In order to simulate and predict the complex mechanism of the high power CO laser excited by transverse dc discharge, a two-dimensional gas flow model has been developed from the authors' one-dimensional model. Based on the control volume method for two-dimensional Cartesian coordinates, the fundamental equations deal with state, continuity, momentum, energy, and reactions. The similar discharge power distribution can be given as the experiment, where the power density is higher around the hollow-cathode array than around the plane anode. Although the speed of the CO gas mixture is in the sub-sonic region, the effect of compression is taken into account. The integration is repeated by SIMPLEST method and the matrices are solved by MICCG method for the pressure equation and by MJLUCR method for the other equations. The computation is carried out by a HITAC S820 supercomputer and a Sun-4 workstation. As a result of the simulation, non-uniform distribution of the gas parameters was made clear.
Telephone +81 471 44 8811, Telefax +81 471 44 8939 ABSTRAO Computer models have been developed for the industrial CO lasers, those are oparated by transverse dc discharge in the temperature region 1 50-200 K. The 1D (dimensional) model has been developed to analyze and predict the output performance characteristics, mainly the laser power. The flow equations are coupled with the kinetic equations of the direct excitation by electron impact in discharge, V-V (vibration to vibration) and V-R/T (vibration to rotation and translation) energy transfer by collision, and spontaneous and stimulated emission. The 2D model to analyze the spatial distribution of the gas temperature and excited molecules is now under development. The flow equations, based on the control volume method for the 2D Cartesian coordinates, are described. The time integration is performed by the SIMPLEST method.
To analyze combustion oscillation in the premixed combustor, a large-eddy simulation program for premixed combustion flow was developed. The subgrid scale (SGS) model of eddy viscosity type for compressible turbulence (Speziale et al., 1988) was adopted to treat the SGS fluxes. The fractal flamelet model, which utilizes the fractal properties of the turbulent premixed flame to obtain the reaction rate, was developed. Premixed combustion without oscillation was analyzed to verify the present method. The computational results showed good accordance with experimental data (Rydén et al., 1993). The combustion oscillation of an “established buzz” type in the premixed combustor (Langhorne, 1988) was also analyzed. The present method succeeded in capturing the oscillation accurately. The detailed mechanism was investigated. The appearance of the non-heat release region, which is generated because the supply of the unburnt gas into the combustion zone stagnates, and its disappearance play an important role.
The successful development of coal-based integrated gasification combined cycle (IGCC) technology requires gas turbines capable of achieving the dry low-nitrogen oxides (NOx) combustion of hydrogen-rich syngas for low emissions and high plant efficiency. Therefore we have been developing a multiple-injection burner for hydrogen-rich syngas fuel in order to achieve high efficiency and low environmental load. This burner consists of a perforated plate with multiple air holes and fuel nozzles. The multiple air holes and the fuel nozzles are arranged coaxially. The burner is based on the concept of premixed combustion configured by mixing fuel and air in the each air hole rapidly and dispersing fuel with multiple fuel-air jet. This rapid mixing can reduce NOx emissions by getting homogeneous lean premixed combustion, and preventing flashback despite the high flame speed for hydrogen-rich syngas fuels. The unsteady phenomena that occur in the combustion field should be understood in detail in order to confirm this burner concept. However, their measurement under high pressure is difficult. Meanwhile computational fluid dynamics (CFD) is able to investigate the detailed distributions of various emissions and temperature even though under combustion fields of high pressure and high temperature. The purpose of this paper is to validate this concept of the multiple-injection burner by using CFD. The burner can change the combustion form between premixed and non-premixed combustion by controlling the mixing, so the combustion field coexisting with premixed combustion and non-premixed combustion is complicated. Therefore, we have developed a hybrid turbulent combustion (HTC) model applicable to both non-premixed and premixed flames. The HTC model is hybridized with the flamelet progress variable (FPV) model and a flame propagation model. The FPV model is based on the laminar flamelet concept. The flame propagation model considers the flame stretch effect, diffusion enhancement effect, and increasing rate of flame surface area. The turbulent flow model adopts large eddy simulation (LES) with a dynamic sub-grid scale (SGS) based on the local inter-scale equilibrium assumption (LISEA4). Both the turbulent combustion model and turbulent flow model were programmed into a simulation tool based on the OpenFOAM library. We validated the concept of this burner for hydrogen-rich syngas fuel by using the simulation tool. The simulation results showed the rapid mixing of fuel and air in the air holes, and by using HTC model we confirmed that premixed combustion is the combustion configuration of this multiple-injection burner. In addition, the multiple-injection burner has high flame stability. There is no zone of high temperature in the air hole and high temperature is maintained near the burner. The multiple-injection burner can thus maintain flame stability without any flashback.
We have developed a burner for the gas turbine combustor, which was high efficiency and low environmental load. This burner is named the “coaxial jet cluster burner” and, as the name indicates, it has multiple fuel nozzles and holes in a coaxial arrangement. To form lean premixed combustion, this burner mixes fuel and air in the multiple holes rapidly. The burner can change the combustion form between premixed and non-premixed combustion by controlling the mixing. However, the combustion field coexisting with premixed and non-premixed combustion is complicated. The phenomena that occur in the combustion field should be understood in detail. Therefore, we have developed the hybrid turbulent combustion (HTC) model to calculate the form in which non-premixed flame coexists with premixed flame. Turbulent flow has been simulated using a large eddy simulation (LES) with a dynamic sub grid scale (SGS) model coupled with the HTC model. These models were programmed to a simulation tool based on the OpenFOAM library. However, there were unclear points about their applicability to an actual machine evaluation and the predictive precision of CO concentration which affects burner performance. In this study, we validate the HTC model by comparing its results with measured gas temperature and gas concentration distributions obtained with a coaxial jet cluster burner test rig under atmospheric pressure. In addition, we analyze the CO generation mechanism for the lean premixed combustion in the burner.
To predict the flame front position, we adopt the large eddy simulation (LES) and incorporate into it a combustion model, the hybrid turbulent combustion model (HTC model), applicable to any flame mode. We take previously obtained test results for the axisymmetric jet lean premixed flame in a cylindrical chamber at high pressure and investigate the effects of equivalence ratio variation on flame front positions. Full details of these tests are available in the literature. We find the simulation results of the axial positions of the flame front points, defined by the inflection point of the OH concentration distributions, show good agreement with test results (less than 4% difference between them). Therefore, we conclude that the HTC model is capable of capturing the actually observed tendency when changing the equivalence ratios and that the combination of the HTC model with LES suggests that flame stretch effect is important to predict the flame front position for lean premixed combustion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
334 Leonard St
Brooklyn, NY 11211
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.