富氧燃烧对柴油机工作特性影响的试验研究

在一台增压柴油机上进行了富氧进气的试验研究,并在此基础上采用EGR技术,研究不同进气氧浓度下EGR率对柴油机排放特性的影响,以期改善柴油机NOx和碳烟的权衡关系。研究表明:富氧进气柴油机在同一进气氧浓度下,其有效燃油消耗率随着负荷的增加而明显减小;同一负荷时有效燃油消耗率随着氧浓度的升高而稍有降低。在富氧燃烧的基础上,引入EGR可以实现柴油机的烟度和NOx排放的同时降低,其关键是在一定的工况点匹配与之相适合的EGR率。当2 200 r/min全负荷工况下,进气氧浓度21%与EGR率20%组合、氧浓度22%与EGR率50%组合,烟度和NOx排放降低比例分别达到20.0%和14.8%、6.7%和19.2%。     

柴油机瞬态工况烟度排放特性及分析

为了研究车用柴油机瞬态工况中,燃烧边界条件对燃烧过程的影响,在试验台上针对增压中冷柴油机在恒转速增转矩瞬态工况下的烟度排放特性进行了试验,并用商业计算软件STAR-CD对此瞬态工况下柴油机的燃烧过程进行了数值模拟分析。针对增压柴油机低转速大负荷排烟较差的特点,试验中发动机转速定为1000r／min,以3种不同的转矩变化率来考察柴油机瞬态工况下的排烟特性。结果表明,柴油机瞬态工况下和稳态工况下的燃烧边界条件有很大的差别,这种差别导致了柴油机瞬态工况下的烟度排放值要明显高于其相应的稳态工况。计算结果表明,随着转矩变化率的升高,最大初始放热率升高及燃烧持续期延长,这些差异同样导致排气烟度值增加。     

煤基柴油及其混合燃料对发动机燃烧与排放的影响

对一台高压共轨增压中冷压燃式发动机燃用煤基F-T合成柴油(CTL)及其与碳酸二甲酯(DMC)的混合燃料进行了燃烧和排放特性试验,揭示了燃料特性和排气再循环对燃烧过程、NOx及微粒排放的影响规律.结果表明:发动机燃用CTL时的有效热效率升高,燃烧过程中滞燃期较短,预混合燃烧量减少,压力升高率明显降低,有利于改善柴油机工作的平顺性.与国V石化柴油相比,燃用CTL燃料时消光烟度、核态微粒、超细微粒及总微粒数量浓度明显降低,积聚态微粒数量浓度略有增加,有利于同时降低微粒质量和数量排放.引入排气再循环(EGR)可以进一步降低CTL燃料的NOx排放,在EGR率达到30%,时,NOx排放降低近75%,.在CTL中添加含氧燃料DMC,有利于抑制EGR导致的烟度增加,与国V柴油相比,在EGR率为30%,条件下,D15燃料消光烟度和微粒总数量的降幅分别为69.1%,和53.9%,.燃用CTL/DMC混合燃料同时引入EGR可以同时降低NOx、消光烟度、微粒质量和数量排放,有利于缓解柴油机NOx和PM之间的矛盾关系.     

文曲利管排气再循环系统在涡轮增压柴油机上的应用研究

以一台 D6 114涡轮增压柴油机为研究对象 ,采用了一套带文曲利管的排气再循环系统进行了试验研究。试验结果表明 ,该系统在高工况下能克服平均排气压力低于平均进气压力的困难 ,方便地实现排气再循环。研究了在不同工况下柴油机的 NOx 排放、烟度和比油耗随 EGR率的变化规律以及 EGR的冷却效果对 NOx 排放的影响     

EGR与进气富氧对直喷柴油机NO和碳烟排放的影响

使用增压中冷直喷柴油机,采用进气富氧与高比率EGR相结合的技术,实现富氧燃烧条件下的低NO-碳烟排放.单独使用富氧燃烧,NO的排放将随氧体积分数的上升而增加.单独使用高EGR,碳烟(Smoke)的排放会随EGR率的增加而增加.将富氧进气与高比率EGR的结合,可以通过富氧的强氧化性降低Smoke排放,通过大比率EGR来控制燃烧温度,抑制NO的过度增长.试验结果表明:1,600,r/min(经济转速)下,EGR率为35%～45%,进气氧体积分数为21%～23%;2,200,r/min(最高转矩)下,EGR率为20%～50%,进气氧体积分数为22%～24%;在上述范围内的EGR与O2搭配,可以实现低于原机的NO-Smoke排放.综合考察发动机在各种掺比下的功率、油耗,探索出适合发动机各个工况的富氧及EGR组合区域,在该区域内发动机的功率、油耗和排放水平都能得到兼顾.     

