In the last years, the development of synthetic aviation jet fuels has attracted much interest, to provide alternatives to crude-oil based kerosene. Synthetic jet fuels can be produced from a variety of feedstocks and processes. To limit possible harmful effects on the environment when burning a jet fuel, discussions are attributed to the effects of the specific composition of a synthetic fuel on its performance and its emission pattern. A numerical tool, if available, would also be helpful within the specification process any aviation jet fuel must pass. The present work contributes to the studies and efforts how to design a synthetic jet fuel to match predefined properties, e.g. the energy content or a less harmful emission characteristics compared to Jet A-1. The approach of a generic fuel will be followed in order to design a synthetic jet fuel with pre-defined chemical properties: A chemical kinetic reaction mechanism will be elaborated capable predicting the fundamental combustion properties of the generic fuel for each possible mixing ratio of the components included. In this work, a generic mixture serving as an innovative synthetic jet fuel was studied, with n -dodecane, cyclohexane, and iso -octane chosen as single fuel components; no aromatics were added to reduce the concentration of soot precursors. Then, their fundamental combustion properties, i.e. laminar burning velocity and ignition delay time, were measured in a burner test rig and applying the shock tube technique, respectively. These experimental data were used for the validation of the reaction mechanisms developed for each single fuel component, which were then combined to the reaction mechanism for the generic fuel under consideration. To allow a comparison of the combustion behavior of the synthetic jet fuel directly, with the same reaction mechanism, to Jet A-1, toluene was added as a model component for aromatics. A reduced surrogate reaction model was produced, too. All the reaction mechanisms elaborated are shown to reasonably predict the fundamental combustion properties within the parameter range considered. The compact reduced surrogate model can serve as a virtual jet fuel within numerical simulations. Thus, ultimately, an estimation of the suitability of an innovative synthetic jet fuel as a blending component to crude-oil kerosene is enabled. As a result, CFD simulations can be run efficiently tackling the combustion of a synthetic fuel in a jet engine under practical conditions and by taking into account the interaction between turbulence and chemistry.

The combustion of conventional fuels (Diesel and Jet A-1) with 10–20% vol. oxygenated biofuels (ethanol, 1-butanol, methyl octanoate, rapeseed oil methyl ester, diethyl carbonate, tri(propylene glycol)methyl ether, i.e., CH 3 (OC 3 H 6 ) 3 OH, and 2,5-dimethylfuran) and a synthetic paraffinic kerosene was studied. The experiments were performed using an atmospheric pressure laboratory premixed flame and a four-cylinder four-stroke Diesel engine operating at 1500 rpm. Soot samples from kerosene blends were collected above a premixed flame for analysis. Polyaromatic hydrocarbons (PAHs) were extracted from the soot samples. After fractioning, they were analyzed by high-pressure liquid chromatography (HPLC) with UV and fluorescence detectors. C 1 to C 8 carbonyl compounds were collected at the Diesel engine exhaust on 2,4-dinitrophenylhydrazine coated cartridges (DNPH) and analyzed by HPLC with UV detection. The data indicated that blending conventional fuels with biofuels has a significant impact on the emission of both carbonyl compounds and PAHs adsorbed on soot. The global concentration of 18 PAHs (1-methyl-naphthalene, 2-methyl-naphthalene, and the 16 US priority EPA PAHs) on soot was considerably lowered using oxygenated fuels, except 2,5-dimethylfuran. Conversely, the total carbonyl emission increased by oxygenated biofuels blending. Among them, ethanol and 1-butanol were found to increase considerably the emissions of carbonyl compounds.

