燃用乙醇、汽油混合物和含水乙醇的GDI发动机运行（英文）

SN1674-8484汽车安全与节能学报,2012年,第3卷第3期09/12CN 11-5904/U J Automotive Safety and Energy, 2012, Vol 3 No. 3257-264GDI Engine Operation with Ethanol/Gasoline Blends andAqueous EthanolRichard STONE, Longfei CHEN, Nathan HINTON, Felix LEACH, Fan XU(Department of Engineering Science, University of Oxford, Oxford OXI 3PJ, UK)Abstract: Ethanol is being promoted as a renewable fuel and as a means of improving energy security. Theblends of gasoline and ethanol from 0-100% ethanol were studied to evaluate their spray characteristics,combustion performances, and particulate emissions with blends of ethanol and water with up to 40% waterby volume being tested to research the combustion performances of different water ethanol blends and themiscibility of water with ethanol/gasoline blends using ternary phase diagrams for gasoline, ethanol, and water.The results show that presence of water in ethanol/gasoline mixtures is not an impediment to their use as a fuelin gasoline direct injection(GDI)engines. Adding ethanol to gasoline increases the injected fuel volume and theersistence of the fuel sprays, especially for a cold engine, leads to reduced mixture homogeneity, a decreasein the combustion stability and an increase in particulate matter emissions for a stoichiometric mixture. Addingwater to ethanol further increases injected fuel volume, but the increase in combustion duration and reduction incombustion stability are not significant with up to 30 water by volumeKey words: gasoline direct injection(GDI)engine; particulate emissions; blends; ethanol; aqueous ethanolsprays combustion燃用乙醇、汽油混合物和含水乙醇的GD|发动机运行(英文)Richard STONE,陈龙飞, Nathan HINTON, Felix LEACH,徐帆(牛津大学工程科学系,牛津OX13PJ,英国)摘要:作为可再生燃料和改善能源安全的手段,乙醇被逐步推广使用。为研究含水的混合乙醇的燃烧性能以及水与乙醇一汽油的溶混性,试验了含乙醇0~100%的汽油、乙醇混合物,评价了混合物的喷雾特性、燃烧性能和颗粒物排放性能,进行了汽油、乙醇、水的三相图分析和试验。结果表明:在含水量不大于40%时,汽油乙醇混合物中水的存在,不妨碍混合物用作汽油直喷发动机燃料。向喷射汽油中加注乙醇,增大了喷射燃料的体积;以这种燃料注入并持续喷雾,尤其是在冷发动机情况下,降低了混合物均匀性,减少了燃烧稳定性,对于当量比混合物,还增加了颗粒物的排放。向喷射燃料的乙醇中加注水,在含水量不大于30%时,燃烧持续时间不眀显增加,燃烧稳定性不明显减小。关键词:汽油直喷(Gu〕发动机;颗粒排放;乙醇;含水乙醇;混合燃料;喷油点火中图分类号:U461.91文献标志码:ADO:10.3969/ssn.1674-84842012.03.009收稿日期/ Received:2012-06-13基金项目/ Supported by: the Engineering and Physical Sciences Research Council and Jaguar Land Rover [UK];“凡舟”青年科研基金资助(20110404)第一作者/ First author: Richard Stone, Professor教授。E-mail: Richard, stone@ leng. Ox.acuk258J Automotive Safety and Energy2012,Vol.3No.3IntroductionHydrous ethanol can be used as a fuel alone, but unlikeEthanol has been used extensively in automotive fuelsanhydrous ethanol, hydrous ethanol is not miscible in all ratiosprimarily as a fuel extender and anti-knock agent in ethanolwith gasoline, so the water fraction is typically removed priorgasoline blends, with numerous advantages including higherto use in gasoline engines. An ethanol blend known as E85octane number (allowing higher compression ratios), reductions(meaning 85 per cent by volume ethanol) is readily availablein unburned hydrocarbon(HC), CO and NOx emissions, asin USA, Sweden and Finland; in Brazil pure ethanol is usedwell as easing overall air pollution and demand on petroleum(E100). To facilitate engine starting in winter the ethanolfuels, e.g. Al-Baghdadi. Pure ethanol fuel(E100) has alsocontent is reduced (E70 in USA, and E75 in Sweden), but itbeen studied e.g. Brewster, demonstrating higher specificis still marketed as E85. However, as will be discussed inoutput and brake efficiency, as well as lower CO, emissionsthe next section there is scope for using aqueous ethanol andgasoline mixturesEthanol is mostly simply made from the fermentation ofsugars, but competition with food use means that second1 Aqueous Ethanol and Gasoline Mixturesgeneration or cellulosic-ethanol needs to be exploited. Ethanol Water and ethanol are fully miscible as are ethanol andhas been produced from cellulose for over 100 years, butthere is now a rapid increase in the commercialisation of thegasoline, but water and gasoline are essentially immiscible, soprocess. Lignocellulosic materials(such as wood) have to behis raises the question of what happens when water is addedfinely divided and then hydrolysed(by an acid) to release theto an ethanol gasoline mixture such as E85, and indeed whatwould happen if aqueous ethanol was blended with gasoline?cellulose. Enzymes then break the cellulose into simple sugars The answer is provided by ternary diagrams such as Fig. I thatuch as glucose, which can be fermented to produce ethanol.Over the course