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Structures of tetrabrachial flames in two-stage autoigniting dimethyl ether (DME)/air mixture under diesel engine relevant conditions are investigated by direct numerical simulation. Three cases with different initial turbulent integral length scales are studied. Results show that the first stage of autoignition initiates in lean mixtures, and subsequently develops into a diffusion-supported cool...
Volatile matter is generally treated as postulated substance or a combination of different species because the detailed chemical compounds in volatile matter are not yet completely understood. However, very few studies investigate the effects of volatile matter composition and chemical reaction mechanism on the pulverized coal combustion characteristics. In this work, numerical simulations of pulverized...
Experiments are conducted to investigate the process of alumina extraction from coal fly ash generated by coal-fired power plants located in the northern parts of China. Coal ash and ammonium sulfate are mixed and granulated under the effect of binder material. The high temperature fluidized bed reactor is used for the first time to recover the alumina in solid state. The whole process is simplified...
The characteristics of flamelets in coal flames stabilized in a laminar counterflow are numerically investigated with detailed chemistry. The behaviors of coal flamelet are compared with those of the gas flamelet. In addition, the effects of strain rate, coal particle mass flow rate and coal particle size on the behaviors of coal flamelet are studied in both the physical space and the mixture fraction...
It is well known that premixed and non-premixed flamelets coexist in the combustion system, especially for multiphase combustion (Luo et al., 2011; Bai et al., 2016). In this work, a multi-regime combustion model for partially premixed multiphase combustion (2PMC) is developed in the framework of large eddy simulation (LES). In this model, the multi-regime combustion mode is decomposed into two pure...
A dynamic second-order moment closure model is developed for turbulent combustion in the form of large eddy simulation. The filtered reaction rate is directly closed in the form of Arrhenius law, and the whole temperature exponential function is treated as a single variable to avoid the traditional Taylor series expansion. The sub-grid unresolved reaction rate is modeled with a second-order moment...
The coal flame structures are investigated based on a three-dimensional compressible point-source direct numerical simulation (DNS) of a turbulent simplified coal jet flame. The coal particles are treated as point sources and tracked in the Lagrangian frame considering the interphase transfers. A comprehensive coal combustion model, including the evaporation, devolatilization and char combustion,...
Comparative studies of three-dimensional spatially-developing supersonic turbulent spray reactive and non-reactive flows have been conducted by direct numerical simulations. The gas-droplet flow system has been captured with the hybrid Eulerian–Lagrangian approach. High-resolution bandwidth-optimized weighted essentially non-oscillatory (WENO) scheme of spatial discretization and total variation diminishing...
A piloted pulverized coal jet flame was simulated by Large Eddy Simulation (LES). For the sub-grid scale (SGS) effects of the turbulence velocity and the scalar fluctuation of the gas flow on the coal particles, the velocity-scalar joint filtered density function (VSJFDF) model was used. Other models such as the governing equations for particles and coal combustion sub-models were also presented....
Direct numerical simulation (DNS) of heptane reacting sprays in a slab region is performed to investigate the effects of turbulence and droplet size on the evolutions of spray combustion. The gas phase is simulated using an Eulerian approach; while the droplets are treated with a Lagrangian method. The coupling between the two phases is considered. It is shown that the mean normalized squared droplet...
A fully compressible solver for direct numerical simulation of supersonic combustion has been developed and applied to investigate a three-dimensional spatially-developing supersonic turbulent jet flame. High-resolution bandwidth-optimized weighted essentially non-oscillatory scheme of spatial discretization and total variation diminishing temporal integration are used to capture the intricate phenomena...
New flamelet equations for spray combustion considering evaporation effects are derived in the mixture fraction space based on the instantaneous Eulerian transport equations for gas phase and Lagrangian descriptions for droplets. The novelty of these equations lies in some source terms related to evaporation which were neglected in previous studies. The influences of spray evaporation on flamelet...
Seven carbon particle diameters, ranging from 0.006 to 16mm; three air temperatures, varying from 1000 to 1800K; four ambient air velocities, namely, 0, 0.5, 5, and 50m/s respectively, are selected to study carbon combustion numerically. Three-dimensional time-dependent numerical procedure is employed. The carbon particle is situated in the center of the computational domain and remained at rest....
To understand three-dimensional dispersion of particles in the flow around a bluff body, direct numerical simulations of particle-laden wakes of a circular cylinder with Reynolds number ranging from 140 to 260 were performed. The domain decomposition method and high-order finite-difference schemes were applied to solve the fluid flow. A Lagrangian tracking solver was developed to trace the trajectories...
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