Alternative aviation fuels are evaluated for lean-flame NO x formation, lean-flame blowout (LFBO), and rich-flame soot threshold. The alternative aviation fuels evaluated are: hydro-processed renewable jet (HRJ) made from camelina and tallow, Fischer-Tropsch (FT) jet made from coal and natural gas, and alcohol-based jet. Chromatographic analysis (from another lab) shows that these fuels are composed mainly of iso-alkanes. These fuels are burned as received and with 10–20% aromatic added. For comparison, petroleum-based jet fuels are burned: JP5, JP8, Jet-A, and an aromatic blend. Additionally, we burn several pure fuels: n-hexane, cyclo-hexane, n-octane, iso-octane, n-dodecane, 1-3-5 tri-methyl benzene (TMB), and toluene. The NO x and blowout experiments are performed in a jet-stirred reactor (JSR), and the soot threshold experiments are performed on a Meker burner. The fuels are burned pre-vaporized, premixed, and preheated. NO x is measured by probe sampling and chemiluminescent analysis at a fixed temperature for each fuel. Soot tendency is measured as the fuel-air equivalence ratio (phi) for the first appearance of yellow tips in the flame. This is termed the soot threshold. LFBO is examined by measuring the JSR temperature immediately prior to blowout. Relatively small changes in NO x , LFBO, and soot threshold are measured for the petroleum-based and alternative jet fuels examined. HRJ-tallow is the cleanest burning jet fuel tested with respect to NO x and soot measurements. It exhibits the lowest NO x and the highest soot threshold among alternative fuels tested. A possible correlation between decreasing NO x and increasing soot threshold is explored. The impact of adding aromatic content to the alternative jet fuels is also examined. With 20% aromatic content added to the alternative jet fuels, the soot threshold decreases, though the HRJ-tallow with 20% aromatic added continues to maintain a higher soot threshold than petroleum-based jet fuels. The addition of 20% aromatic does not show a clear trend in NO x . Over the four alternative jet fuels tested, the 20% aromatic addition causes a maximum change in the NO x emission of ± 13% (relative); the average change is close to zero.

Large-eddy simulation (LES) of a pressurized, swirl stabilized, well-characterized aero-engine model combustor have been conducted at different operating conditions. The combustor is fueled by ethylene and features a secondary air injection system to mimic the rich-quench-lean concept (RQL) of aircraft engine combustors. This paper discusses the influence of three different equivalence ratios on the sooting behavior by means of numerical simulation. A finite-rate chemistry model (FRC) with assumed probability density function model (APDF) is used to describe the turbulent combustion. Polycyclic aromatic hydrocarbons (PAHs), their radicals and soot are modeled by a recently developed sectional approach. Feedback effects such as consumption of gaseous soot precursors by growth of soot are inherently captured by solving the governing equations simultaneously. Quantitative measurement data obtained by different laser diagnostic techniques are used for validation. Predicted temperatures and velocities are in excellent agreement to the measurements. The influence of different equivalence ratios on the sooting behavior of the combustor is qualitatively captured well by the soot model. Details of the soot evolution are discussed and the remaining differences between the simulation and the measurements are analyzed in detail.

This article presents numerical simulations of the Rolls-Royce BR700 combustor operating at various realistic conditions. Emphasis is put on the prediction of soot emissions. Three-dimensional steady Reynolds-averaged Navier-Stokes (RANS) simulations were performed employing the k ϵ-model for turbulence closure. Combustion is modelled by finterate chemistry and the turbulence-chemistry interactions are captured by an APDF-approach (assumed probability density function) for temperature fluctuations. The injection of the liquid fuel Jet A-1 is described by a spray model applying Lagrangian methods for spray transport and atomization. The multi-component fuel is modelled as surrogate of n-decane, iso-octane and toluene. Reaction kinetics are described by a detailed mechanism, which is optimised for Jet A-1 oxidation and accurately resolves the reaction paths up to the smallest aromatic soot precursors benzene and toluene. Heavier PAHs (Polycyclic Aromatic Hydrocarbons) are lumped to sections and hence, modelled by a sectional approach, which leads to soot nucleation. The soot particle dynamics are described by a two equation model. Due to the model’s efficiency feasible computational costs are realised. Overall, four operation points are investigated, which are take-off , climb , approach and taxi . The simulation results at the combustor exit are compared to the experimentally determined Smoke Number of the engine exhaust gas by means of empirical correlations. The comparison shows a very good agreement. In particular, the Smoke Number’s trend is predicted well with respect to the thrust of the operation points.