of many millennia yeasts have been selectivelyhows the region(at the top of the figure)where a single phasecultivated that enable a high concentration(over 15% byis formed. Below the phase boundary a mixture will comprisevolume)of ethanol to be produced by fermentation in aqueouswo separate phases. As well as depending on temperature, thesolutionsposition of the phase boundary depends on the composition ofthe gasoline. Owen and Coley report data that shows thatThe ethanol can be partially separated by distillation, butincreasing the aromatic content increases the water tolerancewater and ethanol form an azeotropic mixture. An azeotropic of gasoline, and that higher alcohols(such as iso-butanol)mixture is one in which the composition of the liquid andact as co-solvents. Johansen and Schramm are essentiallyvapour are identical, so this limits the separation by distillation. concerned with how to form mixtures that stay within theThe azeotrope has a composition 96. 5% ethanol by volumengle phase region. They point out that if a line joining two(95.6% by mass)and is called hydrous ethanol. Water boilsdifferent ternary mixtures lies within the single phase region,at 100C, ethanol boils at 78 4C, but the azeotrope boilsthen any combination of these mixtures will remain as a singleat 78.2C, which is lower than either of its constituents(andphase. In the limiting case the line will be tangential to thethis is known as a positive azeotrope). The production ofphase separation curve. Unlike Johansen and Schramm, theanhydrous ethanol is by two principal methods. Firstly therenterest here is what happens with phase separationis azeotropic distillation, which depends on adding benzene orcyclohexane to the mixture; these are selected since they willEthanoform a ternary azeotrope. With cyclohexane as the entrainerjust sufficient cyclohexane is added to incorporate all the water25℃E85, W0, G15into the ternary azeotrope(7% water, 17% ethanol, and 76%cyclohexane), which boils at 621C. When this mixture isE73, W15, G12distilled it produces anhydrous ethanol in the column bottomEs7W33,G10(+17.5% water(+S0% water)(but with some contamination by the benzene or cyclohexane),and a vapour mixture of water and cyclohexane/benzene, whichE60,W37,G3(90% of mixture)be condensed to form a two-phase liquid mixture fromE30,W2G68hich it is easy to separate the water. The second more recentmethod is much less energy intensive and is just like gaseouspressure swing absorption-it uses molecular sieves to remove2 Phase Regionwater from the ethanol. The pores in the molecular sieveX△入allow absorption of water while they exclude ethanol. Ethanolvapour under pressure is passed through a bed of molecularsieve beads. After a period of time, the bed is regeneratedE73, W15, G12 means 73% ethanol, 15% water, 12% gasolineby the flow of inert atmosphere (e.g. N,)or under vacuum toFig 1 Ternary diagram for ethanol-gasoline-water blend withremove the absorbed water. By using two beds one is available a tie-line(the broken line)to show the composition when a mixto absorb water while the other is being regeneratedture forms two phases, adapted from Johansen and Schramm 4260J Automotive Safety and Energy2012,Vol.3No.32.2 Engine and Test Systemof the dMs500 then converts these ring currents into a sizeIt is well known that Gasoline Direct Injection engines canresolved number concentration. The DMS500 software useoperate with a higher compression ratio than Port Fuel Injection a Bayesian statistical algorithm to generate two lognormal(PFD)engines because the evaporative cooling from the fueldistribution fitting spectra, which are meant tocan be used to cool the incoming air. Since the temperature is nucleation mode and the accumulation mode. This techniquelower at the start of compression, then all subsequent processeshas the additional advantage that it tends to remove noise. Thiswill be at a lower temperature, so for a given octane rating fuel, is particularly important for large particle sizes, for whichthen a higher compression ratio can be used for a given chargeeven small number concentrations lead to large mass valuestemperature at the end of compression. The lower chargePM mass concentrations were derived from PM numbertemperature also increases the volumetric efficiency leading tooncentrations using a PM density modelan increase in the specific output and a consequential additionalreduction in fuel consumption. The increased enthalpy