Microscopic Spray Characteristics Research Articles

Microscopic spray characteristics of diethyl ether–diesel blends under single and split injection strategies

The phase doppler interferometry technique was used to thoroughly investigate microscopic spray characteristics of single and split injection strategies. The diethyl ether blending with diesel resulted in smaller and uniform droplet formation. Diethyl ether–diesel blend spray exhibited a lower droplet axial velocity distribution than baseline diesel, which can be improved by split injection strategies. At atmospheric pressure, the maximum axial velocity for diesel and diethyl ether–diesel blends was almost identical under single and split injection strategies. However, split injection improved the spray droplet's axial velocity at higher ambient pressures compared to single injection. The chances of coalescence and having coarse droplets were higher at elevated ambient pressure, especially for lower fuel injection pressures. Therefore, increasing the fuel injection pressure is more suitable to avoid droplet coalescence. Unlike the split ratio, dwell time strongly influenced fuel spray atomization. The droplet diameter distribution exhibited a higher probability of finer droplets for a longer dwell time of 0.45 ms than a shorter dwell time of 0.15 ms. A major finding of this study is that diethyl ether–diesel blend spray with a longer dwell time exhibited superior spray characteristics.

Experimental investigation on the impact of air flow rates and back pressures on kerosene microscopic spray characteristics discharged from an air-assisted pressure-swirl atomizer

The air-assisted pressure swirl atomizer has attracted considerable interest owing to its exceptional capacity to generate fine droplets and precisely regulate spray characteristics. The primary objective of the study was to investigate the impact of auxiliary air flow rate, orifice diameter, and ambient back pressure on the kerosene spray cone angle, droplet size and distribution. The results indicate that employing a nozzle with a smaller orifice size leads to a larger spray cone angle. The spray cone angles of the other two orifice sizes exhibit an increasing trend as the auxiliary air flow rate increases. Also, increasing the auxiliary air flow rate effectively reduces the Sauter Mean Diameter (SMD). Additionally, as the auxiliary air flow rate gradually increases, the peak of the particle size distribution shifts towards smaller diameters. Furthermore, as the environmental back pressure increases, there is a noticeable decrease in the SMD. With an increase in ambient backpressure, there is a consistent shift of the peak particle size towards smaller diameters. At an elevated ambient pressure of 1.4 MPa, an increase in the axial distance from the nozzle results in a decrease in the volume percentage of the peak diameter, while simultaneously causing the particle size distribution range to broaden.

A mixed primary atomization model with quantification of aerodynamic, turbulence and cavitation effects

Spray atomization has a key impact on the combustion and emission performances of the engines. It involves a highly dynamic two-phase flow process consisting of two distinct stages: primary and secondary breakup. Due to their distinct physical characteristics, it is essential to model these processes separately using different numerical approaches within the spray breakup model. This study focuses on investigating the collective influence of aerodynamic force, cavitation, and turbulent fluctuations on primary breakup. To enhance the accuracy of spray simulations, a mixed primary atomization (MPA) model is proposed by integrating the Wu-Faeth theory along with the classical KH-RT model and the Sarre cavitation model. By comparing simulation results of both macroscopic and microscopic spray characteristics with experimental data under various conditions, the efficacy of the developed MPA model is validated. The sensitivity analyses of specific model parameters and the examination of the contribution ratios of different sub-models under various conditions enhance our understanding of the model calibration. Additionally, considering the complexity of near-nozzle sprays influenced by turbulent flows, cavitation, and interactions with the surrounding gas, a comparative analysis of the classical KH-RT model and the MPA model is conducted based on simulation results, specifically focusing on near-nozzle spray characteristics.

