A proposal for diesel spray model using a TAB breakup model and discrete vortex method

A hybrid model consisting of a modified TAB (Taylor Analogy Breakup) model and DVM (Discrete Vortex Method) is proposed for numerical analysis of the evaporating spray phenomena in diesel engines. The simulation process of the hybrid model is divided into three steps. First, the droplet breakup of injected fuel is analyzed by using the modified TAB model. Second, spray evaporation is calculated based on the theory of Siebers’ liquid length. The liquid length analysis of injected fuel is used to integrate the modified TAB model and DVM. Lastly, both ambient gas flow and inner vortex flow of injected fuel are analyzed by using DVM. An experiment with an evaporative free spray at the early stage of its injection was conducted under in-cylinder like conditions to examine an accuracy of the present hybrid model. The calculated results of the gas jet flow by DVM agree well with the experimental results. The calculated and experimental results all confirm that the ambient gas flow dominates the downstream diesel spray flow.     

Analysis of diesel spray structure using a hybrid model

This study proposes a hybrid model that consists of modified Taylor Analogy Breakup (TAB) model and a Discrete Vortex Method (DVM). In this study the simulation is divided into three steps. The first step is to analyze the breakup of the injected fuel droplets by using a modified TAB model. The second step is based on Siebers’ theory of liquid length, which is an analysis of spray evaporation. The liquid length analysis for injected fuel is used to connect both the modified TAB model and the DVM. The final step is to reproduce the ambient gas flow and the inner vortex flow of the injected fuel by using the DVM. In order to examine this hybrid model, we performed an experiment involving a free evaporating fuel spray at the early injection stage within an environment similar to that found inside of an engine cylinder. The numerical results were calculated by using the present hybrid model and compared to the experimental results. The calculated results of the gas jet flow that were determined through the DVM corresponded well with the experimental results for a downstream evaporative spray. It is also confirmed that an ambient gas flow occupies the downstream region of a diesel spray.     

Numerical and experimental analysis of spray atomization characteristics of a GDI injector

In this study, numerical and experimental analysis on the spray atomization characteristics of a GDI injector is performed. For numerical approach, four hybrid models that are composed of primary and secondary breakup model are considered. Concerning the primary breakup, a conical sheet disintegration model and LISA model are used. The secondary breakup models are made based on the DDB model and RT model. The global spray behavior is also visualized by the shadowgraph technique and local Sauter mean diameter and axial mean velocity are measured by using phase Doppler particle analyzer. Based on the comparison of numerical and experimental results, it is shown that good agreement is obtained in terms of spray developing process and spray tip penetration at the all hybrid models. However, the hybrid breakup models show different prediction of accuracy in the cases of local SMD and the spatial distribution of breakup.     

Experimental analysis and numerical modeling using lisa-ddb hybrid breakup model of direct injected gasoline spray

This paper presents the effect of injection pressure on the atomization characteristics of high-pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a laser sheet method. In order to investigate the atomization process in more detail, the calculations with the LISA-DDB hybrid model were performed. The results provide the effect of injection pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is revealed that the accuracy of prediction is promoted by using the LISA-DDB hybrid breakup model, comparing to the original LISA model or TAB model alone. And the characteristics of the primary and secondary breakups have been investigated by numerical approach.     

Atomization characteristics and prediction accuracy of LISA-DDB model for gasoline direct injection spray

In this paper, the spray atomization characteristics of a gasoline direct-injection injector were investigated experimentally and numerically. To visualize the developing spray process, a laser sheet method with a Nd :YAG laser was utilized. The microscopic atomization characteristics such as the droplet size and velocity distribution were also obtained by using a phase Doppler particle analyzer system at the 5 MPa of injection pressure. With the experiments, the calculations of spray atomization were conducted by using the KIVA code with the LISA-DDB breakup model. Based on the agreement with the experimental results, the prediction accuracy of LISA-DDB breakup model was investigated in terms of the spray shapes, spray tip penetration, SMD distribution, and axial mean velocity. The results of this study provides the macroscopic and microscopic characteristics of the spray atomization, and prediction accuracy of the LISA-DDB model.     

Comparison of experimental and predicted atomization characteristics of high-pressure diesel spray under various fuel and ambient temperature

The aim of this study is to investigate the effects of the fuel temperature and the ambient gas temperature on the overall spray characteristics. Also, based on the experimental results, a numerical study is performed at more detailed and critical conditions in a high pressure diesel spray using a computational fluid dynamics (CFD) code (AVL, FIRE ver. 2008). Spray tip penetration and spray cone angle are experimentally measured from spray images obtained using a spray visualization system composed of a high speed camera and fuel supply system. To calculate and predict the high pressure diesel spray behavior and atomization characteristics, a hybrid breakup model combining KH (Kelvin-Helmholtz) and RT (Rayleigh-Taylor) breakup theories is used. It was found that an increase in fuel temperature induces a decrease in spray tip penetration due to a reduction in the spray momentum. The increase of the ambient gas temperature causes the increase of the spray tip penetration, and the reduction of the spray cone angle. In calculation, when the ambient gas temperature increases above the boiling point, the overall SMD shows the increasing trend. Above the boiling temperature, the diesel droplets rapidly evaporate immediately after the injection from calculation results. From results and discussions, the KH-RT hybrid breakup model well describes the effects of the fuel temperature and ambient gas temperature on the overall spray characteristics, although there is a partial difference between the experimental and the calculation results of the spray tip penetration by the secondary breakup model.     