ofM/kg=172×1024(D,/m)26vaporisation with ethanol blends could lead to additional gains, This equation had been experimentally determined using abut mixtures might also be less homogeneous. The combustion Couette CPMA(Centrifugal Particle Mass Analyser)on a verysystem is essentially the same as that used in the Jaguar AJV8similar SGDI combustion systemengine that has been comprehensively described by Sandfordet al. t. The injection pressure was 150 bar and the injection3 Results and discussiontiming(CA, bTDC)was 280 throughout the experiments3.1 Ethanol and Gasoline MixturesTable 2 Single-Cylinder GDI Optical Engine SpecificationMulti-hole Nozzletal number and total mass the trend for the warm condition i89×903mmless clear. The main reason for these abnormalities is that ulgompression Ratioand its El0 blend produce very low levels of PM emissionsFuel Pressure15.0 kPa(less than 1 order of magnitude more than background noiseIgnition, CA(bTDC)level)due to the low aromatic composition and hence the highManifold Absolute Pressure50 kPa■WARMA series of injection and combustion images was captured ba Photron PCl-1024 high speed video camera at up to 9, 000fps, Illumination of the spray was with a synchronized LEDsystem, whilst the combustion process was visualized withthe visible light flame chemiluminescence. Image processingwas used to separate the spray from the background and the2pixel count within the spray was integrated to give a semiquantitative value for the Mie scatteringPura E10 E20E50E70E85Total Pn with different fuelsA Cambustion HFR400 fFID(fast response Flame lonisation(a) Total Particulate NumberDetector) was used to investigate the variability of the prefame hydrocarbon concentration near the spark plug, usingan offset spark plug with a threaded hole to accommodatea sampling capillary. Particulate Matter(PM)numberconcentrations and size distributions were measured with ausing the Cambustion sampling system which incorporatesa heated sample pipe and dilution air. The diluted exhaustaerosol passes through a corona-wire uni-polar diffusioncharger producing a known charge distribution on the aerosolE10E50E70particles. These particles then drift when subjected to anTotal Pm with different fuelselectric field and impact upon electrometer rings contained(b) Total Particulate Masswithin the DMS500 classifier column. The current from theserings is then measured and is proportional to the number of2 Total particulate number, No,(a)and total particulateparticles impacting upon the rings. The transfer functionmp,(b)emissions for different stoichiometric ULG/ethanolends in a cold(20℃) and a warm(a8o℃) engineRichard SToNE, et al: GDI Engine Operation with Ethanol/ Gasoline Blends and Aqueous Ethanol261noise to signal ratio might have con founded the actual resultssubsequent vaporisation characteristicsAlso, any slight difference in AFR would affect the resultsFigure 3 shows that as the ethanol content in the gasolineIn summary, for a stoichiometric mixture, E85 produces 6-15increased, then the sprays persist for longer, especially for coldtimes higher total PM number and 8-11 times higher total PMengine operation, The ethanol increases the volume of fuelmass than uLG. The total PM mass with the e85 blend is 11that has to be injected and the enthalpy of vaporisation. It cantimes that with ULG under the cold condition whilst it is 8be conjectured that this will increase the inhomogeneity of theimes higher under the warm condition. These phenomena are mixture causing a reduction in combustion stability and theprimarily attributed to the differences in the fuel spray andPM emissions to riseE85E8510Crank angle( bTDC)/()(a) Cold Condition(at 20C)Crank angle(bTDO/(°Fig 3 Integrated Pixel Values as a Function of Crank Angle for the Cold and Warm condition for Different Stoichiometric ULG/Ethanol BlendsTable 3 shows that high levels of ethanol (especially in the cold of the fFID signal was used to represent the hydrocarbonengine)increased the combustion duration, and this in turn(see level, and for a perfectly homogeneous mixture then theseFigure 4)was associated with a reduced combustion stabilityvalues should be constant as the overall air fuel ratio wasFigure 5 shows typical signals from the in-cylinder fFIDfixed. The cycle-to-cycle variation in the fFID signal thussampling system in the region of the spark plug. The fFIDndicates inhomogeneity, and this was quantified by using thsignal rises rapidly during the compression stroke, but thenCoefficient of variation( Cov =standard deviation/mean)rises more slowly until combustion occurs, at which pointFig. 