Spray Atomization Process Research Articles

Study of the effect of cavitation flow patterns in diesel injector nozzles on near-field spray atomization characteristics using a LES-VOF method

The spray atomization process plays a critical role in achieving high efficiency and reducing emissions in internal combustion engines. The fuel injection atomization process, especially the spray primary atomization process, is significantly influenced by turbulent flow and cavitation phenomena within the nozzle. In this study, based on the coupled large eddy simulation(LES) and a volume-of-fluid (VOF)method, the effects of four typical nozzle internal flow patterns on the spray primary breakup in the near-nozzle region were investigated. To realize this objective, the generation of four distinct flow patterns was accomplished through the design and construction of corresponding nozzle structures: (1) nearly single-phase flow in a tapered-orifice nozzle with low orifice location, (2) strong geometry-induced sheet cavitation flow with sheet region extending to the nozzle orifice exit in a normal cylindrical orifice, (3) vortex-induced string cavitation flow in a tapered-orifice nozzle with relative high orifice location, and (4) geometry-induced sheet cavitation is partially suppressed while it is enhanced in the orifice region close to exit in a convergent-divergent orifice. The numerical results unequivocally reveal that the initial atomization of the spray exhibits remarkable efficacy in the case of the conventional cylindrical nozzle, characterized by internal regions of substantial sheet cavitation, despite a relatively minimal flow discharge coefficient. Conversely, the normal tapered-orifice nozzle, lacking significant cavitation, demonstrates a larger flow discharge coefficient, yet its initial atomization performance is notably suboptimal.It is worth noting that the appropriate vortex-induced cavitation in the nozzle can correspond a higher flow rate with a thin string-type cavitation and simultaneously a better spray atomization quality with a strong vortex flow. Also it is concluded that a convergent-divergent nozzle with appropriate transition location can achieve strong atomization .

Primary spray breakup from a nasal spray atomizer using volume of fluid to discrete phase model

Spray atomization process involves complex multi-phase phenomena. Abundant literature and validation of spray modeling for industrial applications like fuel injection in internal combustion and turbine jet engines are available. However, only a handful of studies, primarily limited to discrete phase modeling, of low-pressure applications, such as nasal spray exists. This study aims to provide insight into the external and near-nozzle spray characterization of a continuous spray and establishes good validation against the experiment. A three-dimensional (3D) x-ray scanner was used to extract the internal nasal spray nozzle geometry which was reconstructed to build a 3D computational model. A novel volume-of-fluid to discrete phase transition model was used to track the liquid phase and its transition to droplets, which was based on the shape and size of the liquid lumps. In this study, an early pre-stable and stable phase of spray plume development was investigated. Qualitative and quantitative analyses were carried out to validate the computational model. A liquid column exited a nozzle which distorted at its base with advancement in time and eventually formed a hollow-cone liquid sheet. It then disintegrated due to instability that produced fluctuations to form ligaments resulting in secondary breakup. This study provides in-depth understanding of liquid jet disintegration and droplet formation, which adds value to future nasal spray device designs and techniques to facilitate more effective targeted nasal drug delivery.

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

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

Computational Investigations of Spray Atomization and Evaporation Under Cold-Start Conditions of a Diesel Engine

Abstract Unburnt hydrocarbon emissions and combustion instability are severe issues in diesel engines during cold starting. This simulation study aims to provide insights for improving the cold-start issues of diesel engines. Computational analysis of the diesel spray and evolution of plumes from a 7-hole injector was done in a constant volume quiescent spray chamber for analyzing the effect of fuel temperature. This study was based on a comprehensive numerical analysis using CONVERGE computational fluid dynamics (CFD) software, where an Eulerian–Lagrangian approach was adopted in a large eddy simulation (LES) framework. Diesel engine-like cold-start conditions were replicated by reducing the fuel temperatures to 250 K to simulate freezing conditions outside. This computational study compares fuel sprays at 250 K with 312 K into a relatively colder ambient temperature of 626 K vis-a-vis high-temperature diesel engine-like ambient conditions with ambient temperature to 961 K to investigate the degree of spray characteristics improvements due to increased fuel temperature. The predicted liquid spray penetration obtained by simulations agreed well with the experimental data for fuel temperatures injected into the ambient at cold (626 K) and hot (961 K) engine-like ambient conditions. The available empirical relations justify the simulation results of this study. Results showed that fuel and ambient temperatures significantly affected the spray atomization and evaporation characteristics. A higher reduction in liquid penetration length was found with increasing fuel temperature at hot ambient conditions. Increasing ambient temperature also improved the evaporation characteristics of the spray droplets. Vapor formation for the same increase in fuel temperature was higher at hot ambient temperature than the cold. Fuel temperature had a major role in the spray atomization process, whereas the ambient temperature affected the spray evaporation process. However, fuel and ambient temperatures had only a minor effect on the distribution of total kinetic energy (TKE). Among all test conditions, a fuel temperature of 312 K sprayed in hot ambient conditions showed superior fuel spray atomization and evaporation. Hence, to tackle the cold-start of diesel engines, measures taken to increase the fuel and ambient temperatures simultaneously proved to be useful.