Effects of step hole geometry and spray-wall interactions on spray atomization in LPDI injector

The study aims to analyze the spray atomization of liquefied petroleum gas direct injection (LPDI) injector based on the macroscopic and microscopic experiments. Two experimental injectors were used in the presence and absence of step hole, and the experimental fuels used n-heptane and n-butane.The macroscopic and microscopic spray characteristics as function of the application of step hole were analyzed using two experimental injectors and n-heptane fuel. The macroscopic spray experiments analyzed the initial spray, after the end of injection and nozzle tip wetting using near-field visualization, and microscopic spray experiment analyzed fuel–air atomization phenomenon as function of the application of step hole using PDPA equipment.In addition, macroscopic and microscopic spray characteristics were analyzed for two experimental fuels and spray-wall impingement using the presence of step hole injector. The macroscopic spray experiment analyzed the spray evaporation characteristics for the two experimental fuels and spray-wall impingement using the schlieren visualization, and microscopic spray experiment analyzed the fuel–air atomization phenomenon as function of the two experimental fuels and spray-wall impingement using PDPA equipment.It was found that the presence of step hole injector showed better atomization results than those of the absence of step hole injector. But, the tip wetting of the presence of step hole injector was poor than that of the absence of step hole injector. Furthermore, based on the schlieren experiment, a comparison of free and flat sprays with the two fuels found that the spray width and area of n-heptane in free spray exceeded those of n-butane owing to the vapor pressure of n-butane. However, in the flat spray, the spray width and area of n-butane were exceeded those of n-heptane. It was found that the atomization was promoted after the spray-wall impingement.

Macroscopic and Microscopic Spray Characteristics of Dimethyl Ether in a Constant Volume Spray Chamber Using a Mechanical Fuel Injection System for Automotive Applications

Abstract Spray investigations are critical for understanding internal combustion engine combustion. Optimised spray atomisation helps improve engine output/performance and reduce tailpipe emissions. The spray from the injector nozzle depends on nozzle hole diameter, fuel injection pressure, ambient density, pressure and temperature in the spray chamber, and test fuel properties. This study evaluated macroscopic and microscopic spray characteristics of dimethyl ether (DME) and baseline diesel under atmospheric conditions (1.013 bar pressure at 298 K temperature). It correlated the spray parameters with distinctive physicochemical properties of diesel and DME using dimensionless numbers, namely Reynolds number, Weber number, and Ohnesorge number. The fuel injection system consisted of a high-pressure mechanical injection pump and mechanical fuel injectors having an original equipment manufacturer fixed nozzle opening pressure in the constant volume spray chamber. The microscopic spray investigations were performed using a phase Doppler interferometer along the spray direction at three axial distances (50, 70, and 90 mm) from the nozzle. The three orthogonal spray droplet velocities of diesel and DME were compared. The droplet number-size distributions for baseline diesel and DME were compared. Macroscopic spray characteristics were evaluated using high-speed imaging. Reynolds number was higher for DME, leading to more turbulence in the spray and accelerating the spray breakup phenomenon. Weber number of DME was also much higher than baseline diesel due to its lower surface tension. The higher Weber and lower Ohnesorge numbers justified the finer droplets of DME sprays. DME showed superior spray atomization characteristics than baseline diesel, leading to superior fuel–air mixing and efficient and sootless combustion.

Effects of varying the liquid fuel type and air co-flow conditions on the microscopic spray characteristics in an atmospheric annular co-flow spray burner

The atomization process is critical for combustion systems since it directly influences emissions and performance. Thus injection system should provide the spray required structure and characteristics, e.g., angle and droplet size distribution. Therefore, this work investigates the effects of varying the fuel type, air co-flow rates, fuel mass flow rate and air co-flow temperature on the spray characteristics (e.g., droplet size distribution and droplet velocity) in an annular co-flow spray burner. These effects were investigated by measuring droplet sizes and velocities at different radial and axial positions of n-Heptane, n-Decane and n-Dodecane sprays under non-reacting conditions at a room pressure of 1 atm and temperature of 298K and using the Microscopic Diffused Back-illumination (MDBI) technique. In addition, the Sauter mean diameter (SMD) for different flow conditions were predicted using three well-known correlations and compared to experimental measurements. The outcomes of this research provided a fair understanding of the influence of varying these parameters on the droplet sizes and velocity through a wide test matrix. Finally, the findings reported here will support future research into the function of phase change in flame stability.