6 shows that high levels of ethanol(especially in the coldthe hydrocarbon level falls rapidly. The maximum valucengine)increased the inhomogeneity in the cylinder, and this264J Automotive Safety and energy2012,Vol.3No.30.9)has a lower Cov than with stoichiometric operation(Acknowledgments1.0), and the Pfi has a lower Cov than gDi(which can beattributed to the formation of a more homogeneous mixture).This work was funded by the Engineering and PhysicalSciences Research Council and Jaguar Land Rover [UK]. TheThe differences are more apparent as the water contentauthors also wish to thank Dr roger Cracknell of Shell Globalincreased, as this leads to a longer combustion duration( FigSolutions for providing the test fuel and its compositional8). The faster burn means that combustion is centred closerinformationto top dead centre, so that the effect of volume changes in thecombustion chamber are minimised. With the ethanol andReferenceswater mixtures the particulate Matter number emissions werevery low, and were sometimes below the noise level of the[I] Al-Baghdadi M AR S Measurement and predieDMS500, so these results are too low to be reported.the effect of ethanol blending on the performance and pollutantsemission of a four-stroke spark ignition engine [] Proc IMechE,3 CONCLUSIONSPart D: J Automobile Eng, 2008, 222(5): 859-873[2] Brewster S Initial development of a turbo-charged direct injectionA range of ULG/ethanol blends(E0 to E85 )have been testedE100 combustion system [Cy/ 14 "Asia Pacific Automotive Engunder cold(20 C)and warm( 80 C)coolant conditions,Conf, 2007. Hollywood, California, USA SAE.and water ethanol mixtures have been tested with up to 40%[3]Owen K, Coley T. Automotive Fuels Reference Book [M]. 2nd Ed.water by volume. Spray and combustion characteristics have1995, Society of Automotive Engineers, ISBN 1560915897been investigated using high-speed imaging and the variability [4] Johansen T, Schramm J Low-temperature miscibility of ethanol-of pre-flame HC concentration at the spark plug was alsogasoline-water blends in flex fuel applications [J]. Energymeasured using a Cambustion fFID for the UlG/ethanol testsSources, Part A: Recovery, Utilization, and environmentalThe main findings areEffects,2009,31(18):1634-16455 Anderson JE, Kramer U, Mueller S A, Wallington T J OctaneAn increase in ethanol addition in the ULG/ethanol testsnumbers of ethanol- and methanol-gasoline blends estimated fromled to an increase in both particle number and mass, due tomolar concentrations J]. Energy Fuels, 2010, 24: 6576-6585the deleterious effect of ethanol on spray break-up and theDOI:10.102lef101125cevaporation efficiency as a result of its high vaporization6]Hsieh w D, ChenR H, Wu TL, Lin T H. Engine performance andenthalpy and low energy densitypollutant emission of an SI engine using ethanol-gasoline blendedIn the ULG/ethanol tests, the cold fuel spray plumes arefuels [] Atmospheric Environment, 2002, 36: 403-41more clearly defined and last longer than warm plumes[7] Sandford M, Page G, Crawford P The All New AJV8 [R]. SAEThe IMep and mfb durations for the ulg/ethanol testsTech Paper, 2009-01-1060exhibited less variability for a warm engine than a cold[8] Reavell K, Hands T, Collings N A. Fast response particulateengine for all the test fuelsspectrometer for combustion aerosols [C] SAE PowertrainFluid Systems Conference Exhibition, October 2002: SAE, SanFor fuels with high ethanol blending ratios, the increaseDiego, CA, USA, 2002in ethanol content led to an increase in the mixture[9] Symonds J, Price P, williams P, StoneR. Density of particlesinhomogeneity at the spark plug.emitted from a gasoline direct injection engine[C]12"ETHAs the percentage of water/ethanol mixtures was increasedConference on Combustion Generated Nanoparticles, 2008Zurich(up to 40%water by volume), the combustion durationreased and there was a reduction in combustion stability[10] Braisher M, Price P, Stone R. Particle number emissions from athis was attributed to the longer burn duration and aange of European vehicles [R]. SAE Tech Paper, 2010-01-0786educed level of mixture homogeneityAbout 15% by mass (or 12%by volume)water can beadded to E85 before phase separation occurs. If 50% bymass of water is added to E85 then phase separation occursbut the water/ethanol phase(E60, W37, G3)would still beflammable