Lean Premixed Prevaporized Research Articles

Validation of a Generic Non-Swirled Multi-Fuel Burner for the Measurement of Flame Stability Limits for Research of Advanced Sustainable Aviation Fuels

Future aviation concepts should be both CO2-neutral and without other emissions. One approach to reaching both targets is based on sustainably produced synthetic liquid fuels, which may allow very clean, lean premixed prevaporized (LPP) combustion. For that, fuels are needed with much longer ignition delay times and a lower flashback propensity than current jet fuels. We describe an experimental setup to investigate the flashback stability of liquid fuels in a multi-fuel burner. In this work, the measurement procedure and the determination of the experimentally obtained accuracy are in focus with regard to prevaporized and preheated iso-propanol/air flames in an equivalence ratio range of 0.85 to 1.05 involving three preheating levels (573, 673, and 773 K). As the determination of the accurate unburnt gas temperature just ahead of the flame is of strong importance for flashback but not directly possible, a model is implemented to determine it from the measurable quantities. Even with this indirect method, and also regarding the hysteresis of the experimental preheating temperature, it is found that the relevant quantities, namely, measured temperatures, mass flows, and values derived from them, can be determined with accuracy in the range below 1.7%.

Low-order network modelling of the effect of Helmholtz resonators on nonlinear thermoacoustic modes in annular combustors

Modern aero-engines and land-based gas turbines often use annular combustors where many burners are installed in the circumferential direction. These combustors are often operated under lean-premixed pre-vaporized (LPP) conditions in which the flames are more susceptible to acoustic perturbations than traditional combustion systems. The resulted thermoacoustic instabilities may involve mode patterns varying in both longitudinal and circumferential directions. When nonlinear flame models are considered, our previous work proved that a 2-D low-order network model can capture limit cycle oscillations involving uncoupled and nonlinearly coupled modes, including longitudinal, circumferentially spinning/standing, and slanted modes. This kind of low-order network modelling tool has been recognised as a computationally efficient way of analysing thermoacoustic instabilities in annular combustors. Helmholtz resonators (HRs) are widely used to damp acoustic oscillations. For thermoacoustic instabilities in annular combustors, the presence of the HRs causes modal coupling and mode shape change. For nonlinearly coupled thermoacoustic modes, it is difficult to predict the change of modality accurately. In this paper, HRs are incorporated into the aforementioned low-order network model. The effect of HRs on different nonlinear thermoacoustic mode patterns are studied in detail. This provides a powerful low-order network modelling tool for studying the damping performance of HRs on nonlinear thermoacoustic modes in annular combustors.

Spray characterization in a multi-jet airblast injector with swirling air crossflow

Experimental spray characterization in a multi-jet airblast injector with swirling crossflow of air is the goal of the present work. The current injector allows radial injection of six liquid jets from a central hub into swirling and crossflowing air into the annular region around the hub. In the present study, three different aspects related to jet-in-crossflow are concurrently addressed viz. air flow confinement, air swirl and simultaneous atomization of multiple liquid jets. Such key features have been rarely reported in the past in spite of their relevance to practical injectors such as in Lean Premixed Prevaporized (LPP) gas turbine combustors. The spray structure and spatial distribution of droplets are visualized at different cross-sectional planes in the spray by application of the Laser Sheet Imaging (LSI) technique. The Droplet size, three components of droplet velocities and local liquid mass flux are measured at different axial and radial locations using the Phase Doppler Particle Analyzer (PDPA) technique. The injector is operated over a wide range of aerodynamic Weber number (Weg) of the liquid jets (Weg = 57 – 430). The physics behind the spatial evolution of characteristic droplet size is analyzed by estimating the droplet Weber number and the probability of droplet coalescence. The plume-to-plume interaction, subsequent to droplet generation from the primary atomization of adjacent liquid jets, is found to contribute to the variation of droplet size in the current injector. The influence of Weg on the evolution of spray characteristics is investigated in detail.