Investigation on Primary Breakup of High-Pressure Diesel Spray Atomization by Method of Automatic Identifying Droplet Feature Based on Eulerian–Lagrangian Model

To investigate primary breakup close to an injector, this paper presents both experimental and numerical research on high-pressure common-rail diesel injection. We propose a new method named SD-ELSA model to realize automatically identifying droplet features for high-pressure diesel spray based on the classic ELSA (Eulerian Lagrangian Spray Atomization) model; this method is suitable for varied injection operation conditions. The SD-ELSA first identifies the liquid bulk due to breakup of the continuous phase in near field, and then converts the Eulerian liquid bulk into Lagrangian particles to complete the calculation of the total spray atomization. The SD-ELSA model adopts two key criteria, i.e., the sphericity (S) and the particle diameter (D); the qualified liquid mass is transformed into Lagrangian particle, realizing the coupling of the Eulerian–Lagrangian model. The SD-ELSA model illustrates the total diesel spray atomization process from the breakup liquid column to the droplets.

Research on High Pressure Fine Mist Cultivation Equipment

Most of the existing aerosol cultivation equipments are bulky, simple-structured and poor in functional stability. Based on this, the author developed a set of automatic control high-pressure fine mist cultivation device, designed the PLC automatic control circuit, and simulated and tested the temperature and humidity change curves. The test results verify the simulation model and the overall device runs well, among which the spray atomization process, and the temperature field, humidity field and velocity field under three atomization modes are simulated. Three atomization schemes are analyzed, and in the end the optimal one is selected. In comparison, the side-by-side spray is completely covered; the atomization is more sufficient. The results show that the time when the humidity reaches 90% in the same position is different under different initial humidity conditions. The atomization humidity maintenance time in different environments is approximately the same, and can be maintained for 4 to 5 hours. It can be seen from the comparison of the results that the greater the humidity, the shorter the heat exchange time and the faster the heat exchange.

Design and construction of an open loop subsonic high temperature wind tunnel for investigation of SCR dosing systems

The requirement of high-fidelity experimental data of microscopic properties as well as the whole spray development is fundamental since they are determinant in the understanding of atomization and evaporation process in a variety of multiphase flows. The Selective Catalytic Reduction (SCR) system is one of the industrial applications where understanding the whole spray atomization and development process is essential in developing new systems to cope with stringent emission regulations. A new subsonic heated open-loop wind tunnel has been designed and manufactured specifically with a 0.25 × 0.25 m cross-section and 1.59 m long optically accessible quartz glass side panels. The purpose of the wind tunnel was to investigate Selective Catalytic Reduction (SCR) sprays using Phase Doppler Anemometry (PDA). The wind tunnel is capable of reaching a flowrate equating to 50 m/s in the test section when operating at standard room conditions (25°C and 101,325 kPa). A 145 kW heater is mounted downstream the blower to achieve air temperatures of up to 400°C with maximum air mass flow of 1200 kg/h. The diffuser, flow conditioning and contraction cone sections of the wind tunnel have been designed to minimize velocity and temperature gradients within the test section while minimizing flow disturbances. A diffuser with a cone angle of 5° and an area ratio of 3.95 and a contraction cone with a contraction ratio of 4.05 was selected. The test section has been designed to give complete visible access through top and both sides, while the bottom is made of stainless steel. The two sides are made of quartz glass to provide the best signal transmission quality for usage with any optical equipment e.g. PDA. The top of the test section has sections made of Robax glass with detachable windows for easy mounting and dismounting of any equipment subject to be tested in the flow section. The streamwise turbulence intensity in the test section was found to be less than 2% in the core with similar values for the cross-stream turbulence intensities. The complete design and construction of each section of the wind tunnel has been presented and discussed in this paper.

