生物柴油和DME喷雾研究(何景思).pdf.doc

Fuel Processing Technology 91 (2010) 354363Contents lists available at ScienceDirectFuel Processing Technologyj o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / f u p r o cA study on the macroscopic spray behavior and atomization characteristics of biodiesel and dimethyl ether sprays under increased ambient pressureHyung Jun Kim a, Su Han Park a, Chang Sik Lee b,a Graduate School of Hanyang University, 17 Haengdang-dong, Seoungdong-gu, Seoul 133-791, Koreab Department of Mechanical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Koreaa r t i c l ei n f oArticle history:Received 2 June 2009Received in revised form 3 September 2009 Accepted 4 November 2009Keywords:Spray characteristicsBiodieselDimethyl ether (DME)Light intensity levelAmbient pressurea b s t r a c tThe aim of this work is to investigate the spray behaviors of biodiesel and dimethyl ether (DME) fuels using image processing and atomization performance analysis of the two fuel sprays injected through a common-rail injection system under various ambient pressure conditions in a high pressure chamber. In order to observe the biodiesel and DME fuel spray behaviors under various ambient pressures, the spray images were analyzed at various times after the start of energization using a visualization system consisting of a high speed camera and two metal halide light sources. In addition, a high pressure chamber that can withstand a pressure of 4 MPa was used for adjusting the ambient pressure. From the spray images, spray characteristics such as the spray tip penetration, cone angle, area, and contour plot at various light intensity levels were analyzed using image conversion processing. Also, the local Sauter mean diameters (SMD) were measured at various axial/radial distances from the nozzle tip by a droplet measuring system to compare the atomization performances of the biodiesel and DME sprays.The results showed that the ambient pressure had a significant effect on the spray characteristics of the fuels at the various experimental conditions. The spray tip penetration and spray area decreased as the ambient pressure increased. The contour plot of the biodiesel and DME sprays showed a high light intensity level in the center regions of the sprays. In addition, it was revealed that the atomization performance of the biodiesel spray was inferior to that of the DME spray at the same injection and ambient conditions. 2009 Elsevier B.V. All rights reserved.1. IntroductionIn a high speed direct injection (HSDI) diesel engine, the fuel spray development and atomization characteristics play an important role in the improvement of combustion and engine performance, because they influence the fuelair mixing in the cylinder. Therefore, it is necessary to analyze the spray development and atomization characteristics of various fuels in order to reduce exhaust emissions and improve thermal efficiency of the diesel engine. Among the various alternative fuels, biodiesel and dimethyl ether (DME) fuels are the most popular. This is because biodiesel fuel can be used in a conventional diesel engine without modification of the engine and a diesel engine fueled with DME can be operated with only a partial modification of the fuel supply system. In addition, these alternative fuels contain large amounts of atomic oxygen in comparison with diesel fuel and their exhaust emissions, such as hydrocarbon (HC), soot, and particulate matter (PM), are remarkably decreased. However, biodiesel and DME fuels differ from conventional diesel fuel in some characteristics such as a nozzle cavitating flow, sprayCorresponding author. Tel.: +82 2 2220 0427; fax: +82 2 2281 5286.E-mail addresses: junandjinhanyang.ac.kr (H.J. Kim), psh7836hanyang.ac.kr(S.H. Park), csleehanyang.ac.kr (C.S. Lee).0378-3820/$ see front matter 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2009.11.007behavior, atomization, the combustion process, and formation of emissions 17. Therefore, there have been many investigations into the spray development, combustion and emission characteristics of these two alternative fuels in diesel engines.Teng et al. 812 conducted numerical studies on the thermody-namic properties of liquefied DME fuel such as density, viscosity, latent heat, enthalpy, surface tension and vapor pressure. Based on the existing molecular and chemical structure theories, they developed various equations for the fuel properties according to temperature for the analysis of fuel-system design and modeling. An experimental investigation into the effects of temperature on the properties of biodiesel fuel was conducted by Yoon et al. 13 and Yuan et al. 14. In addition, Park et al. 15 carried out research into biodiesel and biodieselethanol blend fuel properties such as the specific gravity, density, dynamic and kinetic viscosity and developed empirical equations describing them. To compare the spray characteristics of DME and diesel fuel, Suh et al. 16 investigated DME and diesel spray characteristics in the combustion chamber. They reported that the spray tip penetration of DME fuel is shorter than that of diesel fuel and that the DME spray has a smaller Sauter mean diameter (SMD) than diesel spray under the same injection conditions. Experimental investigations into the spray structure of diesel fuel and various oxygenated fuels, including dimethyl ether, using a PIV measuringH.J. Kim et al. / Fuel Processing Technology 91 (2010) 354363355Fig. 1. Schematics of spray visualization and droplet measuring systems.method were carried out by Wu et al. 17. The spray and combustion characteristics of biodiesel-blended fuel at various mixing ratios were investigated by Lee et al. 18. They reported that the spray tip penetrations of biodiesel and biodiesel-blended fuels showed a similar pattern, regardless of the mixing ratio of the biodiesel and the atomization performance of the biodiesel-blended fuel was inferior to that of the conventional diesel fuel due to the high surface tension of the biodiesel fuel. Kim et al. 19,20 conducted experimental and numerical