Atomization characteristics of intermittent multi-hole diesel spray using time-resolved PDPA data

The intermittent spray characteristics of a multi-hole diesel nozzle with a 2-spring nozzle holder were investigated experimentally. Without changing the total orifice exit area, the hole number of the multi-hole nozzle varied from 3 (d_n=0.42 mm) to 5 (d_n=0.32mm). The time-resolved droplet diameters of the spray including the SMD (Sauter mean diameter) and the AMD (arithmetic mean diameter), injected intermittently from the multi-hole nozzles into still ambient air, were measured by using a 2-D PDPA (phase Doppler particle analyzer). The 5-hole nozzle spray shows the smaller spray cone angle, the decreased SMD distributions and the small difference between the SMD and the AMD, compared with that of the 3-hole nozzle spray. From the SMD distributions with the radial distance, the spray structure can be classified into the three regions : (a) the inner region showing the high SMD distribution; (b) the mixing flow region where the shear flow structure would be constructed; and (c) the outer region formed through the disintegration processes of the spray inner region and composed of fine droplets. Through the SMD distributions along the spray centerline, it reveals that the SMD decreases rapidly after showing the maximum value in the vicinity of the nozzle tip. The SMD remains the constant value near the Z/d_n=166 and 156.3 for the 3-hole and 5-hole nozzles, which illustrate that the disintegration processes of the 5-hole nozzle spray proceed more rapidly than that of the 3-hole nozzle spray.     

Turbulent mixing flow characteristics of solid-cone type diesel spray

The intermittent spray characteristics of the single-hole diesel nozzle (d_n=0.32 mm) used in the fuel injection system of heavy-duty diesel engines were experimentally investigated. The mean velocity and turbulent characteristics of the diesel spray injected intermittently into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). The gradient of spray half-width linearly increased with time from the start of injection, and it approximated to 0.04 at the end of the injection. The axial mean velocity of the fuel spray measured along the radial direction was similar to that of the free air jet within R/b=1.0-1.5 regardless of elapsing time, and its non-dimensional distribution corresponds to the theoretical velocity distributions suggested by Hinze in the downstream of the spray flow fields. The turbulent intensity of the axial velocity components measured along the radial direction represented the 20-30% of the Ū_cl and tended to decrease in the outer region. The turbulent intensity in the trailing edge was higher than that in the leading edge.     

Atomization characteristics in pneumatic counterfiowing internal mixing nozzle

In an effort to illustrate the global variation of SMD (Sauter mean diameter, orD ₃₂) and AMD (Arithmetic mean diameter, orD ₁₀) at five axial downstream locations (i. e., at Z=30, 50, 80, 120, and 170 mm) under the different experimental conditions, the radial coordinate is normalized by the spray half-width. Experimental data to analyze the atomization characteristics concerning with an internal mixing type have been obtained using a PDPA (Phase Doppler Particle Analyzer). The air injection pressure was varied from 40 kPa to 120 kPa. In this study, counterfiowing internal mixing nozzles manufactured at an angle of l5^o with axi-symmetric tangential-drilled four holes have been considered. By comparing the results, it is clearly possible to discern the effects of increasing air pressure, suggesting that the disintegration process is enhanced and finer spray droplets can be obtained under higher air assist. The variations inD ₃₂ are attributed to the characteristic feature of internal mixing nozzle in which the droplets are preferentially ejected downward with strong axial momentum, and dispersed with the larger droplets which are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup by higher shear stresses at farther axial locations. The poor atomization around the centre close to the nozzle exit is attributed to the fact that the relatively lower rates of spherical particles are detected and these drops are not subject to instantaneous breakup in spite of the strong axial momentum. However, substantial increases in SMD from the central part toward the edge of the spray as they go farther downstream are mainly due to the fact that the relative velocity of droplet is too low to cause any subsequent disintegration.     

阀芯结构对双流体喷雾粒子特性的影响

为了研究阀芯结构对双流体喷雾粒子特性的影响,提升喷雾效果,运用相位多普勒粒子分析仪（PDPA）对不同阀芯结构的双流体喷雾雾滴粒径、轴向速度以及雾滴数目进行了测试,并对测量结果进行了分析和讨论。结果表明：随着轴向距离的增大,雾滴索特平均直径(SMD)、算术平均直径(AMD)呈先增大后趋于平缓的趋势,轴向速度以及湍流脉动速度均呈减小趋势,雾滴数目呈先增大后减小的趋势;随着气液压力比的增大,SMD呈先增大后减小的趋势,而AMD、轴向速度以及雾滴数目均呈减小趋势;阀芯的喉口直径、出口直径的减小均有利于喷雾效果的提升,但同时导致速度稳定性变差;当喉口直径为1.5mm、出口直径为2.5mm时,与原始阀芯结构相比,雾滴数目和雾滴轴向速度分别增大了82.43%和22.31%,SMD和AMD分别减小了52.18%和21.47%,综合喷雾效果得到了大幅提升。     

