Two—phase Flow of Liquid—gas in Diesel Fuel Injection System and Their Effect on Engine Performances

IntodcttonThe inveshgation of liquldgas tWo-phase flow uP todate indicates the the stUdy is not ouly in ndhaldeveopment period, but also will be a sphere of lwtwith twt views, for itS changeability andcomPlealty[']. For diesel fuel injechon system withW-Pipe-nozale system, liquld-gaS tWo-phaSe fiowPhenom ekistS, will influenee engine PerfOnnanCes,such as fuel economy, stability of engine OPeraon,regUlarity of fuel injection, and Pmpagation velocity ofPressare wave of the fuel injection…     

Fast Vortex Method for the Simulation of Flows Inside Channels With and Without Injection

A fast vortex method is presented for the simulation of fluid flows inside two-dimensional channels. The first channel studied is formed by two parallel walls simulating the entrance length of a developing flow. The second channel is similar to the first one but with an injection of a secondary fluid through a slot on one of its walls. In both cases, results are presented for flows at low Reynolds numbers and for flows at a high Reynolds number. The numerical method used is based on the Random Vortex Method and on the Vortex-In-Cell algorithm. Physical analyses of the numerical results are also presented, mostly in application to film cooling.     

Velocity and Size of Droplets in Dense Region of Diesel Fuel Spray on Transient Needle Opening Condition

In order to investigate the effect of transient needle opening on early stage of spray behavior, simultaneous measurements of velocity and size of droplet were conducted by a newly developed laser 2-focus velocimeter (L2F). The micro-scale probe of the L2F was consisted of two foci with a distance of 36 μm. The tested nozzle had a single hole with a diameter of 0.2 mm. The measurements of injection pressure, needle lift, and crank angle were synchronized with the spray measurement by the L2F at the position 10 mm downstream from the nozzle exit. It has been clearly shown that the velocity and size of droplet increase with needle valve opening and that the probability density distribution of droplet size can be fitted to the Nukiyama-Tanasawa distribution under the transient needle opening condition.     

乙醇/生物柴油/柴油混合燃料试验研究

对不同掺混比下乙醇/生物柴油/柴油(EBD)混合燃料的理化特性及互溶稳定性进行了试验研究。为了确定不同EBD混合燃料雾化性能的差异,基于电控喷射系统,利用马尔文法、高速摄像法研究了不同掺混比、喷射压力及喷油脉宽对燃油宏观和微观喷雾特性的影响。试验结果表明:在生物柴油/柴油混合燃料中添加乙醇,可显著改善混合燃料的雾化品质;在乙醇/柴油混合燃料中掺入生物柴油,又可显著改善混合燃料的互溶稳定性,能够满足车辆行驶需求。E10B25混合燃料的喷雾特性最佳。     

Average Droplet Diameter Measurement and Results for Fuel Aerosol Injected by Certain Types of the Turbojet Burners

INTRODUCTIONMeasurementofthedropletdiameteroffuelaerosolisverydifficult,becauseofthefastchangeofitssize,whichiscausedbyevaporationandassociation.Itisalsoverydifficulttogetaknowledgeofaerosolstreamsinthecourseofconstructionofnewtypeoffuelburn-ersanddiagnosticprocessaswell.Diffractionmethodisoneofthemostusefulmea-suringproceduresinthiscase.Thedropletsizeofmonodispersivemediumiseasytorecognise.Analy-sisofadiffeactionpatternofpolydispersivemediumisconsiderablymoredifficult.Thisworkpresentsam…     

Performance and Emission Characteristics of Tylosema Esculentum Biodiesel in a Diesel Engine： An Experimental Investigation

Biodiesel derived from indigenous feed stocks such as Tylosema esculentum kernel oil is deemed a feasible alternative to petroleum diesel for the diesel engine. This paper presents results of investigation of performance and emissions characteristics of diesel engine using Tylosema biodiesel. In this investigation, Tylosema biodiesel was prepared, analyzed and compared with the performance of petroleum diesel fuel using a single cylinder compression ignition diesel engine. The specific fuel consumption, engine torque, engine brake power, hydrocarbons, carbon monoxide and carbon dioxide were analyzed. The tests showed a decrease in engine brake power and torque with increase in engine load, while specific fuel consumption showed an increasing trend with maximum variation of 33% between the two fuels at engine load of 90%. Emission levels of hydrocarbons, carbon monoxide and carbon dioxide showed an increasing trend with increase in load for both fuels. Tylosema biodiesel produced significantly lower concentrations of hydrocarbons than petroleum diesel, while levels of carbon dioxide and carbon monoxide were largely comparable to those of petroleum diesel. Soot production from combustion ofTylosema biodiesel was found to be approximately 98% lower than that from combustion of petroleum biodiesel, demonstrating insignificant contribution to environmental pollution.     

