摘要:

The space discretized conservation equations for laminar flames are formulated as a system of differential algebraic equations (DAEs). An appropriate constraint is derived, which is used in two new pressure correction schemes. Application to flame simulations with a one-step chemistry model shows that these new pressure correction schemes yield more accurate results than the standard scheme

ISSN:0010-2202    

DOI:10.1080/00102209908952106

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A model is presented to predict turbulent non-adiabatic premixed combustion of methane under gas turbine conditions. Chemical reaction and heat loss are described with four independent scalar variables. These are the enthalpy variable and three reaction progress variables for combustion of methane. hydrogen and carbon monoxide. In the combustion model turbulence is taken into account by weighting with an assumed shape PDF. The model is used to calculate a 32 kW methane flame in an air cooled combustion chamber. The calculated CO. CO2, O2and NOxconcentrations are compared with suction probe measurements at several locations in the combustion chamber. The non-adiabatic calculations and the measurements show good agreement. Adiabatic calculations show a significant overprediction of NO. Radial profiles of mean axial velocity and turbulent kinetic energy were measured with a 2D LDA system. The measurements show a good agreement. It is concluded that the non-adiabatic model is necessary and suitable to predict NO formation in turbulent premixed methane flames with heat loss.

ISSN:0010-2202    

DOI:10.1080/00102209908952107

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A partially premixed turbulent flame has been modelled using the laminar flamelet concept, i.e. the assumption that laminar flames are embedded in the turbulent flow field. A combination of a premixed flamelet model and a diffusion flamelet model has been used for modelling this partially premixed flame. The premixed flamelet model uses a level set function G(x,t) and the diffusion flamelet model is based on the equation for the mixture fraction Z(x,t).

ISSN:0010-2202    

DOI:10.1080/00102209908952108

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The sound spectrum from a turbulent non-premixed flame as measured in the far field is predicted. A closed form description for the sound spectrum is derived assuming infinitely fast chemistry. The sound spectrum can then be described in terms of the ID turbulent spectrum of the mixture fraction at the flame front. The input values for this turbulent spectrum are derived from a steady state CFD flame calculation. The predictions from the sound spectrum model are compared widi experiments performed in an acoustically one-dimensional combustion chamber. The comparison between measurements and prediction is good for flames in which the mixed-is-burnt approach is valid. For flames, whose burning velocity is limited by chemical kinetics the measured spectrum shows a steeper fall off than the spectrum from the predictions

ISSN:0010-2202    

DOI:10.1080/00102209908952109

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This article begins with a synthetic presentation of key issues in the numerical description of combustion phenomena. Different levels of combustion modeling are identified and characterized. It is indicated how these modeling levels may be used to deal with fundamental questions or technological applications. Important advances have been made in detailed numerical modeling of complex flames and in direct simulation of flame/turbulence and flame/flow interactions. Results obtained in these areas have been employed to improve physical modeling methods which are currently used to calculate reactive flowfields in practical combustors operating in the turbulent regime. As physical modeling relies on average Navier-Stokes equations it requires closure rules for turbulent fluxes and for mean reaction rates. Considerable effort has been expanded to devise novel closure schemes or improve current models. Progress has been accomplished in the development of probabilistic methods in which the probability density function is calculated. Recent developments have concentrated on the incorporation of complex chemistry using various reduction schemes. Advances have also been made in descriptions based on flame surface density concepts. Transport equations for the flame surface have been refined by processing flame data bases generated by direct numerical simulations. Detailed experiments have also provided new insights on the fundamental mechanisms of turbulent combustion and observations have led to novel submodels. Another area of considerable interest for the future is that of large eddy simulation (LES). Progress accomplished in nonreactive LES provides a good starting basis but some challenging problems are encountered when dealing with combustion. The main difficulties are related to the determination of the position of the large scale flame on the coarse computational grid and to the definition of subgrid models for reaction in the small scales. Some novel schemes for combustion LES are reviewed and illustrated by typical examples of calculations

ISSN:0010-2202    

DOI:10.1080/00102209908952110

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Formaldehyde is an important intermediate species formed during combustion processes, e.g. inside IC engines. It disappears rapidly during the excitation phase of the ignition process and can be measured by means of laser induced fluorescence (LIF) with high sensitivity. Due to its important role during the combustion of hydrocarbon fuels an accurate knowledge of formaldehyde concentration fields may improve the detailed understanding of the variety of gasdynamical and chemical processes associated with the auto-ignition of the endgas. However, LIF as one of the preferred methods in combustion diagnostics cannot quantitatively determine species concentrations as long as the collisional quenching rates are unknown.

ISSN:0010-2202    

DOI:10.1080/00102209908952111

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The paper describes the computer code REACFLOW, developed at the JRC for the numerical simulation of compressible gas flows with chemical reactions, with the objective of studying large-scale chemical explosions. The code employs a finite-volume scheme on an unstructured 2-D or 3-D grid, coupled with turbulence models, and modules for either finite-rate chemistry source terms or a model for the interaction between turbulence and combustion. To overcome the problems which are related to different scales, an adaptive fully reversible CFD method is used. New grid points are temporarily inserted into the mesh to track strong disturbances in the flow (such as shocks or flame fronts) and removed when not required.

ISSN:0010-2202    

DOI:10.1080/00102209908952112

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The inlet geometry of the combustion chamber of a Helmholtz type pulse combustor was changed by altering the position of a stagnation plate, or flame holder, near the inlet. Three different flame holder positions were studied. The operating characteristics in terms of time resolved pressure and heat release, time averaged tail pipe temperature and concentrations of O2and NOxin the outlet decoupler were investigated. These quantities were measured and also simulated in a model based upon the LES concept. The effect of different flame holder positions on the operating characteristics is discussed. The simulation model was found able to satisfactorily describe the combustion processes for all three cases, although the results indicate that some sub models need further improvement.

ISSN:0010-2202    

DOI:10.1080/00102209908952113

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor