scholarly journals Analysis of the Ignition Behavior Based on Similarity Factor Method

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 873
Author(s):  
Weiwei Fan ◽  
Shengxiong Yang ◽  
Ke Xu ◽  
Mingdong Zhu ◽  
Jie Xu
Keyword(s):  
Negative Temperature Coefficient ◽  
Combustion Process ◽  
Oxidation Mechanism ◽  
Injection Pressure ◽  
Negative Temperature ◽  
Stoichiometric Ratio ◽  
Similarity Factor ◽  
Factor Method ◽  
Chemical Reaction Mechanism ◽  
Spraying Parameters

The chemical kinetics mechanism is an important factor to accurately predict the combustion characteristics of constant-volume bomb (CVB). In this study, an n-heptane oxidation mechanism constructed by Wang et al. is introduced to study the correlation of the ignition behaviors with the mechanism constructed by Chang et al. The effects of the similarity factor method in the analysis of ignition behaviors of fuel in CVB were repeatedly verified by changing the important spraying parameters: injection pressure and hole diameter. Through further verification, it was found that the combustion process was controlled at approximately 850 K and stoichiometric ratio mixture of fuel/air in CVB, which corresponds to the negative temperature coefficient region at stoichiometric ratio mixture in shock tube (ST). The mechanism verified by the experiment under the condition in ST can reflect the chemical ignition in CVB. In addition, the similarity factor method was less dependent on the chemical reaction mechanism and boundary conditions.

scholarly journals Effect of Al3+ Substitution On Magnetic and DC Electrical Resistivity Properties of NiZnCu Nanoferrites

2021 ◽  
Author(s):  
N MURALI
Keyword(s):  
Electrical Resistivity ◽  
Negative Temperature Coefficient ◽  
Sol Gel ◽  
Combustion Process ◽  
Negative Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Auto Combustion ◽  
Ft Ir ◽  
Resultant Material

Abstract Al substituted Ni0.4Zn0.35Cu0.25Fe2-xAlxO4 (x = 0.00, 0.05, 0.10, 0.15, 0.20) samples is synthesized using the sol-gel auto-combustion process. X-ray diffraction shows its cubic spinel structure. The lattice constant decreases as the Al3+ content increases. The sizes of the crystallites are also decreasing in the range of 32.15 nm to 22.89 nm. The wavenumbers of tetrahedral and octahedral sites sighted in the FT-IR spectra are similar to that of the precursor. The increment in the Al3+ content increases the DC conductivity. The electrical resistivity decrease with an increase in the temperature, i.e., it has a negative temperature coefficient with resistance similar to semiconductors. VSM results show their isotropic nature forming single domain ferrimagnetic particles. The resultant material is widely significant, as indicated by its result.

scholarly journals Effect of Cu Substitution on Magnetic and DC Electrical Resistivity Properties of Ni-Zn Nano Ferrites

2021 ◽  
Author(s):  
K. Chandramouli ◽  
P. Anantha Rao ◽  
B. Suryanarayana ◽  
Vemuri Raghavendra ◽  
D. Parajuli ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Negative Temperature Coefficient ◽  
Sol Gel ◽  
Combustion Process ◽  
Negative Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cu Content ◽  
Auto Combustion ◽  
Resultant Material

Abstract Cu substituted Ni0.5Zn0.5-xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3 and 0.4) samples is synthesized using the sol-gel auto-combustion process. X-ray diffraction shows its cubic spinel structure. The lattice constant decreases as the Cu content increases. The sizes of the crystallites are also decreasing in the range of 42.68 nm to 21.75 nm. The wavenumbers of tetrahedral and octahedral sites sighted in the FTIR spectra are similar to that of the precursor. The increment in the copper content increases the DC conductivity. The electrical resistivity decrease with increase in the temperature, i.e. it has a negative temperature coefficient with resistance similar to semiconductors. The remnant ratios R obtained from VSM show their isotropic nature forming single domain ferrimagnetic particles. The resultant material is widely significant, as indicated by its result.

scholarly journals DC Electrical Resistivity and Magnetic Properties of Co Substituted NiCuZn Nano Ferrite

2021 ◽  
Author(s):  
Kanta Jayadev ◽  
M. K. Raju ◽  
N MURALI ◽  
Parajuli D ◽  
K. Samatha
Keyword(s):  
Electrical Resistivity ◽  
Negative Temperature Coefficient ◽  
Sol Gel ◽  
Combustion Process ◽  
Negative Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Octahedral Sites ◽  
Auto Combustion ◽  
Resultant Material

Abstract Co substituted Ni0.3-xCoxCu25Zn0.45Fe2O4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples is synthesized using the sol-gel auto-combustion process. X-ray diffraction shows its cubic spinel structure. The lattice constant decreases as the Co content increases. The sizes of the crystallites are in the range of 20.18–26.24 nm. The wavenumbers of tetrahedral and octahedral sites sighted in the FTIR spectra are similar to that of the precursor. The increment on the Co content increases the DC conductivity. The electrical resistivity decrease with increase in the temperature, i.e. it has a negative temperature coefficient with resistance similar to semiconductors. The remnant ratios R obtained from VSM show their isotropic nature forming single domain ferrimagnetic particles. The resultant material is widely significant, as indicated by its result.