Stiffness Evaluation of the Welded Connection between Guide Thimbles and the Spacer Grids for 16 × 16 Fuel Assemblies Types,Using the Finite Element Method

The present work aims to evaluate the increase in the number of spot welds in the 16 × 16 type fuel assembly structure that connects guide thimbles and spacer grids, in order to provide a proper joint for this connection. This new and improved process can provide more stiffness to the whole structure, since the number of spots raised from four to eight. A 3-D geometric model of a guide thimble section was generated in a CAD （computer aided design） program （SolidWorks）. After that, the geometric model was imported to a CAE （computer aided engineering） program （ANSYS Mechanical APDL, Release 14.0）, where the finite element model was built, considering the guide thimble geometry assembled with the spacer grid through the welded connections. Boundaries conditions were implemented in the model in order to simulate the correct physical behavior due to the operation of the fuel assembly inside the reactor. The analysis covered specific loads and displacements acting on the entire structure. The method used to solve this finite element analysis was a linear static simulation in order to perform the connection between a spacer grid cell and a guide thimble section. Hence, four models was evaluated, differing on the spot weld number in the spacer grid and guide thimble connection. The rotational stiffness results of each model were compared. The results acquired from four and eight spot weld were validated with physical test results. The behavior of the structure under the acting force/displacement and the related results of the analysis, mainly the stiffness, were satisfied. The results of this analysis were used to prove that the increasing spot welds number is an improvement in the dimensional stability when submitted to loads and displacements required on the fuel assembly design. This analysis aid to get more information of extreme importance such as, the pursuance to develop better manufacturing process and to improve the fuel assembly performance due to the increasing of the bum-up.     

Effects of spray characteristics on combustion performance of a liquid fuel spray in a gas turbine combustor

Spray characteristics like mean drop diameter and spray cone angle play an important role in the process of combustion within a gas turbine combustor. In order to study their effects on wall and exit temperature distributions and combustion efficiency in the combustor, a numerical model of a typical diffusion controlled spray combustion in a can‐type gas turbine combustion chamber has been made. A simple k–ϵ model with wall function treatment for near‐wall region has been adopted for the solution of conservation equations in carrier phase. The initial spray parameters are specified by a suitable PDF for size distribution and a given spray cone angle. A radiation model for the gas phase, based on modified first order moment method, and in consideration of the gas phase as a grey absorbing–emitting medium, has been adopted in the analysis. It has been recognized that an increase in mean drop diameter improves the pattern factor. However, the combustion efficiency attains its maximum at an optimum value of the mean diameter. Higher spray cone angle increases the combustion efficiency and improves the pattern factor, but at the same time, increases the wall temperature. Copyright © 1999 John Wiley & Sons, Ltd.     

溶气对不同燃油喷雾特性的影响

对溶有甲烷(CH4)的煤油和柴油稳态喷雾特性进行了试验研究,并对两者的试验结果进行了对比分析。结果表明,溶气对燃油的雾化有正反两方面的影响,它与CH4的浓度、喷嘴的L/D值、燃油的性质有关;柴油和煤油试验结果的规律相似,但促进雾化的临界浓度值不同;由于溶气的膨胀作用,在喷嘴出口处形成均匀的喷雾,喷雾锥角急剧增大;CH4的浓度较大时,燃油雾化粒子分布规律向小粒径方向移动,浓度较小时,向大粒径方向移动;低粘度的燃油有助于增强溶气对燃油雾化的促进作用。     

Numerical investigation of the effects of fuel spray type on the interaction of fuel spray and hot porous medium

The interaction between two types of fuel spray and a hot porous medium is studied numerically by using an improved version of KIVA-3V code. The improved KIVA-3V code is incorporated with an impingement model, a heat transfer model and a linearized instability sheet atomization (LISA) model to model the hollow cone spray. An evaporating fuel spray impingement on a hot plane surface was simulated under conditions of experiments performed by Senda to validate the reasonability of the KIVA-3V code. The numerical results conform well with experimental data for spray radius in the liquid and the vapor phases. Computational results on the interaction of two types of the fuel spray and the hot porous medium show that the fuel spray can be split, which provides conditions for quick evaporation of fuel droplets and mixing of fuel vapor with air. The possibility of fuel droplets from hollow cone spray crossing the porous medium reduces compared with that from solid cone spray, with the same initial kinetic energy of fuel droplets in both injection types. __________ Translated from Journal of Engineering Thermophysics, 2007, 28(2): 354–356 [译自: 工程热物理学报]     

An experimental investigation of the breakup characteristics of secondary atomization of emulsified fuel droplet

In this study, the breakup characteristics of secondary atomization of an emulsified fuel droplet were investigated with a single droplet experiment. In the single droplet experiment, the emulsified fuel droplet suspended from a fine wire was inserted into an electric furnace, and then secondary atomization behavior was observed using a high-speed video camera. Moreover, a mathematical model to calculate the generated water vapor at micro-explosion was proposed by using the mass and energy conservation equations under some assumptions. In the proposed model, that can be calculated by using the inner droplet temperature history at micro-explosion. As a result, puffing and micro-explosion occurred even when the fine ceramics fiber was used. The proposed model showed that about 50–70 wt% of water in the emulsified fuel changed to water vapor instantaneously at the occurrence of micro-explosion. The mass of water necessary for micro-explosion was shown. The breakup time was closely related to the superheat temperature just before the occurrence of micro-explosion.     

