Swirl-stabilized Combustor Research Articles

Impact of the Precessing Vortex Core on NOx Emissions in Premixed Swirl-Stabilized Flames—An Experimental Study

Abstract The reduction of NOx emissions remains a driving factor in the design process of swirl-stabilized combustion systems, to meet legislative restrictions. In reacting swirl flows, hydrodynamic coherent structures, such as periodic large-scale vortices in the shear layer, induce zones with increased heat release rate fluctuations in connection with temperature peaks, which lead to an increase of NOx emissions. Such large-scale vortices can be induced by the helical coherent structure known as precessing vortex core (PVC), which influences the flow and flame dynamics under certain operating conditions. We developed an active flow control system, allowing for a targeted actuation of the PVC, to investigate its impact on combustion properties such as NOx emissions. In this work, a perfectly premixed flame, which slightly damps the PVC, is studied in detail. Since the PVC is slightly damped, it can be precisely excited by means of open-loop flow control. In connection with time-resolved OH*-chemiluminescence and stereoscopic particle image velocimetry (PIV) measurements, the impact of the actuated PVC on flow and flame dynamics is characterized. It turns out that the PVC rolls up the inner shear layer, which results in an interaction of PVC-induced vortices and flame. This interaction considerably influences the measured level of NOx emissions, which grows with increasing PVC amplitude in a perfectly premixed flame. Nearly, the same increase is measured for partially premixed conditions. This is in contrast to previous studies, where the PVC is assumed to reduce the NOx emissions due to vortex-enhanced mixing.

Flame dynamics during intermittency and secondary bifurcation to longitudinal thermoacoustic instability in a swirl-stabilized annular combustor

In this experimental study on a laboratory-scale turbulent annular combustor with sixteen swirl-stabilized burners, we study the flame-flame and flame-acoustic interactions during different dynamical states associated with the longitudinal mode of the combustor. We simultaneously measure the acoustic pressure and CH* chemiluminescence emission of the flame using a high-speed camera. Upon increasing the equivalence ratio, the combustor undergoes the following sequence of transition: combustion noise (CN) to low-amplitude longitudinal thermoacoustic instability (TAI) through the state of intermittency, and from low-amplitude to high-amplitude longitudinal TAI through a secondary bifurcation. We report the first evidence of secondary bifurcation from low-amplitude TAI to high-amplitude TAI for a turbulent thermoacoustic system which allows us to test the flame response at two different amplitude of perturbation in a natural setting. TAI arises at the first longitudinal mode of the combined burner tube and combustion chamber. The frequency of oscillations remain the same during the above transition. We find a significant difference in the dynamics of the flame interactions during the periodic part of intermittency and low- and high-amplitude TAI. Specifically, during the periodic part of intermittency, the phase difference between the local heat release rate (HRR) measured from various burners show significant phase slips in time. During low-amplitude TAI, there are fewer phase slips among the HRR response of the burners, which result in a state of weak synchronization among the flames. During high-amplitude TAI, we find that the flames are in perfect synchrony amongst themselves and with the pressure fluctuations. We then quantify the degree of temporal and spatial synchronization between different flames, and flames and pressure fluctuations using the Kuramoto order parameter and the phase-locking value. We show that synchronization theory can be conveniently used to characterize and quantify flame-acoustic interactions in an annular combustor.

Factors Determining the Flame Configuration and Affecting Combustion Stability in Gas-Turbine Combustors

The possibilities of influencing combustion stability during changeover to low-emission combustion and ways of extending the stable combustion range are analyzed. The flow velocity, temperature, and pressure in the low-emission combustor (LEC) are considered as influencing factors. A premixed swirl-stabilized combustor is considered. The burner unit consists of main and pilot burners. The main burner has two fuel channels that allow controlling the quality of the air-fuel mixture. The LEC developed for an aeroderivative gas turbine was tested at an inlet air pressure of 2 MPa and an inlet air temperature of 475°C and an exhaust gas temperature of up to 1320°C.

