Swirl Spray Research Articles

Effects of temperature on flame structures and local extinctions of swirl spray flames

The effects of air inlet temperature on the flame structures and the local extinctions of n-decane swirl spray flames at constant air flow velocity were clarified by using the simultaneous planar laser induced fluorescence measurements of OH and CH2O. Results show that the blowoff limit decreases 48% as the temperature increases from 298 to 473 K. The OH and the [CH2O] × [OH] overlap are mainly distributed near the shear layer, while a small amount of formaldehyde is also observed in the outer recirculation zone (ORZ), corresponding to the low-temperature reactions. The formaldehyde intensity in the ORZ varies non-monotonically with the temperature. The non-monotonic temperature dependence of the formaldehyde intensity is governed by the competition of the droplet evaporation rate and the initial droplet size. The local extinctions of swirl spray flames can be identified by the formation of holes or breaks in the OH branches together with the accumulation of formaldehyde. It suggests that the combination of OH and CH2O is a good indicator to predict the local extinctions. The probability of the local extinctions decreases gradually with the temperature. The locations of the local extinction move downstream from 333 to 423 K; however, the local extinctions occur frequently near the flame root at 473 K. It reveals that the local extinctions near the flame root are mainly associated with the cooling effect and the perturbation effect of the flame–droplet interactions at low temperature and at high temperature, respectively.

Simultaneous analysis of swirl spray dynamics using a telecentric shadowgraphy system

Abstract Pressure swirl injectors generate conical hollow sprays with a liquid film adjacent to the exit nozzle. This paper describes macroscopic and microscopic parameters of sprays and disturbances of the liquid films formed by dual pressure swirl injectors, utilizing a telecentric shadowgraphy optical system. High-speed images with kHz frequencies were used for the simultaneous measurement of spray cone angles, breakup lengths, mean droplet velocities and wave amplitude ratios. Two injectors were tested with inner nozzles having Abramovich geometric constants Kint = 2 and 2.125 and external nozzles with geometric constants Kext = 2.9 and 1.9792, respectively. Water was used as test fluid and the injection pressures were varied from 0.05 to 0.5 MPa. Simultaneous data from the same set of images allowed the calculation of the maximum surface wave growth rate. The results indicated that the maximum surface wave growth rate varies approximately linearly with the injection pressure. Measured maximum amplitude ratios of the conical liquid film disturbances varied in the range 2.32 < ln⁡〖((η_bu)⁄(η_0))〗 < 4.61, relatively close to recent experimental data on conical liquid films, but significantly lower than the calculated values for planar liquid films. The maximum amplitude ratio is a crucial parameter to determine breakup lengths. A new semi-empirical equation is proposed to describe the disturbance ratios of conical liquid films of pressure swirl injectors. 

Effects of low temperature on near-nozzle breakup and droplet size distribution in airblast kerosene spray

Atomization of low-temperature fuel is encountered in extreme operating conditions of liquid propulsion systems such as cold start and high-altitude relight for aeroengines. Fuel temperature has a great impact on airblast spray characteristics by influencing fuel viscosity and thus the gas–liquid interaction, which raises the demand to clarify the temperature-dependent transition in near-nozzle breakup behavior and the corresponding droplet size distribution. A liquid-centered swirl coaxial injector is tested on the low-temperature swirl spray and combustion test rig at Zhejiang University, using 25 kHz high-speed digital off-axis holography. RP-3 aviation kerosene is atomized under ignition conditions at temperatures of 233, 253, and 301 K, fuel pressures of 0.03 and 0.69 MPa, and air pressure ranging from 0 to 4.0 kPa. Time-resolved near-nozzle dynamics suggest four types of elementary breakup processes: wavy-sheet breakup, pulsating breakup, membrane-type breakup, and nonaxisymmetric Rayleigh breakup. Each process alternately dominates the near field as fuel Reynolds number (Ref) and aerodynamic Weber number (Weg) decrease, corresponding to four primary breakup modes. A mode classification plot is summarized. Spray structures show an extended breakup length and reduced spray cone angle as fuel temperature (Tf) decreases. Increasing air pressure (Pg) promotes spray expansion at 0.03 MPa, but contracts spray cone at 0.69 MPa. Cross-sectional Sauter mean diameter (SMD) distribution indicates a solid-cone spray at 0.03 MPa and a hollow cone spray at 0.69 MPa. Lowering Tf will rise the SMD in the spray center at 0.03 MPa and transform the toroidal SMD distribution at 0.69 MPa into a solid one. Finally, a temperature-related SMD model is derived considering the exponential viscosity–temperature relationship, and a good fit with R2 > 0.95 is achieved. This research aims to deepen the understanding of the effects of low temperature on the transition of near-nozzle atomization characteristics for airblast sprays. Both spray visualization and SMD results provide reference for numerical simulations and near-nozzle spray modeling.

