Lean Direct Injection Research Articles

Predictive Modeling of NOx Emissions from Lean Direct Injection of Hydrogen and Hydrogen/Natural Gas Blends Using Flame Imaging and Machine Learning

Predictive Modeling of NOx Emissions from Lean Direct Injection of Hydrogen and Hydrogen/Natural Gas Blends Using Flame Imaging and Machine Learning

Dynamical Systems Characterisation and Reduced Order Modelling of Thermoacoustics in a Lean Direct Injection (LDI) Hydrogen Combustor

Abstract In this study, the thermoacoustic instabilities of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor are characterised using dynamical systems theory. The combustor is operated at a range of bulk velocities (30 - 90 m/s) and equivalence ratios(0.2-0.6), and time-resolved pressure oscillations and integrated OH* chemiluminescence measurements were taken. The thermoacoustic system reveals a variety of dynamical states in pressure such as period-1 Limit Cycle Oscillation (LCO) with a single characteristic frequency, period-2 LCO with two characteristic frequencies, intermittent, quasi-periodic and chaotic states as either bulk velocity or equivalence ratio is varied. At a bulk velocity of 30 m/s, as the equivalence ratio is gradually decreased from 0.6 to 0.2, the dynamical behaviour follows a sequence from an intermittent state to a period-1 LCO, then to a quasi-periodic state, and eventually reaches a chaotic state. As the equivalence ratio is decreased for a bulk velocity of 60 m/s, the pressure oscillations evolve from a period-2 LCO to quasi-periodic state before flame blows off. The emergence of period-2 and quasi-periodic states indicates the presence of strong non-linear interactions among the cavity acoustic modes. The emergence of period-2 and quasi-periodic states indicates strong non-linear interactions among the cavity acoustic modes. These modes and their spatial behaviour are investigated using a Helmholtz solver, showing that hydrogen flames can excite a wide range of cavity acoustic modes

An experimental study of thermoacoustic instabilities in a RP-3 fueled multi-swirl stabilized lean direct injection combustor

An investigation of self-excited combustion instabilities in a RP-3 fueled, multi-swirl stabilized, lean direct injection (LDI) combustor was performed and investigated with different operating conditions (inlet Reynolds number and fuel–air ratio (FAR)). Pressure fluctuation and heat release data were simultaneously collected using a 3-channel synchronous acquisition system. The results show that as the FAR increases, combustion transitions from a low oscillation mode to a high oscillation mode. During the modal transition, the oscillating flame structure, formed by vortex shedding in the shear layer and the recirculation zone, is then transformed into contraction and expansion movements from the front of the central recirculation zone towards the downstream and radial directions of the combustor. When combustion is in a low oscillation mode, the driving capability of the flame is relatively low. Upon entering a high oscillation mode, the overall driving energy of the flame can maintain combustion in a limit cycle oscillation state.

Lean Blowout Proximity Sensing in a Low Emission Liquid-Fueled Combustor

ABSTRACT Advanced aircraft engine combustor designs, intended for achieving low NOx emissions, necessitate lean combustion with small operating margins above the LBO boundary, posing a high risk of exhibiting lean blowout (LBO) problems. Employing active LBO controllers receiving input from LBO proximity sensors can allow for narrower margins, thereby yielding multiple performance gains. Although several previous studies investigated LBO proximity sensing, they predominantly focused on premixed gas-fueled combustors. The application of proximity sensing approaches to liquid-fueled combustor designs, relevant to aircraft engines have not received adequate attention. Therefore, this study investigates LBO proximity sensing in a low emission lean direct injection (LDI) liquid-fueled combustor design developed by NASA. The combustor operates at atmospheric pressure with preheated air. The proximity sensing is examined by analyzing both OH* and CH* chemiluminescence signals, with a focus on assessing their relative performances. The signal analysis approaches include spectral, partial extinction event (LBO precursor) detection, signal RMS, and the CH*/OH* ratio, with an emphasis on the first two methods. Both steady-state and transient operating conditions have been examined. The combustor did not exhibit large-scale flame partial extinction and re-ignition events near LBO, as commonly observed in gas-fueled combustors. However, an increase in flame unsteadiness and partial extinction events with very subtle signatures in optical signals, have been observed. Low-pass filtering has been observed to considerably enhance the precursor signatures enabling their improved detection. With a reduction in LBO margin, an increase in signal low-frequency power, RMS, and precursor event occurrence rate have been observed, which were utilized for providing LBO proximity measures. A key finding from this study is that CH* signals provide significantly superior performance compared to OH* for the proximity sensing in all the approaches, and the potential reasons are discussed.