旋芯喷嘴高效雾化特性测量研究

分析了旋芯喷嘴的雾化机理,运用三维相位多普勒粒子测速仪(3D-PDPA)设备测量了旋芯喷嘴喷出的细水雾雾滴速度及索太尔平均液滴直径(SMD)。试验结果表明,压力低于2 Mpa时,喷雾状况符合表面波破碎理论规律。压力高于2 Mpa时,喷雾在短距离内由旋芯强制呈空心锥形,最终变为引射方式下的实心锥形。随着喷雾压力升高,空心锥形形状保持的距离缩短。在空心喷雾阶段,随着喷射距离的增大,细水雾的轴向速度和径向速度在喷雾锥边缘处降幂下降。喷雾锥内部雾滴均系从边缘散溅所得,因此在各截面中心处,轴向速度服从普通射流规律,不存在稳定的径向扩散速度。雾滴SMD在各截面均远小于100 μm。     

Numerical research on influence of structural parameters of common-rail injector on injection rate of each nozzle hole

Performance of diesel engines are influenced by fuel spray distribution, fuel-air mixture formation and combustion, which are also influenced by hole-to-hole fuel injection rate from multi-hole injectors. In this study, a customized spray momentum flux experimental test rig was used to measure the transient injection rates from a two-layered 8-hole diesel injector. The results indicated that the fuel injection rate and the cycle fuel injection quantities of the lower-layered nozzle holes were 3–15% higher than the fuel injection rates and the cycle fuel injection quantities of the upper-layered nozzle holes. A three-dimensional (3D) computational fluid dynamics (CFD) model of the two-layered 8-hole diesel injection nozzle was developed and validated by analyzing the relative error between the numerical results obtained from the model and the experimental results measured with the test injector. The simulation results showed that the relative average deviation of hole-to-hole cycle injection quantities were less than ±1%, which is the result of 5% increment in the cross-sectional area of the upper-layered holes.     

Geometrical effects on spray characteristics of air-pressurized swirl flows

In an effort to obtain the significant features associated with the ALR and length/diameter ratio of the final discharge orifice in swirling flows, experimental observations using a 3-D PDPA system were carried out. Profiles of SMD distributions depending on l _o /d _o , correlation between SMD and turbulence intensities in terms of l _o /d _o and correlations between droplet size and turbulence components were quantitatively analyzed. As discussed in a previous literature, an axisymmetric swirl angle of 30° was selected for this investigation because of its strong turbulence levels in the flow-field and finer droplet disintegrations. Three ALRs of 0.093, 0.106, and 0.122 as well as the length/diameter ratio of 0.15, 0.45, and 0.60 were chosen as parameters. Due to the complex interactions in swirling flows under these variables, this experimental observation will be of fundamental importance to the understanding of geometrical effects on spray trajectory. From the observations, it is indicated that increasing the ALR causes the spray development to be more dependent on number density and volume flux. The results indicated that the SMD decreases discernibly with smaller l _o /d _o , substantiating the fact that turbulence intensities are inversely proportional to the SMD. But, l _o /d _o is quite proportional to the SMD.     

Hole number effect on internal and discharged flow characteristics of diesel injector during transient operation

Selecting the proper number of nozzle holes is a critical matter to achieving optimal combustion in diesel engines. In recent years, short transient injections with ultra-high injection pressure have been adopted in diesel engines to achieve cleaner combustion but the effect of hole number on this transient diesel injection has not been thoroughly investigated. The current study performs an experimental observation of discharged flows from diesel injectors during transient operation using the X-ray phase-contrast imaging technique for six multi-hole injectors (three-, five-, six-, eight-, nine- and ten-hole). The observation results showed that discharged flows varied without any distinctive trends among the injectors. The largest spray dispersion angle and fastest velocity deceleration were observed in the 3-hole injector which showed an almost 3 times larger dispersion angle and 10% faster deceleration than the 10-hole injector. To understand possible factors governing such flow characteristics, three-dimensional internal flow simulations were conducted for the injectors. Unlike the results trend of discharged flows, the pressure and vorticity magnitude in the nozzle sac showed a linear change by altering the hole number. However, the hole-to-hole interaction of vortex flows varied in a complex way depending on the nozzle hole number. The nozzles with small and odd hole numbers, in general, showed a stronger hole-to-hole vortex interaction that can be the primary factor governing the discharged flow characteristics during the transient operation.     