Multi-scale flow atomization characteristics of Jatropha biodiesel swirl liquid film breakup

The characteristics of the spray and droplets produced by liquid film breakup are crucial for understanding the atomization process in industrial furnace atomizers. This study employed high-speed camera technology to capture images of Jatropha biodiesel (JB) spray at various pressures and Ohnesorge numbers (Oh). Image processing methods were employed to analyze the evolution morphology and proper orthogonal decomposition (POD) of fuel swirl spray, revealing the instability, breakup length, spray cone angle, fractal characteristics of the liquid film breakup zone, and droplet distribution characteristics. The results indicated that the JB jet evolution progressed through stages: cylindrical jet, torsion liquid film, open swirl, complete swirl, and fully developed mode. The evolution and disintegration of the liquid film exhibited a complex structure with ligaments, perforations, and droplet separation. Flow disturbances induced the Klystron effect, characterizing microscopic droplet motion. As spray pressure increased, the growth rate of the disturbance wave increased, the breakup length decreased, the atomization cone angle enlarged, and the fractal dimension (FD) of the liquid film breakup zone increased. The droplet size distribution followed a log-normal distribution, with a substantial increase in the number of small droplets as injection pressure increased. This study provides valuable insights into the multi-scale flow atomization of biodiesel in industrial furnace, and is of great significance for the design, operation, and optimization of spraying systems in various industrial applications.

Holographic image denoising for dense droplet field using conditional diffusion model.

The Letter delves into an approach to holographic image denoising, drawing inspiration from the generative paradigm. It introduces a conditional diffusion model framework that effectively suppresses twin-image noises and speckle noises in dense particle fields with a large depth of field (DOF). Specific training and inference configurations are meticulously outlined. For evaluation, the method is tested using calibration dot board data and droplet field data, encompassing gel atomization captured via inline holography and aviation kerosene swirl spray through off-axis holography. The performance is assessed using three distinct metrics. The metric outcomes, along with representative examples, robustly demonstrate its superior noise reduction, detail preservation, and generalization capabilities when compared to two other methods. The proposed method not only pioneers the field of generative holographic image denoising but also highlights its potential for industrial applications, given its reduced dependency on high-quality training labels.

Temperature Field Measurements in Swirl Spray Flames Using Two-Line Planar Laser Induced Fluorescence Thermometry

Abstract This paper investigates the temperature fields in a centrally staged swirl spray combustor using two-line OH planar laser induced fluorescence (PLIF) thermometry at elevated inlet pressures and temperatures up to 0.62 MPa and 650 K. The pilot and main stages of the combustor were supplied with RP-3 kerosene. OH radicals were excited using the Q1(5) and Q1(14) transitions within the A2Σ←X2Π (1,0) band. Two laser excitation systems were operated simultaneously, where the two beams were spatially combined and separated by a small interval in time. The PLIF signals excited at the two wavelengths were captured by two identical sets of imaging system. The calibration coefficient needed for quantitative conversion from fluorescence ratio to temperature was determined based on results from independent coherent anti-Stokes Raman scattering (CARS) measurements. A joint threshold mask was developed to remove the noise and weak signals in the raw PLIF images. The high temperature zones in the temperature field were then obtained, and the pilot and main stage flames were identified. In addition, the radial position of the pilot flame showed marked variations at a nominally fixed condition. By extracting the radial profiles, a consistency between the peaks of PLIF intensity and temperature was found, suggesting that PLIF images could be a qualitative substitute for the high temperature zones in the temperature fields of these swirl spray flames. This study demonstrates the feasibility of temperature field measurements using two-line OH PLIF in aero-engine model combustors.