大气压力/VNT/EGR对车用柴油机性能与排放的影响

为了研究可变喷嘴涡轮增压(VNT)技术、排气再循环(EGR)技术及大气压力三者共同作用对车用柴油机性能与排放的影响,利用大气压力模拟装置开展了相应的试验研究,基于响应曲面法以响应曲面图的形式分析研究VNT喷嘴环开度、EGR阀开度及大气压力3个参数交互作用对柴油机性能与排放的影响。结果表明:随着大气压力的降低及EGR阀开度的增大,柴油机动力性下降,经济性恶化。当VNT与EGR耦合时,在最大转矩工况,在EGR阀关闭及开度较小时,随着VNT喷嘴环开度的减小,转矩呈现增大的趋势,有效燃油消耗率逐渐降低;而在EGR阀开度较大及全开时,随着VNT喷嘴环开度的减小,转矩降低,油耗升高。在标定功率工况,无论EGR阀置于何种开度,随着VNT喷嘴环开度的减小,转矩均增大,油耗均降低。随着大气压力的升高,NOx比排放升高,烟度降低。当VNT与EGR耦合时,在不同的运行工况下,NOx比排放与烟度表现出不同的变化趋势。欲获得良好的整机性能,针对不同的运行工况,需要合理匹配VNT喷嘴环开度与EGR阀开度。     

进气压力对汽油低温压燃的影响

在一台装有电液可变气门的单缸柴油机上,通过改变进气压力,研究了不同喷油正时和内部废气再循环(EGR)率下汽油压燃的燃烧特性和排放特性,并对实现汽油燃料高效清洁稳定低温燃烧(如平均指示压力循环波动系数5%,NOx排放低于0.4g/(kW·h),烟度低于0.1FSN,CO和HC排放尽可能低)的控制区间进行了探索研究。内部EGR通过排气门两次开启实现,发动机转速和循环喷油量分别固定为1 500r/min和28mg。研究结果表明,基于燃油早喷、较低内部EGR率和适量进气压力(0.12MPa)的协同控制可以使辛烷值为93的汽油在平均指示压力约为0.47MPa的工况下实现高效清洁燃烧。     

冷EGR技术对柴油机性能及排放的影响

通过在不同转速和负荷工况下进行的冷EGR试验,研究了冷EGR技术对降低柴油机NOx排放的有效性,同时对比分析了EGR开启和关闭时对柴油机性能和排放的影响.试验研究表明:冷EGR技术除了可以有效降低柴油机的NOx排放以外,还将对柴油机的进气流量、燃油消耗率、烟度、排温以及HC,CO等排放物产生影响,且这种影响随着EGR率和工况的不同而变化.     

基于涡流比对某款国Ⅴ柴油机油耗和排放优化的试验研究

为了优化某B款国Ⅴ柴油机比油耗和烟度,通过与排量相近的某A款国Ⅴ柴油机进行试验对比,认为进气涡流比的影响占主要因素,试验内容包括气道测试、摩擦功、外特性、特征点喷油提前角和EGR率扫点对比。基于试验结果优化气道形状,改善涡流比并在同一台B款发动机上进行特征点EGR率扫点和排放特征点DOE(Design of Experiment)优化扫点。结果表明,B发动机新缸盖在部分低速中低负荷烟度基本与旧缸盖一致,油耗略有降低,约在2.3%;中高速中负荷比油耗和烟度具有明显降低优势,可降低8.9%,主要体现在缸内燃烧放热迅速且集中。     

正丁醇对柴油机低温燃烧和排放的影响

在一台改造的单缸柴油机上,研究了柴油中掺入正丁醇燃料在不同EGR率、进气压力下对燃烧、性能和排放的影响.结果表明,柴油中添加正丁醇燃料使着火滞燃期延长,缸内最大爆发压力和燃烧温度下降,低温燃烧"失火"的EGR率降低,指示油耗减少,燃油经济性改善;正丁醇可明显降低碳烟排放,使烟度随EGR率变化趋势更加"平坦",烟度峰值对应的EGR率,变低,正丁醇比例越高,烟度越低;正丁醇对气体排放的影响与进气压力有关,正丁醇可以有效降低NOx排放,进气压力越大,正丁醇降低NOx的效果越明显;进气压力为0.15 MPa时,正丁醇比例越大,CO排放越低,但进气压力为0.24 MPa时,B20燃料CO排放最高;正丁醇对THC排放影响不大,但B20燃料在高EGR率条件下,其THC排放明显增大.因此,柴油燃料添加正丁醇是降低低温燃烧烟度和NOx排放,改善低温燃烧性能的有效途径.     