Soot production in turbulent flames represents an urgent issue for applied systems and raises a range of fundamental challenges. Most of the literature effort on this question has been carried out on non-premixed turbulent flames, where mixing plays a dominant role. It is however interesting to see if soot production can be investigated in a premixed turbulent flame configuration, thus eliminating the role of mixing in this process. It is shown in the present article that this can be accomplished by making use of rich swirled ethylene/air flames under perfectly-premixed rich conditions established in a confined combustor operating at atmospheric pressure. Quantitative measurements of the soot volume fraction (f v ) are carried out by the Laser Induced Incandescence (LII) technique. Although the soot volume fraction levels are one or two orders of magnitude lower than those found in non-premixed flames, it is shown that detection is feasible and that this configuration may be used to analyze effects on soot production of operating parameters such as the equivalence ratio, the power level or the wall temperature. The observed trends are interpreted numerically by considering an idealized model of a rich premixed burner-stabilized stagnation flame. This configuration is here calculated with a detailed kinetic scheme in combination with a soot sectional model. This description is able to account for some of the trends observed experimentally and indicates in particular how an increase in the wall temperature may increase the soot volume fraction as it is effectively observed in the experiment. The model predicts that the soot volume fraction level increases for high equivalence ratios. This finding is in disagreement with the experimental observations on this swirled flame, which exhibits a maximum soot volume fraction for ϕ = 2.1 for all the considered flame powers. This indicates that complex interactions take place between soot, flame, turbulence and thermal environment and that the investigation of these processes will require a comprehensive turbulent simulation. This may be guided by the database developed in the present experimental effort.

The understanding of the processes involved in soot formation and oxidation is a critical factor for a reliable prediction of emissions in aero-engines, particularly as legislation becomes increasingly stringent. This work studies the flame structure and soot formation in a lab-scale burner, which reproduces the main features of a Rich-Quench-Lean (RQL) combustor, using high-fidelity numerical simulations. The investigated burner, developed at the University of Cambridge, is based on a bluff-body swirl-stabilised ethylene flame, with air provided in the primary region through two concentric swirling flows and quenching enabled by means of four dilution jets at variable distance downstream. Measurements for different air split between the two inlet swirling flows and dilution ports, and different height of the dilution jets, indicate noticeable differences in the soot tendency. Numerical simulations have been performed using Large-Eddy Simulation with the Conditional Moment Closure combustion model and a two-equation model for soot, allowing a detailed resolution of the mixing field and to directly take into account the effect of turbulent transport on the flame structure, which has been shown to have an important effect on the soot formation and evolution. The main objective of this work is to study the flow field and mixing characteristics in the burner’s primary region, in order to improve the understanding of the mechanisms leading to the soot behaviour observed in the experiment at different operating conditions. Results show the key role of mixing in determining the level of soot in the burner, with the soot production mainly related to the extension of the flame zone characterized by a rich mixture, with pyrolysis products and soot precursors. The presence of additional dilution air seems to improve the oxidation and leads to a leaner mixture in the primary combustion region whereas the air added through the outer swirl stream seems to have less impact on the mixture formation in the primary region. Analysis of the solution in mixture fraction space shows the importance of residence time for the soot formation and highlights the existence of a range of values of mixture fraction, between 0.1 and 0.2, where the soot production terms are maximum. High residence times and local air-to-fuel ratio in the range of high soot production should be avoided to decrease the level of soot mass fraction in the burner.

