Current Issue : July-September Volume : 2022 Issue Number : 3 Articles : 5 Articles
As an effective clean fuel, ethanol has the characteristics of improving antiknock quality and reducing emissions. It is an ideal antiknock additive for Homogeneous Charge Compression Ignition (HCCI) engines. The oxidation of gasolineethanol surrogates in HCCI engines is a very complex process which is dominated by the reaction kinetics. This oxidation process directly determines the performance and emissions of HCCI engines. Coupling the computational fluid dynamic (CFD) model with the gasoline-ethanol surrogate mechanism can be used for fuel design, so the construction of a reduced mechanism with high accuracy is necessary. A mechanism (278 species, 1439 reactions) at medium and low temperatures and experiments in a HCCI engine for the oxidation of gasoline-ethanol surrogates were presented in this paper. Directed relation graph with error propagation (DRGEP) method and quasi-steady-state assumption (QSSA) method were used in order to get a reduced model. Then, the kinetics of the vital reactions related to the formation and consumption of H and OH were adjusted. To validate the model, the HCCI experiments for the oxidation of gasoline-ethanol surrogates were conducted under different operating conditions. The verification result indicated that the present model can predict the oxidation process of gasoline-ethanol effectively....
In this study, a high-density ZrN/ZrSi2 composite reinforced with ZrO2 as an inert phase was synthesized under vacuum starting with a Zr-Si4N3-ZrO2 blend using combustion-synthesis methodology accompanied by compaction. The effects of ZrO2 additions (10–30 wt%) and compression loads (117–327 MPa) on the microstructure, porosity and hardness of the samples were studied. The process was monitored using XRD, SEM, EDS, porosity, density and hardness measurements. Thermodynamic calculations of the effect of ZrO2 addition on the combustion reaction were performed including the calculation of the adiabatic temperatures and the estimation of the fractions of the liquid phase. The addition of up to 20 wt% ZrO2 improved the hardness and reduced the porosity of the samples. Using 20 wt% ZrO2, the sample porosity was reduced to 1.66 vol%, and the sample hardness was improved to 1165 ± 40.5 HV at 234 MPa....
A composite oxides’ Co-Mn-Ce catalyst was synthesized by a coprecipitation method, and the experiment was carried out to study the effects of reaction parameters and light hydrothermal aging on propane combustion over the Co-Mn-Ce catalyst. The influence of reaction temperature, propane concentration, oxygen concentration, water vapor, and hydrothermal aging was studied during the catalytic combustion of propane. The propane conversion significantly decreased by 10% when the propane concentration increased at 300°C and then further decreased from 80% to 40% as water vapor concentration increased from 0 to 10 vol.%. In addition, water vapor also prolonged the time required to reach equilibrium. After hydrothermal treatment, the catalyst obtained the lowest oxidation capacity of propane. Furthermore, the results of in situ DRIFTs and O2 temperature programmed desorption (O2-TPD) demonstrated that there were fewer oxygen species after hydrothermal aging, and carbonates were the main intermediates formed during the catalytic oxidation of propane....
The technology of flame stabilization on cavity-based scramjet combustor has great significance in the field of future spacecraft. In this paper, a compressible modified FGM model was established based on the idea of the flamelet model, which was adopted to simulate the unsteady combustion process of the hydrogen transverse jet in the upper cavity of the scramjet. The results show that the compressible modified FGM model can accurately reflect the flow field and the propagation process of the flame in the supersonic cavity, and can capture the fine shock structure in the flow field. The coupling effect of shock waves and shear layer cause the shear layer to quickly destabilize, resulting in the turbulence effect, which promotes the mixing of air and fuel. The boundary layer separation at the upper wall of the combustion chamber will reduce the stability of the shear layer....
In recent years, cobalt ferrite has attracted considerable attention due to its unique physical properties. The present study aimed to produce cobalt ferrite magnetic nanoparticles doped with zinc and vanadium using the sol-gel auto-combustion method. For this purpose, Co1−xZnxFe2−yVyO4 (where x = 0.0, 0.1, 0.2, 0.5 and y = 0.00, 0.05, 0.15, 0.25) precursors were calcined at 800 ◦C for 3 h. The prepared samples were characterized with the X-ray diffraction (XRD) method in combination with Rietveld structure refinement, field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometery (VSM). The XRD patterns confirmed the formation of crystalline spinel structure for all samples. However, the diffraction peaks of hematite and iron vanadium oxide phases were observed in the patterns of some doped samples. The average crystallite size for all the synthesized samples was found to be in the range of ~45–24 nm, implying that it decreased by simultaneously doping cobalt ferrite with Zn and V. The FT-IR spectrum confirmed the formation of the spinal structure of ferrite through the observed vibrational bands assigned to the tetrahedral (υ2) and octahedral (υ1) interstitial complexes in the spinel structure. The FE-SEM images showed that morphology, average grain size, and agglomeration of the synthesized powders were affected by doping, which was due to the interactions of the magnetic surface of nanoparticles. The VSM curves demonstrated that saturation magnetization and coercivity values changed in the range of 30–83 emu/g and from 27–913 Oe, respectively. These changes occurred due to the alteration in cation distribution in the spinel structure. This can be attributed to the change in superexchange interactions between magnetic ions by co-substitution of Zn and V ions in Cobalt ferrite and the changes in magnetocrystalline anisotropy....
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