废气再循环率及点火时刻对天然气发动机燃烧和排温的影响

基于一台当量比燃烧的天然气发动机,采用三维燃烧分析与发动机一维热力学计算相结合的方式开展了废气再循环(exhaust gas recirculation,EGR)率及点火时刻对缸内燃烧过程和发动机排温的影响研究.研究结果表明:随着EG R率的增加,燃烧相位后移,燃烧持续期延长,放热率峰值减小,最大压升率、缸内最高燃烧压...     

Effects of EGR on combustion process of DI diesel engine during cold start

Experiments on the effects of external and internal exhaust gas recirculation (EGR) on combustion and emission performance during a cold start process were investigated in a 135 single-cylinder DI diesel engine. Combustion was improved during the initial ignition cycles by introducing internal or external EGR. The addition of an appropriate amount of internal or external EGR can promote the combustion stability significantly. However, excessive amounts of external EGR could lead to extremely unstable combustion or even misfiring. An appropriate amount of internal or external EGR decreased smoke opacity effectively during a cold start. External EGR reduced NO_x emissions effectively while internal EGR led to an increase in NO_x emissions due to thermal effects.     

EGR对生物柴油/异丁醇混合燃料燃烧与排放的影响

在一台四缸四冲程水冷高压共轨柴油机上研究了生物柴油/异丁醇混合燃料在不同EGR率下的燃烧及排放特性.试验结果表明:随EGR率的升高,缸内压力和放热率峰值降低,燃料滞燃期延长,燃烧持续期先缩短后延长,NO排放与核模态颗粒物数密度降低;当EGR率小于6%时,CO和HC污染物的排放都保持在较低水平.相较于生物柴油,燃用混合燃料降低CO污染物的排放;随异丁醇掺混比例的增加,缸内压力与放热率峰值逐渐升高,CO排放降低,但HC与NO的排放逐渐升高,核模态颗粒物数密度升高,积聚态颗粒物数密度和颗粒物质量浓度有不同程度的下降.     

低压EGR对GDI增压汽油机外特性下性能和排放影响

通过一款涡轮增压汽油直喷(gasoline direct injection,GDI)发动机低压废气再循环(exhaust gas recirculation,EGR)的试验,研究了EGR率和点火提前角的综合作用对增压GDI发动机的燃烧、缸压、排放和油耗等方面的影响。结果表明,在GDI增压发动机中加入EGR后,由于废气的稀释和热容作用,使缸内燃烧持续期增大,排气温度下降,燃烧相位也发生了改变。这对发动机外特性的有利影响是油耗减少,CO和NO_x排放也明显减少;不利影响是EGR的加入提高了增压发动机的排气压力,导致泵气损失增加。此外,总碳氢(total hydro carbons,THC)排放也有所增加。在GDI增压汽油机中使用EGR系统并配合点火角的调节能够有效提高热效率,降低NO_x排放。     

直喷汽油机采用不同缸内稀释技术的性能研究

针对一款4缸1.5L废气涡轮增压缸内直喷汽油(GDI)发动机,进行了废气再循环(EGR)缸内稀释燃烧技术、空气缸内稀释燃烧技术与原机燃烧的经济性、排放特性对比试验研究。研究了不同缸内稀释技术对发动机性能和排放影响的变动规律,并对比分析了相同稀释率下、采用不同稀释技术时发动机的性能变化。结果表明:空气稀释率在49.5%时比油耗相比原机下降6.2%,而EGR稀释率在20.5%时经济性改善4.2%,在相同稀释率时,EGR稀释可采用更为提前的点火角实现更优的燃烧相位,但空气稀释所带来的多变指数提升使其经济性优于EGR稀释,且发动机燃烧系统对空气稀释程度具有更强的容忍性;NOx排放在空气稀释率为11.0%时达到峰值水平,随后随着稀释率的提高不断下降,而EGR稀释的NOx排放随着稀释率的提高持续大幅下降;空气稀释的CO排放水平远低于原机,EGR稀释的CO排放随着稀释率的增加而略有下降;对于HC排放,空气稀释的排放量低于EGR稀释,而当空气稀释率由49.5%增加为68.0%时,HC排放出现较大幅度上升。     

Effect of addition of hydrogen and exhaust gas recirculation on characteristics of hydrogen gasoline engine

The effects of exhaust gas recirculation (EGR) on combustion and emissions under different hydrogen ratios were studied based on an engine with a gasoline intake port injection and hydrogen direct injection. The peak cylinder pressure increases by 9.8% in the presence of a small amount of hydrogen. The heat release from combustion is more concentrated, and the engine torque can increase by 11% with a small amount of hydrogen addition. Nitrogen oxide (NOx) emissions can be reduced by EGR dilution. Hydrogen addition offsets the blocking effect of EGR on combustion partially, therefore, hydrogen addition permits a higher original engine EGR rate, and yields a larger throttle opening, which improves the mechanical efficiency and decreases NOx emissions by 54.8% compared with the original engine. The effects of EGR on carbon monoxide (CO) and hydrocarbon (HC) emissions are not obvious and CO and HC emissions can be reduced sharply with hydrogen addition. CO, HC, and NOx emissions can be controlled at a lower level, engine output torque can be increased, and fuel consumption can be reduced significantly with the co-control of hydrogen addition and EGR in a hydrogen gasoline engine.     