Effect of flash boiling on the spray characteristics of pressure swirl spray nozzles using liquid nitrogen

Liquid nitrogen is a widely utilized effective low-temperature cooling medium, also employed in the ATR-GG (Gas Generator cycle Air Turbo rocket) engine to cool high-temperature components. Due to the high-temperature work environment and the ease with which liquid nitrogen evaporates and boils, liquid nitrogen would experience a flash boiling process. In order to study the influence of flash boiling on spray characteristics, experiments and simulations were conducted with two types of hollow-cone nozzles and two types of solid-cone nozzles under subcooled water at normal temperature which is not affect by flash boiling and superheat liquid nitrogen inflow conditions. The research found that flashing already begins inside the nozzle, significantly reducing the discharge coefficient of the solid-cone nozzle. The nitrogen gas-liquid mixture fills the air core of the hollow-cone spray, resulting in a comparatively smaller impact on the discharge coefficient. The liquid nitrogen spray exhibit spray collapse, unable to achieve the spray cone angels as the water spray. The major reason is that during the flashing process, nitrogen vapor expansion enhances the axial velocity, reducing the spray cone angle. The study recommends using hollow-cone nozzles to mitigate the impact of flash boiling on the spray characteristics.

Improved semi-theoretical correlation to predict the Sauter mean diameter of swirl cups

The spray downstream of swirl cups involves complex two-phase flow. Comprehensively, understanding the flow physics of the spray to accurately predict the characteristics of the swirl spray is crucial for developing next-generation low-emission gas turbine combustors. The Sauter mean diameter (SMD) of the spray is an important design parameter in a gas turbine combustor, and the semi-theoretical method is among the most widely used approaches for predicting the SMD of atomizers. Of the available semi-theoretical models for predicting the SMD of prefilming-type atomizers, Shin's phenomenological three-step atomization (PTSA) model is a physics-based correlation. The PTSA model comprises three submodels: those of the pressure-swirl spray, impingement and film formation, and aerodynamic breakup. Based on similar physical mechanisms, the PTSA model can effectively predict the SMD for the spray shear layer of swirl cups. In this study, a new model, called the PTSA-V model, is proposed by introducing the viscosity of the liquid to the three submodels of PTSA. Additionally, the submodel of impingement and film formation was reconstructed, using a simplified model of a round water jet impinging on a cylindrical wall to predict the thickness of the liquid film on the Venturi surface. Experiments were carried out on a swirl cup under different pressures and temperatures of fuel as well as varying pressure drops in the air by using a two-component phase Doppler particle analyzer. The resulting uncertainty in predictions of the PTSA-V model was lower than ±7.4% under the 26 operating conditions considered here, compared with an uncertainty of ±20% in the outcomes of PTSA. Uncertainty in predictions of PTSA-V was lower than ±15% when it was applied to SMD data downstream of the swirl cup from the literature.

Dual-camera off-axis holographic particle tracking velocimetry: Development and application to air-blast swirl spray measurement

Quantifying the droplet field near the atomizer exit poses a challenge due to its three-dimensional (3D), multiscale and turbulent characteristics. An optical measurement method named dual-camera high-resolution holographic particle tracking velocimetry (DCHR-HPTV) is proposed. This method enables the extraction of near-field spatial Sauter mean diameter (SMD) distribution and three-dimensional two-component (3D-2C) velocity field, from off-axis hologram pairs with a frame interval of 6 μs, recorded using two synchronized industrial cameras and pulsed lasers. The system achieves a resolution of 9344 × 7000 pixels with an individual pixel size (dpix) of 3.2 μm. The droplet size measurement range is from 10 μm to above 500 μm with an absolute error within 3 μm. The velocity measurement range is adjustable and is set to be 0 to 38.4 m/s in this study, with errors of 0.23 m/s and 0.15 m/s for horizontal and axial components, respectively. The method is applied to investigate a spray region of 29 mm × 20 mm with a depth of 35 mm (equivalent to 20.3 cm3) at the exit of an air-blast atomizer. The spatial distribution of circumferentially integrated SMD along radial and axial directions is obtained. Statistical analysis is performed on both spatial and quantity distributions of droplet 3D-2C velocities. Concurrently acquired droplet size and velocity in the central toroidal recirculation zone (CTRZ) indicate that both the increasing air pressure and enlarged size range lead to a weakened droplet backflow motion. This method, distinguished by its large field of view and high resolution for particle velocimetry, is suited for dynamic analysis of near-nozzle droplet fields and can be employed in various testing scenarios involving 3D motion of micron-sized particles within multiscale flow fields.

