外文翻译喷油定时对柴油天然气双燃料发动机排放性影响

1、喷油定时对柴油/天然气双燃料发动机排放性影响替代能源，2007，32：2361-2368摘 要导致全球变暖的温室气体排放日益受人关注，现已证明它主要来源于矿物燃料的燃烧。科学家一直在寻求绿色的替代燃料，天然气因其辛烷值高、环保性好被认为最有潜力作为柴油机上的替代燃料。然而进一步研究表明，天然气燃烧速率低，着火延迟长，从而产生高的升功率使柴油机易产生爆燃。这项实验研究了基于柴油机的双燃料发动机喷油定时对排放性的影响：柴油机标准喷油定时为30 BTDC。当喷油定时调整为3 BTDC时，发动机运转不稳，而当喷油定时变为3 BTDC时发动机运行顺畅，特别是在低负荷工况下。故把3 BTDC定为优化喷油定

2、时。试验表明，虽然燃料消耗略有增加，但着火延迟缩短，CO、CO2排放量降低。关键词：一氧化碳（CO）； 二氧化碳（CO2）；碳氢化合物（HC）排放；着火延迟 引言1997年东京各国首脑会谈关注的焦点是温室气体排放对全球环境的影响。它能导致洪灾、山体滑坡等，2005年在美国发生的Katrina、Rita 和Wilma飓风就是最好的例证。这都是由于矿物燃料燃烧产生大量温室气体CO2所致。许多科学家在寻找替代传统矿物燃料的绿色燃料(Nwafor1、 Lowe and Branhan2 、 Horie and Mishizawa3 )，他们不约而同对天然气作为未来柴油机上的替代燃料极为看好。然而天然气

3、要真正替代柴油还有很多问题要解决。比方说，天然气自然温度高，这就要求配有着火系统。再者，天然气因燃烧速率低，着火延迟长，从而缸内压力波动大。不过从最近关于双燃料发动机性能、排放研究可知(Nwafor4 、Stone and Lallommatos5、Karim and Ali6)，天然气辛烷值高(RON 131)，故抗爆性好，可以通过提高压缩比来改进发动机的性能。这个试验研究了基于柴油机的双燃料发动机喷油定时对排放的影响（以天然气为主要燃料柴油天然气双燃料发动机）。在压缩行程终了吸入空气天然气混合气，并喷入一定量的柴油引燃混合气。所需引燃柴油量受爆燃限制(Rani and Rice7 、Nwa

4、for 8)，随柴油量增加，天然气减少，爆燃趋势减弱。优化喷油定时是为了补偿着火延迟和燃烧速率低的影响。研究表明，与标准喷油定时相比，发动机在优化喷油定时下，HC、CO2排放量下降，着火延迟缩短，但燃料消耗量大。发动机在全柴油运行下，HC排放最低，CO排放最高。总的来说，在低负荷、低转速下，优化喷油定时对发动机排放改进很有用，但在高负荷下，发动机温度起着决定作用。 实验装置这个试验所用的发动机为一个Petter型AC1单缸柴油机，它是一种空冷高速直喷式发动机。功率计包括一个分流式Mawdsley型直流发电机和一个能量储存器，力矩则是由相当于牛顿弹簧测量范围的装置测得。燃烧室压力由Kistle型

5、7063A压力计测量（这个压力计是水冷电控压电式的，灵敏度为79pc/bar），再通过数字示波器显示，并把结果储存到软盘里以便随后分析缸内压力最大升高率。排气歧管压力由普通型压力计测量，空气流量由Viscous流量计测。和测量缸内壁温度一样，进、排气道安装有热敏电阻可以监控气体温度变化。柴油由喷油泵输到喷油器，它的流量由一个50cm3的分级式滴管和秒表共同完成。天然气流量由一个能测量多样空间的转子流量计测得，相对温度和环境温度由Vaisala型温度计测，空气天然气混合气由安装在进气歧管的气体控制阀控制。21 天然气组成成份氮2.18% 甲烷92.69% 乙烷3.43% 二氧化碳0.52% 丙烷

6、0.71% 异丁烷0.12%正丁烷0.15% 正戊烷0.09% 正己烷0.11%毛热值=38.59MJ/m3 净热值= MJ/m3Wobbe数= MJ/m3 空燃比=16.65:1 柴油净热值= MJ/kg 柴油相对密度=22 发动机数据缸径=76.20mm 行程=66.67mm排量=304 cc 压缩比=17 喷油压力=183bar标准喷油定时=30BTDC 优化喷油定时=33.5BTDC 实验结果31 一氧化碳（CO）排放CO排放量与空燃比有关，它是表明发动机燃烧效率的一个参数。图1和图2分别显示了发动机转速在3000rpm和2400rpm时，双燃料发动机CO排放情况。由图可知，发动机不同