The Effect of Swirl Number on Lean Blow Out Limits of Lean Direct Injection Combustors

Abstract This is the first study where a single variable sweep of SN is conducted to assess its impact on lean blowout limits (LBO) in a liquid-fueled lean direct injection (LDI) combustor. This study uses a scaled NASA SV-LDI (Swirl Venturi—Lean Direct Injection) hardware and is concerned with the impact of swirl number on the lean blow-out limit of a single-element LDI system at atmospheric pressure. The swirl numbers (SN) were varied from 0.31 to 0.66 using continuously variable active swirl number control system that was developed in-house. It is shown that the minimum operating equivalence ratio is a linearly increasing function of swirl number. While previous literature agrees with the positive slope for this correlation, past work has suggested that the LBO limit is proportional to the swirler vane angle which is shown to be untrue for LDI systems. By actively varying the swirl number, it is proven that LBO is proportional to SN, and it is well known that SN is not proportional to swirler vane angle. Increased SN reduces LBO margin because the better-mixed, high swirl dilutes locally rich pockets of fuel–air mixture in a globally lean flow. In addition to a baseline venturi, which was scaled from NASA's geometry, two other venturis were tested. A low-pressure loss venturi with a large throat diameter showed poor blow-out performance whereas a parabolically profiled venturi improved LBO over the baseline for the same swirl number.

Influence of liquid-fuel swirl injection pressure on the flow dynamics characteristics in a lean direct injection gas turbine combustor using Eulerian-Lagrangian large eddy simulations

Influence of liquid-fuel swirl injection pressure on the flow dynamics characteristics in a lean direct injection gas turbine combustor using Eulerian-Lagrangian large eddy simulations

Experimental Study on OH* Chemiluminescence and Emissions in the Single-Element Lean Direct Injection Combustor

ABSTRACT OH* chemiluminescence and emissions of the convergent swirler module and the Venturi swirler module are studied in a single-element lean direct injection combustor. The OH* chemiluminescence images are captured by a CCD camera with an image intensifier, and the emissions are measured by a gas analysis system. The flame of the Venturi swirler module is closer to the inlet plane of the combustor compared to that of the convergent swirler module. At the equivalence ratio (ϕ) of 0.55, 0.65, and 0.75, the EINOx of the convergent swirler module is 1.02 g/kg, 1.44 g/kg, and 1.98 g/kg, and the EICO is 0.32 g/kg, 0.54 g/kg, and 3.65 g/kg separately. The EINOx of the Venturi swirler module is 0.95 g/kg, 1.37 g/kg, and 2.05 g/kg and the EICO is 0.32 g/kg, 0.93 g/kg, and 5.86 g/kg. The NOx emissions of the two swirler modules are similar. But the CO emission of the convergent swirler module is lower at the ϕ of 0.65 and 0.75. The convergent swirler module has an advantage in reducing emissions. In addition, the influence of the swirl number (S) on OH* Chemiluminescence and emissions of the convergent swirler module is studied. At the ϕ of 0.55, the EINOx is between 0.88 g/kg and 1.17 g/kg and the EICO is between 0.13 g/kg and 0.44 g/kg with different S. With the increase of the S, the NOx emission increases and the CO emission decreases. But at the ϕ of 0.65 and 0.75, with the increase of the S, the NOx emission first increases and then decreases and the CO emission first decreases and then increases.