Microstructural and Mechanical Characterization of Spark-Plasma-Sintered Compact of Al-4.5 wt.% Cu Alloy Powder

Al-4.5 wt.% Cu alloy powder was produced by inert gas spray atomization process. The size of the powder in the range of 10 to 500 µm produced by spray atomization process was analyzed using laser particle analyzer. The smaller powder particles of size less than 25 µm are of spherical shape, whereas larger-sized powders are elongated and irregular-shaped. The smaller powder particles exhibit cellular morphology and are of equiaxed grains. The longer and irregular-shaped powder reveals coarse grains, whereas elongated grains exhibit dendritic morphology. The powder of different sizes was compacted by spark plasma sintering by applying temperature and pressure simultaneously. The density of the compact was determined using water displacement method, and the average density of the compact was 2.65 g/cc. After compacting and sintering the powder, 95 percent relative density of the compact is achieved. The porosity present in the compact was captured by optical metallurgical microscope. The microstructural characterization of powder and sintered compact was carried out by using optical metallurgical microscope and scanning electron microscope. The micro-hardness of the compact was tested using micro-Vickers hardness testing machine, and the hardness was found to be varied from 67.1 to 69.6 HV. The yield strength, ultimate strength and ductility of the sintered compact were determined by conducting the compression test.

Modelling spray performance of alternative aviation fuel

Aviation alternative fuels are becoming the inevitable choice of aviation industry under the background of global environmental protection. Fuel droplets with small size and high velocity can lead to an efficient combustion and reduce pollutant emission. A numerical investigation of Fischer-tropsch (FT) alternative jet fuel injected from a pressure swirl atomizer is conducted by using Ansys Fluent where a 3-D geometry of the atomizer nozzle and the external spray domain are prepared in Solidwork. Phase Dopler Anemometry (PDA) measurements on Chinese jet fuel (RP-3) and FT fuel are conveyed to validate the spray characteristics collected numerically. Small droplets are generally located inside the spray core region and in the spray periphery but can also be found in the central region at high pressure. The droplets with the highest SMD are being formed in the outer spray region and both FT and RP-3 show a higher droplets velocity in the nozzle exit region. It has been observed that the SMD decreases with increase in injection pressure and that using the SSD model provide results in agreement with the experimental ones. It is also proved that computational simulation performed on alternative fuel by using an unsteady RANS in the Euler-Lagrangian frame can precisely predict the spray atomization process.

Emission and performance analysis of DI diesel engines fueled by biodiesel blends via CFD simulation of spray combustion and different spray breakup models: a numerical study

In the current study, computational fluid dynamics code was used to perform 3D simulation of mixture formation and combustion of biodiesel fuel spray in a direct injection diesel engine. Thus, the spray atomization and combustion processes were simulated by applying the improved version of KH–RT spray breakup model coupled with advanced ECFM-3Z model for combustion. To this aim, experimental results were used first to validate the calculated values of NOx, soot, heat release rate, and in-cylinder pressure and good agreement was obtained. To develop the engine performance and reduce the emission, various models of spray breakup of biodiesel fuel were simulated, and the optimum spray breakup model was specified. Also, the accuracy of each model was determined in comparison with the experimental results. The results show that the TAB breakup model has not provided acceptable results for spray characteristics compared to the other models. Since the simulation results of in-cylinder pressure and emissions were consistent with the experimental results by the KHRT model, it could be concluded that this model has correctly predicted the size of droplets produced by spray fragmentation and penetration, and it could be used to simulate the atomization of biodiesel fuel spray under different engine conditions by adjusting the model constants.