Experimental study on spray characteristics of fan nozzle for integrated afterburner in lateral airflow

The spatial distribution of fuel and high atomization quality plays a vital role in combustion performance enhancement for integrated afterburners. This study is based on integrated strut stabilizers using aviation kerosene (RP-3) as the atomizing medium. Specifically, the spray distribution characteristics of the fan nozzle were studied at ambient temperature and pressure, lateral airflow velocities within the range of 5–30 m/s, and a fuel supply pressure difference between 0.2 and 1.2 MPa. Macroscopic and microscopic spray characteristics were studied by high-speed photography method, Spraymaster, and ParticleMaster system respectively. The results show that mean droplet diameters decreased with an increasing lateral airflow velocity and a decreasing fuel supply pressure difference. The recirculation zone at the back of the struts will have an entrainment effect on the downstream of the spray, making part of the spray bend toward the recirculation zone. The results of the spray organization of a fan nozzle in this study can be used to support the design of new integrated afterburners.

Optimising microscopic spray characteristics and particle emissions in a dual-injection spark ignition (SI) engine by changing GDI injection pressure

Regarding reducing particle emissions from dual-injection spark ignition engines, most of the existing research focused on the benefits of using alcohol fuels. However, a comprehensive study of the effects of fuel injection pressure on microscopic spray characteristics and particle emissions in dual-injection spark ignition engines fuelled with gasoline has not been reported before. In this paper, with the assistance of phase Doppler particles analyser system and fast particle analyser, a study of optimising microscopic spray characteristics and particle emissions in a dual-injection spark ignition engine fuelled with gasoline by changing GDI injection pressure was conducted. The results show that by increasing injection pressure from 5.5 to 18 MPa, both normal and tangential components of droplet velocity increase, but the possibility of spray impingement would not increase a lot. Higher injection pressure would increase the probability of small droplets, and more droplets would collapse with a mode of continuous ripping or break down abruptly. From jet’s central axis to sides, Sauter mean diameter increases first, then reduces outside the spray boundary. Increasing injection pressure from 5.5 to 18 MPa reduces total particle number concentration, which is 53.98% and 45.44% at 2 bar and 10 bar, respectively. Meanwhile, the peak of particle number distribution curve decreases from 3.01 × 106 to 1.43 × 106 at 2 bar, whilst reducing from 1.08 × 106 to 5.33 × 105 at 10 bar. Overall, this paper comprehensively analyses the effects of fuel injection pressure on microscopic spray characteristics and particle emissions, whilst offering a practical approach to reduce particle emissions in dual-injection SI engines fuelled with gasoline.

Effects of Varying the Liquid Fuel Type and Air Co-Flow Conditions on the Microscopic Spray Characteristics in an Atmospheric Annular Co-Flow Spray Burner

Effects of Varying the Liquid Fuel Type and Air Co-Flow Conditions on the Microscopic Spray Characteristics in an Atmospheric Annular Co-Flow Spray Burner

Evaluation of stabilizing and destabilizing effects on macroscopic and microscopic spray characteristics using dimensionless analysis

Enhanced atomization performance is vital for gasoline direct injection (GDI) engines to meet stringent legislative requirements. Droplets are subjected to breakup by competition of the stabilizing and disturbing effects. The dimensionless analysis was adopted in the present paper to account for the competition mechanism of liquid jet stability, aerodynamic and internal flow effects. Diffused Back Illumination (DBI) imaging and Phase Doppler Anemometry (PDA) were performed to capture macroscopic and microscopic characteristics issued from a counterbore-type injector suggested by Engine Combustion Network (ECN). Seven different fuels were tested at low-temperature conditions, and distinct spray characteristics dominated by breakup regime were observed, showing high sensitivity to fuel properties. The aerodynamic effects on normalized penetration were varied with the breakup regime, and the stabilizing effect diminished with the increment of fuel temperature. The dominant force of breakup varied with the ambient pressure, resulting in non-monotonous variations of spray angle with the increase in ambient pressure. Dimensionless correlations for spray dispersion under various temperature–pressure conditions were yielded, serving as a supplement for better utilization of the injection strategy to achieve emission standards.