Effect of nozzle geometry for swirl type twin-fluid water mist nozzle on the spray characteristic

Experimental investigations on the atomization characteristics of twin-fluid water mist nozzle were conducted using particle image velocimetry (PIV) system and particle motion analysis system (PMAS). The twin-fluid water mist nozzles with swirlers designed two types of swirl angles such as 0°, 90° and three different size nozzle hole diameters such as 0.5mm, 1mm, 1.5mm were employed. The experiments were carried out by the injection pressure of water and air divided into 1bar, 2bar respectively. The droplet size of the spray was measured using PMAS. The velocity and turbulence intensity were measured using PIV. The velocity, turbulence intensity and SMD distributions of the sprays were measured along the centerline and radial direction. As the experimental results, swirl angle controlled to droplet sizes. It was found that SMD distribution decreases with the increase of swirl angle. The developed twin-fluid water mist nozzle was satisfied to the criteria of NFPA 750, Class 1. It was proven that the developed nozzle under low pressures could be applied to fire protection system.     

Effects of ALR and configuration ratio on turbulent structures in swirling flows

To assess the significant physics associated with the increase of ALR and configuration ratio of the nozzle tip in pneumatic swirling flows, comprehensive observations using a 3-D PDPA system were experimentally carried out. Profiles of mean velocities, turbulence intensities, SMD variations, and correlations between droplet size and turbulence components were quantitatively acquired. As discussed in a previous literature, axisymmetric swirl angle of 30° is selected for this investigation because of its strong turbulence levels in the flowfield and finer droplet disintegrations. Various ALRs (Air-to-Liquid Mass Ratio) as well as the length-to-diameter ratios of nozzle tip as parameters were chosen. Due to the complex interactions in swirling flows under these variables, this experimental observation will be of fundamental importance to the understanding of turbulence structures. From the observations, it indicated that increasing the ALR causes the spray development to be positively fluctuated on the atomization in both axial and tangential RMS velocities. Also, it can be concluded that the SMD decreases continuously with increase of ALR, substantiating the fact that the fluctuations are inversely proportional to the SMD variation. Meanwhile, the spray behavior is characteristic with a reduction of length-to-diameter ratio; smaller the configuration ratio, the higher the turbulence intensities and smaller SMD variations in the flowfield.     

Measurement and analysis of injection characteristics among each nozzle hole within a heavy-duty diesel engine

The mass flow rate from each injector nozzle hole of a diesel engine influences the distribution, atomization, and combustion of fuel in the chamber. Thus affecting the power, the fuel economy, and the emission quality of the diesel engine. A spray momentum flux test bench was built and used to measure the injection rate from each nozzle hole of a multi-hole nozzle in this study. Selected force sensors used for data acquisition were one of the integral parts of the set-up. The influence of the force sensors’ installed position (location in the set-up) on measured results, were analyzed and the optimum position that ensures independence of the results, determined. Additionally, the effects of injection pressure, injection pulse width and injection hole diameter on the injection characteristics were also investigated. Furthermore, in this research, the reliability and robustness of Strain sensor and Piezoelectric sensors were analyzed with regards to their response. The analysis showed that, strain sensors have weak dynamic response characteristic compared to piezoelectric sensors also, the measured result obtained from strain sensors fluctuated greatly. Piezoelectric force sensor gave a more reliable and stable measurement, comparatively. The accuracy of the results were affected by the installation position of the sensors. A distance of 16 mm (between nozzle hole exit and sensor surface) was determined to be adequate for the acquisition of reliable experimental data. As the injection pressure gets higher (during injection), the rate of mass flow increased, the average cycle-to-cycle variation coefficient and nozzle-to-nozzle variability coefficient of injection quantity decreased. Hence, improving the consistency of each cycle and the uniformity of each hole. In addition, increasing the injection pulse width decreased the average cycle-to-cycle variation coefficient. Also, nozzle-to-nozzle variability coefficient had minimal or no influence with regards to injection pressure. At 80 MPa, the uniformity of injection from the multi-hole nozzle improved significantly. In summary, the larger the hole diameters, the higher the maximum value of mass flow rate and the fuel injection quantity.     

