Jan M. Boyde

Validation of an Ignition and Flame Propagation Model for Multiphase Flows

This paper presents a numerical investigation of a generic lab scale combustor with focus on the ignition characteristics. The test case has been examined thoroughly in a comprehensive measurement campaign to provide a detailed set of boundary conditions and a profound data base of results. The experimental setup comprises five parallel-aligned mono-disperse droplet chains which are ignited, using a focused laser beam. One aspect of the experimental study is the ignitability with respect to the imposed boundary conditions. The second covers the growth and the propagation of the flame after the establishment of an initial kernel. The outcome of the numerical simulations is compared to the experimental results which allows an in-depth assessment of the employed numerical models. The chemistry and, thus, the flame propagation behavior is captured by a turbulent flame speed closure approach with an adaptation to render the model suitable to multiphase flows. For the dispersed phase a Lagrangian particle tracking scheme is employed in combination with a continuous thermodynamics fuel model for the evaporation. The overall good agreement demonstrates the capability of a multiphase flow CFD solver in the field of ignition modeling.Copyright

Thermodynamic Process Analyses of SOFC/GT Hybrid Cycles

This paper presents the description of a numerical design tool for the steady state thermodynamic process analysis of SOFC/GT hybrid systems. The tool includes models for all gas turbine components and for a SOFC stack, based on the tubular fuel cell design of Siemens. The modular structure of the code allows the simulation of all kinds of hybrid system configurations with gas turbines from different manufacturers and of varying performance ranges. Furthermore a selection of atmospheric and pressurized hybrid systems based on the Turbec T100 micro gas turbine and a tubular SOFC stack is discussed. Also parameter studies are shown which focus on the operating conditions of the chosen system configurations.

Ignition and Flame Propagation along Planar Monodisperse Droplet Streams

An experimental and numerical study is presented concerning the ignition of a fuel spray under well defined conditions. The development of a flame kernel that follows the generation of a plasma by a focused laser pulse and the subsequent flame propagation along five co-planar monodisperse streams of fuel droplets is investigated. High-speed video of the broadband luminosity and simultaneous fuel- and OH-PLIF provide qualitative and quantitative experimental data. Numerical simulations have shown that the focused laser pulse not only provides an energy/radical source for the ignition but is also responsible for transforming the droplets present in a small region into fuel vapor. Actually, without the quasi-instantaneous phase change there would not be enough vapor fuel to sustain the flame kernel under these time scales and surrounding conditions. The simulations are performed using an Eulerian-Lagrangian turbulent spray combustion code. Detailed chemistry is used to compute the laminar flame speed under relevant conditions, and a turbulent flame closure model (TFC) is then adopted for turbulence-chemistry interaction.

Correlations for the laminar flame speed, adiabatic flame temperature and ignition delay time for methane, ethanol and n-decane

This paper provides a detailed database for curve fitted polynomials to deliver information about the laminar flame speed, adiabatic flame temperature and ignition delay time depending on the equivalence ratio, temperature and pressure. The fuels under investigation are methane, ethanol and n-decane. A new aspect of this paper is the envisaged broad range of validity of the correlations, covering the range of 0.6 1.5 for the equivalence ratio, 293.15 K 593.15 K for the temperature, regarding the laminar flame speed and the adiabatic flame temperature and 1400 K 1800 K, regarding the ignition delay time and 0.5 bar 6 bar for the pressure range. As basis of the mathematical expressions, curves with the highest order of four have been chosen to best describe the behavior of the quantities under examination. Evaluation of well established experimental data sets for each respective fuel generates a first rudimentary groundwork for the derivation of the polynomial. The experimental results are further enhanced by obtaining a large amount of additional points through finite rate chemistry simulations with detailed reaction mechanism. By means of a least squares fit, the coefficients for the algebraic expression are inferred. An error analysis is contained subsequent to the calculation, helping the reader to assess the reliability and quality of the fitted curves.

Spark ignition simulations and the generation of ignition maps by means of a turbulent flame speed closure approach

This paper presents a numerical investigation of ignition phenomena in turbulent partially premixed methane/air flames. In this work, a turbulent flame speed closure model (TFC) is employed with an ignition delay module extension. The model is applied to two partially premixed test cases under standard conditions in the configuration of a shearless flame and a counter flow flame, respectively. For both setups, the flame kernel propagation and consequent establishment or extinction of the flame are examined. A shearless configuration represents the first test case under investigation. The study demonstrates the large influence of the mean flow parameters on achieving a successful ignition of the domain. The second test case under examination is a counterflow geometry. A sensitivity analysis with respect to spark ignition position and ignition energy is performed. The simulations show that flame kernel spreading is largely influenced by the magnitude of turbulence occurring in the flow, leading to an enhanced propagation in areas with a moderate turbulence degree, whereas high turbulence can be detrimental for the flame establishment due to extensive heat losses. Another observation is that a successful ignition of the domain can occur, even in cases in which the ignition energy is not placed in an area with flammable mixture. The comparison with experimental data shows a good agreement, both in terms of successful ignition and flame kernel propagation.Copyright

Evaluation of the RPM-CN approach for broadband combustion noise prediction

The derivation and validation of a broadband combustion noise model is presented. The applied RPM-CN approach, a hybrid CFD/CAA approach relies on the stochastic reconstruction of combustion noise sources in the time domain. The stochastic reconstruction is conducted by the RPM method out of statistical turbulence quantities which can be delivered by a reacting RANS simulation. In the present work, the modeled combustion noise sources are derived for the use in conjunction with the LEE for the computation of the acoustic propagation. The DLR-A and the DLR-B ames, both non-premixed open jet ames which dierentiate in the fuel outlet velocity and the respective Reynolds number, are used for the validation of the RPM-CN approach. Results of the reacting ow computations and the subsequent acoustic predictions are compared to measurements and discussed. The reliability and accuracy of the RPM-CN approach will be demonstrated by a good agreement of the computed sound pressure level spectra with the experimental data.

A numerical investigation of the ignition characteristics of a spray flame under atmospheric conditions

This study presents a numerical investigation of the characteristics of a transient spray ame ignited by laser-induced breakdown. The simulations are carried out under atmospheric conditions within well de ned boundary conditions. The multiphase set-up comprises a kerosene blend as the liquid fuel provided by an air assisted nozzle with droplet velocities up to 40 m/s and an air coow with velocities ranging from 1.0 m/s to 4.5 m/s. An initial ame kernel is created by a laser-induced breakdown at the spray cone edge. Onsetting vaporization and further propagation of the ame, largely on the outskirt of the ame cone surface lead to a growing and convected self-sustaining ame. Results concerning the ame growth and the ame center position, representing the major general characteristics of the instationary combustion process are provided. As experimental data is available for the same set-up and boundary conditions, the simulation outcome is further compared with regard to its qualitative and quantitative agreement. The study shows that the employed numerical tools for predicting transient combustion are of very satisfying quality and can subsequently be used for more complex scenarios to evaluate questions concerning ame kernel development and igniter location.