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1.
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. 相似文献
2.
Sungsik Chung Jongsang Park Sipom Kim Jeongkuk Yeom 《Journal of Mechanical Science and Technology》2007,21(12):2205-2213
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. 相似文献
3.
Dong-Seok Choi Gyung-Min Choi Duck-Jool Kim 《Journal of Mechanical Science and Technology》2002,16(7):999-1008
The spray structures and distribution characteristics of liquid and vapor phases in non-evaporating and evaporating Gasoline
Direct Injection (GDI) fuel sprays were investigated using Laser Induced Exciplex Fluorescence (LIEF) technique. Dopants were
2% fluorobenzene and 9% DEM A (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to study internal structure
of the spray, droplet size and velocity under non-evaporating condition were measured by Phase Doppler Anemometry (PDA). Liquid
and vapor phases were visualized at different moments after the start of injection. Experimental results showed that the spray
could be divided into two regions by the fluorescence intensity of liquid phase: cone and mixing regions. Moreover, vortex
flow of vapor phase was found in the mixing region. About 5μn diameter droplets were mostly distributed in the vortex flow
region. Higher concentration of vapor phase due to vaporization of these droplets was distributed in this region. Particularly,
higher concentration of vapor phase and lower one were balanced within the measurement area at 2ms after the start of injection. 相似文献
4.
Jeongkuk Yeom Jongsang Park Sungsik Chung 《Journal of Mechanical Science and Technology》2005,19(12):2281-2288
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. 相似文献
5.
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. 相似文献
6.
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. 相似文献
7.
Quantitative vapor phase exciplex fluorescence measurements at high ambient temperature and pressure
The exciplex fluorescence technique with the TMPD (tetamethyl-p-phenylene-diamine) / naphthalene dopant system was applied in a combustion-type constant-volume spray chamber. A detailed
set of calibration experiments has been performed in order to quantify the TMPD fluorescence signal. It has been demonstrated
that the TMPD fluorescence intensity was directly proportional to concentration, was independent of the chamber pressure,
and was not sensitive to quenching by either water vapor or carbon dioxide. Using a dual heated-jet experiment, the temperature
dependence of TMPD fluorescence up to 1000 K was measured. The temperature field in the spray images was determined using
a simple mixing model, and an iterative solution method was used to determine the concentration and temperature field including
the additional effects of the laser sheet extinction. The integrated fuel vapor concentration compared favorably with the
measured amount of injected fuel when all of the liquid fuel had evaporated. 相似文献
8.
Jeekuen Lee Shinjae Kang Byoungjoon Rho 《Journal of Mechanical Science and Technology》2002,16(8):1135-1143
The intermittent spray characteristics of the single-hole diesel nozzle (dn=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 Ūcl and tended to decrease in the outer region. The turbulent intensity in the trailing edge was higher than that in the leading
edge. 相似文献
9.
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. 相似文献
10.
Seong Man Choi Seong Ho Jang Dong Hun Lee Gyong Won You 《Journal of Mechanical Science and Technology》2010,24(2):551-558
In micro-turbojet engines with less than 350 kW power, it is not easy to find a suitable fuel injector with good spray quality.
However, the rotating fuel injection system can potentially provide high atomization quality without the high-pressure fuel
pump through the centrifugal forces of the engine shaft. With this motivation, a very small rotating fuel injector with 40
mm diameter is designed for the micro-turbo jet engine. It is directly linked to a high-speed rotational spindle capable of
a speed up to 100,000 rpm. The droplet size, velocity, and spray distribution from the PDPA (Phase Doppler Particle Analyzer)
system are measured. The spray is also visualized by a high-speed camera. The test results show that the length of liquid
column from injection orifice is controlled by the rotational speeds and that SMD (Sauter Mean Diameter) is decreased with
increasing rotational speeds. At a rotational speed of 73.3 m/s (35,000 rpm), SMD is lower than 60 μm at the entirety of the
measuring space in the case of Type 2 (injection orifice diameter of 1.5 mm) and Type 3 (injection orifice diameter of 2.2
mm). Therefore, conceptually, it is possible to apply this small rotating fuel injection system to the micro-turbojet engine
combustor. 相似文献
11.