Hydrodynamic Performance of an Axial Swirling Spray Tray with Guide Vanes

Hydrodynamic Performance of an Axial Swirling Spray Tray with Guide Vanes

Research on the mixing characteristics of the bottom blowing molten pool based on flow characteristics and mixing uniformity

In this study, a new method of combining lance–liquid flow characteristics and mixing uniformity is proposed to evaluate the stirring characteristics in the bottom blowing copper molten pool. A fluid simulation model of a bottom blowing molten pool was established, water was used to simulate the melt environment, and an experimental platform was set up for verification. The effects of swirl, multi-channel, and straight pipe spray on the lance–liquid stirring characteristics of the bottom-blown copper molten pool are compared through quantifying the flow characteristics and mixing uniformity. In addition, digital image processing technologies, such as image entropy variance and eddy current map entropy increase, are introduced. Through numerical simulation research, it is found that the transverse velocity of the swirl spray lance is the largest, which makes the rise time of the bubble increase to the greatest extent. Compared with the straight pipe spray, the swirl spray reduces the liquid splash height by 0.054 m, and the degree of vortex flow is higher. The lance phase stability is increased by 37.87%, and the maximum turbulent kinetic energy can be increased by 8.73%. The spray effect of the multi-channel spray is between the two. It is shown that the swirling spray lance can improve the stability of gas in the molten pool, enhance the uniformity of gas–liquid mixing, and improve the operation cycle and the smelting efficiency of the molten pool.

DETERMINATION OF THE DROP SIZE AND DISTRIBUTIONS IN SWIRL INJECTION IN CROSS FLOWS, IMPINGING, AND EFFERVESCENT INJECTORS

We have extended the primary atomization analysis to swirl injection in cross flows, impinging, and effervescent injectors. Using the integral form of the conservation equations, the drop size can be expressed in terms of injection and fluid parameters, the main variable being the liquid and gas velocities. Using the measured velocities as inputs to this <i>D</i><sub>32</sub>-equation, good agreements with experimental data are found for the drop size in the three spray geometries. Underlying physical mechanisms for the drop formation are also revealed from the analysis. The aerodynamic interaction between the swirl spray and cross flow results in reduction in momentum, with a corresponding decrease in kinetic energy that appears as surface tension of energy of many small droplets. Similarly, cancellation of the lateral momentum in impinging jets and internal deceleration in effervescent injectors are the key primary atomization routes. The use of the analytical drop size-velocity correlation has also been demonstrated for swirl sprays in cross flows. Therefore, this approach can be used to predict the drop size and distributions in different spray geometries, with appropriate changes in the velocity input terms and fluid properties.

Enhancing ammonia engine efficiency through pre-chamber combustion and dual-fuel compression ignition techniques

In pursuit of unleashing ammonia’s potential in internal combustion engines, an extensive computational study was conducted to explore the effects of two advanced combustion techniques: pre-chamber combustion (PCC) and dual-fuel compression ignition (DF−CI) on a heavy-duty ammonia engine. In the PCC mode, hydrogen was introduced into the pre-chamber (PC) to generate distributed reacting jets, with a small energy fraction of 0.5%. The case featuring a slightly narrower PC throat (diameter of 5.4 mm) yielded the highest indicated thermal efficiency (ITE) of 50.4%, owing to the rapid distribution of reacting jets and advanced combustion phasing. Further increase in hydrogen energy fraction and reduction in throat diameter resulted in a lower ITE because of the enhanced wall heat transfer loss. The DF−CI mode also exhibited significant potential for achieving high efficiency. Through a systemic optimization of parameters such as diesel injection timing, spray included angle, injection pressure, swirl ratio, and piston shape, a significantly enhanced ITE of 50.3% was attained, 7.2% higher than the baseline scenario. The improvement was primarily attributed to the promoted mixing of diesel with air. Among the design parameters, the swirl ratio and spray included angle exhibited the most significant impact on the engine performance. Overall, both the PCC and DF−CI modes were found to yield high ITE and low ammonia emissions. However, because 20% of the diesel energy fraction was utilized to mitigate ammonia slip in the DF−CI mode, notably higher greenhouse gas emissions (carbon dioxide of 96 g/kW-h) were generated than in the PCC mode. In this regard, the ammonia-hydrogen PCC mode should be a more promising solution to achieve zero-carbon emissions for future ammonia engines.

