Influences of oscillation on the physical stability and explosion characteristics of solid-liquid mixed fuel

The stratification phenomenon resulting from differences in the physical properties of solid-liquid components seriously affect the final combustion and explosion characteristics of mixed fuel under the action of oscillation.The effects of oscillation on the physical stability of mixed fuel with two solid-liquid ratios and three liquid component distribution ratios have been investigated using a self-designed experimental system at oscillation frequencies of 60-300 r/min.The explosion characteristics of mixed fuel before and after oscillation are gained from a 20 L spherical explosion container system.When the mass ratio of liquid components is controlled at 66.9%,64.7%,62.6%the final explosion characteristics are stable,with a maximum difference of only 0.71%.The volume of liquid fuel precipitation increases with increasing oscillation frequency when the mass ratio of liquid components reaches 71.7%,69.6%,67.7%.The fuel explosion overpressure after oscillation decreases with increasing liquid precipitation volume,and the repeatability is poor,with a maximum standard deviation of 82.736,which is much higher than the ratio without stratification.Properly controlling the mass ratio of liquid components of the mixed fuel can effectively combat the impact of oscillation on the physical state and maintain the stability of the final explosion characteristics.

Numerical simulation and experimental measurement of transport phenomena for coherent jet with CH4 ＋ N2 mixed fuel gas

Coherent jet technology has been widely used in EAF steelmaking process because of the longer potential core length and stronger impacting power of the supersonic oxygen jet. However, more oxygen and fuel gas are consumed to achieve excel- lent characteristics of coherent jets, which causes the increase in steelmaking cost. Computational fluid dynamics simulation and experimental measurement of the coherent jets with CH4 ＋ N2 mixed fuel gas were carried out aiming at reducing the consumption of fuel gas. The numerical simulation results showed good agreement with the experimental data. As a result, high proportion of N2 negatively affects the combustion of CH4, which is not good for the protection of oxygen jets. While the gas composition is 75% CH4 ＋ 25% N2, the N2 addition to the CH4 leads to an expanding of CH4 combustion zone, and the energy generated by the combustion reaction could be delivered to the molten bath more efficiently, which is one control scheme with high performance-price ratio.

Influence of liquid bridge force on physical stability during fuel storage and transportation

The physical stability of solid-liquid fuel is a factor that needs to be considered for fuel product practicability for storage and transportation. To determine the Influence of liquid bridge force on physical stability, two detection devices were designed. The laws obtained from microscopic experiments are used to verify the physical stability of fuel under different component ratios. The liquid bridge force is found to increase with the droplet volume. Multiliquid bridges above one critical saturation can generate significant resultant forces compared to single-liquid bridges of the same volume. There exist four states of solid-liquid mixed fuel with increasing liquid saturation rate. The liquid bridge force between the solid and liquid plays a dominant role in the physical stability of the first three states. There may be two stages involved in the stratification process for state 4 fuel, and the liquid viscosity is another factor that cannot be ignored. In the process of selecting a fuel ratio, a larger liquid bridge force between the components can be obtained by properly improving the wetting effect so that the fuel shows better physical stability.

STUDY ON THE FUEL AIR MIXING INDUCED BY A SHOCK WAVE PROPAGATING INTO A H_2-AIR INTERFACE

2nd-order upwind TVD scheme was used to solve the laminar, fully Navier-Stokes equations. The numerical simulations were done on the propagation of a shock wave with Ma(s) = 2 and 4 into a hydrogen and air mixture in a duct and a duct with a rearward step. The results indicate that a swirling vortex: may be generated in the lopsided interface behind the moving shock. Meanwhile, the complex shock system is also formed in this shear flow region. A large swirling vortex is produced and the fuel mixing can be enhanced by a shock wave at low Mach number. But in a duct with a rearward step, the shock almost disappears in hydrogen for Mns = 2. The shack in hydrogen will become strong if Ma(s) is large. Similar to the condition of a shock moving in a duct full of hydrogen and air, a large vortex cart be formed in the shear flow region. The large swirling vortex even gets through the reflected shock and impacts on the lower wall. Then, the distribution of hydrogen behind the rearward step is divided into two regions. The transition from regular reflection to Mach reflection was observed aswell in case Ma(s) = 4.

Risk in the Prices of Fossil Fuels for Japanese Electric Utility Sector

A risk in the prices of fossil fuels is a major concern to importing countries of them. This study analyzes the risk of an increase in the cost for Japanese electric utility sector during the period 1978-2007 considering the uncertainty in the prices of fossil fuels. The mean-semivariance model, which uses an upper semivariance as an index of the risk, is adopted for the purpose. The result confirms that the semivariance is the better index of the risk than the variance. Furether, the semivariance is decomposed into two factors; the risk caused by price changes in an individual fossil fuel source and the risk caused by correlations among the changes in the prices of fossil fuel sources. The former has been kept at a low level as it appears to be easy to estimate, while the latter has not been maintained at the lowest level as it appears to be difficult to estimate. The Japanese electric utility sector followed the minimum-risk fossil fuel mix up until 2001, but discontinued the same post 2001.