The effects of injector nozzle geometry and operating pressure conditions on the transient fuel spray behavior

Effects of injector nozzle geometry and operating pressure conditions such as opening pressure, ambient pressure, and injection pressure on the transient fuel spray behavior have been examined by experiments. In order to clarify the effect of internal flow inside nozzle on the external spray, flow details inside model nozzle and real nozzle were also investigated both experimentally and numerically. For the effect of injection pressures, droplet sizes and velocities were obtained at maximum line pressure of 21 MPa and 105 MPa. Droplet sizes produced from the round inlet nozzle were larger than those from the sharp inlet nozzle and the spray angle of the round inlet nozzle was narrower than that from the sharp inlet nozzle. With the increase of opening pressure, spray tip penetration and spray angle were increased at both lower ambient pressure and higher ambient pressure. The velocity and size profiles maintained similarity despite of the substantial change in injection pressure, however, the increased injection pressure produced a higher percentage of droplet that are likely to breakup.     

An overview of liquid spray modeling formed by high-shear nozzle/swirler assembly

A multi-dimensioanl model is being increasingly used to predict the thermo-flow field in the gas turbine combustor. This article addresses an integrated survey of modeling of the liquid spray formation and fuel distribution in gas turbine with high-shear nozzle/swirler assembly. The processes of concern include breakup of a liquid jet injected through a hole type orifice into air stream, spray-wall interaction and spray-film interaction, breakup of liquid sheet into ligaments and droplets, and secondary droplet breakup. Atomization of liquid through hole nozzle is described using a liquid blobs model and hybrid model of Kelvin-Helmholtz wave and Rayleigh-Taylor wave. The high-speed viscous liquid sheet atomization on the pre-filmer is modeled by a linear stability analysis. Spray-wall interaction model and liquid film model over the wall surface are also considered.     

Intermittent atomization characteristics of multi-hole and single-hole diesel nozzle

The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole diameter of the 5-hole and the single-hole nozzle was the same as d_n=0.32 mm with the constant hole length to diameter ratio (l_n/d_n=2.81). The droplet diameters of the spray, including the time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter), injected intermittently from the two nozzles into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle spray consisted of the three main parts : (a) the leading edge affected by surrounding air and composed of small droplets ; (b) the central part surrounded by the leading edge and mixing flow region and scarcely affected by the resistance of air ; (c) the trailing edge formed by the passage of the central part. The SMD decreases gradually with the increase in the radial distance, and the constant value is obtained at the outer region of the radial distance (normalized by hole diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the centerline of the spray decrease shapely with the increase in the axial distance after showing the maximum value near the nozzle tip. The SMD remains the constant value near the axial distance (normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle, respectively.     

Fuel spray dynamic characteristics of GDI high pressure injection system

In order to improve the fuel consumption and exhaust emission for gasoline engines,gasoline direct injection (GDI) system is spotlighted to solve these requirements.Thus,many researchers focus on the i...     

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.     

Spray formation by a swirl spray jet in low speed cross-flow

Breakup and spray formation of swirl liquid jets introduced into a low-speed cross-flow are experimentally investigated. Effects of the cross-flows on the macro and microscopic spray parameters are optically measured in terms of jet Weber number and liquid-to-gas momentum ratio. At lower jet Weber numbers, the liquid stream undergoes Rayleigh jet breakup. At higher momentum ratios, bag breakup occurs and tends to distort the liquid column into a loop-like structure. As the jet Weber number rises, stronger aerodynamic interaction and secondary flows cause multi-mode breakup. Regardless of the momentum ratio, the spray profile is hardly altered at higher jet Weber numbers. The cross-flow promotes the jet breakup and renders a finer spray in an entire range of injection velocities.     

MODELING OF A SOLID CONE PRESSURE-SWIRL ATOMIZER

ＭＯＤＥＬＩＮＧＯＦＡＳＯＬＩＤＣＯＮＥＰＲＥＳＳＵＲＥ－ＳＷＩＲＬＡＴＯＭＩＺＥＲＭＯＤＥＬＩＮＧＯＦＡＳＯＬＩＤＣＯＮＥＰＲＥＳＳＵＲＥ－ＳＷＩＲＬＡＴＯＭＩＺＥＲＣｈａｎＴａｔＬｅｕｎｇ（ＴｈｅＨｏｎｇＫｏｎｇＰｏｌｙｔｅｃｈｎｉｃＵｎｉｖｅｒ...     

