Patrick Le Clercq

Validation of a Multicomponent-Fuel Model for Spray Computations

A multicomponent-fuel droplet evaporation model based on the theory of continuous thermodynamics is presented. It was implemented in the framework of a multiphase flow Eulerian-Lagrangian code and computations were validated using measurements of a monodisperse spray injected in a hot turbulent air flow. The continuous description of real fuel composition is briefly presented for two models, one based on a presumed distribution function, namely the gamma distribution function and the second one based on harmonic decomposition, namely the Fourier series. Then, the validation test case is described and the computation results pertaining to the continuous phase mean velocity and temperature fields are validated against measurement results. Finally, based on these validated computations of the surrounding flow, the monodisperse spray computation results concerning the evaporation of light heating oil are compared with the experimental results. The agreement is very good. The two-way coupling implementation methodology, which is necessary for spray combustion applications is also demonstrated.

Investigation of GTL-Like Jet Fuel Composition on GT Engine Altitude Ignition and Combustion Performance: Part II—Detailed Diagnostics

The ignition and combustion performance of different synthetic paraffinic kerosenes (SPKs) under simulated altitude relight conditions were investigated at the altitude relight test rig at the Rolls-Royce Strategic Research Centre in Derby. The conditions corresponded to a low stratospheric flight altitude between 25,000 and 30,000 feet. The combustor under test was a twin-sector representation of an advanced gas turbine combustor and fuel injector. Five different SPKs and Jet A-1 were tested at different mass flow rates of air and fuel, and at two different sub-atmospheric air pressures and temperatures. The fuel temperature was kept approximately constant. Simultaneous high-speed imaging of the OH* and CH* chemiluminescence, and of the broadband luminosity was used to visualize both the transient flame initiation phenomena and the combustion behavior of the steady burning flames. In addition, flame luminosity spectra were recorded with a spectrometer to obtain spectrally resolved information concerning the different chemiluminescence bands and the soot luminosity. These investigations were performed in conjunction with the comparative evaluation of the ignition and stability regimes of the five SPKs, which is the subject of a separate complementary paper [1]. We found that the observed flame initiation phenomena, the overall combustion behavior and the different ratios of the chemiluminescence from the OH*, CH* and C2 * radicals were not strongly dependent on the fuels investigated. But, the SPK flames showed for all combustor operating conditions significantly lower soot luminosities than the corresponding Jet A-1 flames, indicating a potential benefit of the SPK fuels.Copyright

Impact of Fischer-Tropsch fuels on aero-engine combustion performance

In this paper a detailed numerical investigation of an aero-engine single sector combustor model is carried out. The main goal of this study is to compare its combustion characteristics when fueled with a single component surrogate Jet A-1 fuel to the ones when fueled with a multicomponent Jet A-1 as well as with multicomponent Fischer-Tropsch (F-T) fuels under the same operating conditions. The combustor geometry under investigation mirrors at smaller scale many salient features of modern aero-engine combustors such as high swirling flow, eusion cooling at the walls, head cooling flow and, dilution flow. The numerical simulations are performed by means of an Eulerian-Lagrangian method for the gas and liquid phase, respectively. A finite-rate chemistry combustion model, which explicitly takes all species into account and an assumed-PDF approach for the turbulence-chemistry interaction are used to model the turbulent reacting flow. A multicomponent-fuel droplet evaporation model is implemented and enables to study real-fuel eects on the overall combustion process. A former numerical study had shown good results when comparing the reacting velocity and temperature fields and spray pattern for Jet A-1 combustion with LDA, CARS and Mie scattering measurements respectively. In the present study, a fully synthetic jet fuel which contains 50 % Coal-to-Liquid (CtL) fuel and a 100 % Gas-to-Liquid (GtL) fuel, both synthesized from a Fischer-Tropsch process are substituted to Jet A-1. The simulations are repeated under the same nominal operating conditions. A comparison in terms of temperature distribution, OH radical concentration and, main reactants concentration is carried out in order to outline the influence of the fuel composition on the combustor performance. Additionally, an analysis of certain soot precursors concentration and spray evaporation characteritics is delivered.