Heat Transfer in an Injector-Scaled Additively Manufactured Fuel Passage

Abstract Knowledge of heat transfer in fuel wetted passages is important for informing injector design and life estimates due to the effects of temperature on fuel degradation. Future injectors will be manufactured using additive methods in an effort to reduce production costs and time, while also facilitating more agile design practices. Additive manufacturing (AM) is known to result in increased surface roughness compared to conventional manufacturing techniques, however limited data exist on how this roughness impacts heat transfer, particularly in liquid flows. This paper solves the inverse heat conduction problem for heat transfer coefficient in liquid flows through rough 90 deg channel bends typical of the pilot gallery in a lean direct-injection fuel spray nozzle. Heat transfer distributions across two rough surfaces are compared to an equivalent smooth surface. The two rough surfaces have different morphologies but have the same relative effective sand grain roughness which is matched to a prototype AM fuel injector. The sand grain roughness is predicted from a correlation that has been adapted for the high relative roughness scales characteristic of additively manufactured fuel passages. The effective sand grain roughness estimated from surface measurements of a prototype AM fuel gallery was ∼13% of the passage hydraulic diameter. For the two rough surfaces, the heat transfer enhancement is up to three times the smooth surface value for the straight section preceding the bend and up to four times around the bend. Heat transfer distributions across the two rough surfaces are similar, but the magnitudes differ by ∼17% depending on the surface morphology. This highlights the importance of the heat transfer effectiveness of surface features, which unlike the sand grain roughness is not matched for the two surfaces considered. Adjusting the data for differences in heat transfer effectiveness corrects the average heat transfer for the rough surfaces to within 7%.

Experimental and Simulation Study on the Emissions of a Multi-Point Lean Direct Injection Combustor

Spurred by the world’s attention to pollution emissions from commercial aero-engines, the International Civil Aviation Organization (ICAO) has made more stringent emission regulations for civil aircraft engines, especially the NOx emission.This paper develops a Five-Point lean direct injection (LDI) combustor with three swirler schemes to reduce the emissions of commercial aircraft engines. The flowfield of the combustor is studied numerically. Moreover, the combustion efficiency and gaseous emissions in different inlet conditions and fuel ratios of the main stage (α) are studied experimentally. The corresponding results reveal that, under a fuel-air ratio (FAR) between 0.0130 and 0.0283 and an α value between 30% and 60%, the combustion efficiency is 99.18%, 98.83%, and 99.03% when the pilot stage works alone, and 99.69%, 99.23%, and 99.75% when the pilot and main stage work simultaneously. Furthermore, the experimental results suggest that the NOx emission decreases as α increases, demonstrating that the convergent swirler has a tremendous advantage in reducing NOx emissions over Venturi.

Spray Flamelet Modeling of Turbulent Two-Phase Reacting Flows with Multi-Component Fuel in a Lean Direct Injection Combustor

ABSTRACT Towards the numerical evaluation of the performance in aero-engine combustors, implementing detailed reaction kinetics into the large eddy simulation (LES) cost-effectively is highly desirable. In this work, a newly-developed spray flamelet model is combined with a four-component jet fuel surrogate model to allow integration of the detailed kinetics in the open-source CFD code. The spray flamelet approach (SFGM) can take into account the non-adiabatic effect caused by the evaporating spray and can directly reflect the preferential evaporation, as well as multiple combustion regimes present in complex spray combustion systems. The coupling of the SFGM-LES approach is assessed by comparison with the experimental data from a Lean Direct Injection (LDI) combustor, where the real aviation kerosene, Jet-A, was utilized. The SFGM-LES approach well predicts the experimental statistics in both gas and liquid phases. It is capable of capturing the rich physics and complex flame structures, including the preferential evaporation effect and the multi-regime combustion phenomenon. The present work demonstrates that the complex nature of multi-components and the multiple-combustion regimes in the two-phase combustion can be directly included in the spray flamelet approach, and thus this model can provide new insights into the turbulent spray combustion phenomena.

Numerical Investigation on the Characteristics of a Novel Multi-Swirl Lean Direct Injection Burner With Large Eddy Simulation-Flamelet Generated Manifold Method

Abstract The lean direct injection (LDI) concept can eventually replace the current combustion systems in aviation engines because of its low NOx emissions without compromising other parameters. A novel multiswirl LDI burner with distributed fuel injection surrounded by air- flow through multiple hexagonal swirlers of vane angle 45 deg was developed. In this study, large eddy simulation (LES), using the dynamic Smagorinsky-Lilly subgrid model together with the flamelet generated manifold (FGM) combustion model, has been used to analyze the correlation between aerodynamics, mixing, and combustion characteristics of the burner. The agreement between the experimental data and the LES simulation was good, and it can accurately predict the trend of variables like velocity, temperature, and mixture fraction at different Reynolds number and equivalence ratios. The LES-FGM results demonstrated the rapid formation of a homogeneous fuel-air mixture over a short distance, which results in excellent flame stability, and it has ultralow NOx emission due to low flame temperature and negligible internal recirculation. It was discovered that going from a global equivalence ratio of 0.7 to 0.9 increases the flame liftoff distance because the high fuel volume flowrate causes the mixing of swirling air and fuel jet to become more and more delayed. The research in this paper provides an insight into the ability of the LES-FGM method to capture the complex flow field structures and the flame behavior globally of a novel low NOx multiswirl burner that might be a competitor in the combustors of commercial gas turbine engines.