Characteristics of a liquefied butane spray

The characteristics of a butane spray from pintle-type injector were studied by droplet velocity and diameter measurements and high speed photography. The accumulator type injector operated off a common rail fuel supply system operated at 13 MPa, and was controlled by a high-speed solenoid valve. Injection was carried out in a chamber at ambient temperature and at the pressure above (0.37 MPa) and below (0.15 MPa) the fuel vapor pressure. Two component phase/Doppler particle analyzer and traverser were used to obtain the droplet diameter and the velocity at numerous locations in the spray. The entire injection event was analyzed as a time-average and also subdivided into three temporal intervals. A, B, and C. The high-speed photographs showed a narrower cone angle during the quasi-steady spray period at the 0.37 MPa chamber pressure compared to the 0.15 MPa case.     

Swirl effect on the spray characteristics of a twin-fluid jet

In the liquid fuel combustion chamber, employed fuel must be atomized before being injected into the combustion zone. Therefore, the complete fuel atomization is the most important condition for the combustion efficiency. The atomization quality strongly affects the combustion performance, exhaust pollutant emissions, and flame stability. Therefore, the whole process of spray atomization is of fundamental significance. During past decades many experimental and theoretical studies in this field have been carried out and some improved results have been obtained. Two-phase atomizers, having a variety of advantages such as spray uniformity, appreciable atomization, and smaller SMD with an increase of ambient gas, are considered to be applied in various industrial processes. The purpose of present study is to investigate the mean velocity, turbulence shear stress, turbulence intensity, mean drop size distribution, and droplet data rate in a two-phase swirling jet using PDPA systems.     

喷射压力对生物柴油混合燃料喷雾特性的影响

基于KH-RT液滴破碎模型对定容燃烧弹内生物柴油-正丁醇混合燃料的喷雾贯穿距离、喷雾锥角、索特平均粒径、速度场以浓度场进行数值模拟,通过定容燃烧弹试验台架获取的生物柴油-正丁醇混合燃料的喷雾特性对数值模型进行验证,结果表明:随着喷射压力的增加,BD70N30混合燃料的喷雾贯穿距和喷雾锥角增加;索特平均粒径降低;雾束中心...     

A comparative study on CFD simulation of spray penetration between gas jet and standard KIVA-3V spray model over a wide range of ambient gas densities

CFD simulation of spray penetration with standard KIVA-3V were compared with those using both an ‘original gas jet model’ and a ‘normal gas jet profile model that features a new breakup length formula’ by implementing them in the standard KIVA-3V code. The effects of entrainment coefficient on the spray penetration simulated with the gas jet profile were compared to that simulated with the standard KIVA-3V spray model. The accuracy of the CFD simulation results was estimated by comparing them with available experimental data. Both the standard KIVA-3V spray model and the normal gas jet profile model with the breakup length formula predict well the spray tip penetration up to a gas density of 60 kg/m³. The CFD simulation of spray tip penetration with the standard KIVA-3V predicts better with the ‘original gas jet model’ when the ambient gas density is lower than 60 kg/m³. For higher densities, the normal gas jet profile model with breakup length formula predicts the spray penetration better.     

Transient liquid jet breakup model and comparison with phase doppler measurements

A new liquid jet breakup model is developed based on the transient breakup mechanism and incorporated into the KIVA-II code. Liquid column is considered as a chain of balls. Rayleigh-Taylor instability and Kelvin-Helmholtz instability was applied to the liquid jet column. Liquid jet column is continuously surveyed to apply breakup mechanisms. Once liquid droplets are separated from the main liquid jet column, these droplets are subjected to the single breakup mechanism. When Bond number is greater than a critical Bond number, single droplets continue to break up by Rayleigh-Taylor instability or Kelvin-Helmholtz instability. Computational results were compared with the PDPA measurement data. Gross behavior of the spray and detailed droplet sizes and velocities predicted by KIVA calculations which include proposed drop breakup model are compared with those produced from droplet size/velocity measurements.     

两相脉冲爆震发动机头部燃油雾化试验研究

在不同油、气流量下,采用LS-2000激光喷雾粒度分析仪测试了脉冲爆震发动机头部为空心腔体结构、文丘里结构情况下的油滴索太尔平均直径(SMD),并与实验中所采用的直射式喷油嘴雾化结果进行了比较,简要分析了头部几何结构对喷入燃油的二次雾化过程。研究发现,除了喷嘴性能以外,发动机头部几何结构对油滴粒度也具有较为显著的影响,而且设计中应使所采用的喷嘴型式与其相匹配。     

乙醇圆柱射流雾化破碎过程的PIV试验研究

在喷雾容弹上利用PIV激光测试系统,研究了容弹背压、容弹温度和喷射脉宽对乙醇圆柱射流破碎雾化的影响。试验结果表明：容弹背压升高,乙醇圆柱射流贯穿距离减小,射流锥角变大;温度由20℃变为60℃时,乙醇运动黏度变小,射流贯穿距离增大,射流锥角略有增加;喷射脉宽的改变对乙醇圆柱射流贯穿距离和射流锥角影响很小,然而大脉宽的乙醇射流雾化困难。