Experimental Research on the Macroscopic and Microscopic Spray Characteristics of Diesel-PODE3-4 Blends

Polyoxymethylene dimethyl ether (PODE) is a low-viscosity oxygenated fuel that can improve the volatility of blended fuels. In this work, the macroscopic and microscopic spray characteristics of diesel-PODE3-4 under different ambient temperatures and injection pressures (IP) are studied. The studied blends consisted of pure diesel (P0), two diesel blend fuels of 20% (P20) and 50% (P50) by volume fraction of PODE3-4. The Mie scattering and Schlieren imaging techniques are used in the experiment. The results show that with the increase in IP, the vapor phase penetration distance and the average cone angle of the three fuels increased, and the Sauter mean diameter (SMD) of the three fuels decreased. When the ambient temperature increased, the vapor phase projection area and the average vapor phase cone angle of P20 and P50 increased, and the SMD decreased, but the vapor phase projection area of pure diesel did not change significantly. The results indicate that the blended fuel with PODE3-4 has better spray characteristics than P0 at low temperature, and the SMD hierarchy between the three fuels is P0 > P20 > P50. Through the visualization experiment, it is helpful to further understand the evaporation characteristics of different fuel properties and develop appropriate alternative diesel fuel.

Experimental investigation of spray characteristics of gliding arc plasma airblast fuel injector

High atomization quality plays a vital role in combustion performance enhancement for aero-engines and ramjets. Low enthalpy and low pressure at low flight Mach number result in poor atomization quality of airblast fuel injector. Underlying mechanism of how plasma assisted combustion on spray characteristics still remains unclear. In present study, a novel gliding arc plasma airblast fuel injector is proposed for atomization quality improvement of airblast fuel injector in order to achieve high combustion efficiency, low pollutant emission, and to prolong life of injectors. Spray and atomization characteristics of aviation kerosene (RP-3) under different working conditions which includes gliding arc plasma excitation, air flow velocity and air/fuel ratio were investigated. A string-like gliding arc discharge plasma column was generated between the two electrodes mounted at the exit port plane of plasma airblast fuel injector. Macroscopic and microscopic spray characteristics were studied by simultaneous LIF/MIE technique and particle/droplet image analysis (PDIA) system. Results reveal that mean droplet size were decreased with increase of air flow velocity and air/fuel ratio. Influenced by the thermal and transport effect of gliding arc plasma excitation, more homogeneous fuel spray with smaller mean drop size and greater spray cone angle was witnessed. Sauter mean diameter was decreased by around 50% at 17 m/s, while droplet uniformity index and spray cone angle were increased by up to 24.6% and 35%, respectively. The gliding arc plasma mainly take effect on reducing mean droplet size of kerosene in the near-field spray (<20 mm) which is very near from the ignitor to improve high initial evaporation rates for rapid ignition and combustion efficiency improvement.

Microscopic spray characteristics of ethanol and methanol blended gasoline in a direct injection spark ignition engine

Renewable fuels are continuously being refined/ upgraded for automotive applications to reduce dependence on conventional fossil fuels. However, optimized use of these renewable fuels in existing and new engines/ vehicles requires comprehensive characterization and understanding of spray atomization and fuel-air mixture formation processes. Spray atomization and mixture formation depends on fuel injection pressure (FIP), fuel injection quantity and ambient conditions. This study is aimed at exploring microscopic spray characteristics of ethanol and methanol blended gasoline for automotive applications, particularly in direct injection Spark Ignition (DISI) engines. Phase Doppler interferometer (PDI) technique was used for comparative microscopic spray characterization in a constant volume spray chamber (CVSC) at ambient pressure condition, to evaluated spray droplet size-velocity distributions and joint probability density function (JPDF) of different test fuels. In this study, two gasohol mixtures [15% v/v ethanol and methanol blended with 85% v/v gasoline] and baseline gasoline were experimentally evaluated for comparing spray droplet size-velocity distributions at two different FIPs of 80 and 160 bars, at two different fuel injection quantities of 12 and 28 mg/injection, which are typical representative conditions for a DISI engines. The results from this experimental investigation are valuable for automotive and fuel industries, and spray community, which are continuously upgrading renewable and oxygenated fuels and engine technologies for efficiency improvement and emission reduction.

Microscopic Spray Characteristics of Biodiesels Derived From Karanja, Jatropha, and Waste Cooking Oils

Abstract This study aims to assess the microscopic characteristics of Jatropha, Karanja, and Waste cooking oil-based biodiesels vis-a-vis conventional diesel under different ambient conditions in order to understand the in-cylinder processes, while using biodiesels produced from different feedstocks in the compression ignition engines. All test-fuels were injected in ambient atmosphere using a common-rail direct injection (CRDI) fuel injection system at a fuel injection pressure (FIP) of 40 MPa. Microscopic spray characteristics were measured using phase Doppler interferometer (PDI) in the axial direction of the spray at a distance of 60–90 mm downstream of the nozzle and at 0 to 3-mm distance from the central axis in the radial direction. All biodiesels exhibited relatively larger Sauter mean diameter (SMD) of the spray droplets and higher droplet velocities compared to baseline mineral diesel, possibly due to relatively higher fuel viscosity and surface tension of biodiesels. It was also observed that SMD of the spray droplets decreased with increasing distance in the radial and axial directions and the same trend was observed for all test-fuels.