Recent studies on experimental gas turbines suggest that the addition of ethanol or butanol to Jet A are viable alternatives for reducing CO and NOx emissions while maintaining similar performance to that of pure Jet A. In light of this potential, experimental data regarding the burning characteristics of Jet A/ethanol and Jet A/butanol blends are required in order to better understand their combustion process. Following a previous study on Jet A/butanol droplet combustion, the scope has been extended in order to also include ethanol and a Jet A/ethanol mixture as well as to perform a more detailed characterization. In this work the combustion characteristics of Jet A, butanol, ethanol and their mixtures (20% vol. alcohol in kerosene) are presented for different test conditions. The evaluated combustion characteristics include droplet, flame and soot shell size evolutions, burning rates and image-based soot estimations. The influence of oxygen availability is also ascertained. The evolution of droplet diameter and burning rates for Jet A and its blends with both alcohols are very similar, whereas pure ethanol and butanol display more distinct behaviors. Soot indices are found to be quite different, with a clear reduction in the sooting propensity of the Jet A/alcohol mixtures when compared to neat kerosene. These results support the feasibility of kerosene-alcohol mixtures as promising alternative fuels with similar combustion characteristics, but with much lower sooting propensity than pure kerosene.

Lean burn combustion is increasing its popularity in the aeronautical framework due to its potential in reducing drastically pollutant emissions (NO x and soot in particular). Its implementation however involves significant issues related to the increased amount of air dedicated to the combustion process, demanding the redesign of injection and cooling systems. Also the conditions at the combustor exit are a concern, as high turbulence, residual swirl and the impossibility to adjust the temperature profile with dilution holes determine a harsher environment for nozzle guide vanes. This work describes the final stages of the design of an aeronautical effusion-cooled lean burn combustor. Full annular tests were carried out to measure temperature profiles and emissions (CO and NO x ) at the combustor exit. Different operating conditions of the ICAO cycle were tested, considering Idle, Cruise, Approach and Take-Off. Scale-adaptive simulations with the Flamelet Generated Manifold combustion model were performed to extend the validation of the employed CFD methodology and to reproduce the experimental data in terms of RTDF/OTDF profiles as well as emission indexes. The satisfactory agreement paved the way to an exploitation of the methodology to provide a deeper understanding of the flow physics within the combustion chamber, highlighting the impact of the different operating conditions on flame, spray evolution and pollutant formation.

Whichever the type of combustion installation, liquid fuels burned in gas turbines tend to generate particulate matter (PM) emissions, which consist in soot only or in ash plus soot, according to their ash-free or ash-forming character. Standard diffusion flame combustion systems are known as “universal” combustors, capable to burn both ash-free (naphtha, light and heavy distillates) and ash-forming (crude and heavy) fuels. In contrast, DLN systems are designed to burn gaseous fuels and light distillates. PMs in the range of a few parts per million represent a solid micropollutant, the measurement and abatement of which creates specific technical challenges. In order to fully characterize soot emission and investigate their reduction, GE has undertaken a multi-year investigation program covering (i) an exploratory engineering study starting from the EN13284-1 standard and (ii) the testing of a number of inorganic oxidation catalysts used in the form of fuel additives (“soot inhibitors”). In this framework, a joint work involving GE and Electricity Authority of Cyprus has been conducted in the first half of 2017 and a full-scale test plan has been performed at the Vasilikos power plant in Cyprus, involving a Frame 6F.03 DLN2.6 that burns light distillate oil and is equipped with a DeNOx water injection system. Four types of soot inhibitor additives: cerium (IV) and (III), iron (III) and (II) were tested. This paper reviews the results of this field test and compares them with data previously acquired at other power plants featuring different liquid fuels and combustion systems. Its goal is to provide the gas turbine community with a better understanding of PM emissions and their abatement using various soot inhibitor candidates, in function of liquid fuel type and combustion system.