DNS analysis of turbulence modulation by lean premixed prevaporized spray flames in a model combustor

Turbulence modulation by lean premixed prevaporized (LPP) spray flames, which involve droplet motion, evaporation and gaseous reaction, is complicated and essential to organizing clean and efficient combustion. Direct numerical simulations of LPP combustion in a model swirling combustor under high pressure of 20 bar are performed. The gaseous flow is solved in the low-Mach-number limit, and the droplets are tracked as two-way coupled Lagrangian particles. The corrected infinite thermal conductivity model is adopted to describe droplet evaporation, and a reduced two-step kerosene/air chemistry mechanism is used to present combustion. Four cases, i.e., a non-reacting gaseous flow, a non-reacting spray flow and two reacting spray flows with different droplet sizes, are conducted to cover key features of LPP flame on turbulence modulation. The results show that the spray combustion significantly depresses the mean axial velocity on the centerline in the upstream, indicating an enhancement of the inner recirculation zone. The influence of droplets on the mean and fluctuating velocities is generally negligible except on the azimuthal modulation, while combustion can increase the velocities, which is more evident in downstream due to the pressure effect. In reacting cases, the turbulent kinetic energy (TKE) spectra in the shear layers reduce at high wavenumbers, reflecting the combustion-induced dissipation at small scales (below the laminar flame thickness scale). Besides, droplet evaporation can introduce energy at small scales while this modulation is balanced by combustion. Moreover, TKE budget analysis indicates that spray combustion mainly depresses the TKE and redistributes mean shear along the radial direction. Heat release increases the local fluid viscosity, depresses local turbulent transport, and increases viscous dissipation. Finally, the vortex stretching analysis shows that LPP combustion enhances the alignment with the intermediate strain rate component.

Breakup Mechanism of a Jet in the L-Shape Crossflow of a Gas Turbine Combustor

Experimental investigations are conducted to determine the mechanism and characteristics of a jet in an L-shape crossflow simulating the radial swirl injector of a lean premixed-prevaporized (LPP) combustor. To simplify the radial flow of the actual injector while ignoring the centrifugal effect, the L-shaped 2D-channel is used for the crossflow, and water is used as a fuel simulant. The jet breakup is captured using a high-speed camera, and the density gradient magnitude is post-processed to clarify the spray. The Sauter mean diameter (SMD) of the spray is measured via a laser diffraction method with a helium–neon laser optical system (HELOS). The characteristics of the jet in the L-shape crossflow are compared with the characteristics of the jet in a typical crossflow through the flat channel. The results for different outlet heights of the L-shape channel (H/d0) and different injector positions (L/d0) are presented. A dimensionless number (τ) consisting of a time ratio is introduced to describe the jet characteristics. In a previous work, the spraying tendency was demonstrated for different injector positions. In addition, the effect of the recirculation area on H/d0 was empirically shown. H/d0 determines the size of the recirculation area, and the range of τ determines the jet breakup mechanism inside the L-shape channel. The results of this study present the breakup mechanism of the jet in the L-shape channel flow, which simulates a jet in a radial swirler injector for gas turbine engines. It is expected that these results can be used to assist in designing gas turbine engines with more combustion efficiency.

MID-IR laser absorption spectroscopy of 1- and 2-butanol in a shock tube facility

E-fuels are CO2-neutral fuels generated using renewable fuels such as wind and solar energy, where the carbon is taken out of the atmosphere or from biomass. One of the suitable e-fuel classes are alcohols with a low number of carbon atoms. Obtaining the low pollutant emissions on combusting liquid fuels such as fuel oil and kerosene, e-fuels with lean, premixed, pre-vaporized (LPP) concept plays a pivotal role. So, in this framework, the present work focuses on the combustion properties in the low pressure and high-temperature regime of 1- and 2-butanol isomers to evaluate their potential as future sustainable aviation fuels. The study investigates the fuel-lean conditions of 1- and 2-butanol in the fuel/oxygen equivalence ratios of 0.25, 0.5, and 0.9 relevant to the LPP (Yan et al. 2015) combustion concept for its applications in aviation. The flame chemistry of butanol isomers has been widely investigated; however, more investigations on ignition chemistry are needed. For this, tunable diode laser absorption spectroscopy is utilized to obtain the time-resolved CO formation history, ignition delay time (IDT), and progress in the butanol consumption by applying the central wavelength of 2059.91 cm−1 and 2948.27 cm−1, respectively. The measurements were performed in the temperature range of 1150–1500 K near 1.5 and 3 bar. The experimentally obtained IDT were validated with several recent reaction mechanisms available in the literature. The correlation between measured IDT, CO formation, and butanol consumption data was captured by the simulations satisfactorily. However, the CO formation from the simulation shows disagreement with the experimentally obtained signal. In addition, discrepancies in the absolute CO were observed between simulation and experiment. Moreover, a sharp drop was observed for the butanol consumption histories predominantly at ϕ= 0.9 in both 1-and 2-butanol, which could not be predicted from the available mechanisms. Furthermore, by updating the rate constants of several key reactions near the sharp fall region, a better prediction from the mechanism was seen. The time-resolved CO profile and butanol consumption history, along with the absorption cross-section data for 1- and 2-butanol isomers, are reported for the first time in this paper.