柴油机恒转速增转矩瞬态工况的燃烧过程分析及其对烟度的影响

采用自行设计的瞬态工况控制及测量系统，对增压中冷柴油机进行了恒转速增转矩瞬态工况下发动机的空燃比、消光烟度及示功图参数的测试．试验结果表明：随转矩增加率的上升，空燃比减小，引起混合气变浓，燃烧恶化；燃烧始点后移，而燃烧持续期延长；预混燃烧比明显下降．上述原因导致了在恒转速增转矩瞬态工况下，随转矩增加率的升高，排气烟度上升．     

Engine performance and emissions of a diesel engine operating on diesel-RME (rapeseed methyl ester) blends with EGR (exhaust gas recirculation)

The effects of biodiesel (rapeseed methyl ester, RME) and different diesel/RME blends on the diesel engine NO_x emissions, smoke, fuel consumption, engine efficiency, cylinder pressure and net heat release rate are analysed and presented. The combustion of RME as pure fuel or blended with diesel in an unmodified engine results in advanced combustion, reduced ignition delay and increased heat release rate in the initial uncontrolled premixed combustion phase. The increased in-cylinder pressure and temperature lead to increased NO_x emissions while the more advanced combustion assists in the reduction of smoke compared to pure diesel combustion. The lower calorific value of RME results in increased fuel consumption but the engine thermal efficiency is not affected significantly. When similar percentages (% by volume) of exhaust gas recirculation (EGR) are used in the cases of diesel and RME, NO_x emissions are reduced to similar values, but the smoke emissions are significantly lower in the case of RME. The retardation of the injection timing in the case of pure RME and 50/50 (by volume) blend with diesel results in further reduction of NO_x at a cost of small increases of smoke and fuel consumption.     

Effects of exhaust gas recirculation (EGR) on combustion and emissions during cold start of direct injection (DI) diesel engine

Through experiments conducted on a single cylinder direct injection (DI) diesel engine, effects of exhaust gas recirculatoin (EGR) on combustion and emission during cold start were investigated. Combustion of first firing cycle can be promoted significantly by introducing EGR. In experiments, when partially closed choking valve and partially or fully opened EGR valve, peak cylinder pressure of first firing cycle was about 45% higher than that under normal condition without EGR, and the start of combustion (SOC) was also much earlier. EGR also had effects on combustion stability. In the case, which kept 50% or 100% opening of EGR valve (OEV) and kept 100% opening of choking valve (OCV), more stable combustion process was achieved when common rail pressure decreased during cold start. However, excessive amount of EGR led to extreme unstable combustion and even misfiring. Opacity and NO emissions were also analyzed in detail. In the case with maximum EGR, the lowest average opacity, which was less than 4%, was achieved during initial several firing cycles of cold start. But in the later phase, excessive amount of EGR led to a great deal of white smoke emission. NO emission during initial phase of cold start is mainly affected by increase in fuel amount of injection. When combustion became stable gradually, EGR showed significant effect on NO reduction.     

Experimental study of various effects of exhaust gas recirculation (EGR) on combustion and emissions of an automotive direct injection diesel engine

Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NO_x production and is used on most modern high-speed direct injection (HSDI) diesel engines. However EGR has different effects on combustion and emissions production that are difficult to distinguish (increase of intake temperature, delay of rate of heat release (ROHR), decrease of peak heat release, decrease in O₂ concentration (and thus of global air/fuel ratio (AFR)) and flame temperature, increase of lift-off length, etc.), and thus the influence of EGR on NO_x and particulate matter (PM) emissions is not perfectly understood, especially under high EGR rates. An experimental study has been conducted on a 2.0 l HSDI automotive diesel engine under low-load and part load conditions in order to distinguish and quantify some effects of EGR on combustion and NO_x/PM emissions. The increase of inlet temperature with EGR has contrary effects on combustion and emissions, thus sometimes giving opposite tendencies as traditionally observed, as, for example, the reduction of NO_x emissions with increased inlet temperature. For a purely diffusion combustion the ROHR is unchanged when the AFR is maintained when changing in-cylinder ambient gas properties (temperature or EGR rate). At low-load conditions, use of high EGR rates at constant boost pressure is a way to drastically reduce NO_x and PM emissions but with an increase of brake-specific fuel consumption (BSFC) and other emissions (CO and hydrocarbon), whereas EGR at constant AFR may drastically reduce NO_x emissions without important penalty on BSFC and soot emissions but is limited by the turbocharging system.