Recirculation zone plays an important role in flame stabilization in combustors and gas turbines. The location, size, and strength of recirculation zones are important features of a combustor. However, the quantitative role of recirculation zones in affecting soot formation from an aero combustor is not fully understood. In a turbulent flow field with swirling flows and high frequency oscillations of the inflow jets, inner recirculation zones and outer recirculation zones have different functions in determining soot evolution. In this study, large-eddy simulation (LES) of soot formation with detailed physical and chemical models is used in order to study the dynamic aspects of soot formation. The soot population is modeled using the hybrid method of moments (HMOM), while the gas phase precursor evolution is modeled using detailed chemical kinetics. A model aero combustor, studied experimentally at DLR, is used as the baseline flow configuration. The simulations are used to understand the transport of soot particles within such complex flows. In particular, the ability of recirculation regions to increase soot formation by increasing residence times is explored. A Lagrangian particle tracking (LPT) analysis is carried out and statistical roles of recirculation zones are determined from these streamlines. Furthermore, source term analysis of these particles are performed to determine the key physical processes that contribute to soot mass in the recirculation zones. From a numerical stand-point, such soot evolution introduces limitations for statistical convergence, which will also be discussed. In particular, a time-scale analysis will be conducted to determine total computational time needed to obtain converged soot statistics.

Operating combustion systems at elevated pressures has the advantage of improved thermal efficiency and system compactness. However, it also leads to increased soot emission. We report herein a computational study to characterize the effect of oxygenation on PAHs (Polycyclic Aromatic Hydrocarbons) and soot emissions in ethylene diffusion flames at pressures 1–8atm. Laminar oxygenated flames are established in a counterflow configuration by using N 2 diluted fuel stream along with O 2 enriched oxidizer stream such that the stoichiometric mixture fraction (ζ st ) is varied, but the adiabatic flame temperature is not materially changed. Simulations are performed using a validated fuel chemistry model and a detailed soot model. The primary objective of the study was to expand the fundamental understanding of PAH and soot formation in oxygenated flames at elevated pressures. At a given pressure, as the level of oxygenation (ζ st ) is increased, we observe a significant reduction in PAHs (benzene and pyrene) and consequently in soot formation. Further, at a fixed ζ st , as pressure is increased, it leads to increased benzene and pyrene formation, and thus increased soot emission. The reaction path analysis indicates that this can be attributed to the fact that at higher pressures, the C2/C4 path becomes more significant for benzene formation compared to the propargyl recombination path.

Lean burn combustion is increasing its popularity in the aeronautical framework due to its potential in reducing drastically pollutant emissions (NO x and soot in particular). Its implementation, however, involves significant issues related to the increased amount of air dedicated to the combustion process, demanding the redesign of injection and cooling systems. A reduced coolant mass flow rate in conjunction with higher compressor discharge temperature negatively affect the cooling potential thus requiring the exploitation of efficient schemes such as effusion cooling. This work describes the experimental and numerical final validation of an aeronautical effusion-cooled lean-burn combustor. Full annular tests were carried out to measure temperature profiles and metal temperature distributions at different operating conditions of the ICAO cycle. Such an outcome was obtained also with an in-house developed CHT methodology (THERM3D). RANS simulations with the Flamelet Generated Manifold combustion model were performed to estimate aerothermal field and heat loads, while the coupling with a thermal conduction solver returns the most updated wall temperature. The heat sink within the perforation is treated with a 0D correlative model that calculates the heat pickup and the temperature rise of coolant. The results highlight an overall good capability of the proposed approach to estimate the metal temperature distribution at different operating conditions. It is also shown how more advanced scale-resolving simulations could significantly improve the prediction of turbulent mixing and heat loads.

Nowadays, models predicting soot emissions are, neither able to describe correctly fine effects of technological changes on sooting trends nor sufficiently validated at relevant operating conditions to match design office quantification needs. Yet, phenomenological descriptions of soot formation, containing key ingredients for soot modeling exist in the literature, such as the well-known Leung et al. model (Combust Flame 1991). This approach indeed includes contributions of nucleation, surface growth, coagulation, oxidation and thermophoretic transport of soot. When blindly applied to aeronautical combustors for different operating conditions, this model fails to hierarchize operating points compared to experimental measurements. The objective of this work is to propose an extension of the Leung model, including an identification of its constants over a wide range of condition relevant of gas turbines operation. Today, the identification process can hardly be based on laboratory flames since few detailed experimental data are available for heavy-fuels at high pressure. Thus, it is decided to directly target smoke number values measured at the engine exhaust for a variety of combustors and operating conditions from idling to take-off. A Large Eddy Simulation approach is retained for its intrinsic ability to reproduce finely unsteady behavior, mixing and intermittency. In this framework, The Leung model for soot is coupled to the TFLES model for combustion. It is shown that pressure-sensitive laws for the modelling constant of the soot surface chemistry are sufficient to reproduce engine emissions. Grid convergence is carried out to verify the robustness of the proposed approach. Several cases are then computed blindly to assess the prediction capabilities of the extended model. This study paves the way for the systematic use of a high fidelity tool solution in design office constraints for combustion chamber development.