Operability of a premixed combustor holding hydrogen‐enriched oxy‐methane flames: An experimental and numerical study

This work presents a detailed investigation on the stability, flame macrostructure and combustion characteristics of oxy-methane/hydrogen (H2CH4O2CO2) flames in a premixed swirl-stabilized model gas turbine combustor. The effects of equivalence ratio, inlet Reynolds number and inlet swirl number on stability and combustion characteristics were examined experimentally and numerically. A base operation case was selected as a reference to study the effects of the different parameters with equivalence ratio of 1.0, bulk mean throat velocity of 5.2 m/s, and swirl number of 0.98. Fixed compositions of the oxidizer (30%O2/70%CO2) and fuel (50%H2/50%CH4) streams were considered throughout the study. Large eddy simulation (LES) technique was adopted to compute the premixed turbulent flame regime. Experimentally captured flame images were compared with the flame contours obtained from the numerical simulations, and good conformations were observed. The results showed that near-stoichiometry flames exhibit strong inner recirculation zone (IRZ) and are stabilized between two shear layers. At lower equivalence ratios, the flames are corner-stabilized, and the flow is dominated by a single primary eddy in the IRZ. The calculated strain rates predict flame quenching at equivalence ratio of 0.5, which was also confirmed experimentally. It was observed that the effect of Reynolds number on the flame shape is not significant; however, the flow is dominated by larger primary eddy with strong IRZ as the Reynolds number increases. The IRZ also gets stronger with the increase in the flow swirl number. At higher swirl numbers, the flame stabilization occurs at the inner shear layer and the outer recirculation zone (ORZ) diminishes. It was found that the chemical time scale for all cases under investigation is shorter than the Kolmogorov time scale, signifying that the chemical reactions are dominated by the laminar flame speed.

Effect of different syngas compositions on the combustion characteristics and emission of a model combustor

There is a growing need to design fuel flexible combustors. This require understanding of the combustion and emission characteristics of the combustors under varying fuel compositions. In the present study, the combustion characteristics and emission of methane and syngas flames were investigated numerically in a swirl stabilized combustor. The numerical model was developed using ANSYS-fluent software and validated using experimental values of temperature, CO2 and NOx emissions. A two-step chemical mechanism was used to model methane-air combustion. Results of the numerical validation showed similar trend between the experimental and predicted temperature along the combustor axis with about 5 % over prediction of the temperature. Syngas-air combustion was thereafter modeled using a 21 step chemical mechanism. Syngas compositions studied were: syngas A (67% CO: 33% H2), syngas B (50% CO: 50% H2) and syngas C (33% CO: 67% H2). Results showed that for pure methane, a V-shaped flame was observed with the flame attached to the fuel nozzle, while a lifted flame was observed for case of syngas A composition. CO gas with higher ignition temperature and flammability as compared to H2 gas is the dominant gas in syngas A fuel composition. Jet flames were observed for syngas B and syngas C. Carbon monoxide is a slow burning gas. Therefore syngas with low CO content has a low tendency of emission of CO from the combustor. This suggests that syngas with high CO content such syngas A may require more residence time to completely combust the CO gas. The NOx emission was observed to have the same trend as that of the combustor maximum temperature. Syngas C flame had the highest NOx emission, while, syngas A flame had no NOx emission. This is due to low combustor temperature observed in the case of syngas A flame.
 Keywords: Syngas, ANSYS-FLUENT, Swirl-stabilized combustor, NOx emission, Chemical Mechanism

Stability diagram and blow-out mechanisms of turbulent non-premixed combustion

This study is concerned with investigating the stability limits and physical mechanisms of flame blow-out in non-premixed combustion through theoretical analysis and numerical simulations. By applying expressions for fuel/air equivalence ratio and strain rate to diffusion flames, stability conditions are derived that arise from modulating fuel- and air-flow rates in combustors. One-dimensional flame calculations are performed to construct a stability diagram, and three distinct stability limits are identified that are associated with strain-induced extinction, fuel-lean extinction and fuel-rich extinction. Experimental data are examined to verify these stability limits, and large-eddy simulations of a swirl-stabilized combustor are performed to computationally explore these stability boundaries, showing good agreement with theoretical predictions.

Early Prediction of Lean Blowout from Chemiluminescence Time Series Data

ABSTRACT Lean combustion systems are usually employed in gas-turbine engines, particularly in land-based applications, to reduce NOx emission. These combustion systems are often susceptible to lean blowout (LBO), which can be detrimental for operation and productivity of gas-turbine engines. An abrupt decrease in the equivalence ratio during a throttling operation, which is often encountered in power plants due to sudden decrease in load demand and also in aircraft engines at the time of landing, may lead to an unexpected LBO. From this perspective, online data-driven algorithms are deemed necessary for early prediction of potential transitions to near-blowout conditions. This procedure would provide the human operator/active controller with an appropriate lead time to alter the operating conditions so that the system can be brought back to a desired stable condition. The paper emulates pertinent conditions of LBO on a laboratory-scale apparatus of swirl-stabilized dump combustor with transient time series of CH* chemiluminescence data, where the objective is early prediction of LBO. The underlying algorithms are constructed based on a well-known statistical learning tool, called Hidden Markov Modeling (HMM), which can be used in the setting of supervised learning to discern near-blowout time series data from stable data. Being solely data-driven, the proposed methodology is model-free; it has been shown to be numerically efficient as well as sensitive to regime changes when the combustion system moves toward or away from LBO.