Spray response on a model prefilmer under unsteady airflows of various frequencies

An appealing concept for jet engine combustors is the Lean Premixed Prevaporized (LPP) combustor, which operates at high pressures. The low NOx emissions achieved by lean combustion are one of the targets for modern aircraft engines. However, these types of combustors can introduce thermoacoustic instabilities that can potentially damage the engine and reduce its lifespan. Since the potential instabilities on the fuel spray characteristics, i.e. the spray mass flux, can affect the flame stability, the need arises to investigate the spray response under an unsteady airflow. For this study, a model prefilmer was experimentally investigated to produce a two-dimensional droplet flow without swirl flow. An acoustic forcing in the range of 100–500 Hz was introduced into the airflow, characterized by a hot wire Constant Temperature Anemometry (CTA) setup. Droplet characteristics, namely the droplet diameter distribution and velocity, were determined using a Phase Doppler Anemometry (PDA) setup, while the acquired data were phase-averaged in one period of the airflow oscillation. The influence of the excitation frequency and the air-to-liquid ratio (ALR) on the spray was studied: the spray responded to the acoustic excitation and therefore critical performance parameters, such as the spray mass flux, oscillated indicating potential problems regarding the flame stability.

Kinetic Modeling Study on the Combustion Characterization of Synthetic C3 and C4 Alcohols for Lean Premixed Prevaporized Combustion

To reach sustainable aviation, one approach is to use electro-fuels (e-fuels) within the gas turbine engines. E-fuels are CO2-neutral synthetic fuels which are produced employing electrical energy generated from renewable resources, where the carbon is taken out of the atmosphere or from biomass. Our approach is, to find e-fuels, which can be utilized in the lean premixed prevaporized (LPP) combustion, where most of the non-CO2 emissions are prevented. One of the suitable e-fuel classes is alcohols with a low number of carbons. In this work, the autoignition properties of propanol isomers and butanol isomers as e-fuels were investigated in a high-pressure shock tube (HPST) at temperatures from 1200 to 1500 K, the pressure of 10 bar, and lean fuel-air conditions. Additional investigations on the low-temperature oxidation and flame speed of C3 and C4 alcohols from the literature were employed to develop a comprehensive mechanism for the prediction of ignition delay time (IDT) and laminar burning velocity (LBV) of the above-mentioned fuels. A numerical model based on newly developed chemical kinetics was applied to further study the IDT and LBV of fuels in comparison to the Jet-A surrogate at the engine-related conditions along with the emissions prediction of the model at lean fuel-air conditions.

Numerical analysis of flame shape bifurcation in a two-stage swirled liquid burner using Large Eddy Simulation

A flame shape bifurcation in the liquid-fueled two-stage swirled BIMER combustor is studied using Large Eddy Simulations. This combustor, developed at the EM2C Laboratory to study Lean Premixed Prevaporized (LPP) burners, is composed of a two-stage injection system: a central swirled pilot stage fueled with a pressure-swirl atomizer, to sustain a piloting flame, and an outer swirled stage fed with a multi-point injection, to generate the LPP regime. After ignition in the pilot-only operating condition, a V flame is stabilized near the Inner Shear Layer (ISL). When switching to multipoint-only injection, a flame shape transition is observed and the flame bifurcates into a M-shape. In this work, we identify the mechanisms that lead to this bifurcation, and we show that the transition is driven by a complex coupling between the flame, the chamber acoustics and the ISL vortices. By switching to a multipoint-only injection, the fuel is essentially given to the ISL flame, which is mainly premixed. Because of the increased heat release rate and thanks to positive Rayleigh criterion, the quarter wave mode of the chamber is promoted. The ISL vortices, locked to this mode, increase in size until they are large enough to merge the flame in the CRZ, the radial momentum budget forcing the flow topology to switch to a bubble-like structure. Therefore, these results show that it is the existence of two possible flow topologies that renders this flame shape transition possible, the instability being responsible for transferring sufficient energy to the flow to enable the transitioning and the flame then changing its shape simply to adapt to the new topology.