This paper reports an investigation of soot formation in ethylene-air partially premixed flames over a wide range of premixedness. An axisymmetric co-flow configuration is chosen to establish partially premixed flames from the fully non-premixed to fully premixed conditions. Reducing the fuel flow rate as a percentage of the maximum from the core stream and supplying the same to the annular stream leads to stratification of the reactant concentrations. The thermal power, overall equivalence ratio, and the average velocity in the both streams are maintained constant under all conditions. The soot volume fraction is estimated by light attenuation method, and laser induced incandescence is performed to map the soot distribution in the flow field. The soot volume fraction is observed to exhibit a ‘S’-type trend as the conditions are traversed from near the premixed to the non-premixed regimes. That is, when traversing from the non-premixed to near-premixed regime, below 60% fuel flow rate in core, the soot volume fraction drops drastically. The onset of sooting in the partially premixed flames is clearly seen to be at the tip of the rich-premixed flame branch of their triple flame structure, which advances upstream towards the base of the flame as the premixing is reduced. The ‘S’-type variation is clearly the effect of partial premixing, more specifically due to the presence of the lean premixed flame branch of the triple flame. Laser induced incandescence intensities are insufficient to capture the upstream advance of the soot onset with decreased premixedness. So, a quick and inexpensive technique to isolate soot luminescence through flame imaging is presented in the paper involving quasi-simultaneous imaging with a 650 nm and a BG-3 filter using a normal color camera.

Two RR Lean Direct Injection (LDI) injector versions with different amounts of pilot swirl were investigated. Experiments, performed at elevated pressure and temperature, corresponding to engine conditions at idle include Mie scattering. LII and absorption measurements are used for soot concentration within the primary zone. The soot emission at the outlet is measured by an SMPS instrument. These experimental studies are complemented with PIV measurements. The acquired data allows evaluation of the combustion process from the liquid phase, followed by evaporation, reaction and finally soot production with high spatial resolution. The change of swirl produced rather moderate changes in the flow field, nevertheless qualitative changes in the fuel placement were observed. Starting from there, differences in heat release and soot formation can be explained, which lead to larger changes of soot emission. These observations show that a good knowledge of the interaction of gas and liquid phase is necessary to predict the occurrence of behavioral changes in the operating regime.

In light of the potential of butanol as an alternative fuel for blending with petroleum fuels such as gasoline, diesel or Jet A, experimental data regarding the burning characteristics of these blends are required in order to better understand their combustion process. In this study, freely-falling droplets of butanol, Jet A, and their mixtures (10, 20 and 50% butanol by volume) were examined in a combustion chamber which provides representative conditions of real flames, both in terms of temperature and oxygen availability. The combustion characteristics reported here include evolution of droplet sizes, burning rates, soot measurements, and the occurrence of microexplosions and soot shells. Results show that the evolution of droplet diameter for butanol, Jet A and their blends are very similar, regardless of the obvious compositional differences. Sooting behaviors are found to be quite different, with a clear reduction in the sooting propensity as the butanol content in the fuel increases. These results are consistent with a previous study in a gas turbine showing similar performance among Jet A and its blends with butanol, suggesting that such mixtures are promising alternative fuels with very similar combustion characteristics to Jet A, but with much less propensity to soot. Moreover, this study provides new results on the combustion properties of Jet A/butanol blends, for which very scarce data exist in the open literature.