7、转速下，CO的排放特性是不同。总的来说，在发动机运转在双燃料时，与标准喷油定时相比，优化喷油定时下CO排放量明显低。两者CO排放变化趋势相似，但CO排放量集中区段不同。全柴油运转时，CO排放量最少，但它随负荷增加而加大。CO排放量最大点是在全柴油运转高负荷下产生的。图1 CO排放(n=3000rpm)图2 CO排放 （n=2400rpm）32 二氧化碳（CO2）排放图3和图4显示了CO2的排放特性。由图可知，喷油定时对CO2排放影响很大。在优化喷油定时下，不管发动机处于哪个转速下，CO2的排放都很低。CO2排放量最高是在全柴油运转下，而在标准喷油定时下，CO2排放量处于中间。试验表明，随空燃比

8、的减小，CO2的排放量呈增多趋势。我们知道在理想燃烧下，燃料燃烧产物为CO2和H2O，故CO2可以作为衡量燃烧效率的一个参数。使发动机排放尽量多的CO2和少的HC一直是我们追求的目标。图3 CO2排放（n=3000rpm）图4 CO2排放(n=2400rpm)33 碳氢化合物（HC）排放图5显示了发动机转速为3000rpm时，分别在双燃料和全柴油运行下HC的排放。全柴油运行下，HC排放量最少。与标准喷油定时相比，在优化喷油定时在低负荷下排放低但在高负荷下排放高。图6显示发动机转速为2400rpm时HC的排放性与图5相似。实验表明，在燃烧开始时，有大量天然气未及时参与反应，这可能是因为天然气燃烧

9、速率慢的原故。双燃料运行下，HC排放量大主要原因有：稀薄燃烧、缸内壁熄火作用、天然气空气混合气不均匀等。由图还可知，不同工况，不管是在标准喷油定时还在优化喷油定时HC排放量都比较高。当在进气行程，由于气门重叠角大导致大量已吸入的新鲜气又被排出很可能是重要原因。图5 HC排放(n=3000rpm)图6 HC排放(n=2400rpm)34 着火延迟着火延迟指柴油机燃料被引燃到燃料正式燃烧之间的时间段。图7和图8显示了发动机在双燃料和全柴油运行下，着火延迟的情况。从两图中可知，虽发动机转速不同，但全柴油运行下着火延迟都比较短。与优化喷油定时相比，标准喷油定时在高负荷下着火延迟长。在发动机转速为240

10、0rpm时，双燃料与全柴油运行着火延迟有明显不同，标准喷油定时下着火延迟最长。实验知，双燃料下，随转速下降，着火延迟变长，这与全柴油运行下刚好相反。因为在低转速时，大量气体参与预燃从而增加了发动机爆燃趋势。在双燃料运行下总的比全柴油运行下着火延迟要长，因天然气自燃温度（704 oC）比柴油（245 oC）高很多，在压缩行程终了缸内温度达不到气体自燃温度。柴油的雾化程度和喷油锥角取决于缸内气体密度，雾化不良导致着火延迟长可能是由于油滴原因。图7 点火延迟(n3000rpm)图8 点火延迟(n2400rpm) 结论试验表明，替代燃料都有着火延迟特性，有人认为是受发动机负荷和转速和影响。同时每一种替

11、代燃料都有各自的最佳喷油定时，试验发现，在最佳喷油定时下，发动机的燃料消耗量都略微增加，但CO2的排放量明显下降，CO排放集中的也下降。在双燃料运行下，HC排放比较高，但在优化喷油定时下，它的排放有明显改进。在双燃料时，与标准喷油定时相比，优化喷油定时在低负荷运行下优为顺畅，但当喷油定时调整为3BTDC时，发动机运转就不稳了。在高负荷下，燃烧温度起决定作用，进而增加了柴油的蒸发可缩短着火延迟。故调整喷油定时不适合高负荷工况。双燃料发动机据说受着火延迟影响。参考文献1 O.M.I. Nwafor and G. Rice, Combustion characteristics and perfor

12、mance of natural gas in high speed, indirect injection diesel engine, WREC, UK (1994) p. 841.2 W. Lowe and R.T. Brandham, Development and application of medium speed gas burning engines, IMechE 186 (1971), p. 75.3 K. Horie and K. Mishizawa, Development of a high fuel economy and performance four-val

