellet forming combination of submerged and free flame zones. Nonequilibrium thermal condition between the gas and solid phases was implemented and governing equations were solved in a two-dimensional model using finite volume method. Detailed chemistry based on reduced GRI 3.0 mechanism with 41 reaction steps and 16 species including NOx mechanisms was utilized to simulate the combustion processes and pollutant emissions. In order to investigate the validation of the implemented numerical model, the burner was manufactured and tested. The predicted results were consistent with the experimental data. Comparison of the combined porous-free flame burner with porous burner showed that the flame stability limits of the combined burner were higher than those of porous burner. Multimode heat transfer within the porous medium was perused and the effect of heat recirculation on the flame stabilization was discussed. Investigation of the effect of pore density on the flame stabilization showed that the lower pore densities were desirable in order to improve the flame stability limits. Pollutant emission analysis proved that the NO concentration increased with increasing the equivalence ratio while the minimum quantity of CO concentration was evaluated at an equivalence ratio of 0.6.

Skeletal Kinetic Modeling for the Combustion of Endothermic Hydrocarbon Fuel in Hypersonic Vehicle

2021 ◽  
pp. 1-24
Author(s):  
Hui-Sheng Peng ◽  
Bei-Jing Zhong
Keyword(s):  
Surrogate Model ◽  
Laminar Flame ◽  
Combustion Process ◽  
Hydrocarbon Fuel ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Vital Role ◽  
Reacting Flow ◽  
Combustion Properties ◽  
Endothermic Hydrocarbon Fuel

Abstract Chemical kinetic mechanism plays a vital role in the deep learning of reacting flow in practical combustors, which can help obtain many details of the combustion process. In this paper, a surrogate model and a skeletal mechanism for an endothermic hydrocarbon fuel were developed for further investigations of the combustion performance in hypersonic vehicles: (1) The surrogate model consists of 81.3 mol% decalin and 18.7 mol% n-dodecane, which were determined by both the composition distributions and key properties of the target endothermic hydrocarbon fuel. (2) A skeletal kinetic mechanism only containing 56 species and 283 reactions was developed by the method of “core mechanism​ sub mechanism”. This mechanism can be conveniently applied to the simulation of practical combustors for its affordable scale. (3) Accuracies of the surrogate model and the mechanism were systematically validated by the various properties of the target fuel under pressures of 1-20atm, temperatures of 400-1250K, and equivalence ratios of 0.5-1.5. The overall errors for the ignition and combustion properties are no more than 0.4 and 0.1, respectively. (4) Laminar flame speeds of the target fuel and the surrogate model fuel were also measured for the validations. Results show that both the surrogate model and the mechanism can well predict the properties of the target fuel. The mechanism developed in this work is valuable to the further design and optimization of the propulsion systems.

A Numerical Study on the Low Limit Auto-Ignition Temperature of Syngas and Modification of Chemical Kinetic Mechanism

2019 ◽  
Author(s):  
Seung Eon Jang ◽  
Jin Park ◽  
Sang Hyeon Han ◽  
Hong Jip Kim ◽  
Ki Sung Jung ◽  
...  
Keyword(s):  
Low Temperature ◽  
Temperature Region ◽  
Ignition Delay ◽  
Delay Time ◽  
Ignition Delay Time ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Numerical Results ◽  
Auto Ignition ◽  
Chemical Kinetic Mechanism

Abstract In this study, the auto ignition with low limit temperature of syngas has been numerically investigated using a 2-D numerical analysis. Previous study showed that auto ignition was observed at above 860 K in co-flow jet experiments using syngas and dry air. However, the auto ignition at this low temperature range could not be predicted with existing chemical mechanisms. Inconsistency of the auto ignition temperature between the experimental and numerical results is thought to be due to the inaccuracy of the chemical kinetic mechanism. The prediction of ignition delay time and sensitivity analysis for each chemical kinetic mechanism were performed to verify the reasons of the inconsistency between the experimental and numerical results. The results which were calculated using the various mechanisms showed significantly differences in the ignition delay time. In this study, we intend to analyze the reason of discrepancy to predict the auto ignition with low pressure and low temperature region of syngas and to improve the chemical kinetic mechanism. A sensitive analysis has been done to investigate the reaction steps which affected the ignition delay time significantly, and the reaction rate of the selected reaction step was modified. Through the modified chemical kinetic mechanism, we could identify the auto ignition in the low temperature region from the 2-D numerical results. Then CEMA (Chemical Explosive Mode Analysis) was used to validate the 2-D numerical analysis with modified chemical kinetic mechanism. From the validation, the calculated λexp, EI, and PI showed reasonable results, so we expect that the modified chemical kinetic mechanism can be used in various low temperature region.