In this work a single sector lean burn model combustor operating in pilot only mode has been investigated using both experiments and computations with the main objective of analyzing the flame structure and soot formation at conditions relevant to aero-engine applications. Numerical simulations were performed using the Large Eddy Simulation (LES) approach and the Conditional Moment Closure (CMC) combustion model with detailed chemistry and a two-equation model for soot. The CMC model is based on the time-resolved solution of the local flame structure and allows to directly take into account the phenomena associated to molecular mixing and turbulent transport which are of great importance for the prediction of emissions. The rig investigated in this work, called Big Optical Single Sector (BOSS) rig, allows to test real scale lean burn injectors. Experiments, performed at elevated pressure and temperature, corresponding to engine conditions at part load, include OH-PLIF and PDA and have been complemented with new LII measurements for soot location. The wide range of measurements available allows a comprehensive analysis of the primary combustion region and can be exploited to further assess and validate the LES/CMC approach to capture the flame behaviour at engine conditions. It is shown that the LES/CMC approach is able to predict the main characteristics of the flame with a good agreement with the experiment in terms of flame shape, spray characteristics and soot location. Finite-rate chemistry effects appear very important in the region very close to the injector exit leading to the lift-off of the flame. Low levels of soot are observed immediately downstream of the injector exit, where a high amount of vaporized fuel is still present. Further downstream, the fuel vapour disappears quite quickly and an extended region characterised by the presence of pyrolysis products and soot precursors is observed. The strong production of soot precursors together with high soot surface growth rates lead to high values of soot volume fraction in locations consistent with the experiment. Soot oxidation is also very important in the downstream region resulting in a decrease of the soot level at the combustor exit. The results show a very promising capability of the LES/CMC approach to capture the main characteristics of the flame, soot formation and location at engine relevant conditions. More advanced soot models will be considered in future work in order to improve the quantitative prediction of the soot level.

Recuperation and high turbine inlet temperatures could enable miniature (<20 kW) gas turbines to match the fuel efficiency and installed weight of current internal combustion (IC) engines. However, these strategies create unusual challenges for combustor development. As the engine transitions from ignition to steady state, changes in the preheated air temperature, fuel/air mixture, evaporation, and chemical timescales make operability difficult with a fixed-geometry combustor at all operational states. The flame must also be exceptionally clean in all conditions because any soot will foul the recuperator. Furthermore, preheated air is less effective for cooling, potentially creating extreme thermal loads on the liner, especially during transients, and any ignition device that protrudes into the unusually hot primary zone could melt. This paper describes the preliminary design of a combustor being developed to meet these challenges, and reviews the late progress on subsystem testing and experiments. The combustor is a single-can type with a radial swirler and single atomizer nozzle at one end. An optically accessible burner is being used to explore fundamental aspects of swirler aerodynamics, ignition strategies, liner cooling, and lean blow off behavior. Particle image velocimetry (PIV) is enabling quantitative velocity measurements of swirler jet decay and interaction with the liner wall. Two different methods for projecting an ignition source into the primary zone from outside the liner, a micro-torch and a conventional spark igniter, have been tested.

In order to exploit the potential of computational modeling for the reduction of particulate emissions in future aero engines, reliable modeling approaches applicable in system scale simulations are required. Achieving this goal crucially depends on bridging the gap between academic test cases often used for model validation and real world applications. In this work, Large-Eddy Simulations of a model aero engine combustor experimentally investigated at the German Aerospace Center (DLR) are performed using an integrated modeling approach based on the Radiation Flamelet/Progress Variable model and a detailed bivariate soot particle description combined with the Hybrid Method of Moments. First, a non-reacting flow case is simulated to validate the computational setup in absence of the complex interaction of turbulence, chemistry, and soot. Then, the reacting flow is analyzed in terms of velocity, temperature, and soot volume fraction predictions. Measured velocity profiles for the non-reactive case are very well predicted. For the fired combustor, the velocity and temperature fields are well predicted. Soot is overpredicted by the simulation, but qualitatively in reasonable to good agreement with the experimental data.