Jeong-Kuk Yeom Myung-Jun Lee Sung-Sik Chung Jong-Yul Ha Jiro Senda Hajime Fujimoto 《Journal of Mechanical Science and Technology》2002,16(4):532-548
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. 相似文献
12.
Spray characteristics of an injector employed in the 5 Newton-class of liquid-propellant thruster are addressed with an evolutionary
feature of droplets. Information for the droplets is obtained through Dual-mode phase Doppler anemometry (DPDA) measurement
in terms of the velocity, diameter, number density, and turbulent intensity. In addition, instantaneous images for the macroscopic
view of spray are supplemented by flow visualization technique using laser sheet. It is demonstrated by the investigation
of spray images that the injector under consideration meets an angular injection requirement at all of the injection pressures
specified. Spray shedding is also featured with a schematization of the frozen images. Dynamic behavior of spray droplets
and their atomization evolution along the geometric axis of injector-nozzle orifice with varying injection pressures are scrutinized
by depicting the cumulative droplet populations mapped onto a velocity-diameter domain. The evolutionary behavior is further
authenticated on the basis of the distribution for number density and turbulent intensity of droplets. It is inferred that
the higher injection pressure generates the smaller droplets undergoing the greater deceleration along the spray stream due
to the augmented Reynolds number and Weber number. Even though spray characterization of the current type of injectors is
to be inevitable to their performance estimation at the design stage, it has never been reported to date. It is expected that
the present results will be able to contribute to the appreciation of injector performance and to the design engineering of
brand-new thrusters as well.
This paper was recommended for publication in revised form by Associate Editor Jun Sang Park
Jin Seok Kim obtained his B.S. and M.S. degrees in Mechanical Engineering in 2005 and 2007, respectively, from Sunchon National University,
Korea. He is currently a Ph.D. candidate.
Jeong Soo Kim took his master’s and Ph.D. degrees in Aerospace Engineering in 1987 and 1992, respectively from KAIST, Korea. Since then,
he worked for Agency for Defense Development and Korea Aerospace Research Institute as a principal researcher up to 2004.
Also he researched at TRW (USA) as an assistant program manager from 1996 to 1998. He is currently a faculty member in the
School of Mechanical Engineering of Pukyong National University, Korea. His research fields extend into the development of
space propulsion engines with their components design, T&E of liquid rocket engines, and the numerical simulation of combustion
phenomena. 相似文献
13.
作为离心泵的一种演变泵型,燃油汽心泵在航空发动机中应用前景良好,叶轮区形成的汽心对泵的工作状态和性能影响较大。基于RNG κ-ε湍流模型对汽心泵内流场进行了非定常汽液两相数值模拟,研究了进口节流活门开度与出口负载对汽心区域的影响规律。为验证数值模拟结果的精度,利用汽心泵样机开展了基本特性试验。结果表明,汽心泵内燃油汽化发生于叶轮进口端;汽心区域随出口负载减小逐渐扩张。扩张至叶片区后,燃油全部从叶片压力面一侧流道进入蜗室;其他工况不变时汽心区随节流活门开度减小而迅速扩张,2mm开度时泵的效率最低可降至20%以下。数值模拟与样机试验误差基本在10%以内。 相似文献
14.
Won-Tae Kim Sam-Goo Lee Byung-Joon Rho Shin-Jae Kang 《Journal of Mechanical Science and Technology》1998,12(5):907-916
The quality of spray atomization ejected from an injector has a definitive influence upon the engine’s performance. Furthermore,
considerable attention to the Earth’s environmental pollution is increasing now more than ever before. This experimental investigation
has been carried out to clarify the characteristics of the intermittent spray using a pintle type gasoline fuel injector.
Both the image processing system and the Phase Doppler Anemometer are utilized for the visualization of a spray behavior and
the simultaneous measurements of dropsizes and their velocities, which have been conducted at the axial downstream from the
injector exit plane. The fuel injection duration was fixed at 3ms and the injection pressure was varied from 250 kPa to 350
kPa. For a high injection pressure of 350 kPa, the spray tip arrival time was fluctuated at the vigorously disintegrated regions.
It evidently shows a linear correlation between the axial velocity and the fuel drop size farther downstream. 相似文献
15.