Experimental study on flame/flow dynamics in a multi-nozzle gas turbine model combustor under thermo-acoustically unstable condition with different swirler configurations

This paper presents an experimental study on the combustion stability characteristics and flame/flow dynamics in a multi-nozzle, lean premixed prevaporized (LPP), swirl-stabilized gas turbine model combustor with different swirler configurations in the presence of self-excited combustion instability. The flame structure was characterized using high-speed OH⁎ chemiluminescence imaging and the flow field across the centerline of three interacting flames was measured by high-speed planar Particle Image Velocimetry (PIV). Two sets of the swirler configurations were considered in this paper, featuring different combinations of swirl rotational directions. The first one consisted of three co-rotating swirlers, whereas the central swirler in the second configuration was replaced by a swirler with counter-rotation direction. These two configurations were termed as COS and CNS combustors respectively in the rest of the paper. It was found that these two combustors exhibited similar stable and unstable operating domains in terms of different equivalence ratios and inlet air velocities. At the same test condition, the amplitude of dominant instability of COS combustor was 130 dB, which was stronger than that of CNS combustor (120 dB). Phase-averaged PIV measurements showed that both COS and CNS combustor featured three recirculation zones downstream the swirlers, and high axial velocity was present after the merging of the adjacent flames. These two flow structures varied periodically, but in different manners for COS and CNS combustors. Phase-averaged OH⁎ chemiluminescence images indicated that the flame was primarily anchored in recirculation zones close to the swirler and most of the heat release was found to occur in flame interaction regions, where large-scale reaction intensity variations occurred. Furthermore, a greater phase delay between heat release rate and acoustic pressure was observed in CNS combustor, which contributed to a weaker instability comparing with that in the COS combustor.

Experimental study on NOx emission correlation of fuel staged combustion in a LPP combustor at high pressure based on NO-chemiluminescence

Experimental investigations on NOx emissions of a single-cup, Lean Premixed Prevaporized (LPP), module combustor were carried out at elevated inlet temperature and pressure up to 810 K and 2.0 MPa, close to the real operating conditions of aero-engine combustors. This LPP combustor adopts centrally staged fuel injections which could produce separated stratified swirling spray flame. In the NOx emissions measurements, the ranges of dome equivalence ratio and fuel stage ratio were from 0.55 to 0.58 and 8% to 24%, respectively. The optical diagnosis on separated stratified swirling spray flame were carried out with fuel stage ratio changing from 15% to 30%. Therefore, NO* and OH* chemiluminescence images were obtained. The results show that NOx emissions increase with the increase of the fuel stage ratio. And from the chemiluminescence images, the main flame and pilot flame are found weakly coupled. The pilot flame plays a significant role in NOx emission production because of its higher adiabatic flame temperature. Based on the results of chemiluminescence optical tests, a new NOx emission prediction model is proposed based on the Lefebvre’s single flame model. The estimate of local equivalence ratio of the pilot stage’s non-premixed flame is modified considering the characteristics of spray combustion, and a “PLUS” emission prediction model suitable for separated stratified swirling spray flame is obtained. Compared to the experimental data, the “PLUS” model exhibits a good prediction in a range of ±13% of deviation.

Inlet temperature driven supercritical bifurcation of combustion instabilities in a lean premixed prevaporized combustor

The present article reports experimental observation and analyses of a supercritical bifurcation of combustion instabilities triggered by the air inlet temperature (Ta). The studies are performed with a pressurised kerosene fuelled Lean Premixed Prevaporized (LPP) combustor operated under elevated temperature. Unlike some previous studies, starting from an unstable condition of the system, the amplitude of combustion instabilities suddenly decrease when Ta exceeds a critical value of Ta = 570 K. When the temperature is lowered back the system returns to being unstable without featuring any hysteresis behaviour, as expected in case of a supercritical bifurcation. The unstable flames feature a periodic axial motion of lift-off and re-ignition, characterized as Helmholtz mode. The phase difference between chemiluminescence and pressure signals is found to increase with Ta, exceeding 90 degrees (out of phase) for temperatures higher than 570 K. A low order network framework is conducted, illustrating that when Ta is increased a stability shift of this mode is predicted at Ta near 570 K, in good agreement with the experimental observations. The impact of Ta on the spray characteristics is also examined, finding that higher Ta promotes fuel evaporation and reduces equivalence ratio fluctuation at the exit of the swirler.