Coupled droplet dynamics: Investigation of acoustic-spray interactions in a reacting flow field

Droplet dynamics in a self-excited thermoacoustic instability are not well understood due to the tight coupling of competing effects and difficulty in taking high-quality data. In this investigation, droplet data from a combustion instability is used to illustrate how a spray couples with a thermoacoustic instability. Commonly accepted ensemble averaging techniques such as the Sauter mean diameter (D32) is shown to be inadequate in describing the coupling phenomena, and instead, a new approach based on droplet surface area is used to characterize the spray. The present study extends literature concerning nonreacting acoustic-spray interactions and considers these in a fully self-excited instability. A lean direct injection (LDI) geometry is used at atmospheric pressure and phased averaged Phase Doppler Particle Analyzer (PDPA) measurements, acoustic pressure measurements, and OH* chemiluminescence images are taken to characterize the flow field. It is shown that while some of the trends found in nonreacting experiments apply to reacting systems, the mechanisms are notably different due to the presence of a flame. Flame response is shown to be important due to its influence on the evaporation of droplets.

Numerical Investigation of a Coupled Blow-Off/Flashback Process in a High-Pressure Lean-Burn Combustor

Abstract Large eddy simulation is used to investigate the flashback mechanism caused by the combustion-induced vortex breakdown (CIVB) in a high-pressure lean-burn annular combustor with lean direct injection of kerosene. A single sector of the geometry, including a central pilot flame surrounded by a main flame, is simulated at takeoff conditions. A previously developed flamelet-based approach is used to model turbulence–combustion interactions due to its relatively low cost, allowing to simulate a sufficiently long time window. In stable operations, the flame stabilizes in an M-shape configuration and a periodic movement of the pilot jet, with the corresponding formation of a small recirculation bubble, is observed. Flashback is then observed, with the flame accelerating upstream toward the injector as already described in other studies. This large eddy simulation (LES), however, reveals a precursor partial blow-out of the main flame induced by a cluster of vortices appearing in the outer recirculation region. The combined effect of vortices and sudden quenching alters the mixing level close to the injector, causing first the main, then the pilot flame, to accelerate upstream, and initiate the CIVB cycle before the quenched region can re-ignite. Main and pilot flames partly extinguish as they cross their respective fuel injection point, and re-ignition follows due to the remnants of the reaction in the pilot stream. The process is investigated in detail, discussing the causes of CIVB-driven flashback in realistic lean-burn systems.

Impact of pilot swirling combination on the flow and emission characteristics of staged lean direct injection combustors

This paper considers a concentric staged triple swirler lean direct injection (LDI) combustor and conducts numerical analysis to investigate the impact of inner and outer swirl flow of the pilot stage on the spray combustion characteristics and NOx emission. To simulate the flow field, spray dispersion, and the combustion process within the combustion chamber Large eddy simulation (LES) is employed. Three geometric dome parameters are studied including the pilot inner swirl angle, pilot outer swirl angle, and pilot flow rotating direction. The results indicate that: (1) The inner swirling flow is the main factor affecting the spray atomization process inside the swirl cup; (2) In downstream of the dump plane, the outer swirling flow determines the evolution of the precessing vortex core (PVC) structures which affect turbulence intensities in the shear layer and efficient spray dispersion, and (3) NOx emissions are related to the spray atomization efficiency and the average flame length in the combustion chamber. It is also shown that NOx emission in the triple swirler LDI combustors is significantly reduced by increasing the swirling intensity and flow rate of the pilot outer swirler.

