复合EGR对增压柴油机性能和排放影响的试验研究

在一台两级增压高压共轨柴油机上,在B25和B50工况进行了高压、低压及复合EGR三种EGR方式的试验研究。研究结果表明:在试验研究工况,低压EGR能够保持充足进气量,实现较高EGR率,获得低NOx排放,并在较大EGR率范围保持低碳烟比排放,但是其泵气损失较高,燃油经济性较差。高压EGR在一定EGR率范围内可以有效降低泵气损失,但其对增压器工作能力影响较大,EGR引入能力受到限制;采用进气节流的方法,可以提升其EGR引入能力,但是会造成比油耗明显上升,同时碳烟比排放迅速增大。对高、低压EGR比例进行优化后的复合EGR方式能够有效降低泵气损失,在宽广EGR范围内保持良好的燃油经济性。同时,由于复合EGR一方面增强了EGR引入能力,同时具有较高的进气量,在B25工况复合EGR的EGR率在47%时,此时其NOx比排放为0.67g/(kW·h),碳烟比排放为0.016g/(kW·h);B50工况复合EGR率为33%时,NOx比排放为1.27g/(kW·h),碳烟比排放为0.080g/(kW·h)。复合EGR在较大EGR率下可以同时实现低NOx和碳烟比排放。     

VNT对柴油机NOx排放特性优化的研究

为了研究可变喷嘴涡轮(VNT)技术对降低柴油机NO_x排放的作用,首先对带排气旁通阀涡轮增压器(WG)和文丘里管高压废气再循环(vEGR)的WG-vEGR涡轮增压柴油机原机,运用GT-Power软件和AVL FIRE软件进行VNT的匹配,对柴油机综合性能进行了仿真计算,确定欧洲稳态测试循环(ESC)工况最优VNT开度规律,组成VNT-vEGR柴油机。随后对WG-vEGR柴油机和VNT-vEGR柴油机进行了ESC工况台架试验研究。研究结果表明:VNT能够提高柴油机的废气再循环(EGR)率,VNT-vEGR柴油机的ESC工况加权NO_x排放值为3.53g/(kW·h),与WG-vEGR柴油机原机的4.92g/(kW·h)相比,下降约28.25%;ESC工况加权比油耗为232.1g/(kW·h),相比于WG-vEGR柴油机原机的235.5g/(kW·h),降低约1.44%;ESC工况加权碳烟排放值为0.055g/(kW·h),相比于WG-vEGR柴油机原机的0.058g/(kW·h),降低约5.17%。且从加权比油耗和碳烟排放值的变化情况可以看出,该系统具有采用更大EGR率以获得NO_x排放进一步优化的潜力。     

船用柴油机EGR技术仿真研究

采用某船用中速单缸柴油机进行了EGR对性能及排放影响的仿真研究,并进行了试验验证。研究结果表明,采用EGR技术后,NOx加权排放下降到1.94(g.(kW.h)-1),但加权燃油消耗率上升至9.93(g.(kW.h)-1);通过提前喷油和增加EGR率相结合进行优化,虽然NOx加权排放上升到2.09(g.(kW.h)-1),但加权燃油消耗率下降至4.36(g.(kW.h)-1),柴油机燃油经济性得到明显优化。试验验证显示:仿真和试验结果吻合较好,表明经标定的DI-jet燃烧模型精度满足要求,能较准确预测柴油机性能及排放。     

基于数值模拟的某柴油机燃烧室优化研究

用AVL FIRE软件建立了柴油机喷雾燃烧过程研究的计算模型,根据模型分析了燃烧室关键特征对经济性和排放的影响,并设计了燃烧室优化方案。研究发现,在A100工况,优化方案改善了油气混合状况,提高了空气利用率,并加速了燃烧后期速度,使得经济性得到提高,同时NO_x排放也有所增加;而在部分负荷A25工况,优化方案降低了燃烧室碗底的流动速度,减少了壁面传热损失,经济性得到提高,同时NO_x排放也有所降低。发动机台架试验结果表明,相对于原始方案,优化方案的外特性油耗平均降低了约2.0g/(kW·h);ESC循环加权油耗降低了2.2g/(kW·h),且加权NO_x比排放相当。     