Assessing fuel properties effects of 2,5-dimethylfuran on microscopic and macroscopic characteristics of oxygenated fuel/diesel blends spray

2,5-Dimethylfuran (DMF) is a type of attractive sustainable green energy for diesel engines that is designed to reduce soot emission. This study investigated the effect of fuel properties on the macroscopic and microscopic spray characteristics of four test blends under injection pressures of 90, 120 and 150 MPa and ambient pressure of 5 MPa in a common diesel rail injection system. The macroscopic results indicate that with higher density, lower viscosity and lower latent heating of DMF20, the spray tip penetration and spray area are increased and the average spray angle is slightly increased. Interestingly, the effect of latent heating on the average spray angle is more obvious than that of kinematic viscosity. The microscopic results suggest that higher density, lower viscosity and lower latent heating of DMF20 have an adverse effect on the breakup of small droplets. The results of comparative analysis show that the change rules of the spray parameters remain nearly unchanged with increased injection pressure, and the influence of DMF20 properties produces a different change in different spray parameters with increasing injection pressure. The meaningful conclusion is that the properties of DMF are favourable to improvement of the spray and atomization parameters under high injection pressure.

Application of electrostatic force for the atomization improvement of urea-water sprays in diesel SCR systems

Urea-based selective-catalytic-reduction (SCR) system is one of the techniques applied to reduce NOx emission in diesel engines. Due to the application of low injection pressure to prevent the wall-wetting of the urea-water solution to the exhaust pipe, the spray atomization, which is important to increase the NOx conversion efficiency, is still unsatisfactory. In this study, we pay attention to the electrostatic force as a source to improve the spray atomization of the urea-water solution. An electric voltage up to 7 kV was charged to a single-hole nozzle injector and various injection pressures up to 7 MPa were applied to investigate how the effect of electric charge on spray atomization appears differently in different flow regimes. High-speed visualization was conducted to observe the macroscopic spray structure. The microscopic spray characteristics were analyzed by a laser diffraction technique. The results showed that the electrostatic force effect, which results in finer droplet size and wider spray coverage area, is obtained especially at higher applied voltage in two different manners depending on the injection pressure, i.e. electrostatic induced jet breakup as a dominant effect at low injection pressures and electrostatic repulsion force-induced spray expansion as a dominant effect at high injection pressures.

Experimental and numerical analysis of the spray characteristics of biodiesel–ethanol fuel blends

The effects of adding ethanol on the macroscopic and microscopic spray characteristics of biodiesel were investigated by experimental and numerical methods. The spray tip penetration (STP) was recorded with a high-speed camera system, while the statistical size distribution of atomized droplets and the Sauter mean diameter (SMD) were obtained using a Malvern laser particle size analyzer. The spray calculation models were established with Fluent software, and the calculation results were validated by the experimental results. Then the numerical simulation of the spray characteristics for diesel, biodiesel, and biodiesel–ethanol fuel blends were conducted. The results showed that the farther the distance is from the nozzle exit, the lower the concentration and the velocity of atomized droplets. The concentration and the velocity of atomized droplets gradually decrease along the radial direction, extending from the center to the periphery. The turbulent kinetic energy (TKE) at the front and rear of the spray is relatively lower, while the TKE is higher in the middle of the spray, and turbulent vortices appear on both sides of the axial spray center. In addition, the spray characteristics of the different fuels revealed that compared to diesel, the STP and SMD of biodiesel increase by 33.59% and 33.08% on average, respectively. The maximum concentration of biodiesel is higher than that of diesel, and the concentration distribution is more concentrated. The droplet velocity and TKE of biodiesel respectively decrease by 7.38% and 14.49% in comparison to diesel. When ethanol was added to biodiesel by a volume percentage of 30%, the STP and SMD of biodiesel–ethanol fuel blends reduce by 22.05% and 20.88%, respectively. The concentration distribution, the velocity distribution, and the TKE distribution of the fuel blends are similar to that of diesel. This indicates that adding 30% ethanol to biodiesel can effectively improve its spray quality.

