An investigation of the spray characteristics of diesel-DME blended fuel with variation of ambient pressure in a constant volume combustion chamber

We compared the spray characteristics of a typical fuel (100% diesel, DME) and diesel-DME blended fuel in a constant volume combustion chamber (CVCC). The typical fuel (100% diesel, DME) and diesel-DME blended fuel spray characteristics were investigated at various ambient pressures (pressurized nitrogen) and fuel injection pressures using a common rail fuel injection system when the fuel mixture ratio was varied. The fuel injection quantity and spray characteristics were measured including spray shape, penetration length, and spray angle.     

An analysis on structure of impinging and free diesel spray with exciplex fluorescence method in high temperature and pressure field

Because an injected spray development process consists of impinging and free spray in the diesel engine, it is needed to analyze the impinging spray and free spray, simultaneously, in order to study the diesel spray behavior. To dominate combustion characteristics in diesel engine is interaction between injected fuel and ambient gas, that is, process of mixture formation. Also it is very important to analyze liquid and vapor phases of injected fuel on the investigation of mixing process, respectively and simultaneously. Therefore, in this study, the behavior characteristics of the liquid phase and the vapor phase of diesel spray was studied by using exciplex fluorescence method in high temperature and injection pressure field. Finally, it can be confirmed that the distribution of vapor concentration is more uniform in the case of the high injection than in that of the low injection pressure.     

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.     

Effects of needle response on spray characteristics in high pressure injector driven by piezo actuator for common-rail injection system

The common-rail injection systems, as a new diesel injection system for passenger car, have more degrees of freedom in controlling both the injection timing and injection rate with the high pressure. In this study, a piezo-driven injector was applied to a high pressure common-rail type fuel injection system for the control capability of the high pressure injector’s needle and firstly examined the piezo-electric characteristics of a piezo-driven injector. Also in order to analyze the effect of injector’s needle response driven by different driving method on the injection, we investigated the diesel spray characteristics in a constant volume chamber pressurized by nitrogen gas for two injectors, a solenoid-driven injector and a piezo-driven injector, both equipped with the same injection nozzle with sac type and 5-injection hole. The experimental method for spray visualization was based on back-light photography technique by utilizing a high speed framing camera. The macroscopic spray propagation was geometrically measured and characterized in term of the spray tip penetration, spray cone angle and spray tip speed. For the evaluation of the needle response of the above two injectors, we indirectly estimated the needle’s behavior with an accelerometer and injection rate measurement employing Bosch’s method was conducted. The experimental results show that the spray tip penetrations of piezodriven injector were longer, on the whole, than that of the solenoid-driven injector. Besides we found that the piezo-driven injector have a higher injection flow rate by a fast needle response and it was possible to control the injection rate slope in piezo-driven injector by altering the induced current.     

Diagnosis of the behavior characteristics of the evaporative diesel spray by using images analysis

In this study, the effects of change in injection pressure on spray structure have been investigated on the high temperature and pressure field. To analyze the structure of evaporative diesel spray is important in speculation of mixture formation process. Also emissions of diesel engines can be controlled by the analyzed results. Therefore, this study examines the evaporating spray structure in a constant volume chamber. The injection pressure is selected as the experimental parameter, is changed from 72 MPa to 112 MPa with a high pressure injection system (ECD-U2). The PIV (Particle Image Velocimetry) technique was used to capture behavior variation of the evaporative diesel spray. Analysis of the mixture formation process of diesel spray was executed by the results of flow analysis in this study. Consequentially the large-scale vortex flow could be found in downstream spray and the formed vortex governs the mixture formation process in diesel 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.     

Qualitative and quantitative analysis of spray characteristics of diesel and biodiesel blend on common-rail injection system

An experimental study was performed on spray characteristics of spray diesel (D100) and biodiesel blend (BD65) injected into an atmospheric chamber. A qualitative analysis of spray images was conducted through exploiting the image processing with common image processing software. The results showed that the posterization of the images offered more detailed qualitative information on the spray compared to the more commonly-used threshold method. The posterized images showed the existence of layers in the spray with its transition at different grey levels. At lower injection, the spray tip penetration of BD65 was slightly lower than D100, whereas at high injection pressure, spray tip penetration of BD65 was higher than D100. Although BD65 had lower maximum velocity, the higher density of biodiesel may have resulted in greater momentum that enabled BD65 to have longer spray tip penetration at higher injection pressure. At higher injection pressure, the spray angle of BD65 tended to be less than that of D100.     

Steady-flow characteristics and its influence on spray for direct injection diesel engine

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.     