Swirl rotation direction effects on lean direct injection pilot mixer performance: Experiments and LES modeling

In order to improve the understanding of the effects of various practical design parameters on the performance of Lean Direct Injection (LDI)-based combustors, the impact of varying the relative rotation direction of the outer air swirler (OAS) and inner air swirler (IAS) on the performance of a methane-fueled LDI-type mixer/injector is investigated under non-reacting and reacting conditions by both experiments and computational fluid dynamics (CFD) simulations. Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) models are used and compared in CFD modeling of counter- and co-swirling LDI mixers, while the adoption of a nonpremixed Flamelet Generated Manifold (FGM) method to predict reacting flows is investigated for comparison with experimental measurements of the mean and fluctuating velocity fields and OH* chemiluminescence. In addition, a self-consistent and robust CFD mesh generation strategy is developed to create notionally grid-independent CFD meshes for non-reacting and reacting flow simulations. The experimental non-reacting flow fields and flame lift-off limits demonstrate that while the basic structure of the flow field does not change by altering the relative rotation direction of IAS and OAS, the details of the center recirculation zone including its width and length do, resulting in slightly reduced flame lift-off equivalence ratio for the counter-rotating configuration. Although LES-FGM is able to capture the major flow and flame patterns in both counter- and co-swirling reacting flows, some substantial disparities are apparent, particularly in the region within/near the venturi that adversely impact the predictive abilities of this LES-FGM approach.

Numerical simulation of combustion characteristics in a multi-point lean direct injection combustor

A numerical investigation was conducted to study the combustion characteristics in a five-point lean direct injection combustor. The influence of the pilot's swirl number to the combustion characteristics at both idle and takeoff conditions was carried out. The simulation results show that the radial dimension of the central recirculation zone without-reaction is lower than under-reaction at idle condition; but at takeoff condition, there're few distinctions on the structure of the central recirculation zone between the flow fields under-reaction and without-reaction. With the increasing of the pilot's swirl number, the radial dimension of the central recirculation zone increases. The temperature distributions of the center section are different because of the mutual interferences of the pilot and main stage. And with the increasing of the pilot's swirl number, the NOx emissions of the exit of the combustor increases.

Large Eddy Simulation Based Computational Fluid Dynamics Investigation of the Ignition Process in Lean Spray Burner

Abstract During the last decades, several new technologies were investigated in order to reduce the pollutant emissions and increase the overall engine efficiency. Unluckily, some of them including the lean direct injection spray combustion hinder the ignition performances of the combustor. Moreover, several expensive tests under very challenging operating conditions must be carried out to obtain the required certifications and assess the combustor behavior with respect to the ignition process. Therefore, a deeper knowledge of the phenomena involved in the flame onset is mandatory to shorten the design process and achieve the required performances from the very beginning. In the last years, computational fluid dynamics (CFD) simulations established a valid alternative to the experiments to investigate the complex phenomena involved in the ignition process. In fact, several examples are available in scientific literature about the use of simulations to predict the development of the flame starting from an initial kernel. In particular, large eddy simulation (LES) proved to be a reliable tool to uncover new mechanisms of ignition and flame stabilization in gas turbines. In this work, two reactive LES of the ignition process were attempted using ansysfluent 2019R1, with the aim of testing the thickened flame model already implemented in the solver. In fact, compared to the previous versions, a new formulation for the efficiency function based on the pioneering work of Colin was made available. Such promising tool was validated against some detailed experimental results of a lean swirled flame, known as knowledge for ignition, acoustics and instabilities (KIAI)-CORIA spray flame. At first, a non-reactive and reactive LES were carried out to validate the cold field and the stabilized flame structure respectively. Finally, two ignition simulations were performed, from initial spark deposition up to flame stabilization or kernel quenching. All the obtained results have been extensively compared against the available experimental data showing that the employed simulation setup is fairly capable of describing the phenomena involved in the rig ignition.

Influence of key geometrical features on the non-reacting flow of a Lean Direct Injection (LDI) combustor through Large-Eddy Simulation and a Design of Experiments

Lean Direct Injection (LDI) emerged as an interesting concept to limit NOx emissions in aero engines at the cost of operating close to the flame lean blow-off limit. In this technology, fuel is injected into a swirled airstream that generates recirculating flow structures that stabilize the flame. It is then of paramount importance at the design stage to understand the effect of various features on these structures. The present investigation makes use of Eulerian-Lagrangian Large-Eddy Simulations (LES) previously validated against existing experimental data for a reference condition to study the liquid non-reacting flow inside the CORIA Spray LDI burner with the help of Adaptive Mesh Refinement (AMR). A Design of Experiments (DoE) is proposed to analyze the significance of several geometrical features on the flow field, namely the combustor width, the air swirler vane angle, the number of swirler vanes and the axial location of the fuel injector tip. The study covers the qualitative appearance of the flow and the quantitative characterization of the spray dispersion and fuel-air mixing process. In this way, the chosen response variables include the size of the relevant coherent flow structures (Central Toroidal Recirculation Zone induced by the Vortex Breakdown Bubble, Corner Recirculation Zone and Swirled Jet) and their associated velocities, spray features (global drop sizes and spray penetration), pressure drop across the swirler and induced swirl number. Besides, the Precessing Vortex Core (PVC) relevance and frequency content is studied through Proper Orthogonal Decomposition (POD). Results from the statistical analysis show that the number of swirler vanes and their angle are the geometrical parameters that most importantly influence the flow features: stronger recirculation zones leading to an improved atomization and mixing have been found both when decreasing the number of swirler blades and increasing the blade angle. However, both solutions also increase the pressure losses across the swirler. As far as the spectral analysis is concerned, the number of swirler vanes is the most influencing factor on both the frequency and intensity of the PVC modes, being crucial for the possible activation and the energetic content of a double-helix PVC mode.