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.

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.

Jet A-1 Fuel Spray Evaporation in a Turbulent Flow: Experimental Investigations and Validation of Numerical Models

An experimental system was built to study the evaporation of sprays in well controlled environment. Appropriate measurement techniques were used to study in detail the evaporation of a single component fuel and the multicomponent-fuel Jet A-1. Boundary conditions and initial conditions, necessary to perform accurate computations are determined precisely. The single component fuel is used for a basic matching of computation with experiments. To describe the evaporation of Jet A-1 a single component surrogate model and a continuous thermodynamics model (CTM) are employed. The composition of the Jet A-1 fuel used in the experiments is known and thus it was possible to determine accurately the distribution parameters of the CTM model. Finally the experimental data inferred about the evaporation of Jet A-1 is used to validate the models.

Numerical Simulation of Heat Transfer in a 3D Cavity-Receiver

The unsteady 3D fluid flow coupled to radiative, convective, and conductive heat transfers are computed within a cavity-receiver that was successfully tested experimentally. A Monte-Carlo radiation model is used in the fluid regions of the reactor with source terms outside the cavity’s window to account for the concentrated radiative power input. Darcy’s law for the viscous regime and the Forchheimer’s term for the inertial regime are used in the momentum equation to account for the pressure drop within the porous region (RPC).Two separate energy equations for the solid and for the fluid regions of the porous domain are solved in order to capture the non-equilibrium effects in that region. Rosseland diffusion approximation is used in the solid regions of the RPC domain. The material properties and boundary conditions were taken from published experimental measurements. The simulation results are compared to the measurement data collected during the pre-heating and the ceria reduction phases, which sum up to four different radiative power inputs. Results of the comparison are very good and constitute the verification that the numerical methods, physical sub-process models and material properties are adequately selected and implemented. An analysis regarding the heat balance, the recirculating flow and, the effect of dual-scale porosity is also presented.Copyright

GTL fuels and their effects on aircraft aas turbine altitude ignition – detailed diagnostics

Abstract There has been growing interest for alternative fuels in aviation in the past three years. An alternative fuel can be defined by the triplet ‘feedstock-process-fuel’. Presently, the triplet with one of the highest technology readiness levels for gas turbine (GT) applications involves using natural gas in a Fischer-Tropsch thermo-chemical process to derive synthetic paraffinic kerosene (SPK). Generic Fischer-Tropsch fuels were approved in September 2009 for use as 50% blends with Jet A-1. Gas-to-Liquid (GTL), as a final product of the aforementioned triplet meets those specifications and is in a deployment stage, with one plant currently under construction in Qatar. The product of a Fischer-Tropsch process, such as GTL, is feedstock agnostic. As such, its composition can be tailored to meet or exceed some of the current specifications for jet fuel. Investigating the potential benefits of composition changes in GTL-like jet fuel defines the general scope of our research program. This article presents the results of tests conducted on the Rolls-Royce plc TRL3 sub-atmospheric altitude ignition facility in Derby, UK. The test campaign aimed at investigating the impact of the carbon number distribution (narrow/wide cut), the iso- to normal-paraffin ratio and the total cyclic paraffin content characterizing the surrogate GTL-like fuel composition on the ignition and combustion performance of a single sector advanced GT combustor and fuel injector under simulated altitude conditions. The detailed diagnostics consisted of simultaneous high-speed imaging of hydroxyl (OH*) and methylidyne (CH*) chemiluminescence and broadband luminescence measurements of the ignition process. By observing the processes in the visible and the UV simultaneously, it was possible to distinguish between radiation (originating from e.g. soot) and the chemiluminescent emissions from the OH* and CH* radicals. These are markers for chemical activity in the different regions of the combustor and therefore provide information concerning the temporal and spatial development of the flame kernel.