The purpose of this study is to investigate the stratification of fuel vapor with different in-cylinder flow, piston cavity
and injection timings in an optically accessible engine. Three different piston shapes that are F(Flat), B(Bowl) and R(Re-entrance)
types were used. The images of liquid and vapor fuel were captured under the motoring condition using Laser Induced Exciplex
Fluorescence technique. As a result, at early injection timing of 270° BTDC, liquid fuel was evaporated faster by tumble flow
than swirl flow, where most of fuel vapor were transported by tumble flow to the lower region and both sides of cylinder for
the F-type piston. At late injection timing of 90° BTDC, tumble flow appears to be moving the fuel vapor to the intake side
of the cylinder, while swirl flow convects the fuel vapor to the exhaust side. The concentration of mixture in the center
region was highest in the B-type piston, while fuel vapor was transported to the exhaust side by swirl flow in F and Rtype
pistons. At the injection timing of 60° BTDC, the R-type piston was better for stratification due to a relatively smaller
bowl diameter than the others. 相似文献
16.
Comparison of experimental and predicted atomization characteristics of high-pressure diesel spray under various fuel and ambient temperature 总被引:1,自引:0,他引:1
Su Han Park Hyung Jun Kim Chang Sik Lee 《Journal of Mechanical Science and Technology》2010,24(7):1491-1499
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. 相似文献
17.
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 (dn=0.42 mm) to 5 (dn=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/dn=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. 相似文献
18.
The present article aims to perform numerical calculations for inter-spray impingement of two diesel sprays under a high injection pressure and to propose a new hybrid model for droplet collision on the basis of literature findings. The hybrid model is compared with the original 0’ Rourke’s model, which has been widely used for spray calculations. The main difference between the hybrid model and the O’Rourke’s model is mainly in determination of the collision threshold condition, in which the preferred directional effect of droplets and a critical collision radius are included. The Wave model involving the cavitation effect inside a nozzle is used for predictions of atomization processes. Numerical results are reported for different impingement angles of 60° and 90° in order to show the influence of the impinging angle on spray characteristics and also compared with experimental data. It is found that the hybrid model shows slightly better agreement with experimental data than the O’Rourke’s model. 相似文献
19.
Dong-Seok Choi Duck-Jool Kim Soon-Chul Hwang 《Journal of Mechanical Science and Technology》2000,14(10):1143-1150
The effects of ambient conditions on vaporizing sprays from a high-pressure swirl injector were investigated by an exciplex fluorescence method. Dopants used were 2% fluorobenzene and 9% DEMA (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to examine the behavior of liquid and vapor phases inside of vaporizing sprays, ambient temperatures and pressures similar to engine atmospheres were set. It was found that the ambient pressure had a significant effect on the axial growth of spray, while ambient temperature had a great influence on the radial growth. The spatial distribution of vapor phase at temperatures above 473K became wider than that of liquid phase after half of injection duration, From the analysis of the area ratio for each phase, the middle part (region II) in the divided region was the region which liquid and vapor phases intersect. For liquid phase, fluorescence-intensity ratio was greatly changed at lms after the start of injection. However, the ratio of vapor phase was nearly uniform in each divided region throughout the injection. 相似文献
20.
Recently, the electrically controlled fuel injection type motorcycle has been emphasized in order to meet regulations for
exhaust emissions. However, there are many difficulties in selecting the control parameters because the pulsation phenomenon
occurs in the intake port due to the higher speed operating range and the smaller layout than for a passenger car. Therefore,
we investigated the injector spray characteristics which are applied to a 4-valve motorcycle gasoline engine. The spray characteristics
were visualized by using a CCD camera synchronized with the stroboscope at 6000 rpm. Furthermore, we compared the simulation
results using the VECTIS code with experimental results. The results showed that the trajectory of the spray was directed
towards the lower wall of the intake port when the fuel was injected at closed valve timing. On the other hand, when the fuel
was injected at open valve timing, a large portion of the fuel was lifted towards the upper half of the port. In addition,
open valve injection makes fuel evaporation time short; this resulted in better mixture formation than a closed valve injection.
From this result, we found that injection timing has a great effect on the mixture formation within a motorcycle cylinder. 相似文献