Determination of the optical depth of a DI diesel spray

The optical depth is responsible of limiting the optical diagnostic using visible wavelength in the sprays. This paper proposes to measure the optical depth directly in a real Diesel spray through line-of-sight laser extinction measurements. This easily reproducible method which does not require expensive or complex optical techniques is detailed and the measurement procedure is presented in this paper. As diesel sprays are mostly optically thick, the measurements in the denser region are not reliable and a fuel concentration model has been used to derive the results to the entire spray. This work provides values of SMD at different distance from the nozzle tip depending on the specific parameters like injection pressure or discharge density. The values extracted from a combined experimental/computational approach have been compared to PDPA measurements under the same testing conditions. The results have shown that the maximum optical depth was higher than 10 and that an increase of the injection pressure led to higher τ values. The SMD values appeared to be below the results measured by the PDPA and the droplet diameter showed to be the main responsible of the optical depth of the jet under the tested conditions.     

A study on the spray characteristics of a piezo pintle-type injector for DI gasoline engines

We studied the spray flow initiated from a piezo pintle-type injector for DI gasoline engines in an environment supplied by a constant volume vessel by means of laser diagnostics. To fully grasp the effects of the characteristic parameters, including designed spray angle, needle lift, injection pressure (P _inj ) and ambient pressure (P _b ), on the spray atomization and mixture preparation, particle image velocimetry (PIV) and phase Doppler anemometry (PDA) are used in the experiment, respectively. The gas perpendicularly enters into the outer periphery of the conical spray injected through the pintle-type injector activated by piezo, which creates two large-scale vortices: the vortex A and vortex B. The velocity standard deviation of the spray field is introduced to analyze the gas flow motion in the vicinity of nozzle. The droplet information of spray field is also recorded by PDA in variable boundary conditions. The time dividing method is used to study the droplet characteristics in four parts of spray. The injector with 98° designed spray angle has smaller droplet mean diameter (D10 and D32), due to a larger spray distribution. When the droplet velocity of the spray field is close to 0 m/s, the D10 and D32 hold at around 10 μm and 20 μm, respectively, in atmospheric pressure condition, which are about 20 μm and 40 μm, respectively, at ambient pressure of 1.1 MPa.     

多孔射流钻头破岩钻孔规律试验研究

利用自行研制的射流破岩系统,对淹没和围压条件下多孔射流钻头的破岩钻孔规律进行了试验研究,重点考虑了水力参数(冲蚀时间、射流压力、围压、喷距)和结构参数(孔眼数量和侧向孔眼扩散角)对破岩效果的影响,结果表明:随着冲蚀时间的增加,破岩效果先增加,后趋于平缓;随着射流压力的增大破岩效果随之增大;随着围压的增加破岩效果随之减小;随着喷距的增加破岩效果呈先增大后减小的趋势,存在最优喷距范围;随着孔眼数量的增多,破岩成孔形状越来越圆整;随着侧向孔眼扩散角的增大,破岩效果呈先增大后减小趋势,存在最优扩散角范围。试验结果可为多孔射流钻头水力参数选择和结构参数设计提供依据。     

An investigation on effect of geometrical parameters on spray cone angle and droplet size distribution of a two-fluid atomizer

A visual study is conducted to determine the effect of geometrical parameters of a two-fluid atomizer on its spray cone angle. The liquid (water) jets exit from six peripheral inclined orifices and are introduced to a high speed gas (air) stream in the gravitational direction. Using a high speed imaging system, the spray cone angle has been determined in constant operational conditions, i.e., Reynolds and Weber numbers for different nozzle geometries. Also, the droplet sizes (Sauter mean diameter) and their distributions have been determined using Malvern Master Sizer x. The investigated geometrical parameters are the liquid jet diameter, liquid port angle and the length of the gas-liquid mixing chamber. The results show that among these parameters, the liquid jet diameter has a significant effect on spray cone angle. In addition, an empirical correlation has been obtained to predict the spray cone angle of the present two-fluid atomizer in terms of nozzle geometries.     

水力喷射径向水平井射流钻头优选试验研究

射流钻头的破岩性能对井眼深度和大小有重要影响。本文对径向水平井常用的2种射流钻头——多孔喷嘴和混合射流喷嘴采用室内试验的方法对它们的破岩规律和破岩性能进行了分析和对比。结果表明,冲击时间、喷嘴压降、喷距和围压对2种喷嘴破碎效果的规律基本相同,混合射流喷嘴的最优喷距不明显,多孔喷嘴的最优喷距为5～6倍喷嘴当量直径,多孔喷嘴的破岩性能要优于混合射流喷嘴,同时混合射流喷嘴在破碎孔径大小方面优于多孔喷嘴。本文可以为水力喷射径向水平井射流钻头的选择提供试验依据。     

The effect of spray characteristics on the etching of invar alloy with FeCl3 solution

