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Fouzi Tabet - One of the best experts on this subject based on the ideXlab platform.
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entropy generation in turbulent syngas counter flow diffusion flames
International Journal of Hydrogen Energy, 2017Co-Authors: Khadidja Safer, Ahmed Ouadha, Fouzi TabetAbstract:Abstract Efficiency is one of the major objectives when designing energy systems. Irreversibilities of combustion processes can be characterized by analyzing entropy generation which is proportional to exergy destruction. In this paper, entropy generation is investigated in turbulent non-premixed counter-flow syngas flames at a high strain rate over a wide range of hydrogen percentage (H2/CO molar fraction from 0.4 to 2.0). The aim is to define the most efficient syngas composition to reduce irreversibilities. Irreversibilities involved in NO formation process are also examined. RANS (Reynolds Averaged Navier Stokes) technique including k-e turbulence model is used for the flow field estimation. Flame structure is calculated using SLFM (Steady Laminar Flamelet Model) and EPFM (Eulerian Particle Flamelet Model) is applied for NOx predictions. Total entropy generation rate accounts for Chemical, heat conduction, mixing and viscous Effects. Computational results show that the total volumetric entropy generation decreases with H2 enrichment as well as its different contributing Effects. Chemical Effect is dominant, followed by heat conduction and mixing Effects. Viscous Effect is negligible. The maximum of both thermal and prompt NO formation routes are influenced by the three main entropy generation modes, with the predominance of the Chemical Effect. At high strain rates, H2-rich syngas flames are efficient in regards to irreversibilities and NO emissions reduction.
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numerical investigation of counter flow diffusion flame of biogas hydrogen blends Effects of biogas composition hydrogen enrichment and scalar dissipation rate on flame structure and emissions
International Journal of Hydrogen Energy, 2016Co-Authors: Abdelbaki Mameri, Fouzi TabetAbstract:This study addresses numerically the influence of several operating conditions on the structure and NO emissions of a biogas diffusion flame. The analysis is conducted at atmospheric pressure in counter-flow configuration and mixture fraction space. CO2 volume in biogas is varied from 25% to 60%, H2 enrichment from 0% to 20% and the scalar dissipation rate from near equilibrium to near extinction. Particular attention is paid to CO2 Chemical Effect. CO2 contained in biogas can have Chemical Effects when it participates in Chemical reactions and thermal Effects when it acts like a pure diluent. Chemical Effects of CO2 are elucidated by using the inert species technique. Flame structure is characterized by solving flamelet equations with the consideration of radiation and detailed chemistry. It is observed that flame properties are very sensitive to biogas composition, hydrogen addition and scalar dissipation rate. CO2 increment decreases flame temperature, mass fraction of chain carrier radicals and NO emission index. Blending biogas with hydrogen increases the mixture heating value and makes the fuel more reactive. Hence, chain carrier radicals and NO index emission are all increased. The Chemical Effect of CO2 is found to be present overall scalar dissipation rate values where it reduces the maxima of temperature and OH mass fraction and increases the maxima of CO and NO mass fractions. H2 enrichment has a weak influence on CO2 Chemical Effect. Hydrogen-rich biogas flames produce less NO at high scalar dissipation rates.
Vahid Hosseini - One of the best experts on this subject based on the ideXlab platform.
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various Effects of reformer gas enrichment on natural gas iso octane and normal heptane hcci combustion using artificial inert species method
Energy Conversion and Management, 2018Co-Authors: Masoud Reyhanian, Vahid HosseiniAbstract:Abstract Reformer gas (syngas) addition to main fuel is a practical solution for combustion timing control in HCCI engines. This study emphasizes the understanding of various Effects of reformer gas (RG) addition, with composition of 75%vol H2 and 25%vol CO, in HCCI combustion by developing an artificial inert species method and using a detailed Chemical kinetics multi-zone model. Three fuels (iso-octane, n-heptane, and natural gas) with different autoignition characteristics were used in this study. The developed multi-zone model was validated for mentioned fuels at various percentages of RG using six experimental cases of a single-cylinder CFR engine. The results showed that increasing reformer gas fraction in the fuel mixture advanced methane fuel combustion timing, retarded the combustion of n-heptane and had insignificant Effect on iso-octane combustion. Thermal Effect of RG in all fuels resulted in earlier start of combustion (SOC) because of the mixture specific heat ratio enhancement. The SOC for methane and iso-octane fuels was advanced by RG addition due to the Chemical Effect of RG. However, the Chemical Effect of RG for methane fuel is more significant. By adding 30% RG to methane fuel, H2 advanced the SOC by −5.6 °CA and CO retarded it by 1.4 °CA due to Chemical Effect and also the interaction Effect of CO and H2 advanced the SOC by −1.8 °CA. For iso-octane fuel, adding 30% RG, both CO and H2 advanced the SOC by 0.4 CA due to their Chemical Effect. On the other hand, in n-heptane fuel, H2 is almost responsible for all of the Chemical Effects of RG for retardation of SOC.