13、ve lean burn engine, IMechE C448/014 (1992), p. 137.4 O.M.I. Nwafor, Effect of advanced injection timing on the performance of natural gas in diesel engine, Int J Indian Acad Sci, Sadhana 25 (2000), p. 11. HYPERLINK :/ sciencedirect /science?_ob=ArticleURL&_udi=B6V4S-4NT57K0-1&_user=1492036&_coverDa

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15、n combustion system for gaseous fuels at high compression ratios, J Inst Energy 64 (1991), p. 202. HYPERLINK :/ sciencedirect /science?_ob=ArticleURL&_udi=B6V4S-4NT57K0-1&_user=1492036&_coverDate=11%2F30%2F2007&_alid=730971422&_rdoc=9&_fmt=high&_orig=search&_cdi=5766&_sort=d&_docanchor=&view=c&_ct=8

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17、5/75) (1975), p. 135. HYPERLINK :/ sciencedirect /science?_ob=ArticleURL&_udi=B6V4S-4NT57K0-1&_user=1492036&_coverDate=11%2F30%2F2007&_alid=730971422&_rdoc=9&_fmt=high&_orig=search&_cdi=5766&_sort=d&_docanchor=&view=c&_ct=87&_acct=C000053168&_version=1&_urlVersion=0&_userid=1492036&md5=099d579552958

18、2a3cfc18f3ddf151767 l bbib7#bbib7 7 Bari S, Rice G. Knocking in gas-fumigated dual-fuel engine. In: Proceedings of the fourth international conference on small engines, their fuels and the environment. 2124 September 1993. HYPERLINK :/ sciencedirect /science?_ob=ArticleURL&_udi=B6V4S-4NT57K0-1&_user

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20、ormance using natural gas as primary fuel, J AMSE, Modelling, Simulation Control, Fr 71 (3) (2002), p. 29.Effect of advanced injection timing on emissioncharacteristics of diesel engine running on natural gasO.M.I. NwaforDepartment of Mechanical Engineering, Federal University of Technology, Owerri,

21、 Imo State, NigeriaReceived 30 November 2005; accepted 10 December 2006Available online 23 May 2007AbstractThere has been a growing concern on the emission of greenhouse gases into the atmosphere, whoseconsequence is global warming. The sources of greenhouse gases have been identied, of which themaj

22、or contributor is the combustion of fossil fuel. Researchers have intensied efforts towardsidentifying greener alternative fuel substitutes for the present fossil fuel. Natural gas is now beinginvestigated as potential alternative fuel for diesel engines. Natural gas appears more attractive dueto it

23、s high octane number and perhaps, due to its environmental friendly nature. The test resultsshowed that alternative fuels exhibit longer ignition delay, with slow burning rates. Longer delayswill lead to unacceptable rates of pressure rise with the result of diesel knock. This work examines theeffec

24、t of advanced injection timing on the emission characteristics of dual-fuel engine. The engine hasstandard injection timing of 301 BTDC. The injection was rst advanced by 5.51 and given injectiontiming of 35.51 BTDC. The engine performance was erratic on this timing. The injection was thenadvanced b

25、y 3.51. The engine performance was smooth on this timing especially at low loadingconditions. The ignition delay was reduced through advanced injection timing but tended to incur aslight increase in fuel consumption. The CO and CO2emissions were reduced through advancedinjection timing.r 2007 Elsevi

26、er Ltd. All rights reserved.Keywords: Carbon monoxide; Carbon dioxide and hydrocarbon emissions; Ignition delay1. IntroductionThe 1997 Kyoto-Japan summit focused on the impact of greenhouse gases on theenvironment, a consequence of global warming. These results in ooding and landslides.The 2005 hurr

27、icane Katrina, Rita and Wilma effects in USA been typical examples. The0960-1481/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.doi:HYPERLINK /10.1016/j.renene.2006.12.0062362ARTICLE IN PRESSO.M.I. Nwafor / Renewable Energy 32 (2007) 23612368issue has been attributed to the

28、combustion of fossil fuel which emits greater proportion ofcarbon dioxide. Literature review showed quite a number of research work carried outwith the aim of identifying greener substitute for the present high pollutant conventionalhydrocarbon (HC) fuels Nwafor HYPERLINK #81, Lowe and Branham HYPER

29、LINK #82 and Horie and Mishizawa HYPERLINK #83.There is a great interest in natural gas as alternative fuel for diesel engines. However, itsuse as viable substitute for diesel fuel has not yet become a reality due to related problems.First, natural gas has high self-ignition temperature (SIT) and re