The objective of this study was to investigate the significant characteristics in the sprays of industrial etching nozzles for the sake of process design. The experiment was carried out with different spray pressures and industrial nozzles in the spray etching. Characteristics of the spray, such as the axial velocity and the Sauter mean diameter (SMD), were obtained through the Phase-Doppler Anemometer (PDA). The impact force was calculated through the spray characteristics. It was found that liquid with higher spray pressure resulted in a smaller SMD, higher droplet velocity, and greater impact force. The depth of etching was increased in the case of higher spray pressure. When the spray angle oscillated between 20° and −20°, the effect of etching remained constant. The relationships between the spray characteristics and the etching characteristics were analyzed. The depth of etching had significant, positive correlations with the axial velocity and the impact force. Four liquids of different kinematic viscosities were used to reveal the effects of the kinematic viscosity on the spray characteristics. The results indicated that a lower viscosity of the spray yielded a higher etching rate than a higher viscosity of the liquid. The results clearly show that the characteristics of the spray etching are strongly related to the spray characteristics with the spray conditions.     

Experimental investigation of mixing-enhanced swirl flows

The experimental objective was to compare disintegration characteristics from the internal mixing pneumatic nozzles under the different operating conditions in terms of swirl angles. For this investigation, supplied air pressures and nozzle configuration ratios were fixed. This experimental comparison is of fundamental importance to the understanding and modeling of turbulent atomization because the axisymmetric swirling flows involve relatively complex interactions. For the measurement, four internal swirl mixing nozzles with axisymmetric holes at swirl angles of 15°, 30°, 45°, and 60° to the central axis were employed, which is responsible for the enhancement of mixing in pneumatic jets. To illustrate the swirl phenomena quantitatively, the distributions of mean velocities, turbulence intensities, and SMD (Sauter mean diameter, or D₃₂) variations with different configuration ratio were comparatively analyzed. It indicated that the atomization characteristics are performed well in the case of 30° of swirl angle, and that turbulence intensities are gradually degenerated with the increase of radial distances, showing a slight increment of SMD at downstream region. In particular, measurements showed that nozzle configuration is one of the significant geometrical parameters affecting the spray trajectories. This paper was recommended for publication in revised form by Associate Editor Jun Sang Park     

Twin spray characteristics between two impinging F-O-O-F type injectors

This paper presents twin spray characteristics of two impinging F-O-O-F type injectors in which fuel and oxidizer impinge on each other to atomize under the various conditions. The droplet size and velocity in the impinging spray flow field were measured using PDPA. The droplet size and velocity were investigated at the mixture ratios of 1.5, 2.0, 2.47 and 3.0 for four injectors in which two single F-O-O-F injectors were arranged at the intervals of 20.8, 31.2, 41.6 and 62.4mm respectively. In general, the arithmetic mean diameter, SMD and standard deviation of droplet size in the interaction area (X=0 andY=0mm) were smaller, while the axial velocity in the interaction area was slightly higher. An empirical correlation is obtained for the (D ₁₀) _D /(D ₁₀) _C value under the assumptions of two identical droplets and these with different size and velocity. The droplets with low Weber numbers below 40 have possibility to coalesce, while those over 40 tend to disintegrate after impingement in the interaction area.     

Experiments and theoretical approaches on the burning behaviors of single n-heptane droplet

This study was conducted to improve the theoretical prediction of the burning characteristics of an n-heptane droplet by comparing them with experimental results. To achieve this, numerical approaches were conducted by assuming that the droplet combustion can be described by both quasi-steady behavior for the region between the droplet surface and the flame interface, and transient behavior for the region between the flame interface and ambient surrounding. Comparisons were considered for droplet diameter (d _t ), flame diameter (d _f ), flame standoff ratio (FSR), and viscous drag induced fluxes which are Stefan flux and thermophoretic flux for various initial droplet diameter (d ₀ ) and oxygen (O ₂ ) concentration conditions. It was revealed that the flame diameter (d _f ) and flame standoff ratio (FSR) initially increase dramatically and approach quasi-steady behavior within the observation period, and the flame standoff ratio (FSR) increases a little with the initial droplet diameter (d ₀ ) both experimentally and theoretically. The value of flame diameter (d _f ) decreases from its maximum value when oxygen (O ₂ ) concentration is increased from a value of 18% to 40%. The burning rate (K) constant becomes higher as the oxygen (O ₂ ) concentration increases since the increase of oxygen (O ₂ ) concentration produces a higher maximum flame temperature (d _f ) which enhances the effective thermo-physical properties of the gas-phase bounded by droplet and flame front.