investigations of the atomization characteristics of diesel, biodiesel, DME and biodieselethanol blended fuels. In their work, the calculated atomization results show good agreement with experimental results. Kim et al. 21 also carried out experimental and numerical studies to compare diesel and DME sprays for two chamber shapes under high ambient pressure conditions.In spite of the research into biodiesel and DME fuels, detailed information about their spray behaviors and atomization characteristics under various ambient pressures is not available. The aim of this work is to investigate the spray behavior and atomization characteristics of biodiesel and DME fuels under various ambient pressure conditions in a high pressure chamber using spray image visualization and spray droplet measuring results. Using the spray images obtained from visualization system, the spray tip penetration, spray cone angle, spray area, and contour plot according to light intensity were measured andTable 1Specifications of experimental apparatus.Visualization system with high speed cameraLight sourceTwo metal halide lampsFrame rate10,000 fpsShutter speed1/20,000 sResolution512 512Droplet measuring systemLight sourceAr-ion laserWave length514.5 nm, 488 nmLaser beam diameter1.4 mmFocal lengthTransmitter : 500 mmReceiver : 250 mmCollection angle30 degreesFilter frequency40 MHzPMT voltage500 Vanalyzed to compare the biodiesel and DME sprays. The local SMD at various axial and radial distances and under various ambient pressure conditions were measured and compared to evaluate the atomization performance of biodiesel and DME sprays.2. Experimental apparatus and procedures2.1. Experimental apparatusAs illustrated in Fig. 1, spray visualization and droplet measuring systems were used to investigate the spray characteristics under ambient pressure, such as the increasing rate of spray penetration, spray cone angle, spray area, and the mean droplet size distribution. The spray visualization system consisted of a high speed camera (Photron, Fastcam-APX RS) with two metal halide lamps as a light source. The frame rate and shutter speed of the high speed camera were set to 10,000 fps (frames per second) and 1/20,000 s, respectively. The resolution of the spray images was set to 512 512. The input signals to the high speed camera and a test injector with a single hole were synchronized by a digital delay/pulse generator (Berkeley Nucleonics Corp, Model 555). The test injector had a 0.8 mm nozzle depth and a 0.3 mm nozzle diameter, and was operated by an injector driver (TEMS, TDA-3200H). The droplet measuring system was a phase Doppler particle analyzer (PDPA) system composed of a receiver, a transmitter, and a signal analyzer, with an Ar-ion laser for a light source. The Ar-ion laser had a maximum power of 5 W, a laser beam diameter of 1.4 mm and two wave lengths of 514.4 nm and 488 nm. To measure the droplet size (SMD), the transmitter and receiver were moved by a 3-D traverse at periods of 10 mm in the axial direction, and 2 mm in the radialTable 2Properties of biodiesel and DME fuels.Fuel propertyBiodieselDimethyl ether(soybean oil)(DME)Density (kg/m3)884660Viscosity (mm2/s)4.06.00.120.15Surface tension (kg/s2)0.0280.012Boiling point temperature (C)31535023Flash point temperature (C)10017042Cetane number486568356H.J. Kim et al. / Fuel Processing Technology 91 (2010) 354363Table 3Experimental conditions.Injection systemCommon-railFuelBiodiesel, DMENozzle typeMini-sacNumber of nozzle holesSingle holeHole diameter0.3 mmInjection pressure50 MPaInjection duration1.2 msAmbient temperature293 KAmbient pressure0.1, 1.0, 2.0 MPadirection. The detailed specifications of the visualization and droplet measuring systems are shown in Table 1.2.2. Experimental proceduresIn this work, a high pressure chamber which could be pressurized to 4 MPa (max.) was utilized to study the effects of the ambient gaspressure on the overall spray characteristics. The pressure conditions in the high pressure chamber were created using nitrogen gas. In the experiments, the residual gas and fuels in the high pressure chamber were exhausted through the suction chamber after every injection.Biodiesel derived from soybean oil and DME were used as test fuels. To use DME fuel in the liquid phase, DME fuel in the gas phase was pressurized in the fuel tank to higher than the vapor pressure of DME fuel at the ambient temperature. The detailed specifications of the test fuels are listed in Table 2. The macroscopic spray characteristics were analyzed using the spray images obtained from the visualization system. In the after-process spray images, the cell image changed with the threshold level, and the spray area was defined as the sum of the total cells. In addition, the spray cone angle indicated the angle between the two lines formed by the nozzle tip and the two furthest radial points. Based on the data acquisition rate and signal intensity 22,23, the laser output and PMT (photomultiplier tube) voltage were at 700 mW and 500 V, respectively. The sub-range of the diameter for the effective range of the PDPA signal analyzer was from 2 m to 80 m considering that the nozzle diameter was 300 m, and approximatelyFig. 2. (a) Definition of spray characteristics and conversion of spray image according to the light intensity level, and (b) injection rate of biodiesel and DME spray.H.J. Kim et al. / Fuel Processing Technology 91 (2010) 354363357Fig. 3. Spray evolution processes of the fuels at different ambient pressures from 0.9 ms to 1.3 ms after the start of energization. (a) Teng = 0.9 ms (b) Teng = 1.1 ms, (c) Teng = 1.3 ms.358H.J. Kim et al. / Fuel Processing Technology 91 (2010) 354363Fig. 4. Outline of the biodiesel and DME spray evolution process at different ambient pressures (tasoe = 1.4 ms).5000 droplets were collected and averaged at each measurement point. When fuel droplets pass through the measurement volume of fringe created by the laser beam from the Ar-ion laser, the dispersed beam is detected at the receiver. The detected phase difference and Doppler signal fre