Processing of Cu–Al–Ni Alloy by Spray Atomization and Deposition Process

The present work describes a new route for the preparation of Cu–Al–Ni alloy strips via spray atomization and deposition route. The route consists of atomizing liquid Cu–Al–Ni alloy with a jet of argon gas in a closed chamber, at a pressure of 1 MPa. The semi-solid Cu–Al–Ni droplets are subsequently collected on the steel substrate placed vertically below the liquid metal stream in the atomization chamber to form a three-dimensional preform. The deposit produced on the substrate contains ~ 5% porosity. The microstructural details of the spray deposited Cu–Al–Ni strips explains particularly the presence of porosity, formation of splats during the flight of spray casting and the associated microstructural evolution in Cu–Al–Ni spray deposit are explained.

Experimental investigation on the macroscopic and microscopic spray characteristics of dieseline fuel

The application of dieseline fuel (blends of diesel and gasoline) into compression ignition engines has been intensively investigated in recent years due to its good combustion performance and low smoke emissions. In this study, the main objective was to investigate the spray characteristics of dieseline fuel. Macroscopic spray characteristics in terms of spray morphology and penetration were investigated in a constant volume vessel under elevated ambient pressures using high-speed imaging system, while the microscopic spray characteristics including droplet size and velocity distribution were measured at atmospheric condition using Phase Doppler Particle Analyzer (PDPA) system. The results have shown that the gasoline/diesel blending ratio played an important role in affecting the spray atomization process. With the increase of the gasoline/diesel blending ratio, spray penetration length, droplet mean velocity, and droplet Sauter Mean Diameter (SMD) decreased gradually, especially at low injection pressure and low ambient pressure conditions. Both the results of macroscopic and microscopic studies indicate a better atomization quality can be achieved by increasing the proportion of gasoline in the dieseline.

Numerical investigation on liquid sheets interaction characteristics of liquid-liquid coaxial swirling jets in bipropellant thruster

Spray atomization process of a liquid-liquid coaxial swirl injector in bipropellant thruster has been investigated using volume of fluid (VOF) method coupled with large eddy simulation methodology. With fine grid resolution, detailed flow field of interacted liquid sheet has been captured and analyzed. For coaxial swirling jet, static pressure drop in the region between the liquid sheets makes two liquid sheets to approach each other and merge. A strong pressure, velocity and turbulent fluctuations are calculated near the contact position of two coaxial jets. Simulation results indicate that additional perturbations are generated due to strong radial and axial shear effects between coaxial jets. Observation of droplet formation process reveals that the Rayleigh mode instability dominates the breakup of the ligament. Droplet diameter and distribution have been investigated quantitatively. The mean diameter of the coaxial jets is between that of the inner and the outer jets. Compared with the individual swirling jets, wider size distributions of droplets are produced in the coaxial jets.

Experimental investigation on spray and atomization characteristics of diesel/gasoline/ethanol blends in high pressure common rail injection system

The effects of gasoline and ethanol addition on the spray and atomization characteristics of diesel spray from a common rail injection system, was investigated in a constant volume chamber at different ambient and injection pressures. The fuel spray evolution process was recorded with high spatial and time resolution and the corresponding spray tip penetration (STP), the cone angle were extracted. The results show that increased gasoline proportion in the test blends causes decreased STP and increased spray cone angle. Additionally, the microscopic spray characteristics such as the local average droplet diameter and statistical size distributions were measured by particle/droplet image analysis (PDIA) technique. As gasoline blending ratio increases, significantly smaller droplet size was observed which indicates that the spray breakup and atomization processes were promoted. Further adding ethanol slightly increased the droplet size, but it is still much smaller than the droplet size of neat diesel spray. Moreover, the local droplet size increases along the radial direction but the local droplet volume fraction and normalized droplet number density decreases, indicating a reduced fuel concentration along the radial direction. Along the axial direction, the droplet size, the local droplet volume fraction and the normalized droplet number density were almost constant.