Chemical and physical effects on lean blowout in a swirl-stabilized single-cup combustor

Understanding the lower stability limit of gas turbine combustors is imperative for safe operation as well as for the approval of novel sustainable aviation fuels. Previous results have indicated that at relatively low temperatures and pressures (Tair = Tfuel = 238 and 258 K, P = 101 kPa, ΔP/P = 2%), the lean blowout (LBO) limits correlated to fuel physical properties, while at relatively high temperatures and pressures (Tair = 394 K, Tfuel = 322 K, P = 207 kPa, ΔP/P = 3%) chemical properties were highly correlated. This suggests that a transition occurs between physical and chemical property dependency. In the present effort, a single nozzle swirl-stabilized combustor was used to study the LBO for fuels with varying chemical and physical properties as well as operating conditions to study a transition from physical property dependence at low pressures and temperatures to chemical property dependence at higher temperatures and pressures. Four fuels with a wide range of physical and chemical properties were tested at combustor inlet conditions of Tair = Tfuel = 305–355 K, P = 107 kPa, and ΔP/P = 2–6%. It was found that the transition of LBO dependence from fuel physical to chemical properties does not happen at a single point. Rather, a transition range of conditions was observed for changes made to the pressure drop across the combustor dome (ΔP) as well as changes made to air and fuel temperature. Changes in ΔP/P were found to change the relative LBO performance across fuels and demonstrated a change in physical to chemical property dependence as ΔP/P increased. Analysis via random forest regression using dimensionless parameters such as an approximate Weber number and Ohnesorge number further highlighted the transition from physical to chemical property dependency with increasing ΔP/P.

Extracting information overlap in simultaneous OH-PLIF and PIV fields with neural networks

Simultaneous measurements, such as the combination of particle image velocimetry (PIV) for velocity fields with planar laser induced fluorescence (PLIF) for species fields, are widely used in experimental turbulent combustion applications for the analysis of a plethora of complex physical processes. Such physical analyses are driven by the interpretation of spatial correlations between these fields by the experimenter. However, these correlations also imply some amount of intrinsic redundancy; the simultaneous fields carry overlapping information content. The goal of this work lies in the quantitative extraction of this overlap in simultaneous field measurements. Specifically, the amount of PIV information contained in simultaneously measured OH-PLIF fields in the domain of a swirl-stabilized combustor is sought. This task is accomplished using machine learning techniques based on artificial neural networks designed to optimize PLIF-to-PIV mappings. It was found that most of the velocity information content could be retrieved when considering linear combinations of neighborhoods of OH-PLIF signal spanning roughly two integral lengthscales (half of the considered domain), and that PLIF signal interactions residing in smaller, local regions (less than half of the domain) captured no PIV information. Further, by visualizing the coherent structures within the neural network parameters, the role of multi-scale interactions related to velocity field retrieval from the OH-PLIF signal became more apparent. Overall, this study reveals a useful pathway (in the form of overlapping information content extraction) to develop diagnostic tools that capture more information using the same experimental resources by minimizing redundancy.

Heat transfer measurements in a hydrogen-oxyfuel combustor

ABSTRACT In the context of emission-free electricity generation, the authors developed a novel hydrogen-oxygen combustor, which is based on swirl-stabilized combustion technology and steam dilution. Following previous burner characterization, the current study investigates the heat transfer conditions in the combustion chamber wall. To this end, a carefully controlled co-flow of air is used to cool the combustion chamber in an annular duct, which surrounds it. Temperature measurements enable the evaluation of the heat flux from the combustor flow to the walls, local wall temperatures, and the Nusselt numbers on the hot and the cold side. The extremely high wall temperatures, caused by the H2/O2 flame, can be reduced by steam dilution down to approximately 900 K. Even better cooling could be reached by using the dilution steam as the coolant before it flows to the plenum. The Nusselt numbers at the inner combustion chamber wall are in the order of 10–50 and increase with the thermal power and the steam dilution ratio.