Experimental and Numerical Study of the Effect of Fuel/Air Mixing Modes on NO_(x) and CO Emissions of MILD Combustion in a Boiler Burner

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emissions,stable combustion and low noise for various kinds of fuel,which has great potential in the industry.The aim of this study is to investigate the effect of fuel/air mixing modes on NO_(x) and CO emissions of MILD combustion in a boiler burner by experiments and numerical simulations.Three types of fuel/air mixing modes (premixing mode,diffusion mode and hybrid mode) have been considered in this study.The realizable k-ε turbulent model and the Eddy Dissipation Concept (EDC) combustion model were used in numerical simulations.In addition to the temperature near the burner head,the calculation results match very well with the axial temperature distribution at the furnace center.The flow pattern under different mixing modes is similar,while the hybrid mode has a higher OH concentration near the diffusive fuel nozzle than the premixing mode,and the corresponding position of the peak OH concentration is closer to the rear half of the furnace.The distribution of temperature is extremely uniform for the premixing mode in the main reactive zone,which is typical for MILD combustion.There is a distinct area where the reaction temperature is higher than 1600 K for the hybrid mode.Moreover,in the main reactive zone,the gas recirculation ratio is high enough to ensure flue gas recirculation,which is beneficial to achieve MILD combustion at local areas.At the location where the axial distance is greater than 0.2 m,the gas recirculation ratio of the premixing mode is larger than that of the hybrid mode,which strengthens the entrainment of hot flue gas into the recirculated gas.The experimental results show that when the thermal intensity is less than 1.67 MW·m^(-3),the NO_(x) emissions are less than 15× 10^(-6)@3.5%O_(2) in near stoichiometric ratio in the premixing mode,and the CO emissions are less than 10× 10^(-6)@3.5%O2 under the same conditions.In the diffusion mode,the NO_(x) emissions are less than 30×10^(-6)@3.5%O_(2).In order to keep NO_(x) and CO emissions low,the hybrid modes with optimized fuel distribution ratio are found under different thermal intensities.

Research on combustion characteristics of scramjet combustor with different flight dynamic pressure conditions

Combustion characteristics in a scramjet combustor equipped with a thin strut were observed and discussed in this paper.A series of numerical simulations were carried out under different flight dynamic pressure conditions.The parameters of cold flow field and combustion field were used to analyze the combustion characteristics.Based on the basic data,the mixing efficiency,characteristics of flame establishment and propagation as well as combustion field characteristics were discussed in this paper.The influence laws of lower dynamic pressure conditions were further revealed to optimize combustor performance.Results indicated that properly reducing the flight dynamic pressure can enhance the mixing of kerosene.The diffusion of kerosene determined the distribution of combustion zone and heat release.Then,the influencing factor that affected the chemical reaction rate was revealed to shorten chemical reaction time.And the higher flight Mach number made the flame propagation velocity faster and the combustion stability stronger.The fuel mixing became the main factor and low dynamic pressure had little effect on laminar flame propagation velocity under high Mach number conditions.The investigations in this paper are helpful for understanding the combustion characteristics under low dynamic pressure conditions.

Effect of methane-hydrogen mixtures on flow and combustion of coherent jets

Coherent jets are widely used in electric are furnace （EAF） steelmaking to increase the oxygen utilization and chemical reaction rates. However, the influence of fuel gas combustion on jet behavior is not fully understood yet. The flow and combustion characteristics of a coherent jet were thus investigated at steelmaking temperature using Fluent software, and a detailed chemical kinetic reaction mecha- nism was used in the combustion reaction model. The axial velocity and total temperature of the supersonic jet were measured via hot state experiments. The simulation results were compared with the experimental data and the empirical jet model proposed by Ito and Muchi and good consistency was obtained. The research results indicated that the potential core length of the coherent jet can be prolonged by optimizing the combustion effect of the fuel gas. Besides, the behavior of the supersonic jet in the subsonic section was also investigated, as it is an important factor for controlling the position of the oxygen lance. The investigation indicated that the attenuation of the coherent jet is more notable than that of the conventional jet in the subsonic section.

Single step low temperature synthesis of gadolinium gallium garnet nanopowders

Solution combustion synthesis of single-phase gadolinium gallium oxide （Gd3GasO12, GGG） nanopowders, by a fuel mixture approach using urea and glycine at a low temperature of 500 ℃, was being reported for the first time. Based on the fact that urea and glycine are good fuels for gallium oxide and gadolinium oxide synthesis, the fuel mixture composition was obtained, which could lead to direct phase pure cubic Gd3Ga5O12 formation without any subsequent calcination step. Combustion was carried out in furnace pre-heated at 500 ℃. Thermogravimetric analysis （TGA） of combustion product showed negligible mass loss indicating direct formation of GGG powder. Fourier transform infrared （FTIR） spectrum of combusted product showed peak characteristic of GGG in case of mixed fuel. X-ray diffraction （XRD） confirmed formation of phase pure GGG at 500 ℃ in preheated furnace. Very fine, well dispersed nanometric particles of size range of 50-100 nm were obtained, being uniform and close to spherical morphology as observed by transmission electron microscope （TEM）.

Flow-Field of an Axisymmetric Lobed Mixer

The flow-field of a fuel/air mixing system with an axisymmetric lobed mixer was numerically investigated. Large-scale streamwise vortices are formed immediately downstream of the mixer trailing edge, stretched further downstream, and finally broken into fragments where more intense mixing occurs. Both numerical and experimental results indicate that the length required for streamwise vortices breakdown in the confined flow-field of an axisymmetric lobed mixer is much shorter than that in the case of planar lobed mixers subject to parallel freestreams. For the conditions studied, the streamwise vortices start to breakdown at three wavelengths downstream of the mixer trailing edge.