High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers

Recent advances in numerical methods coupled with the substantial enhancements in computing power and the advent of high performance computing have presented first principle, high fidelity simulation as a viable tool in the prediction and analysis of spray atomization processes. The credibility and potential impact of such simulations, however, has been hampered by the relative absence of detailed validation against experimental evidence. The numerical stability and accuracy challenges arising from the need to simulate the high liquid-gas density ratio across the sharp interfaces encountered in these flows are key reasons for this. In this work we challenge this status quo by presenting a numerical model able to deal with these challenges, employing it in simulations of liquid jet in crossflow atomization and performing extensive validation of its results against a carefully executed experiment with detailed measurements in the atomization region. We then proceed to the detailed analysis of the flow physics. The computational model employs the coupled level set and volume of fluid approach to directly capture the spatiotemporal evolution of the liquid-gas interface and the sharp-interface ghost fluid method to stably handle high liquid-air density ratio. Adaptive mesh refinement and Lagrangian droplet models are shown to be viable options for computational cost reduction. Moreover, high performance computing is leveraged to manage the computational cost. The experiment selected for validation eliminates the impact of inlet liquid and gas turbulence and focuses on the impact of the crossflow aerodynamic forces on the atomization physics. Validation is demonstrated by comparing column surface wavelengths, deformation, breakup locations, column trajectories and droplet sizes, velocities, and mass rates for a range of intermediate Weber numbers. Analysis of the physics is performed in terms of the instability and breakup characteristics and the features of downstream flow recirculation, and vortex shedding. Formation of “Λ” shape windward column waves is observed and explained by the combined upward and lateral surface motion. The existence of Rayleigh-Taylor instability as the primary mechanism for the windward column waves is verified for this case by comparing wavelengths from the simulations to those predicted by linear stability analyses. Physical arguments are employed to postulate that the type of instability manifested may be related to conditions such as the gas Weber number and the inlet turbulence level. The decreased column wavelength with increasing Weber number is found to cause enhanced surface stripping and early depletion of liquid core at higher Weber number. A peculiar “three-streak-two-membrane” liquid structure is identified at the lowest Weber number and explained as the consequence of the symmetric recirculation zones behind the jet column. It is found that the vortical flow downstream of the liquid column resembles a von Karman vortex street and that the coupling between the gas flow and droplet transport is weak for the conditions explored.

Numerical study of heat transfer and solidification behavior of gas-atomized Fe-6.5%Si (mass fraction) droplets

During spray atomization process, the heat transfer and solidification of droplets play very important roles for the deposition quality. Due to the difficulties of experimental approach, a numerical model is developed, which integrates liquid undercooling, nucleation recalescence and post-recalescence growth to present the full solidification process of Fe-6.5%Si (mass fraction) droplet. The droplet velocity, temperature, cooling rate as well as solid fraction profiles are simulated for droplets with different sizes to demonstrate the critical role of the size effect during the solidification process of droplets. The relationship between the simulated cooling rate and the experimentally obtained secondary dendrite arm spacing is in excellent agreement with the well-established formula. The pre-constant and exponent values lie in the range of various rapid solidified Fe-based alloys reported, which indicates the validity of the numerical model.

Experimental visualization and LES investigations on cloud cavitation shedding in a rectangular nozzle orifice

Shedding of cloud cavitation in a nozzle orifice is a common phenomenon of cavitation instability which has a great influence on erosion damage and spray atomization process, but it hasn't been studied in details and the mechanism remains unclear. In this paper, visualization experiments and Large Eddy Simulation (LES) were carried out to study the process of periodic cloud cavitation shedding and re-entrant jet happened in a 2mm-width nozzle with fuel of diesel. Numerical and experimental images provide a better insight into this physical mechanism. The results show that cavitation inception is formed at the edge of inlet and the recirculation zone which below the shear layer. Then the attached cavitation grows and shedding of cloud cavitation occurs due to the re-entrant jet located between cavity and wall. Moreover, the dynamic mechanism causing shedding of cloud cavitation is a combination of shedding vortex and pressure fluctuations. Cavitation shedding frequency can also be measured by experiment and numerical simulation. As a result, inception of cavitation, re-entrant jet and cavitation cloud shedding are accurately predicted by LES in accordance with the quantitative images observed in the experiment.