Combustion characteristics of butanol, butyl butyrate, and Jet A-1 in a swirl-stabilized combustor

Significant growth in the aviation industry has also raised concern on the impact of this sector in terms of environmental pollution. Bio-derived fuels are going to play an important role as potential alternative aviation fuels in the near future to mitigate the carbon footprint. Ethanol is a candidate biofuel which is widely used in many countries in the petrol-ethanol blend for S.I. engines. However, the interest in utilizing biofuels in aviation gas turbine engines is relatively recent. In comparison to ethanol, n-butanol possesses some better fuel properties such as higher energy density, less hygroscopic, lower vapor pressure, higher flash point. Butyl butyrate is another potential candidate which can fulfill the chemical property requirements of alternative aviation fuels. However, compatible substitutes for currently used aviation fuel (such as Jet A-1) are still at the early stage of development. The present study deals with experimental investigations of combustion characteristics of aviation kerosene (Jet A-1), butanol, butyl butyrate, and blends of the last two fuels with Jet A-1 in a swirl-stabilized gas turbine type combustor. Visualization of flame, measurement of temperature inside the flame, and exhaust emissions at the combustor exit are carried out to compare the performance of various fuels relative to Jet A-1. Spray penetration length, ligament length, droplet diameter, and spray cone angle of various fuels obtained using high-speed imaging technique are analyzed to understand the combustion characteristics. Fuel properties of individual fuels and blends are also measured and compared to probe the variation in spray and combustion performances.

Cross-talk-interaction-induced combustion instabilities in a can-annular lean-premixed combustor configuration

The prediction of self-excited combustion instabilities in a can-annular gas turbine combustion system is a significant challenge, mainly because the instabilities originate from the acoustic interactions between adjacent combustors via a cross-talk region upstream of the first stage turbine nozzles. Detailed characterization of these instabilities requires a thorough understanding of engine-level dynamics. Until now, a comprehensive experimental examination of such a can-annular configuration had not been conducted. Here we present new experiments using four lean fully-premixed swirl-stabilized combustors connected via a full-annular cross-talk section. We demonstrate that the global fluctuations at limit cycles are either in-phase interactions (push-push modes) or one of two different forms of out-of-phase interactions (push-pull modes), subject to uniform and non-uniform equivalence ratio combinations. Under certain symmetric conditions, the can-annular system undergoes in-phase synchronous modulations (Type I), giving rise to the formation of pressure antinodes at the inlets of the four combustors and in the cross-talk region. By contrast, out-of-phase interactions are sustained in the form of either an alternating pattern in four-coupled combustors (Type II) or a push-pull interaction in two opposite combustors only (Type III). The latter is dictated by strong out-of-phase fluctuations between two of the combustors and a pressure node-like condition – thermoacoustically decoupled from the global fluctuations – over the entire region of the other two combustors, experimentally demonstrating the existence of mode localization in can-annular thermoacoustic instabilities. We show that the mode clustering phenomenon is responsible for the excitation of closely-spaced multiple eigenmodes in the can-annular acoustic environment, and as a consequence the system can feature a mixed state with several distinct types of interaction patterns. By analyzing a large amount of experimental data acquired systematically for coupled two-combustor and four-can-annular configurations, we demonstrate that longitudinal-mode instabilities in a can-annular combustion system will preferentially emerge in the form of out-of-phase interactions.

스월-안정화 연소기에서 화염구조와 연소불안정에 대한 연구

스월-안정화 연소기에서 화염구조와 연소불안정에 대한 연구

Influence of m-xylene addition to Jet A-1 on spray structure, flow field and soot production in turbulent swirl-stabilized spray flames in a model combustor