增压中冷柴油机EGR数值模拟与试验研究

建立了带废气再循环(EGR)系统的增压中冷柴油机工作过程热力学计算模型,并进行数值模拟,模拟计算与试验结果表明两者基本吻合,误差在合理范围内。在此基础上,研究EGR在不同工况下对柴油机动力性、经济性和排放性的影响,并根据柴油机的综合性能对各工况下最佳EGR率进行优化,得出理想的EGR控制MAP图。最后按照模拟计算结果搭建试验平台,并进行试验研究。研究结果表明:13工况排放测试循环工况的NOx和碳烟排放分别为3.0g/(kW.h)和0.45g/(kW.h),满足欧Ⅳ排放法规的要求。     

基于EGR技术的国Ⅳ重型柴油机燃烧系统开发

在一台电控重型柴油机上进行了基于EGR技术的燃烧系统开发研究,组建了基于WGT增压器的电控高压EGR系统,研究了燃烧室、喷油器、增压器、EGR率及喷油参数等对柴油机性能和排放的影响,确定了最终的重型柴油机国IV燃烧系统优化方案.结果表明:通过优化匹配燃烧室和增压器并采用孔径较小的多孔喷油器能显著改善柴油机NOx和烟度之间的折衷关系;小负荷时,推迟喷油可以使NOx在降低较多的情况下烟度略有下降;随着EGR率增加,提高喷油压力与推迟喷油相结合,可以同时降低大负荷的NOx和烟度排放,并能改善燃油经济性.ESC循环测试结果表明,通过对燃烧系统、EGR和喷油控制参数的综合优化,在不采用后处理器的情况下,柴油机各气体排放(NOx、HC和CO)及微粒(PM)均达到国Ⅳ排放标准,十三工况加权油耗率与原机基本相当.     

采用VNT/EGR和DOC降低柴油机排放的试验

在一台高压共轨柴油机上进行了采用基于可变喷嘴环涡轮增压器(VNT)的废气再循环(EGR)系统(VNT/EGR)和柴油机氧化催化器(DOC)降低排放的试验研究。结果表明,通过调节VNT开度可以有效实现EGR循环和控制EGR率,显著降低NOx排放,并且在一定EGR率范围内对烟度影响较小。提高喷射压力可以较明显改善NOx和烟度的折衷关系,采用合理的后喷参数能够在不明显影响经济性和NOx排放的前提下显著降低烟度。对燃烧室进行降低压缩比的合理设计也可以明显改善NOx和烟度的折衷关系。在燃烧系统优化的基础上,最终加装DOC的ESC循环排放测试结果满足了国Ⅳ要求,其中PM为0.0191g/(kW·h),NOx为2.88g/(kW·h),HC和CO排放远低于国Ⅳ限值。     

外部EGR对于汽油机性能和排放的影响研究

外部废气再循环(EGR)技术可以提升汽油机的燃油经济性,降低爆震倾向,搭建了低压EGR系统,研究了外部EGR对于汽油机性能和排放的影响.外部EGR可以降低NOx和CO排放,但是THC排放增加.通过优化后处理配方比例,可以降低后处理成本;对于经济性,EGR率达到23％,油耗可以降低约10 g/(kW·h),对于动力性,E...     

基于当量燃烧的天然气发动机燃烧室优化研究

在一台采用废气再循环(exhaust gas recirculation,EGR)策略的当量燃烧天然气发动机上开展了不同挤气比、压缩比的活塞对燃烧、热效率和排放影响的对比试验研究。结果表明:在50%负荷与中低转速75%负荷下,增大EGR率拓展了爆震边界,使得主燃烧相位(CA50)提前,指示热效率提高;而在100%负荷及高转速75%负荷下,EGR率的增大对燃烧持续期的延长作用更为明显,且CA50后移,指示热效率降低。增大压缩比和适当增大挤气比有利于增强缸内湍流运动,加快天然气火焰传播速度,使CA50更靠近上止点,热功转换效率提高,最高指示热效率提高了0.24%,NO_x和CH₄排放分别升高了2.30g/(kW·h)、0.55g/(kW·h)。进一步增大挤气比会受到爆震的限制,最佳点火时刻推迟,燃烧定容度小,燃烧持续期延长,最高指示热效率下降了0.51%,NO_x和CH₄排放分别降低了2.20g/(kW·h)、0.44g/(kW·h),CO排放升高了0.36g/(kW·h),因此挤气比存在一个优化的范围。     