Computer Simulation of Combustion Process in a Piston Engine With a Porous Medium Regenerator

2013 ◽  
Vol 5 (4) ◽  
Author(s):  
Lei Zhou ◽  
Maozhao Xie ◽  
Ming Jia ◽  
Junrui Shi
Keyword(s):  
Porous Medium ◽  
Combustion Process ◽  
Kinetic Mechanism ◽  
Combustion Efficiency ◽  
Pollutant Emissions ◽  
Mixture Formation ◽  
Computational Fluid Dynamics Cfd ◽  
Reduce Emissions ◽  
Detailed Kinetic Mechanism ◽  
Reciprocating Movement

In the regenerative engine, effective heat exchange and recurrence between gas and solid can be achieved by the reciprocating movement of a porous medium regenerator in the cylinder, which considerably promotes the fuel-air mixture formation and a homogeneous and stable combustion. A two-dimensional numerical model for the regenerative engine is presented in this study based on a modified version of the engine computational fluid dynamics (CFD) software KIVA-3V. The engine was fueled with methane and a detailed kinetic mechanism was used to describe its oxidation process. The characteristics of combustion and emission of the engine were computed and analyzed under different equivalence ratios and porosities of the regenerator. Comparisons with the prototype engine without the regenerator were conducted. Results show that the regenerative engine has advantages in both combustion efficiency and pollutant emissions over the prototype engine and that using lower equivalence ratios can reduce emissions significantly, while the effect of the porosity is dependent on the equivalence ratio used.

Numerical study of the effect of thermal boundary conditions and porous medium properties on the combustion in a combined porous-free flame burner

2018 ◽  
Vol 232 (7) ◽  
pp. 799-811 ◽  
Author(s):  
Seyed Abdolmehdi Hashemi ◽  
Majid Nikfar ◽  
Seyed Amin Ghorashi
Keyword(s):  
Porous Medium ◽  
Wall Temperature ◽  
Numerical Study ◽  
Stability Limit ◽  
Chemical Mechanism ◽  
Pore Density ◽  
No Emission ◽  
Constant Wall Temperature ◽  
Wall Condition ◽  
Flame Burner

The effect of wall thermal conditions, pre-heating of the inlet air–fuel mixture ( Tin), and pore density of the porous medium (λ) on the stability limit and NO emission in a porous-free flame burner is numerically investigated. A reduced chemical mechanism and realizable k-ɛ turbulence model are used for the simulation. The numerical simulation is validated with the experimental data. The results show that the flame stability limit is extended with increasing the pore density while the maximum and minimum NO emissions are produced in pore densities of 8 ppc and 16 ppc, respectively. It is observed that the use of insulated wall condition causes the flame blow-off to occur at higher inlet velocities compared to that of the constant wall temperature condition. On the other hand, the use of constant wall temperature condition (cooled wall), causes flashback to occur in lower inlet velocities compared to that of the insulated wall. Constant wall temperature condition decreases NO emission in comparison with the insulated wall condition approximately by 18%. The flame stabilizes at higher inlet velocities and so stability limit is extended when inlet mixture temperature increases. This also causes NO emission to increase.