Structural, optical and electrical properties of thermal evaporated nano sized In2Te3 thin films

2018 ◽  
Vol 1 (1) ◽  
pp. 21-25
Author(s):  
R Revathi ◽  
R Karunathan
Keyword(s):  
Thin Films ◽  
Negative Temperature Coefficient ◽  
Thermal Evaporation ◽  
Structural Parameters ◽  
Negative Temperature ◽  
Resistivity Measurements ◽  
Allowed Transition ◽  
Evaporation Technique ◽  
Indium Telluride ◽  
Made In

Indium Telluride thin films were prepared by thermal evaporation technique. Films were annealed at 573K under vacuum for an hour. Both as-deposited and annealed films were used for characterization. The structural parameters were discussed on the basis of annealing effect for a film of thickness 1500 Å. Optical analysis was carried out on films of different thicknesses for both as - deposited and annealed samples. Both the as- deposited and annealed films exhibit direct and allowed transition. Electrical resistivity measurements were made in the temperature range of 303-473 K using Four-probe method. The calculated resistivity value is of the order of 10-6 ohm meter. The activation energy value decreases with increasing film thickness. The negative temperature coefficient indicates the semiconducting nature of the film.

Preliminary Studies on Non-Reactive Flow Vortex Cooling

2019 ◽  
Vol 12 (3) ◽  
pp. 262-271
Author(s):  
T.N. Rajesh ◽  
T.J.S. Jothi ◽  
T. Jayachandran
Keyword(s):  
Combustion Chamber ◽  
Inner Core ◽  
Rocket Engine ◽  
Injection Pressure ◽  
Chamber Pressure ◽  
Reactive Flow ◽  
Stoichiometric Ratio ◽  
Gaseous Oxygen ◽  
Mixture Ratio ◽  
Vortex Combustion

Background: The impulse for the propulsion of a rocket engine is obtained from the combustion of propellant mixture inside the combustion chamber and as the plume exhausts through a convergent- divergent nozzle. At stoichiometric ratio, the temperature inside the combustion chamber can be as high as 3500K. Thus, effective cooling of the thrust chamber becomes an essential criterion while designing a rocket engine. Objective: A new cooling method of thrust chambers was introduced by Chiaverni, which is termed as Vortex Combustion Cold-Wall Chamber (VCCW). The patent works on cyclone separators and confined vortex flow mechanism for providing high propellant mixing with improved degree of turbulence inside the combustion chamber, providing the required notion for studies on VCCW. The flow inside a VCCW has a complex structure characterised by axial pressure losses, swirl velocities, centrifugal force, flow reversal and strong turbulence. In order to study the flow phenomenon, both the experimental and numerical investigations are carried out. Methods: In this study, non-reactive flow analysis was conducted with real propellants like gaseous oxygen and hydrogen. The test was conducted to analyse the influence of mixture ratio and injection pressure of the propellants on the chamber pressure in a vortex combustion chamber. A vortex combustor was designed in which the oxidiser injected tangentially at the aft end near the nozzle spiraled up to the top plate and formed an inner core inside the chamber. The fuel was injected radially from injectors provided near the top plate and the propellants were mixed in the inner core. This resulted in enhanced mixing and increased residence time for the fuel. More information on the flow behaviour has been obtained by numerical analysis in Fluent. The test also investigated the sensitivity of the tangential injection pressure on the chamber pressure development. Results: All the test cases showed an increase in chamber pressure with the mixture ratio and injection pressure of the propellants. The maximum chamber pressure was found to be 3.8 bar at PC1 and 2.7 bar at PC2 when oxidiser to fuel ratio was 6.87. There was a reduction in chamber pressure of 1.1 bar and 0.7 bar at PC1 and PC2, respectively, in both the cases when hydrogen was injected. A small variation in the pressure of the propellant injected tangentially made a pronounced effect on the chamber pressure and hence vortex combustion chamber was found to be very sensitive to the tangential injection pressure. Conclusion: VCCW mechanism has been to be found to be very effective for keeping the chamber surface within the permissible limit and also reducing the payload of the space vehicle.

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