外文翻譯噴油定時對柴油天然氣雙燃料發(fā)動機排放性影響

1、噴油定時對柴油/天然氣雙燃料發(fā)動機排放性影響替代能源，2007，32：2361-2368摘 要導(dǎo)致全球變暖的溫室氣體排放日益受人關(guān)注，現(xiàn)已證明它主要來源于礦物燃料的燃燒?？茖W(xué)家一直在尋求綠色的替代燃料，天然氣因其辛烷值高、環(huán)保性好被認為最有潛力作為柴油機上的替代燃料。然而進一步研究表明，天然氣燃燒速率低，著火延遲長，從而產(chǎn)生高的升功率使柴油機易產(chǎn)生爆燃。這項實驗研究了基于柴油機的雙燃料發(fā)動機噴油定時對排放性的影響：柴油機標準噴油定時為30 BTDC。當噴油定時調(diào)整為3 BTDC時，發(fā)動機運轉(zhuǎn)不穩(wěn)，而當噴油定時變?yōu)? BTDC時發(fā)動機運行順暢，特別是在低負荷工況下。故把3 BTDC定為優(yōu)化噴油定

2、時。試驗表明，雖然燃料消耗略有增加，但著火延遲縮短，CO、CO2排放量降低。關(guān)鍵詞：一氧化碳（CO）； 二氧化碳（CO2）；碳氫化合物（HC）排放；著火延遲 引言1997年東京各國首腦會談關(guān)注的焦點是溫室氣體排放對全球環(huán)境的影響。它能導(dǎo)致洪災(zāi)、山體滑坡等，2005年在美國發(fā)生的Katrina、Rita 和Wilma颶風就是最好的例證。這都是由于礦物燃料燃燒產(chǎn)生大量溫室氣體CO2所致。許多科學(xué)家在尋找替代傳統(tǒng)礦物燃料的綠色燃料(Nwafor1、 Lowe and Branhan2 、 Horie and Mishizawa3 )，他們不約而同對天然氣作為未來柴油機上的替代燃料極為看好。然而天然氣

3、要真正替代柴油還有很多問題要解決。比方說，天然氣自然溫度高，這就要求配有著火系統(tǒng)。再者，天然氣因燃燒速率低，著火延遲長，從而缸內(nèi)壓力波動大。不過從最近關(guān)于雙燃料發(fā)動機性能、排放研究可知(Nwafor4 、Stone and Lallommatos5、Karim and Ali6)，天然氣辛烷值高(RON 131)，故抗爆性好，可以通過提高壓縮比來改進發(fā)動機的性能。這個試驗研究了基于柴油機的雙燃料發(fā)動機噴油定時對排放的影響（以天然氣為主要燃料柴油天然氣雙燃料發(fā)動機）。在壓縮行程終了吸入空氣天然氣混合氣，并噴入一定量的柴油引燃混合氣。所需引燃柴油量受爆燃限制(Rani and Rice7 、Nwa

4、for 8)，隨柴油量增加，天然氣減少，爆燃趨勢減弱。優(yōu)化噴油定時是為了補償著火延遲和燃燒速率低的影響。研究表明，與標準噴油定時相比，發(fā)動機在優(yōu)化噴油定時下，HC、CO2排放量下降，著火延遲縮短，但燃料消耗量大。發(fā)動機在全柴油運行下，HC排放最低，CO排放最高。總的來說，在低負荷、低轉(zhuǎn)速下，優(yōu)化噴油定時對發(fā)動機排放改進很有用，但在高負荷下，發(fā)動機溫度起著決定作用。 實驗裝置這個試驗所用的發(fā)動機為一個Petter型AC1單缸柴油機，它是一種空冷高速直噴式發(fā)動機。功率計包括一個分流式Mawdsley型直流發(fā)電機和一個能量儲存器，力矩則是由相當于牛頓彈簧測量范圍的裝置測得。燃燒室壓力由Kistle型

5、7063A壓力計測量（這個壓力計是水冷電控壓電式的，靈敏度為79pc/bar），再通過數(shù)字示波器顯示，并把結(jié)果儲存到軟盤里以便隨后分析缸內(nèi)壓力最大升高率。排氣歧管壓力由普通型壓力計測量，空氣流量由Viscous流量計測。和測量缸內(nèi)壁溫度一樣，進、排氣道安裝有熱敏電阻可以監(jiān)控氣體溫度變化。柴油由噴油泵輸?shù)絿娪推?，它的流量由一個50cm3的分級式滴管和秒表共同完成。天然氣流量由一個能測量多樣空間的轉(zhuǎn)子流量計測得，相對溫度和環(huán)境溫度由Vaisala型溫度計測，空氣天然氣混合氣由安裝在進氣歧管的氣體控制閥控制。21 天然氣組成成份氮2.18% 甲烷92.69% 乙烷3.43% 二氧化碳0.52% 丙烷

6、0.71% 異丁烷0.12%正丁烷0.15% 正戊烷0.09% 正己烷0.11%毛熱值=38.59MJ/m3 凈熱值= MJ/m3Wobbe數(shù)= MJ/m3 空燃比=16.65:1 柴油凈熱值= MJ/kg 柴油相對密度=22 發(fā)動機數(shù)據(jù)缸徑=76.20mm 行程=66.67mm排量=304 cc 壓縮比=17 噴油壓力=183bar標準噴油定時=30BTDC 優(yōu)化噴油定時=33.5BTDC 實驗結(jié)果31 一氧化碳（CO）排放CO排放量與空燃比有關(guān)，它是表明發(fā)動機燃燒效率的一個參數(shù)。圖1和圖2分別顯示了發(fā)動機轉(zhuǎn)速在3000rpm和2400rpm時，雙燃料發(fā)動機CO排放情況。由圖可知，發(fā)動機不同