A study on the behavior characteristics of diesel spray by using a high pressure injection system with common rail apparatus

The effects of change in injection pressure on spray structure in high temperature and pressure field have been investigated. The analysis of liquid and vapor phases of injected fuel is important for emissions control of diesel engines. Therefore, this work examines the evaporating spray structure using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 22 MPa to 112 MPa using a high pressure injection system (ECD-U2). Also, we conducted simulation study by modified KIVA-II code. The results of simulation study are compared with experimental results. The images of liquid and vapor phase for free spray were simultaneously taken by exciplex fluorescence method. As experimental results, the vapor concentration of injected fuel is leaner due to the increase of atomization in the case of the high injection pressure than in that of the low injection pressure. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.     

A study on the behavior of evaporating diesel spray using LIEF measurement and kiva code

The effects of change in injection pressure on spray structure in high temperature and pressure field have been investigated. The analysis of liquid and vapor phases of injected fuel is important for emissions control of diesel engines. Therefore, this work examines the evaporating spray structure using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 400 bar to 800 bar by using a common rail injection system. Also, we conducted simulation study by modified KIVA-II code. The results of simulation study are compared with experimental results. The images of liquid and vapor phase for free spray were simultaneously taken by exciplex fluorescence method. As experimental results, the vapor concentration of injected fuel is leaner due to the increase of atomization in the case of the high injection pressure than in that of the low injection pressure. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.     

A study on the mixture formation process of evaporating diesel spray by offset incidence laser beam

This paper analyzes heterogeneous distribution of branch-like structure at the downstream region of the spray. The liquid and vapor phase of the spray are obtained using a 35mm still camera and CCD camera in order to investigate spray structure of evaporating diesel spray. There have been many studies conducted on diesel spray structure but have yet only focused on the analyses of 2-D structure. There are a few information which is concerned with 3-D structure analysis of evaporating spray. The heterogeneous distribution of droplets in inner spray affects the mixture formation of diesel spray and the combustion characteristics of the diesel engines. In this study, the laser beam of 2-D plane was used in order to investigate 3-D structure of evaporating spray. The incident laser beam was offset on the central axis of the spray. From the analysis of images taken by offset laser beam, we will examine the formation mechanism of heterogeneous distribution of the diesel spray by vortex flow at the downstream of the spray. The images of liquid and vapor phase of free spray are simultaneously taken through an exciplex fluorescence method. Through this, the branch-like structure consisting of heterogeneous distribution of the droplets forms high concentrated vapor phase at the periphery of droplets and at the spray tip.     

The effect of injection pressure and fuel viscosity on the spray characteristics of biodiesel blends injected into an atmospheric chamber

An experimental study was conducted to examine the effect of injection pressure and fuel type on the spray tip penetration length and the angle of spray injected into atmospheric chamber. The objective of the present study is to formulate empirical correlations of the spray tip penetration and the spray angle for non-evaporative condition. The experiment was performed by a common rail type high-pressure injector for the diesel engine at the injection pressure 40??100 MPa and four different fuels (D100, BD25, BD45, and BD65). The results showed that the biodiesel content increased the spray tip penetration and decreased the spray angle. The correlation of spray tip penetration is expressed for each region before and after spray break-up time in terms of injection pressure, fuel viscosity and time after start of injection. The correlation is also obtained for spray angle equation terms of injection pressure and fuel viscosity.     

Phase doppler measurements: system set-up optimization for characterization of a diesel nozzle

A commercial phase Doppler system was set up, optimized and used to measure the time resolved characteristics of the droplets inside a diesel spray. The purpose of this work was to understand exactly the influence of each system parameter, and to find the best setup enabling measurements in the spray zones that are densest and closest to the injector. Parametric studies were performed to gain an understanding of the particle density limits of the system and their dependence on the system parameters. Then the diesel spray produced by a single-hole injector was measured, with the fuel pressure ranging from 300 to 1300 bar and gas density in the test chamber ranging from ambient conditions to 40 kg/m³. The optic parameters (beam waist size, lenses focal length) were chosen to the best expected values allowed by the optical stand-off of the spray enclosure. The receiver slit width, which was found to have a dramatic effect on the detection of droplets during the injection main period, was tested in the range from 100 μm to 25 μm. Tests were carried out with two different slit lengths, namely 1 mm and 50 μm, with results indicating minimal effect on performance. PMT voltage (gain) was held to a moderately low value between 400 and 500 V and the laser power between 400 and 800 mW in the green line. An optimum burst threshold was found to obtain the best quality data regardless of signal background level, which varies greatly in high-density pulsed sprays. In the end, a set of results from the complete nozzle characterization in various conditions is presented in order to show the practical application of the optimization study and to provide some means of appreciating the results accuracy. The results obtained were also used to show that the gas-jet theory can be used to predict if PDPA measurement are possible in a given experimental situation.     

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.     