30、quires separate means ofinitiating combustion. Secondly, it has longer delay period with slow burning rate resultingin pressure uctuation. Works reported by Nwafor HYPERLINK #84 and Stone and Ladommatos HYPERLINK #85,constitute some recent research efforts to determine the performance and emissionch

31、aracteristics of gaseous-fuelled engines. Natural gas has high resistance to knock whenused in internal combustion engines due to its high octane number (RON 131), Karim and*AliHYPERLINK #86HYPERLINK #8. It is therefore, suitable for engines of high compression ratios with possibleimprovement in per

32、formance. This work examines the effect of advanced injection timingon emission characteristics of diesel engine using natural gas as primary fuel. A mixture ofgas and air was inducted during the induction stroke and towards the end of compressionstroke a metred quantity of pilot diesel fuel was inj

33、ected into a hot compressed charge toinitiate combustion. The maximum quantity of pilot fuel needed is limited by the knocking*tendency of the engine, Bari and RiceHYPERLINK #87and NwaforHYPERLINK #88HYPERLINK #8. The knocking tendency isreduced by introducing more pilot fuel and/or reducing primary

34、 (alternative) fuel. Theadvanced injection timing is intended to compensate for the longer ignition delay and slowburning rate of natural gas fuelled engine. The test results showed decrease in CO and CO2emissions, and the delay period was also reduced with advanced injection timing compareto standa

35、rd dual timing. The highest fuel consumption was recorded with the advancedtiming. Diesel fuel operation produced the lowest HC and the highest CO2emission. Theoverall results indicate that advanced timing is benecial at low-speed and low-loadingconditions. The system temperature became the dominant

36、 factor at high-loadingconditions.2. Experimental apparatusA Petter model AC1 single cylinder energy cell diesel engine was used for this work. It isan air-cooled high speed indirect injection four-stroke engine. The dynamometer used toload the engine comprised of a shunt wound Mawdsley d.c generato

37、r and load bank. The*reaction force and torque were measured by means of a 1000.5 Newton-spring scale.Measurement of combustion chamber pressure was obtained by installing a kistler type7063 A, sensitivity 79 pc/bar, water-cooled piezo-electric pressure transducer into the aircell of the combustion

38、chamber. The cylinder pressure was displayed on a digitaloscilloscope (Nicolet 4094) and stored in a diskette for later analysis of maximum rate ofcylinder pressure rise. Pressure in the inlet manifold was measured by a normal U-tubemanometer. Airow was measured by means of a viscous ow metre. Therm

39、ocouples wereinstalled to monitor gas temperature at inlet and outlet ducts as well as cylinder walltemperatures. Fuel was fed to the injector pump under gravity and the volumetric ow ratewas measured by the use of a 50 cm3graduated burette and stopwatch. Gas ow wasmeasured by a variable area ow rot

40、ameter. The relative humidity and ambienttemperature were monitored by hygrometer type Vaisala. Natural gasair mixture wascontrolled by the gas control valve with fumigation taking place in the engine inletARTICLE IN PRESSO.M.I. Nwafor / Renewable Energy 32 (2007) 236123682363manifold. The HC emissi

41、ons were measured by a Rotork ame ionisation detector (FID)analyser model 523. The CO and CO2emissions were measured by an Oliver k550 infraredanalyser.2.1. Typical composition of natural gas2.18% nitrogen, 92.69% methane, 3.43% ethane, 0.52% carbon dioxide, 0.71%propane, 0.12% iso-butane, 0.15% n-b

42、utane, 0.09% pentane and 0.11% hexaneGross caloric value ? 38.59 MJ/m3Net caloric value ? 34.83 MJ/m3Gross Wobbe number ? 49.80 MJ/m3Stoichiometric air/fuel ratio ? 16.65:1Net caloric value of diesel fuel ? 42.70 MJ/kgRelative density of diesel fuel ? 0.844.2.2. Engine dataBore ? 76.20 mm, stroke ?

43、66.67 mm, engine capacity ? 304 cc, compression ratio ? 17,*fuel injection release pressure ? 183 bar, standard fuel injection timing ? 301BTDC,advanced fuel injection timing ? 33.51 BTDC.3. Test results3.1. Carbon monoxide (CO) emissionsCarbon monoxide production relates to the fuelair ratio and it

44、 is a measure of thecombustion efciency of the system. HYPERLINK #4Figs. 1 and 2 compare CO emission characteristics ofdiesel fuel operation with the standard and advanced injection timing when running onnatural gas at the speeds of 3000 and 2400 rpm, respectively. The advanced injection timingshowe