Flame macrostructures and thermoacoustic instabilities in stratified swirling flames

The present article investigates the correlation between flame macrostructures and thermoacoustic combustion instabilities in stratified swirling flames. Experiments are carried out in a laboratory scale longitudinal test rig equipped with the Beihang Axial Swirler Independently-Stratified (BASIS) burner, a novel double-swirled combustion system developed by adapting an industrial lean premixed prevaporized (LPP) combustor. At first, the flame macrostructures are investigated and discussed for various total equivalence ratios (ϕtotal) and stratification ratios (SRs). Depending on operating conditions, three different flame types are stabilized in the combustor: two attached flames comprising a stratified flame and a V-shaped flame (V-flame), as well as a lifted flame. Thermoacoustic instabilities are then investigated. The amplitude of the oscillations is found to be more sensitive to SR than the ϕtotal. Large amplitude limit cycles are found for low and high values of SR, for which the V-flame and the lifted flame are observed in the combustor, respectively. The flame dynamics are also investigated using local Rayleigh index maps. It is found that for both the lifted flame and V-flame, the major driving force comes from the flame-to-wall impingement region. Coherent structures associated with flame wrinkling are found along the flame brushes of the V-flame. On the contrary, the stratified flame is found to be more thermo-acoustically stable. Finally, incompressible Large Eddy Simulations is used to obtain the flame responses to forcing at 300 Hz, which is very close to the frequencies at which limit cycle oscillations occur. The results show that the global heat release rate response of the stratified flame exhibits a significant phase shift compared to the responses of the other two flame types, and this is the most likely cause of thermoacoustic stabilization.

Methods for Reducing Emission of Harmful Substances in the Combustion Chambers of GTE and GTP

Methods for Reducing Emission of Harmful Substances in the Combustion Chambers of GTE and GTP

Combustion Oscillation Characteristics and Flame Structures in a Lean Premixed Prevaporized Combustor

The combustion oscillation characteristics in the lean premixed prevaporized (LPP) combustor at different equivalence ratios and inlet velocities of the combustor were experimentally investigated. Acoustic modal analysis was carried out to identify the acoustic eigenmodes in the LPP combustor. The flame structures under different operating conditions were investigated. The evolution laws of flame structures, coordinates and velocities of the flame centers, and heat release rates throughout a combustion oscillation cycle were investigated by phase-locked OH planar laser-induced fluorescence (PLIF). The result shows that there is a periodical process of flame roll-up for the flame close to the LPP combustor axis and a periodical process of separation and consolidation for the flame far from the LPP combustor axis. The spatial distribution of the normalized Rayleigh index in the LPP combustor was calculated to determine the driving zones of the combustion oscillation. The mechanism of combustion oscillation ...

Bistability and Transitions between Stable Operation and Thermo-Acoustic Instability in a Staged Liquid-Fuel Combustor

Because of increasingly stringent regulations on jet engines pollutant emissions, new ways of reducing them are needed. A promising way is the use of Lean Premixed Prevaporized (LPP) combustion where the liquid fuel is vaporized and mixed with air in excess before burning. In the present work, a model gas turbine combustor fed with liquid dodecane is studied experimentally. It is equipped with two fuel injection stages: a pressurized nozzle called the pilot and a multipoint device. When the split of the fuel injection between the stages is changed, several phenomena can be observed. The flame shapes can change drastically and present different behaviors, some of them showing a strong acoustic activity. In particular, two different flame shapes can be obtained for the exact same operating conditions depending on the burner history. The first flame, named sV, is stabilized thanks to an internal reaction zone that modifies the air flow compared to non-reacting conditions. The second state, associated with a Lifted flame, exhibits a strong thermo-acoustic instability linked to the quarter-wave mode of the chamber. A switch from the sV to the Lifted state can be triggered by air flow rate modulations while the opposite change can occur naturally as the fuel split is changed. These complex phenomena originate from multiple interactions between the fuel spray, the gaseous flow and the flame itself.

Influence of Main Swirler Vane Angle on the Ignition Performance of TeLESS-II Combustor

In order to balance the low emission and wide stabilization for lean premixed prevaporized (LPP) combustion, the centrally staged layout is preferred in advanced aero-engine combustors. However, compared with the conventional combustor, it is more difficult for the centrally staged combustor to light up as the main stage air layer will prevent the pilot fuel droplets arriving at igniter tip. The goal of the present paper is to study the effect of the main stage air on the ignition of the centrally staged combustor. Two cases of the main swirler vane angle of the TeLESS-II combustor, 20 deg and 30 deg are researched. The ignition results at room inlet temperature and pressure show that the ignition performance of the 30 deg vane angle case is better than that of the 20 deg vane angle case. High-speed camera, planar laser induced fluorescence (PLIF), and computational fluids dynamics (CFD) are used to better understand the ignition results. The high-speed camera has recorded the ignition process, indicated that an initial kernel forms just adjacent the liner wall after the igniter is turned on, the kernel propagates along the radial direction to the combustor center and begins to grow into a big flame, and then it spreads to the exit of the pilot stage, and eventually stabilizes the flame. CFD of the cold flow field coupled with spray field is conducted. A verification of the CFD method has been applied with PLIF measurement, and the simulation results can qualitatively represent the experimental data in terms of fuel distribution. The CFD results show that the radial dimensions of the primary recirculation zone of the two cases are very similar, and the dominant cause of the different ignition results is the vapor distribution of the fuel. The concentration of kerosene vapor of the 30 deg vane angle case is much larger than that of the 20 deg vane angle case close to the igniter tip and along the propagation route of the kernel, therefore, the 30 deg vane angle case has a better ignition performance. For the consideration of the ignition performance, a larger main swirler vane angle of 30 deg is suggested for the better fuel distribution when designing a centrally staged combustor.