Spray combustion of Jet A-1 and a Jet A-1/10% m-xylene blend was investigated to assess the influence of m-xylene addition on the spray characteristics and soot formation in a swirl-stabilized model combustor with dimensions of 94 mm × 94 mm cross-section and 188 mm length. Keeping the thermal power output constant at 10 kW, globally fuel lean flames were established for the neat Jet A-1 and 10% m-xylene blend fuels. The velocity field of the model combustor, spray characteristics, and soot volume fraction and primary particle size were measured, respectively, using stereoscopic particle image velocimetry, a Fraunhofer diffraction based droplet sizer, and auto-compensating laser-induced incandescence. Addition of m-xylene to Jet A-1 caused measurable differences in the flow field and the spray characteristics under identical air and fuel flow rates. Soot concentrations were modified throughout the flame by the addition of m-xylene, resulting in significant alterations in the cumulative soot loading within the spray flame envelope. In both flames, peak soot volume fractions were detected in the lower central portion of the combustor at the base of the inner recirculation zone and in the upper portion of the combustor in the fuel shear layer. Our results demonstrate the nontrivial influence of altered distillation characteristics (and other physical properties) of the fuel, induced by m-xylene addition, on flow field structure and spray properties. Potential mechanisms for the influence of changing flow field and spray characteristics, in addition to m-xylene doping of the Jet A-1, on soot processes are discussed.

Effects of swirler vane angle on palm biodiesel/natural gas combustion in swirl-stabilised gas turbine combustor

Combustion characteristics of palm biodiesel/methyl esters (PME) and natural gas (NG) blend were examined using a model gas turbine swirl burner at vane angle (θ) 30°, 45° and 60°. A twin fluid air blast atomiser was utilised for atomising liquid fuel at air-to-liquid ratio (ALR) 2.50. Swirling flow was initiated by using an axial swirler as main air passed through it. Combustible mixture was formed as swirling air flow mixed up with liquid fuel spray at burner outlet. Flame colour for PME/NG was mainly bluish, resembling that of neat PME despite subtle liftoff was observed in PME/NG swirl flames. Flame spectroscopic analysis showed that PME/NG swirl flames were more intense than baseline PME. Furthermore, θ = 60° operation led to significantly lower reaction intensity. Meanwhile, PME/NG combustion with 20%-30% NG input power fraction was observed to lower nitric oxide (NO) emission by a factor of 2.7 when compared with diesel and neat PME in θ = 60° combustion. Novel empirical models for emissions were also proposed, enabling the estimation of NO emission from PME/NG combustion at different NG input power proportions and vane angle. This research shows that PME/NG combustion is a promising way of reducing NO emission against neat PME and diesel in gas turbine operation. Moreover, flame instability provoked by liftoff in dual fuel operation is not aggravated, mainly due to nullification by intensified global reaction when NG is added. Such attributes feature PME/NG as a viable alternative fuel for use in land-based power generation gas turbines.

Visualisation and performance evaluation of biodiesel/methane co-combustion in a swirl-stabilised gas turbine combustor

While dual fuel firing of power generation combustion systems can improve the fuel flexibility of such systems, several studies on compression ignition engines have also shown a positive impact on NOX and PM emissions. Previous multiphase fuel combustion studies for combustion turbines are limited, thus the present study addresses that gap by fuelling a model swirl stabilised gas turbine combustor with a blend of waste cooking oil-derived biodiesel and methane. Methane was increasingly injected into swirling combustion air flow while simultaneously reducing the biodiesel spray flowrate across a pressure atomiser, thus maintaining an overall equivalence ratio of 0.7 while delivering a thermal power output of 15 kW in all cases, except for flame stability range trials. Direct flame imaging, CH* and C2* chemiluminescence imaging, post combustion emissions as well as stability performance of the flames were evaluated. NOX emissions were found to decrease by 29% and unburnt hydrocarbons increased by 10% as the fraction of methane in fuel mix increased to 30%. Further, flame images suggest increased wrinkling and perturbing of the flame front as gas fraction of the biodiesel/methane flame increases. However, the temporal variation of integral intensity of CH* and C2* species chemiluminescence point to at least an 8% improvement in flame stability when 30% of flame heat output is supplied by methane compared to neat biodiesel burn. Also, it was found that flame stability limits reduce as methane partly replaces biodiesel in the flame.

Application of recurrence quantification analysis for early detection of lean blowout in a swirl-stabilized dump combustor.

Lean blowout (LBO) is a serious issue in modern gas turbine engines that operate in a lean (premixed) mode to follow the stringent emission norms. When an engine operates with a lean fuel-air mixture, the flame becomes unstable and is at times carried out of the combustion chamber by the unburnt flow. Thus, the sudden loss of the flame, known as lean blowout, leads to fatal accidents in aircrafts and loss of production in power plants. Therefore, an in-depth analysis of lean blowout is necessary as the phenomenon involves complex interactions between flow dynamics and chemical kinetics. For understanding the complex dynamics of this phenomenon, recurrence analysis can be a very useful method. In the current study, we observe a transition to LBO as the global fuel-air ratio is reduced from stoichiometric condition and perform recurrence quantification analysis (RQA) with the CH∗ chemiluminescence data obtained experimentally. The extent of fuel-air mixing is varied with an objective of developing some robust early predictors of LBO that would work over a wide range of premixing. We find some RQA measures, such as determinism, laminarity, and trapping time, which show distinctive signature toward LBO and thereby can be used as early predictors of LBO for both premixed and partially premixed flames. Our analysis shows that the computational time for laminarity and trapping time is relatively less. However, computational time for those measures depends upon the dynamics of the combustor, size of the data taken, and choice of recurrence threshold.

Effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustor

This numerical study investigated the effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustion chamber by utilizing high-fidelity, fully compressible large eddy simulations. At low fresh mixture temperatures, the side recirculation zone stabilized the premixed flame on the boundary of the burner rim, while the central part of the flame was detached from the burner due to the inability of the central recirculation zone to assist in flame stabilization. However, the central recirculation zone became stable enough to stabilize the central portion of the flame near the burner rim as the fresh mixture temperature increased. Moreover, the coherencies and penetration depths of the coherent structures and precessing vortex cores in the combustor increased with the fresh mixture temperature. Analyses showed that the limit cycle instabilities that occurred at low fresh mixture temperatures resulted from coupling between heat release fluctuations and the first tangential acoustic mode of the combustor. However, as the fresh mixture temperature increased, a combustor dynamics transition occurred, through which the coupling between heat release and pressure fluctuations shifted toward the mixed tangential and radial acoustical modes of the combustor. During this mode transition, limit cycle oscillations were replaced by burst oscillations. The results revealed that recirculation zones are the key features that trigger thermoacoustic instabilities at low fresh mixture temperatures, while coherent structures and precessing vortex cores are the main combustion instability drivers at high fresh mixture temperatures.

Diesel/syngas co-combustion in a swirl-stabilised gas turbine combustor

Multiphase fuel combustion was carried out in a swirl-stabilised combustor with the aim of expanding the fuel flexibility of the gas turbine for, at least, land-based applications. Improved capability of the gas turbine in this regard will not only augur well for energy security but also could be useful in tackling harmful emissions. In the study, varying amounts of syngas was premixed with air and swirled into a burning diesel spray, the flowrate of which was altered to maintain the same heat output at all times. Across the several heat outputs tested, the range of stable flame operation was found to reduce as gas content of fuel mix increased. Moreover, for a combined heat output of 15 kW and a global equivalence ratio of 0.7, a steady increase in flame stability was noted and NOx emissions were found to decrease while CO emissions increased as syngas content in fuel mix increased from 10% to 30%. The increase in flame stability, achieved at the cost of lower heat release rate, was attributed to the changes in reacting flow dynamics evinced by the C2* and CH* species chemiluminescence intensity variation as well as chemical kinetics analysis. The NOX and CO emissions trend was ascribed to increasingly inefficient combustion due to the poorer spray quality obtained from pressure atomiser as liquid flow rate reduces and further worsened by the lower heat release rate and decreasing adiabatic flame temperature as gas ratio of combusted fuel increases.

Experimental characterization of liquid–gas slip in high-pressure, swirl-stabilized, liquid-fueled combustors

This paper implements a recently developed technique to conditionally analyze the liquid vs gaseous phase velocity vectors in a high-pressure, liquid-fueled, swirl-stabilized combustor. The technique consists of joint analysis of high repetition rate stereoscopic particle image velocimetry (s-PIV) and fuel planar laser-induced fluorescence (fuel PLIF). The s-PIV measurement is conducted simultaneously on the gas and liquid phases by seeding the gas with titanium dioxide flow tracers. The liquid fuel spray serves as its own flow tracer. A fuel PLIF measurement is used to distinguish the vectors that represent liquid fuel velocities from the vectors that represent gas-phase velocities. This technique provides two useful capabilities to the combustion diagnostics community. First, it enables the removal of bias error that the larger, high Stokes number fuel droplets can introduce to the gas-phase velocity measurements due to gas–liquid slip. Second, it enables the simultaneous study of gas- and liquid-phase velocity fields where there may be liquid–gas slip. In the present study, the results show that the liquid fuel spray is a reasonable flow tracer for the time-averaged flow. However, this study does identify regions in the time-averaged flow that contain sufficiently high accelerations and sufficiently large droplets to introduce liquid–gas slip.