7、轉(zhuǎn)速下，CO的排放特性是不同。總的來說，在發(fā)動機運轉(zhuǎn)在雙燃料時，與標準噴油定時相比，優(yōu)化噴油定時下CO排放量明顯低。兩者CO排放變化趨勢相似，但CO排放量集中區(qū)段不同。全柴油運轉(zhuǎn)時，CO排放量最少，但它隨負荷增加而加大。CO排放量最大點是在全柴油運轉(zhuǎn)高負荷下產(chǎn)生的。圖1 CO排放(n=3000rpm)圖2 CO排放 （n=2400rpm）32 二氧化碳（CO2）排放圖3和圖4顯示了CO2的排放特性。由圖可知，噴油定時對CO2排放影響很大。在優(yōu)化噴油定時下，不管發(fā)動機處于哪個轉(zhuǎn)速下，CO2的排放都很低。CO2排放量最高是在全柴油運轉(zhuǎn)下，而在標準噴油定時下，CO2排放量處于中間。試驗表明，隨空燃比

8、的減小，CO2的排放量呈增多趨勢。我們知道在理想燃燒下，燃料燃燒產(chǎn)物為CO2和H2O，故CO2可以作為衡量燃燒效率的一個參數(shù)。使發(fā)動機排放盡量多的CO2和少的HC一直是我們追求的目標。圖3 CO2排放（n=3000rpm）圖4 CO2排放(n=2400rpm)33 碳氫化合物（HC）排放圖5顯示了發(fā)動機轉(zhuǎn)速為3000rpm時，分別在雙燃料和全柴油運行下HC的排放。全柴油運行下，HC排放量最少。與標準噴油定時相比，在優(yōu)化噴油定時在低負荷下排放低但在高負荷下排放高。圖6顯示發(fā)動機轉(zhuǎn)速為2400rpm時HC的排放性與圖5相似。實驗表明，在燃燒開始時，有大量天然氣未及時參與反應(yīng)，這可能是因為天然氣燃燒

9、速率慢的原故。雙燃料運行下，HC排放量大主要原因有：稀薄燃燒、缸內(nèi)壁熄火作用、天然氣空氣混合氣不均勻等。由圖還可知，不同工況，不管是在標準噴油定時還在優(yōu)化噴油定時HC排放量都比較高。當在進氣行程，由于氣門重疊角大導(dǎo)致大量已吸入的新鮮氣又被排出很可能是重要原因。圖5 HC排放(n=3000rpm)圖6 HC排放(n=2400rpm)34 著火延遲著火延遲指柴油機燃料被引燃到燃料正式燃燒之間的時間段。圖7和圖8顯示了發(fā)動機在雙燃料和全柴油運行下，著火延遲的情況。從兩圖中可知，雖發(fā)動機轉(zhuǎn)速不同，但全柴油運行下著火延遲都比較短。與優(yōu)化噴油定時相比，標準噴油定時在高負荷下著火延遲長。在發(fā)動機轉(zhuǎn)速為240

10、0rpm時，雙燃料與全柴油運行著火延遲有明顯不同，標準噴油定時下著火延遲最長。實驗知，雙燃料下，隨轉(zhuǎn)速下降，著火延遲變長，這與全柴油運行下剛好相反。因為在低轉(zhuǎn)速時，大量氣體參與預(yù)燃從而增加了發(fā)動機爆燃趨勢。在雙燃料運行下總的比全柴油運行下著火延遲要長，因天然氣自燃溫度（704 oC）比柴油（245 oC）高很多，在壓縮行程終了缸內(nèi)溫度達不到氣體自燃溫度。柴油的霧化程度和噴油錐角取決于缸內(nèi)氣體密度，霧化不良導(dǎo)致著火延遲長可能是由于油滴原因。圖7 點火延遲(n3000rpm)圖8 點火延遲(n2400rpm) 結(jié)論試驗表明，替代燃料都有著火延遲特性，有人認為是受發(fā)動機負荷和轉(zhuǎn)速和影響。同時每一種替

11、代燃料都有各自的最佳噴油定時，試驗發(fā)現(xiàn)，在最佳噴油定時下，發(fā)動機的燃料消耗量都略微增加，但CO2的排放量明顯下降，CO排放集中的也下降。在雙燃料運行下，HC排放比較高，但在優(yōu)化噴油定時下，它的排放有明顯改進。在雙燃料時，與標準噴油定時相比，優(yōu)化噴油定時在低負荷運行下優(yōu)為順暢，但當噴油定時調(diào)整為3BTDC時，發(fā)動機運轉(zhuǎn)就不穩(wěn)了。在高負荷下，燃燒溫度起決定作用，進而增加了柴油的蒸發(fā)可縮短著火延遲。故調(diào)整噴油定時不適合高負荷工況。雙燃料發(fā)動機據(jù)說受著火延遲影響。參考文獻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

14、te=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=099d5795529582a3cfc18f3ddf151767 l bbib5#bbib5 5 C.R. Stone and N. Ladommatos, Design and evaluation of a fast-burn spark ignitio

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

16、7&_acct=C000053168&_version=1&_urlVersion=0&_userid=1492036&md5=099d5795529582a3cfc18f3ddf151767 l bbib6#bbib6 6 G.A. Karim and A.I. Ali, Combustion, knock and emission characteristics of a natural gas fuelled s.i. engines with particular reference to low intake temperature conditions, IMechE 189 (2

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

19、=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=099d5795529582a3cfc18f3ddf151767 l bbib8#bbib8 8 O.M.I. Nwafor, Effect of oxygen supply on dual-fuel engine perf

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