Fuel spray characteristics investigation in LPP combustor

Purpose This paper aims to get an in-depth understanding of the fuel spray characteristics to further improve the emission performance of a lean premixed prevaporized (LPP) combustor with staged lean combustion. Design/methodology/approach In this paper, the fuel spray characteristics in the LPP combustor are experimentally studied by using particle image velocimetry (PIV), and raw data are processed by image-processing technologies for different inlet conditions. The effects of the fuel allocation and pilot atomizer position on fuel spray characteristics are investigated. Findings Experiment results show that when only the pilot atomizer is operated, the fuel spray characteristics is worsened by increasing fuel flow rate. The fuel spray fields generated by the pilot atomizer are better at the throat than that at the pilot swirler outlet; when the pilot atomizer and primary injector are operated at the same time with the same inlet fuel air ratio, the spray characteristics are improved by increasing the primary fuel flow rate and decreasing the pilot fuel flow rate. Meanwhile, fuel spray fields generated by the pilot atomizer are better at the throat than that at the pilot swirler outlet. Practical implications The present results are useful for further development of the LPP combustor. Originality/value An LPP combustor with staged lean combustion technology was proposed; to obtain fuel spray characteristics, image-processing program was compiled; the fuel spray characteristics in the LPP combustor were investigated, especially the effects of the fuel allocation and pilot atomizer position.

Spectroscopic analysis of crude rapeseed oil flame

Utilizing crude vegetable oils in all types of heat engines can be a part of a sustainable economy in the future. Focusing on their local usage, they can possibly compete with fossil fuels. Furthermore, to keep the pollutant emissions at the lowest possible level, the feedback control of the equivalence ratio is essential. Regarding the harsh environment of the combustion chambers, optical flame diagnostics is a potential tool. Therefore, in order to examine its feasibility, the comparison of flame emission spectroscopy (FES) of rapeseed oil with standard diesel oil was carried out at atmospheric conditions in a lean premixed prevaporized (LPP) burner at 15kW of firing power. The well-known chemiluminescence intensity ratios of OH*, CH*, and C2* at 516nm (C2, 516*) were investigated. A further significant peak was found at 554nm in case of rapeseed oil firing, which probably corresponds to C2* (C2, 554*). The corrected chemiluminescence intensity ratios as a function of air–fuel equivalence ratio are shown in the current work. It was found that these ratios involving C2* at either 516 or 554nm show less sensitivity to the pressure of atomizing air than OH*/CH*, therefore they are more suitable for diagnostics and for the control of the equivalence ratio of liquid fired burners.

Experimental study of flow dynamics and fuel spray characteristics in Lean Premixed Prevaporized Combustor

Further improving the emission performance of a Lean Premixed Prevaporized (LPP) combustor is a hot topic for gas turbine research. An in-depth understanding of the combustion characteristics is therefore highly desirable. In this paper, the flow fields and fuel spay characteristics in a LPP combustor are experimentally studied by using Particle Image Velocimetry (PIV). The effects of the fuel allocation and pilot atomizer position on fuel spray characteristics are investigated. Experimental results show that: (1) A Primary Recirculation Zone (PRZ), Corner Recirculation Zone (CRZ) and Lip Recirculation Zone (LRZ) are presented in the flow field in a LPP combustor; (2) The width of the primary recirculation zone initially increases along axial direction from the combustor inlet, and starts to decrease after certain distance; (3) When only the pilot atomizer is operated, the fuel spray characteristics is worsened with the increase of fuel flow rate. Locating the pilot atomizer at the throat results is a better fuel spray distribution than locating it at the outlet of the pilot swirler. The present results are useful for future development of the LPP combustor.