Comprehensive JP8 Mechanism for Vitiated Flows

2010 ◽  
Vol 4 (1) ◽  
Author(s):  
K.M. Hall ◽  
X. Fu ◽  
K. Brezinsky
Keyword(s):  
Combustion Process ◽  
Combustion Products ◽  
Chemical Kinetic ◽  
Fused Silica ◽  
Liquid Fuels ◽  
Outer Diameter ◽  
Jet Engines ◽  
Flat Flame ◽  
Major Species ◽  
Flame Burner

With the intent of optimizing the combustion process of complex hydrocarbon liquid fuels such as JP8 in internal combustion jet engines and their afterburners, simpler surrogate hydrocarbon compounds were used in a counterflow diffusion flat flame burner to validate the chemical kinetic modeling process. The combustion products sampled from the flame produced during the burning of the validation fuels methane and n-heptane were analyzed using a Varian CP3800 gas chromatograph. The effects of sampling with a 350 micron outer diameter (OD) fused-silica tube were compared to those of a 3.5 mm quartz probe in order to minimize sampling effect on the flame. Simulations of the sampled species were performed using the OPPDIF package of CHEMKIN with chemistry models provided by UIC. Concentrations of major species (e.g. CO, CH4, CO2, O2) were found to be well simulated with the models, with the best fit occurring for methane and n-heptane, and wider variation occurring with some species in all validation fuels.

Numerical Simulation of Pollutant Emissions in a Can-Type Low NOx Gas Turbine Combustor

2010 ◽  
Author(s):  
Di Wang ◽  
Wenjun Kong ◽  
Yuhua Ai ◽  
Baorui Wang
Keyword(s):  
Gas Turbine ◽  
Plug Flow ◽  
Combustion Process ◽  
Chemical Reactor ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Pollutant Emissions ◽  
Inlet Temperature ◽  
Gas Turbine Combustor ◽  
In Series

A research program is in development in China in order to realize a demonstrator of combined cooling heating and power system (CCHP) with net electrical output around 100kW by using of a can-type micro gas turbine. In this paper, numerical simulations were completed to investigate the pollutant emissions in a can-type low NOx gas turbine combustor. Based on the analysis of the computational fluid dynamics (CFD) results, a Chemical Reactor Network (CRN) model was set up to simulate the pollutant emissions in the combustor with detailed gas-phase chemical kinetic mechanism of GRI-Mech 3.0. The CRN consists of a number of ideal reactors of the perfectly stirred reactors (PSR) and plug flow reactors (PFR) in series and parallel structures. Two types of CRN models were designed. One is relatively simple, another is more complex. The results show that the complex CRN model corresponds with the actual combustion process better. The trends of nitrogen oxides (NOx) and carbon monoxide (CO) varying with the equivalence ratio were conducted. Effects of the inlet temperature and pressure on NOx and CO emissions were also presented in this paper. At last, the numerical results are compared with the experimental results.

Numerical Study of Premixed Combustion of Methane Stabilized on Porous Medium

2016 ◽  
Author(s):  
Valerio Giovannoni ◽  
Rajnish N. Sharma ◽  
Robert R. Raine
Keyword(s):  
Porous Medium ◽  
Numerical Study ◽  
Burning Velocity ◽  
Combustion Process ◽  
Heat Losses ◽  
Low Flow ◽  
Small Scale ◽  
High Porosity ◽  
Flow Rates ◽  
Flame Holder

The present study focuses on the numerical analysis of the combustion process occurring in a small scale cylindrical combustion chamber using a commercial computational code. The chosen diameter is 18 mm, being the same as the flat flame regenerative combustor currently under experimental investigation by the author (Giovannoni), and it includes a 10 mm thick porous flame holder and a 1 mm thick stainless steel outer wall. A 17 species and 73 reactions skeletal mechanism related to methane oxidation is employed for the simulations. A parametric study is performed and results in terms of temperature profiles, major species’ concentrations and flow velocities are presented. Results show that the flame holder can considerably affect combustion and heat losses from the combustor. In particular at low flow rates, when the laminar burning velocity is much higher than the flow velocity, heat is lost mainly through the flame holder to the walls and to the surroundings. At high flow rates the flame appears to be slightly lifted from the porous medium and heat is mainly dispersed to the walls. This causes preheating of the mixture upstream of the combustion through axial conduction in the wall, achieving superadiabatic temperature. It is also clear from the simulations that employing a flame holder with low thermal conductivity and high porosity yields benefits in limiting heat losses and in widening flammability limits.

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