Multiscale descriptions of particle-droplet interactions in multiphase spray processing

Composite particles are solid particulates that consist of two mixed material phases so that a dispersed phase is homogeneously distributed in the host matrix phase of each particle. Metal-matrix-composite (MMC) particles may be produced through mixing of ceramic particles and metallic droplets in a spray atomization and co-injection process. In this paper, multi-scale descriptions of particle-droplet interactions in spray processing of MMC particles are realized based on multiscaled Multiphase Computational Fluid Dynamics (M-CFD) models. On the macro-scale, the mixing configuration of solid-particle laden jets and liquid droplet sprays is investigated based on an Euler–Lagrange–Lagrange (ELL) method. The particle-droplet mixing degree in this stage is mainly influenced by the atomization gas mass flow rate through affecting droplet break-up (thereby droplet inertia) and droplet solidification rate. On the meso-scale, the particle-droplet collision probability and process between a metallic droplet and solid particles along the droplet trajectory is derived according to kinetic theory of gases and simulations based on the Lagrangian tracking. The collection efficiency of solid particles by a liquid droplet in this stage is derived as a function of droplet size and atomization gas pressure. On the micro-scale, the critical kinetic conditions for a solid particle to penetrate into a liquid droplet is derived based on the particle-droplet collision regime map by taking into account the variation of the droplet consistence in a solidifying droplet. The simulation results indicate that a large quantity of ceramic particles can be incorporated into the metal matrix particles or captured by the MMC-particle surfaces by optimizing the process configuration and the process operation conditions. It is shown that gas atomization of a melt with co-injection of particulates is a viable approach to generate MMC particles.

A numerical investigation on combustion and emission characteristics of a dual fuel engine at part load condition

Dual fuel engines are more attractive due to lower emission levels in comparison with conventional diesel engines particularly at full loads. But it is required to study dual fuel combustion process with more details at part loads due to the poor performance and high CO and UHC emissions at these conditions. In the present study, numerical modeling of OM-355 dual fuel (injection of diesel pilot fuel to premixed mixture of air and methane) engine has been performed by using KIVA-3V code at part and full loads. Sub-models of the code were modified to simulate the fuel spray atomization, combustion and pollutants emissions processes, accurately. Results indicate that in-cylinder pressure, heat release rate and exhaust emissions predictions are in good agreement with experiments at all loads. Results show that a lean premixed natural gas mixture is ignited slowly. The slow progress of combustion process at part load, leads the heat release to be drawn more toward the expansion stroke which causes incomplete combustion, and consequently high amounts of UHC and CO will be emitted. It is found that at part loads, areas that are influenced by diesel diffusion flames are ignited and premixed natural gas flame could not be propagated properly. Hence development of diesel diffusion flame is required to burn lean natural gas mixture. But at full load, in addition to the diesel diffusion flames, premixed natural gas flame could be propagated suitably. Also, at part load because of low gas temperature in the environment of diesel spray and low diesel fuel temperature, diesel liquid droplets evaporate lately which are far from injector nozzles. Hence, it causes diesel diffusion flame from spray of each injector nozzles to be developed distinctly. It can be deduced that the flame structure is affected by operating conditions. Finally the effect of increasing the diesel fuel quantity on improving methane combustion is studied. The studied strategy could help to improving natural gas combustion due to enlarge the size of diesel combustion region.

Visualization research on spray atomization, evaporation and combustion processes of ethanol–diesel blend under LTC conditions

Utilization of ethanol in diesel engines has been widely studied by means of engine experiments and emission detection. However, pertinent studies on the spray combustion process of ethanol–diesel blends are scarce. In order to verify the effect of ethanol in modern diesel engines, an experiment is conducted to visualize the spray combustion process of ethanol–diesel blend under LTC conditions. Stages including atomization, evaporation and combustion, are investigated individually to realize synergistic analysis. Meanwhile, considering the long time scale of combustion after fuel injection finishes, characteristics during and after injection period are both targeted in this paper. Moreover, measurement of macroscopic characteristics, such as spray tip penetration, spray spreading cone angle and flame lift off length, provides a quantitative profile of the spray structure. Results show that, evaporation, different from atomization, has little influence on spray penetration, but promotes the spray spreading angle and spray projected area. So does combustion, which enlarges the spray projected area further. Ignition takes place on the periphery behind the spray tip, then quickly extends to the whole head of the spray and forms a U-shape diffusion structure. After the injection period, the residual spray tail develops into wavelike structures due to absence of subsequent entrainment force. Also, the penetration speed falls greatly to an extent much slower than flame propagation, which frees the flame from the lift-off effect. Subsequently, the flame propagates upstream towards the nozzle orifice. After consumed all fuel in the spray tail, flame retreats downstream to the far end and combusts for a time much longer than the injection duration.