Topology characteristics of liquid ammonia swirl spray flame

The utilization of liquid ammonia in gas turbines can reduce energy loss and start-up time. However, the flash boiling phenomenon and the high latent heat of liquid ammonia make the spray flame difficult to stabilize. Increasing the preheated air temperature or adding a small amount of hydrogen as a piloted fuel are considered as effective methods to enhance the stability. To understand the flame topological structure, simultaneous Mie scattering and planar laser-induced fluorescence of OH (OH-PLIF) techniques were used to visualize the liquid ammonia spray structure and flame region information. Results show that the liquid ammonia swirl spray flame exhibits the flame topological structure of distinct zoning characteristics, including the droplet zone, the mixing zone, and the flame zone. Increasing the preheated air temperature accelerates the evaporation of liquid ammonia, leading to an increase in the local equivalence ratio and radial flame splitting. At lower air temperature conditions, increasing the hydrogen blending ratio has minimal impact on the flame topological structure. However, at higher temperature conditions, hydrogen blending significantly promotes reaction intensity upstream and reduces the flame lift-off height, which makes the mixing zone smaller. In general, to achieve a better flame stability effect, the two factors need to be reasonably matched, which has important reference value for the development of liquid ammonia fueled gas turbine combustors.

Machine learning based spray process quantification

Droplet size distribution and liquid loading are two of the most important properties to characterise spray processes. For example, nitrogen oxide (NOx) formation of liquid fuel-operated combustion systems is dominated by mixture homogenisation that is heavily dependent on atomization. While phase Doppler interferometry (PDI) is the technique of choice to measure droplet size distribution, shadowgraphy enables the detection of liquid bodies of arbitrary shape, e.g. ligaments, and thus can be used to delineate primary atomization. For this purpose, a data analysis tool is developed that enables a quantitative description of droplet size and the primary break-up process simultaneously. In this context, machine learning-based (ML) object detection provides a generally applicable approach that is used here to characterise a pressure swirl water spray. The deep neural networks are trained using synthetic training data with physics-informed domain randomisation. Two different network architectures (namely Mask R-CNN and SparseInst), backbones (ResNet50 and ResNet101) and several different training approaches are evaluated. The inference accuracy of the ML models is validated against PDI measurements in terms of droplet size distribution. The best-performing ML model provides a robust detection method for a wide range of measurement conditions. The validated ML model is used to characterise the primary break-up to delineate the effect of aerodynamic forces on the atomization of a hollow cone pressure swirl spray in high momentum gaseous co-flow. The results show the largest and most deformed liquid bodies away from the centre line in regions of high co-flow velocity.

Effect of low fuel temperature on combustion deterioration of kerosene swirling spray flames using OH-PLIF

The low fuel inlet temperature poses challenges to the flame stability of aircraft engine combustors. In order to investigate the combustion deterioration of swirl-stabilized kerosene spray flames under conditions of low fuel inlet temperature (T < −16 °C), a comprehensive system was established, comprising a burner commonly used in aircraft engines and a cooling setup. Upon analyzing OH-PLIF images, it becomes evident that sub-zero Celsius temperatures significantly lead to a decrease in OH radical concentration, resulting in a diminished heat release rate. The strongest signals decrease by a minimum of 5 times. Additionally, through the analysis of LIF spectra and detuned images, the differences between OH-LIF and kerosene-LIF are beneficial for recognizing the kerosene particles from the OH-LIF signals at the same time. For atomization assessment, employing the LOG operator blob detection method, it is found that at sub-zero Celsius temperatures, the overall count of fuel LIF particles experiences a slight reduction, while the count of larger particles increases across various air flow rates. This observation highlights an inferior droplet distribution at lower fuel temperatures. The image processing of kerosene LIF particles opens up the possibility for a rapid evaluation of atomization, especially when assessing combustion deterioration in kerosene spray flames through the use of a simple OH-PLIF technique.