45、d a signicant reduction in CO emissions compared to standard dual-fuel operation.The diesel fuel operation produced the lowest CO emissions at low loading conditions andincreased with load. There was marked difference in CO concentrations at the exhaustbetween the advanced injection timing and the s

46、tandard timing for dual-fuel operation.The speed of 2400 rpm produced different emission characteristics. The standard andadvanced dual operations showed similar trends. The advanced injection timing gave a netreduction in CO production at high-loading conditions. The highest CO production wasobtain

47、ed when running on diesel fuel at high load levels.3.2. Carbon dioxide (CO2) emissionsHYPERLINK #5Figs. 3 and 4 are the plots of CO2emissions. The effect of advanced injection timing isevidence for the production of carbon dioxide. The advanced injection timing producedthe lowest CO2emissions at bot

48、h speeds. The highest CO2concentrations in the exhaustwere recorded when running on pure diesel fuel. Standard injection timing at both speedsoffered a net reduction in CO2emissions compared to the results obtained when running2364ARTICLE IN PRESSO.M.I. Nwafor / Renewable Energy 32 (2007) 23612368Fi

49、g. 1. Injection advanced effect on carbon monoxide emissions. Engine speed ? 3000 rpm.Fig. 2. Injection advanced effect on carbon monoxide emissions. Engine speed ? 2400 rpm.on pure diesel fuel. The observed trends were increased CO2emissions as the A/F ratiodecreased. CO2and H2O are the products of

50、 combustion that will appear in the exhaustunder an ideal combustion process. The emission of CO2is therefore, a measure ofcombustion efciency of the system. It is desirable to have high CO2and less HC emissionsunder any operating condition.3.3. HC emissionsHYPERLINK #6Fig. 5 shows the plots of HC e

51、missions in dual-fuel and diesel fuel operations obtainedat the speed of 3000 rpm. The diesel fuel operation gave the lowest HC emissions. TheARTICLE IN PRESSO.M.I. Nwafor / Renewable Energy 32 (2007) 23612368Fig. 3. Injection advanced effect on carbon dioxide emissions. Engine speed ? 3000 rpm.Fig.

52、 4. Injection advanced effect on carbon dioxide emissions. Engine speed ? 2400 rpm.2365advanced injection timing showed low and high HC emissions at low and high loadingconditions compared to the standard injection timing operation, respectively. The plots ofHC emissions with the dual standard and a

53、dvanced timing operations at 2400 rpm weresimilar as presented in HYPERLINK #6Fig. 6. Diesel fuel operation offered a remarkable reduction in HCemissions. It was also noted that diesel fuel operation gave the highest CO2emissionswhich reected on the low HC production. This result is attributed to an

54、 efcientcombustion realised when running on pure diesel fuel. The overall results indicate thatgreater proportion of natural gas escaped primary combustion when running on dualsystem due perhaps, to the slow burning rates of natural gas. HC emissions increase due toseveral factors including quenched

55、, lean combustion, wall wetting and poor mixture2366ARTICLE IN PRESSO.M.I. Nwafor / Renewable Energy 32 (2007) 23612368Fig. 5. Injection advanced effect on hydrocarbon emissions. Engine speed ? 3000 rpm.Fig. 6. Injection advanced effect on hydrocarbon emissions. Engine speed ? 2400 rpm.preparation.

56、The HC level was high in both advanced and standard operations throughoutthe load range. The wider valve overlap of diesel engine is likely to result in greaterproportion of fresh charge leaving with the products of combustion since a mixture of gasand air is inducted during the induction stroke.3.4

57、. Ignition delayIgnition delay in diesel engine is dened as the time interval between the start of fuelinjection and the start of combustion. The ignition delay for dual-fuel operations iscompared with the baseline diesel fuel operation shown in HYPERLINK #7Figs. 7 and 8. The diesel fueloperation ha

58、d the shortest delay periods at both speeds tested. The standard injectionARTICLE IN PRESSO.M.I. Nwafor / Renewable Energy 32 (2007) 23612368Fig. 7. Injection advanced effect on ignition delay. Engine speed ? 3000 rpm.Fig. 8. Injection advanced effect on ignition delay. Engine speed ? 2400 rpm.2367t

59、iming showed the longest delay periods at high load levels, than the advanced timingoperation. There was very signicant difference between the ignition delay of diesel fueland dual-fuel operations at 2400 rpm. The standard timing also produced the longest delayperiods at this speed. In the fumigated

60、 dual-fuel engine, the measured data indicate thatignition delay increases with decreased in engine speed. This is contrary to the pure dieselfuel operation as shown in the plots. At low speed, greater proportion of pilot fuel will takepart in premixed combustion hence increasing the tendency of die