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investigating various Effects of reformer gas enrichment on a natural gas fueled hcci combustion engine
International Journal of Hydrogen Energy, 2014Co-Authors: Sina Voshtani, Masoud Reyhanian, Mohammad Ali Ehteram, Vahid HosseiniAbstract:Abstract Homogenous charge compression ignition (HCCI) combustion has the potential to work with high thermal efficiency, low fuel consumption, and extremely low NOx-PM emissions. In this study, zero-dimensional single-zone and quasi-dimensional multi-zone detailed Chemical kinetics models were developed to predict and control an HCCI combustion engine fueled with a natural gas and reformer gas (RG) blend. The model was validated through experiments performed with a modified single-cylinder CFR engine. Both models were able to acceptably predict combustion initiation. The result shows that the Chemical and thermodynamic Effects of RG blending advance the start of combustion (SOC), whereas dilution retards SOC. In addition, the Chemical Effect was stronger than the dilution Effect, which was in turn stronger than the thermal Effect. Furthermore, it was found that the strength of the Chemical Effect was mainly dependent on H2 content in RG. Moreover, the amount of RG and concentration of species (CO–H2) were varied across a wide range of values to investigate their Effects on the combustion behavior in an HCCI engine. It was found that the H2 concentration in RG has a more significant Effect on SOC at lower RG percentages in comparison with the CO concentration. However, in higher RG percentages, the CO mass concentration becomes more Effective than H2 in altering SOC.
Junfu Lu - One of the best experts on this subject based on the ideXlab platform.
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Effects of inert dilution on the propagation and extinction of lean premixed syngas air flames
Fuel, 2015Co-Authors: Yang Zhang, Wenfeng Shen, Hai Zhang, Yuxin Wu, Junfu LuAbstract:The dilution Effects of inert components N2 and CO2 on the propagation and extinction of lean premixed H2/CO/air syngas flames were experimentally and numerically investigated. Extinction stretch rates were measured using the counterflow technique while laminar flame speed data were obtained from literatures. Numerical simulations were conducted at 1-D freely propagating configuration and opposed-jet configuration with detailed chemistry and molecular transport description. The numerical results well predicted the experimental measurements. Both results revealed that CO2 dilution had more profound Effect on flame propagation and extinction than N2 dilution. In addition, numerical simulation assessed the preferential importance in a rather quantitative manner among the three Effects, i.e., the thermal Effect, the diffusivity change Effect and the Chemical Effect with artificial manipulation of mass diffusivities and Chemical reactions of CO2 and N2. The results showed that the thermal Effect dominated the reduction of laminar flame speed and extinction strain rate. The Chemical Effect caused by CO2 dilution was slightly stronger to the reduction of extinction limit than to that of laminar flame speed. The diffusivity change Effect is negligible for both CO2 and N2 dilutions. N2 only acts as a thermal inert in the propagation and extinction of the H2/CO/air flames.
Fengshan Liu - One of the best experts on this subject based on the ideXlab platform.
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numerical and experimental study of the influence of co2 and n2 dilution on soot formation in laminar coflow c2h4 air diffusion flames at pressures between 5 and 20 atm
Combustion and Flame, 2015Co-Authors: Fengshan Liu, Ahmet E Karatas, Omer L GulderAbstract:Abstract The Effects of fuel dilution by CO 2 and N 2 on soot formation and the flame structure in laminar coflow C 2 H 4 /air diffusion flames at pressures between 5 and 20 atm were investigated both experimentally and numerically. Experimentally a constant ethylene flow rate and a constant dilution rate of 1:2 (fuel:diluent by mass) were maintained throughout the experiments. The flames were stable and non-smoking over the pressure range investigated. The radially-resolved soot volume fraction and temperature distributions were measured by the spectral soot emission (SSE) technique. Numerical calculations were conducted using two C 2 chemistry models with formation of PAHs up to pyrene and a soot model incorporating pyrene collision as the soot inception step and hydrogen-abstraction acetylene addition mechanism and PAH condensation as the surface growth processes. The two C 2 chemistry models were the ABF mechanism [Appel et al. (2000)] and the DLR mechanism [Slavinskaya and Frank (2009)]. The DLR mechanism predicted little or no Chemical Effect of CO 2 dilution, depending on the pressure, in the present context. Numerical results are in qualitative agreement with experimental measurements. Soot volume fractions and carbon conversion are lower in the CO 2 -diluted flames due to the additional Chemical Effect of CO 2 . CO 2 is still more Effective than N 2 as a diluent to suppress soot formation at elevated pressures. The primary pathway for the Chemical Effect of CO 2 dilution is through the reverse reaction of CO + OH ↔ CO 2 + H. The Chemical Effect of CO 2 lowers the rates of soot inception, C 2 H 2 addition, and PAH condensation. The Effectiveness of the CO 2 Chemical Effect on soot formation suppression diminishes with increasing pressure. The diminishing Effectiveness of the Chemical Effect of CO 2 dilution with increasing pressure is due to the significant decrease in the H radical mole fraction.