Flame dynamics and combustion instability induced by flow-flame interactions in a centrally-staged combustor

This study mainly investigates the flame and flow characteristics under combustion instability in a centrally-staged swirl spray combustor, using 5 kHz CH* chemiluminescence (CL) and 15 Hz particle image velocimetry (PIV). The inlet air total temperature and total pressure are up to 600 K and 1 MPa, respectively. A dynamic pressure sensor with an acquisition frequency of 20 kHz is located downstream of the combustor casing. The pressure signal shows large-amplitude limit cycle oscillations when the fuel split ratio of the pilot stage decrease. The phase-averaged CH* CL images indicate that the periodic ignition/extinction of the main stage flame triggers combustion instability. A proper orthogonal decomposition (POD) analysis based on the reacting flow field further explains this phenomenon. The first two POD modes containing three coherent vortex pairs are associated with the extinction and ignition of the main stage flame, respectively. The vortex pairs located at the central shear layer (CSL) generated by Kelvin-Helmholtz (K-H) instability affect the primary recirculation zone (PRZ). The change in the size of the PRZ influences the main stage flame dynamics. In a cycle of oscillation, ignition happens when the size of PRZ increases and the coupling between the main and pilot stages enhances. Extinction takes place when the opposite happens. The flow-flame interaction mechanism demonstrated in this study provides strong experimental support for understanding combustion instability in aero-engine combustors.

CFD investigation of a fast-response humidifier for high-power PEMFC test stations

Unlike operating PEMFC systems with internal humidification from hydrogen recirculation, fuel cell stack test stations mainly rely on external humidification. Response time in the order of 10s and power over 100 kW are crucial requirements for test stations for vehicle fuel cell stacks. In the present study, a 3D computational fluid dynamics (CFD) model of a swirl spray humidifier is developed to simulate the conjugated heat and mass transfer in such a humidifier. In the model, hot, dry air enters from the bottom portion of the humidifier tangentially and mixes with liquid droplets from a nozzle placed near the middle. A discrete phase model (DPM) is employed to model the atomized droplets. Time variations of the flow structure and humidity distribution are studied. A parametric study with the nozzle parameters on humidifier performance is carried out, showing that optimal humidifier performance can be obtained with a single nozzle and spray temperature at 300 K. The humidity response at the humidifier exit subject to a load change is investigated. The simulation results show that the humidifier's dynamic response time for the baseline case is about 32s, with a steady relative humidity of 95.25% and an evaporation rate of 98.4% at the exit. The present model can guide the future design of fast-response, high-power humidifiers for fuel cell stack test stations.

Investigation on suitable swirl ratio and spray angle of a large-bore marine diesel engine using genetic algorithm

The swirl flow and spray angle are crucial to the organization of the combustion process in marine engines. In this work, to explore the suitable swirl ratio and corresponding spray angle for large-bore marine diesel engines, the artificial neural network (ANN) coupled with the genetic algorithm (GA) was used. At the same time, to increase the swirl ratio without affecting the scavenging efficiency, the cylinder gas recirculation (CGR) strategy was adopted in this manuscript. Compared with the original design, results indicate that the optimal swirl ratio is about 10 for the large-bore marine diesel engine when applying the CGR strategy. Due to the improved fuel–air mixing process and combustion process, the thermal efficiency and the output power of the optimal case increased by 4.86% and 5.2%, respectively. The present results are helpful for the design and optimization of the fuel–air mixing and combustion processes for large-bore marine diesel engines.

Experimental investigations on central vortex core in swirl spray flames using high-speed laser diagnostics

Centrally staged swirl combustion can effectively reduce NOx emission. However, the complex combustion field is susceptible to producing large-scale coherent structures, such as precessing vortex core and central vortex core (CVC). This study mainly investigates the effect of CVC on the flow and flame in a centrally staged swirl spray combustor at elevated temperature and pressure using 10 kHz high-speed CH* chemiluminescence (CL), 20 kHz particle image velocimetry, and CH2O planar laser-induced fluorescence (PLIF). For the pilot flame, both CH* CL and CH2O PLIF flame are fork-shaped with three long parts, and the middle parts of flame dynamics indicate CVC structure. For the stratified flame, the CVC structure exists in an extended strip area of strong vorticity near the centerline of the combustor. The analysis of proper orthogonal decomposition modes shows that the motion of CVC is mainly swing, followed by precessing. Simultaneous diagnostics indicates that the entrainment of CVC leads to CH2O transport from the shear layer to the central region of the combustor. In general, the CH2O signal is mainly distributed in two positive velocity regions, the pilot/main jet and around CVC. Taking advantage of the CVC effect on radical transportation is a potential method to improve the mixing of the combustor, such as temperature distribution.