Experimental study on spray characteristics of long-chain alcohol-diesel fuels in a constant volume chamber

This study aims at study effects of blending long-chain alcohol (n-butanol or n-pentanol) with diesel on the spray characteristics and compare the differences of those spray characteristics between n-butanol-diesel blends and n-pentanol-diesel blends. Results showed that with the addition of long-chain alcohols, the spray tip penetration decreased, the spray cone angle increased and the spray area increased, while with the increasing proportions of long-chain alcohols in blended fuels, the spray area decreased whereas the peak tip velocity increased. Under the same blended ratios, n-butanol-diesel blends showed longer tip penetration, larger cone angle, larger spray area and lower peak tip velocity compared to n-pentanol-diesel blends in the same injection conditions. Furthermore, from the comparison between spray morphology of each tested fuel with each other, it can be inferred that n-butanol-diesel blends have largest spray areas and thinnest spray boundaries, followed by n-pentanol-diesel blends and then pure diesel fuel.     

Numerical study on flash‐boiling spray of multicomponent fuel

Flash‐boiling occurs when a fuel is injected into a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. It has been known that flashing is a favorable mechanism for atomizing liquid fuels. On the other hand, alternative fuels, such as gaseous fuels and oxygenated fuels, are used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility and flash‐boiling takes place easily in the fuel spray when injected into the combustion chamber of an internal combustion engine under high pressure. In addition the multicomponent mixture of high‐ and low‐volatility fuels has been proposed in the previous study in order to control the spray and combustion processes in an internal combustion engine. It was found that the multicomponent fuel produces flash‐boiling with an increase in the initial fuel temperature. Therefore, it is important to investigate these flash‐boiling processes in fuel spray. In the present study, the submodels of a flash‐boiling spray are constructed. These submodels consider the bubble nucleation, growth, and disruption in the nozzle orifice and injected fuel droplets. The model is implemented in KIVA3V and the spray characteristics of multicomponent fuel with and without flashing are numerically investigated. In addition, these numerical results are compared with experimental data obtained in the previous study using a constant volume vessel. The flashing spray characteristics from numerical simulation qualitatively show good agreement with the experimental results. In particular, it is confirmed from both the numerical and experimental data that flash‐boiling effectively accelerates the atomization and vaporization of fuel droplets. This means that a lean homogeneous mixture can be quickly formed using flash‐boiling in the combustion chamber. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 369–385, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20117     

柴油中溶入甲烷对发动机燃烧排放特性的影响

设计了几种不同甲烷含量的甲烷／柴油混合燃料,在实用柴油机上对它们的燃烧和排放特性进行了试验研究。研究结果表明,根据柴油中甲烷含量的不同,溶气对比油耗和热效率有正反两方面的影响;溶有甲烷的柴油与纯柴油相比有较长的着火滞燃期和较低的最大放热率;柴油中甲烷的溶解量越大,滞燃期越长,最高放热率越低;与纯柴油相比,溶有甲烷柴油的NOx排放降低,HC排放增加;在较高的甲烷溶解度时,NOx和烟度排放能够同时降低。     

Effects of multiple-injection strategies on overall spray behavior,combustion, and emissions reduction characteristics of biodiesel fuel

This study described the combustion and exhaust emissions characteristics of biodiesel fuel with multiple-injection strategies. Also, this investigation included the free spray characteristics and in-cylinder spray behaviors of the multiple-injection modes. Free spray and in-cylinder spray images were obtained from the spray visualization system. Combustion and exhaust emissions characteristics were analyzed using a single cylinder diesel engine with a displacement volume of 373.33 cm³ and a compression ratio of 17.8. The exhaust emissions were analyzed using a smoke meter and an exhaust gas analyzer. A scanning mobility particle sizer (SMPS) was utilized to measure the particle number and size distribution of the nano-sized particle matter.     

小流量离心式喷嘴雾化特性的实验研究

离心式喷嘴在燃气轮机燃烧室中应用广泛,因此人们对其雾化特性及影响雾化特性的因素已经进行了很长时间的研究。本文对小流量离心式喷嘴雾化特性及其影响因素进行了实验研究,着重研究了其他研究者很少涉及的切向孔总面积对离心式喷嘴雾化特性的影响,并对离心式喷嘴燃料分布特性进行了研究。通过实验获得了不同喷嘴出口直径及不同切向孔总面积下离心式喷嘴喷油量、雾化角及雾化粒度的数据,得出了一些有用的结论。这些结论为离心式喷嘴的设计和改良提供了依据,也为离心式喷嘴的改造提供了一条新的思路。