A modified boundary condition of velocity for continuity equation with non-uniform density distribution at outlet boundary plane

Boundary conditions in computational fluid dynamics significantly affect the prediction of flow field. However, the outlet boundary conditions for the continuity equation have been rarely investigated. In addition, the velocities at the outlet boundary might not be accurately predicted with the conventional outlet boundary conditions when a flow that has non-uniform density distribution on the outlet boundary is simulated. In the present study, we modified a boundary condition for the continuity equation in consideration of the non-uniform density distribution on the outlet boundary plane, comparing the numerical results of combustion between the conventional and modified boundary conditions. As a result, the proposed boundary condition can resist the generation of an unrealistic temperature field better than the conventional methods

Prediction of polycyclic aromatic hydrocarbons formation using flamelet approach with additional transport equations

It is known that the formation of minor species such as polycyclic aromatic hydrocarbons (PAHs) cannot be well captured by the standard flamelet/progress-variable (FPV) model. In this study, the extended method in which additional transport equations for PAHs were solved (FPV-TE model) was verified in the numerical simulations of a laminar counter-flow diffusion flame. The numerical results obtained from FPV-TE model were in better agreement with the solutions of the detailed chemistry than that in the standard FPV model in terms of the mass fractions of PAHs

Improvement of the prediction accuracy of NO emissions in counter-flow diffusion flames on using NO mass fraction as a progress variable

Computational fluid dynamics has been widely used to predict the production of nitrogen oxide (NO). Flamelet approach is commonly used as a modelling technique to perform turbulent combustion simulations. As the prediction of NO emissions with the flamelet approach is not reliable, when predicting the NO emission, the NO emissions are calculated with the conservation equation of NO mass fraction, and the NO production rate is predicted with the flamelet approach. In this study, we used the mixture fraction and NO mass fraction to predict the NO production rate in the conservation equation of the NO mass fraction, comparing the numerical results calculated with proposed method with those with the conventional methods and detailed chemistry model. Numerical simulations of counter-flow diffusion flames where NO was not supplied, that was supplied with fuel, and that was supplied with oxidizer indicated that the distribution of NO mole fraction calculated with the proposed method was in better agreement with that of the detailed chemistry model than that of the conventional methods

DRGEP-based mechanism reduction considering time dependency of reaction rate

Importance of the method to determine interaction coefficient in the DRGEP method is explored by considering the pyrolysis reaction with time variation of temperature. To take into account time dependency, the interaction coefficients were determined using four different methods: the original method and three alternative methods. Two of the three alternative methods use the overall interaction coefficient computed from direct interaction coefficient determined by maximum value of ratio of production rate in each time, and the overall interaction coefficient computed from direct interaction coefficient determined by the averaged value of ratio of production rate in each time, respectively. The other method considers overall interaction coefficient computed from time-dependent direct interaction coefficient. The analytical condition for the mechanism reduction and the assessment of reduction accuracy are the pyrolysis of the gas composed of C2H2, C2H4, and N2 at 1000–1600 K and 0.1 MPa. The concentration of benzene during the simulation by the reduced mechanism was compared with original mechanism. In case of the DRGEP with method, the smallest reduced mechanism with accuracy has 60 species. In contrast, the reduced mechanisms constructed by the DRGEP with the latter two methods of the four accurately predict the concentration with only 45 species. In particular, the method that takes into account the time dependence of the reaction rate was able to describe the behavior in which the formation rate of the target chemical species, benzene, gradually approaches zero near equilibrium, even when the number of chemical species is 40

AGF1, an AT-Hook Protein, Is Necessary for the Negative Feedback of AtGA3ox1 Encoding GA 3-Oxidase

Negative feedback is a fundamental mechanism of organisms to maintain the internal environment within tolerable limits. Gibberellins (GAs) are essential regulators of many aspects of plant development, including seed germination, stem elongation, and flowering. GA biosynthesis is regulated by the feedback mechanism in plants. GA 3-oxidase (GA3ox) catalyzes the final step of the biosynthetic pathway to produce the physiologically active GAs. Here, we found that only the AtGA3ox1 among the AtGA3ox family of Arabidopsis (Arabidopsis thaliana) is under the regulation of GA-negative feedback. We have identified a cis-acting sequence responsible for the GA-negative feedback of AtGA3ox1 using transgenic plants. Furthermore, we have identified an AT-hook protein, AGF1 (for the AT-hook protein of GA feedback regulation), as a DNA-binding protein for the cis-acting sequence of GA-negative feedback. The mutation in the cis-acting sequence abolished both GA-negative feedback and AGF1 binding. In addition, constitutive expression of AGF1 affected GA-negative feedback in Arabidopsis. Our results suggest that AGF1 plays a role in the homeostasis of GAs through binding to the cis-acting sequence of the GA-negative feedback of AtGA3ox1

Large-scale simulation of CO2 gasification reaction with mass transfer for metallurgical coke: Comparison with lab-scale experiment at 1373 K in early stage

The large-scale simulation of gasification using a highly resolved coke model is a powerful tool for predicting structural changes in metallurgical coke in a blast furnace. The objective of this study was to evaluate the accuracy of a numerical simulation using the results obtained from laboratory-scale gasification experiments. For the experiment, a cylindrical coke sample with a radius of 20 mm was gasified using CO2 gas at 1373 K in a coke gasification reaction furnace until the conversion reached 0.2. In addition, a numerical simulation of the coke model developed from X-ray computer tomography images of the coke sample before the reaction was conducted at 1373 K. Three low-resolution coke models were developed using the full-resolution coke model. The reaction rate and the coke structure after reaction were compared between the experiment and the numerical simulation. As a result, the prediction accuracies of reaction rate and structural change decreased with decreasing the image resolution as overall trend

Application of flamelet/progress-variable approach to the large eddy simulation of a turbulent jet flame of pulverized coals

In this study, the flamelet/progress-variable (FPV) approach was applied to a large eddy simulation of a pulverized coal jet flame. The FPV approach considers the characteristics of the pulverized coal flame, e.g., non-adiabatic system and several types of fuel streams, via additional representative variables. First, the applicability of the FPV approach to a turbulent flame with pulverized coals was confirmed through a comparison of the numerical solutions and experimental data. In this study, the pure pilot case was also investigated to clarify the effects of pulverized coals on the flame. The flame structure changes significantly upon the injection of pulverized coals, and the flame index suggests the coexistence of premixed and diffusion combustion modes even in the downstream region. In particular, the combustion mode fluctuates with time in the middle region of the flame. The fuel gas released from the pulverized coals should increase in this region; therefore, the release and combustion behavior of the volatile matter must be involved in the combustion mode variation. The evaluation of the combustion modes of fuel gas in the coal flame is useful for the design and optimization of pulverized coal combustors with next-generation technologies