LES predictions of confinement effect on swirling flow generated by single helical axial swirler

PurposeFor higher swirling flows (swirl > 0.5), flow confinement significantly impacts fluid flow, flame stability, flame length and heat transfer, especially when the confinement ratio is less than 9. Past numerical studies on helical axial swirler type systems are limited to non-reacting or reacting flows type Reynolds averaged Navier Stokes closure models, mostly are non-parametric studies. Effects of parametric studies like swirl angle and confinement on the unsteady flow field, either numerical or experimental, are very minimal. The purpose of this paper is to document modeling practices for a large eddy simulation (LES) type grid, predict the confinement effects of a single swirler lean direct injection (LDI) system and validate with literature data.Design/methodology/approachThe first part of the paper discusses the approach followed for numerical modelling of LES with the minimum number of cells required across critical sections to capture the spectrum of turbulent energy with good accuracy. The numerical model includes all flow developing sections of the LDI swirler, right from the axial setting chamber to the exit of the flame tube, and its length is effectively modelled to match the experimental data. The computational model predicts unsteady features like vortex breakdown bubble, represented by a strong recirculation zone anchored downstream of the fuel nozzle. It is interesting to note that the LES is effective in predicting the secondary recirculation zones in the divergent section as well as at the corners of the tube wall.FindingsThe predictions of a single helical axial swirler with a vane tip angle of 60°, with a duct size of 2 × 2 square inches, are compared with the experimental data at several axial locations as well as with centerline data. Both mean and unsteady turbulent quantities obtained through the numerical simulations are validated with the experimental data (Cai et al., 2005). The methodology is extended to the confinements effect on mean flow characteristics. The time scale and length scale are useful parameters to get the desired results. The results show that with an increase in the confinement ratio, the recirculation length increases proportionally. A sample of three cases has been documented in this paper.Originality/valueThe novelty of the paper is the modelling practices (grid/unsteady models) for a parametric study of LDI are established, and the mean confinement effects are validated with experimental data. The spectrum of turbulent energies is well captured by LES, and trends are aligned with experimental data. The methodology can be extended to reacting flows also to study the effect of swirl angle, fuel injection on aerodynamics, droplet characteristics and emissions.

Heat Transfer and Residence Time in Lean Direct Injection Fuel Galleries

Abstract In radially staged lean direct injection (LDI) systems, pilot fuel plays an important role in cooling the mains fuel gallery in regions of the flight envelope where the mains fuel is stagnant. Under these conditions, managing wetted wall temperatures is vital to avoid the formation of carbonaceous particles, which become deposited on the surfaces of the fuel gallery and can lead to a deterioration in system performance. The prediction of wetted wall temperatures therefore represents an important aspect of the injector design phase. Such predictions are often based on injector thermal models, which tend to rely on the application of convective boundary conditions from empirical heat transfer correlations. The use of these correlations leads to questions over the accuracy of predicted wetted wall temperatures and therefore uncertainty over the probability of deposition. This paper seeks to improve on the current situation by applying the inverse conduction technique to determine heat transfer coefficients (HTCs) specific to the pilot fuel gallery. These HTCs are crucial for determining wetted wall temperatures in the pilot and mains fuel galleries and principally govern the risk of deposition in the stagnant mains. The pilot heat transfer data are further examined alongside measurements of the pilot residence time distribution, which together control the risk of pilot deposition at low fuel flow rates. Both the heat transfer and residence time measurements demonstrate the opportunity for future fuel gallery design refinement and provide the supporting data to facilitate this.