Investigation of soot formation in a D.I. diesel engine by using laser induced scattering and laser induced incandescence

Soot has a great effect on the formation of PM (Paniculate Matter) in D.I. (Direct Injection) Diesel engines. Soot in diesel flame is formed by incomplete combustion when the fuel atomization and mixture formation were poor. Therefore, the understanding of soot formation in a D.I. diesel engine is mandatory to reduce PM in exhaust gas. To investigate soot formation in diesel combustion, various measurements have been performed with laser diagnostics. In this study, the relative soot diameter and the relative number density in a D.I. engine was measured by using LIS (Laser Induced Scattering) and LII (Laser Induced Incandescence) methods simultaneously which are planar imaging techniques. And a visualization D.I. diesel engine was used to introduce a laser beam into the combustion chamber and investigate the diffusion flame characteristics. To find the optimal condition that reduces soot formation in diesel combustion, various injection timing and the swirl flow in the cylinder using the SCV (Swirl Control Valve) were applied. From this experiment, the effects of injection timing and swirl on soot formation were established. Effective reduction of soot formation is possible through the control of these two factors.     

防爆柴油机油腔喷射特性试验研究

防爆柴油机在高瓦斯、低通风效率的工作环境下具有较强的适应能力，是工业生产中重要的内燃机设备。根据喷油动量方程建立油腔喷射模型，引入喷油效率参数，通过试验方法得出不同喷嘴孔与进油口间距下的捕捉率。试验中设定油压范围0.25~0.45 MPa，喷油温度范围60~90 ℃，采用单因素试验法得出临界孔口间距随温度、压力的变化规律。试验结果表明，随着喷油压力或喷油温度的增大，油喷扩散角增大，临界孔口间距减小，油束发散性更为显著，为防爆柴油机的结构优化设计提供了重要依据。     

Effects of different piezo-acting mechanism on two-stage fuel injection and CI combustion in a CRDi engine

In this study, the effects of two piezo injectors operated by different mechanisms on multi-injection and Compression ignition (CI) combustion were investigated. High-pressure injectors for CI engines are divided into two categories according to the actuator: Solenoid and piezo injectors. It is commonly known that both injectors have a hydraulic circuit for fuel injection; thus, the performance of the injector is highly dependent on not only hydraulic characteristics such as volume of internal chambers and nozzle geometry, but also the actuation mechanism. Specially, the direct needle-Driven piezo injector (DPI) is introduced in this study and compared with the indirectacting Piezo injector (PI) to investigate the injection characteristics and influences on CI combustion performance by using spray visualization, injection rate measurement, and single cylinder diesel engine experiments, as well as numerical simulation for injection rate modeling of DPI. In the spray visualization experiment, a high-speed camera was used to examine spray tip penetration length and spray speed with respect to each injector. Also, in order to investigate injection rate information, which is a significantly dominant factor in combustion characteristics, the Bosch-tube method was adapted under the condition of a back pressure of 4.5 MPa, corresponding to engine motoring pressure. Also, a single-cylinder CRDi (Common-rail direct-injection) engine experiment was carried out to determine the effects of different piezo-acting mechanisms on two-stage fuel injection and CI combustion. From the key results obtained by this study, the direct needle-driven piezo injector has a faster SOI (Start of injection) and EOI (End of injection). In addition, the overall shape of the injection rate of DPI was narrow and the injection had a higher spray speed than that of PI. Also, DPI has a higher heat release rate and peak pressure, as verified by the engine experiment. In particular, it was found that DPI showed the possibility of combustion improvement when applying a pilot injection strategy.

     

Experimental study on spray etching process in micro fabrication of lead frame

The objective of this study is to obtain detailed information for the micro fabrication of lead frames by applying spray technology to wet etching process. Wet etching experiments were performed with different etching parameters such as injection pressure, distance from nozzle tip to etched substrate, nozzle pitch and etchant temperature. The characteristics of single and twin spray were measured to investigate the correlation between the spray characteristics and the etching characteristics. Drop size and velocity were measured by Phase-Doppler Anemometer (PDA). Four liquids of different viscosity were used to reveal the effects of viscosity on the spray characteristics. The results indicated that the shorter the distance from nozzle tip and the nozzle pitch, the larger etching factor became. The average etching factor had good positive correlation with average axial velocity and impact force. It was found that the etching characteristics depended strongly on the spray characteristics.     

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.     

柴油机喷油嘴的结构改进及三维流场数值模拟

喷油嘴头部细微的结构变化会对内部的流动状态产生显著的影响,进而影响到油束雾化性能。通过CFD软件对STD(Standard)标准型、VCO(Valve Closed Orifice)无压力室型及IMP(IM-PROVED)改进型的多孔喷嘴进行了三维流场数值模拟,通过对比分析得出改进型喷嘴在低油速率下获得相对好的喷雾性能,综合特性优于标准型和无压力室型的喷嘴。