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

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

Analysis of flame structure using detailed chemistry and applicability of flamelet/progress variable model in the laminar counter-flow diffusion flames of pulverized coals

Pulverized coal is still found in many practical devices even though it is recognized as ‘‘dirty fuel” because of its CO2 and pollutant emissions. To overcome this problem, advanced coal utilization technologies have been developed using numerical simulations. In this study, the structures of the laminar counter-flow diffusion flames of pulverized coals were investigated by performing simulations based on detailed chemistry. The high-temperature region became narrower as the coal/air ratio increased, because of the departure from the stoichiometric mixture and local quenching by the heat transfer between the gas and solid phases. Further, the applicability of the flamelet/progress-variable (FPV) model was investigated through a priori and a posteriori tests. The a priori test confirmed that the FPV model is capable of reproducing the numerical solutions obtained using the detailed chemistry, including the mass fractions of minor species. In the a posteriori test, there was a slight difference between the FPV model and detailed chemistry results due to overestimation of the progress of the chemical reactions. Given the sufficiently high accuracy of the FPV model in various numerical conditions, it can be concluded that the extended FPV model has potential for use in turbulent coal combustion simulations

Effects of infinitely fast chemistry on combustion behavior of coaxial diffusion flame predicted by large eddy simulation

Large eddy simulations (LES) based on turbulent combustion models aid the design and optimization of combustors. Of the various combustion models available, the eddy break up (EBU) model is widely used because it assumes an infinitely fast chemistry. However, omitting the actual chemical kinetics can cause unexpected behavior, and the characteristics of the combustion models need to be elucidated. Here, the effects of an infinitely fast chemistry on the combustion behavior of a coaxial diffusion flame as predicted by an LES were analyzed. Although the EBU model captured the overall behavior of the chemical species as well as the flow field, the gas temperature and mass fractions of the combustion products in the mixing region of the fuel and oxidizer streams were overestimated. In contrast, the flamelet/progress variable (FPV) model yielded results that were in better agreement with the experimental data, because while the EBU model assumes an infinitely fast chemistry, the look-up tables used in the FPV model are based on the actual chemical kinetics. As these models can be used for the CFD simulations of coal and spray combustion, the results of this study should be useful for efficiently simulating practical combustion systems

Accurate numerical integration of β-PDF for the flamelet approach

When turbulent combustion simulations are performed using the flamelet approach, which indirectly considers the detailed chemical reaction mechanism, the probability density function (PDF) gets applied to statistical distributions for turbulent fluctuations in the mixture fraction that are modeled using the Reynolds-averaged Navier-Stokes or the large eddy simulation. In this case, the so-called “presumed PDF”-i.e., one in which the PDF is assumed and the flamelet table is constructed in advance-is generally employed, and the β-function is widely used for the PDF. This study investigated numerical integration for the equation with the β-function and examined the appropriate method. We succeeded in establishing the optimum value of the parameter for the integration interval and determining the appropriate numerical integration method

Alteration of aluminum tolerance mediated by insertion of same transposable element at different sites in the upstream region of <i>HvAACT1</i> in Japanese barley accessions

Aluminum (Al) toxicity is a major limiting factor for crop production in acid soils. Barley is highly sensitive to Al, so the genetic improvement of its Al tolerance is required. However, useful breeding materials and genetic factors for improving its tolerance are remain largely unclear. Here, we compared the Al tolerance of ‘Minorimugi’ and ‘Fibersnow,’ both six-rowed hulled barley cultivars grown mainly in northern Japan, using relative root length (RRL) as an index, and found that Minorimugi had higher tolerance. Quantitative trait locus (QTL) analysis using recombinant inbred lines (RILs) derived from the two cultivars detected a major QTL at the HvAACT1 (Al-ACTIVATED CITRATE TRANSPORTER 1) locus that explained approximately 36% of the variance. The PCR amplification analysis revealed a 1-kb transposable element (TE) insertion at −1.9 kb in the upstream region of HvAACT1 in Minorimugi that enhances HvAACT1 expression. The TE has the same nucleotide sequence as one previously found at −4.8 kb in the upstream region of HvAACT1 in ‘Murasakimochi,’ which is an Al tolerant cultivar. In the Japanese barley population, the Murasakimochi-type HvAACT1 upstream allele is shared mainly among barley accessions developed in the Shikoku area, while the Minorimugi-type allele is shared mainly among accessions developed in the Hokuriku and Nagano area. This geographic difference indicates that both alleles are shared among different subpopulations in Japanese barley, which may be advantageous for growth in acid soils. Our results provide information about a new allele of the HvAACT1 upstream region and potential breeding materials for improving the Al tolerance of barley.</p

Evaluation of the flamelet/progress-variable approach and flamelet-generated manifolds method in laminar counter-flow diffusion flame

To evaluate characteristics of the Flamelet/Progress-Variable approach (FPV) and Flamelet-Generated Manifolds method which can consider a detailed chemical reaction mechanism, a combustion simulation was performed in a laminar counter-flow diffusion flame. While the numerical solutions of the FPV reproduced the measurements and almost completely agreed with those of the detailed chemical reaction mechanism, the numerical solutions of the FGM method overpredicted the measurements of CO mole fraction and underpredicted the ones of CO2 especially in fuel-rich region, and differed from those of the detailed chemical reaction mechanism. This is because the flamelet table of the FGM indicates the state close to chemical equilibrium and overpredicts dissociation of CO2 when the combustion reaction sufficiently progresses