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Effects of water vapor addition to the air stream on soot formation and flame properties in a laminar coflow ethylene air diffusion flame
Combustion and Flame, 2014Co-Authors: Fengshan Liu, Jean-louis Consalvi, Andres FuentesAbstract:Abstract The Effects of adding water vapor to the air stream on flame properties and soot volume fraction were investigated numerically in a laminar coflow ethylene/air diffusion flame at atmospheric pressure by solving the fully elliptic conservation equations and using a detailed C 2 reaction mechanism including PAH up to pyrene and detailed thermal and transport properties. Thermal radiation was calculated using the discrete-ordinates method and a statistical narrow-band correlated- k based wide band model for the absorption coefficients of CO 2 and H 2 O. Soot formation was modeled using a PAH based inception model and the HACA mechanism for surface growth and oxidation. Addition of water vapor significantly reduces radiation heat loss from the flame primarily through reduced soot loading and flame temperature. The added water vapor affects soot formation and flame properties through not only dilution and thermal Effects, but also through Chemical Effect. The Chemical Effect is as significant as the dilution and thermal Effects. The primary pathway for the Chemical Effect of water vapor is the reverse reaction of OH + H 2 ↔ H + H 2 O. Our numerical results confirm that the reduced H radical concentration leads to lower PAH concentrations and consequently lower soot inception rates. In contrast, the radiation Effect due to the added water vapor was found to have a minor influence on both flame structure and soot formation in the laminar diffusion flame investigated.
Yang Zhang - One of the best experts on this subject based on the ideXlab platform.
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dilution Effect on the propagation and extinction of lean premixed syngas air flames
Springer Theses, 2018Co-Authors: Yang ZhangAbstract:The dilution Effects of inert components N2 and CO2 on the propagation and extinction of lean premixed H2/CO/air syngas flames were experimentally and numerically investigated. It was found that CO2 dilution had more profound Effect on flame propagation and extinction than N2 dilution. The three Effects, probably caused by the presence of CO2 and N2 diluents, namely the thermal Effect, the diffusivity change Effect and the Chemical Effect, and their preferential importance were numerically assessed. The thermal Effect dominated the overall dilution Effect in reduction of laminar flame speed and extinction strain rate. The Chemical Effect caused by CO2 dilution was slightly stronger to the reduction of extinction limit than to that of laminar flame speed. The diffusivity change Effect is negligible for both CO2 and N2 diluents. N2 only act as a thermal inert in the propagation and extinction of the H2/CO/air flames.
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Effects of inert dilution on the propagation and extinction of lean premixed syngas air flames
Fuel, 2015Co-Authors: Yang Zhang, Wenfeng Shen, Hai Zhang, Yuxin Wu, Junfu LuAbstract:The dilution Effects of inert components N2 and CO2 on the propagation and extinction of lean premixed H2/CO/air syngas flames were experimentally and numerically investigated. Extinction stretch rates were measured using the counterflow technique while laminar flame speed data were obtained from literatures. Numerical simulations were conducted at 1-D freely propagating configuration and opposed-jet configuration with detailed chemistry and molecular transport description. The numerical results well predicted the experimental measurements. Both results revealed that CO2 dilution had more profound Effect on flame propagation and extinction than N2 dilution. In addition, numerical simulation assessed the preferential importance in a rather quantitative manner among the three Effects, i.e., the thermal Effect, the diffusivity change Effect and the Chemical Effect with artificial manipulation of mass diffusivities and Chemical reactions of CO2 and N2. The results showed that the thermal Effect dominated the reduction of laminar flame speed and extinction strain rate. The Chemical Effect caused by CO2 dilution was slightly stronger to the reduction of extinction limit than to that of laminar flame speed. The diffusivity change Effect is negligible for both CO2 and N2 dilutions. N2 only acts as a thermal inert in the propagation and extinction of the H2/CO/air flames.