Effect of the injection pressure and orifice diameter on the spray characteristics of biodiesel

The purpose of this study was to analyze the influence of the injection pressure and orifice diameter on the spray characteristics of soybean biodiesel. The macroscopic spray characteristics of the spray tip penetration (STP) and spray cone angle (SCA) were tested with a high-speed camera system. The microscopic spray characteristics, such as the statistical size distribution, Sauter mean diameter (SMD), representative diameters and dispersion boundary, were obtained using a Malvern laser particle size analyzer (PSA). The test results showed that with an increasing injection pressure, the STP and the SCA of the biodiesel increased, but the curves of size-volume distribution and cumulative volume distribution of the atomized droplets shifted to smaller diameters. The SMD and representative diameters decreased, and the dispersion boundary was reduced. Moreover, with a decreasing orifice diameter, longer STP and smaller SCA values were observed. Similarly, the size distribution curves of the atomized biodiesel droplets shifted to smaller diameters. The SMD and representative diameters were reduced, and the relative size range of the atomized biodiesel droplets was enlarged. Higher injection pressures and smaller orifice diameters improved the biodiesel atomization; however, the smaller orifice diameters caused an inhomogeneous size distribution of the atomized biodiesel droplets.

Macroscopic and Microscopic Spray Characteristics of Diesel and Gasoline in a Constant Volume Chamber

The aim of this study is to investigate the spray characteristics of diesel and gasoline under various ambient conditions. Ambient conditions were simulated, ranging from atmospheric conditions to high pressure and temperature conditions such as those inside a combustion chamber of an internal combustion engine. Spray tip penetration and spray cross-sectional area were calculated in liquid and vapor spray development. In addition, initial spray development and end of injection near nozzle were visualized microscopically, to study spray atomization characteristics. Three injection pressures of 50 MPa, 100 MPa, and 150 MPa were tested. The ambient temperature was varied from 300 K to 950 K, and the ambient density was maintained between 1 kg/m3 and 20 kg/m3. Gasoline and diesel exhibited similar liquid penetration and spray cross-sectional area at every ambient density condition under non-evaporation. As the ambient temperature increased, liquid penetration length and spray area of both fuels’ spray were shortened and decreased by fuel evaporation near the spray boundary. However, the two fuels were characterized by different slopes in the decrement trend of spray area as the ambient temperature increased. The decrement slope trend coincided considerably with the distillation curve characteristics of the two fuels. Vapor spray boundary of gasoline and diesel was particularly similar, despite the different amount of fuel evaporation. It was assumed that the outer spray boundary of gasoline and diesel is always similar when using the same injector and injection conditions. In microscopic spray visualization, gasoline spray displayed a more unstable and asymmetric spray shape, with more dispersed and distributed fuel ligaments during initial spray development. Large amounts of fuel vapor cloud were observed near the nozzle at the end of the injection process with gasoline. Some amounts of this vapor cloud were attributed to the evaporation of residual fuel in the nozzle sac.

Comparison of Near-Nozzle Spray Performance of Gas-to-Liquid and Jet A-1 Fuels Using Shadowgraph and Phase Doppler Anemometry

The gas-to-liquid (GTL) fuel, a liquid fuel synthesized from natural gas through Fischer–Tropsch process, exhibits better combustion and, in turn, lower emission characteristics than the conventional jet fuels. However, the GTL fuel has different fuel properties than those of regular jet fuels, which could potentially affect its atomization and combustion aspects. The objective of the present work is to investigate the near-nozzle atomization characteristics of GTL fuel and compare them with those of the conventional Jet A-1 fuel. The spray experiments are conducted at different nozzle operating conditions under standard ambient conditions. The near-nozzle macroscopic spray characteristics are determined from the shadowgraph images. Near the nozzle exit, a thorough statistical analysis shows that the liquid sheet dynamics of GTL fuel is different from that of Jet A-1 fuel. However, further downstream, the microscopic spray characteristics of GTL fuel are comparable to those of the Jet A-1 fuel.