不同增压系统对重型柴油机性能和排放影响的试验研究

在一台电控高压共轨重型柴油机上,基于高压冷却废气再循环(EGR),对比研究了带废气放气阀式单级固定涡轮截面增压器(WGT)、单级可变涡轮截面增压器(VGT)、二级固定涡轮截面增压器(WGT-FGT)和二级可变涡轮截面增压器(VGT-FGT)四种增压方式对柴油机性能与排放的影响。结果表明:可变截面相对固定截面增压系统(VGT相对WGT,VGT-FGT相对WGT-FGT),能显著提高涡前与进气压差,实现更高EGR率和更低的NO_x排放,同时能够提高进气充量,从而改善燃烧过程。随着NO_x比排放的降低,四种增压方式的油耗都呈现上升趋势,并且VGT-FGT、VGT、WGT-FGT和WGT的燃油消耗率依次升高。当NO_x原始排放控制在5.0g/(kW·h)左右,采用WGT-FGT时燃油消耗率相对WGT获得一定改善(与VGT和VGT-FGT相当),碳烟排放与VGT-FGT接近,明显优于WGT。随NO_x排放降低,可变截面增压系统相对固定截面增压系统逐渐表现出优势:当NO_x原始排放控制在3.5g/(kW·h)左右,VGT可以获得与VGT-FGT接近的燃油经济性和碳烟排放;当NO_x原始排放更低(2.8g/(kW·h)以下),VGT-FGT降低油耗和碳烟排放的优势更加明显。     

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。     

Influence of high rates of supplemental cooled EGR on NOx and PM emissions of an automotive HSDI diesel engine using an LP EGR loop

Previous experimental studies on diesel engine have demonstrated the potential of exhaust gas recirculation (EGR) as an in‐cylinder NO_x control method. Although an increase in EGR at constant boost pressure (substitution EGR) is accompanied with an increase in particulate matter (PM) emissions in the conventional diesel high‐temperature combustion (HTC), the recirculation of exhaust gases supplementary to air inlet gas (supplemental EGR) by increasing the boost pressure has been suggested as a way to reduce NO_x emissions while limiting the negative impact of EGR on PM emissions. In the present work, a low‐pressure (LP) EGR loop is implemented on a standard 2.0 l automotive high‐speed direct injection (HSDI) turbocharged diesel engine to study the influence of high rates of supplemental cooled EGR on NO_x and PM emissions. Contrary to initial high‐pressure (HP) EGR loop, the gas flow through the turbine is unchanged while varying the EGR rate. Thus, by closing the variable geometry turbine (VGT) vanes, higher boost pressure can be reached, allowing the use of high rates of supplemental EGR. Furthermore, recirculated exhaust gases are cooled under 50°C and water vapour is condensed and taken off from the recirculated gases. An increase in the boost pressure at a given inlet temperature and dilution ratio (DR) results in most cases an increase in NO_x emissions and a decrease in PM emissions. The result of NO_x–PM trade‐off, while varying the EGR rate at fixed inlet temperature and boost pressure depends on the operating point: it deteriorates at low load conditions, but improves at higher loads. Further improvement can be obtained by increasing the injection pressure. A decrease by approximately 50% of NO_x emissions while maintaining PM emission level, and brake specific fuel consumption can be obtained with supplemental cooled EGR owing to an LP EGR loop, compared with the initial engine configuration (HP moderately cooled EGR). Copyright © 2008 John Wiley & Sons, Ltd.     

二级增压重型柴油机排放和燃烧特性的试验研究

在一台电控高压共轨柴油机上进行二级增压优化匹配,并以单级增压作为对比基准,分析了不同工况下二级增压柴油机的性能、排放与燃烧特性,研究了进气温度对其的影响。试验结果表明:相对单级增压,柴油机二级增压后低速外特性扭矩达到1 170N.m,烟度与燃油经济性改善幅度分别为99.3%和13.4%;二级增压能够提高EGR的引入能力,减小进气节流损失,并可显著改善中低转速、高负荷时NOx与烟度和燃油消耗率之间的平衡关系;在压气机特性图中二级增压柴油机的运行线远离喘振边界线;在各个工况下,进气温度升高使NOx比排放快速增加,导致柴油机NOx与烟度之间的平衡关系变差。     

CA498车用柴油机EGR的试验研究

进行了不同工况下EGP率对发动机排放和性能影响的试验研究。在试验中按ECE R49十三工况法研究了有EGR时NOx和微粒的变化规律,并对柴油机性能进行了分析。在综合考虑EGR对各工况的排放及性能影响的基础上,确定十三工况中应进行EGR的工况及相应的最佳EGR率。     

Low-load hydrogen-diesel dual-fuel engine operation – A combustion efficiency improvement approach

Hydrogen-diesel dual-fuel operation can provide significant benefits to the performance and carbon-based emissions formation of compression-ignition engines. The wide flammability range of hydrogen allows engine operation at extremely low equivalence ratios while its high diffusivity and flame speed promote wide range combustion inside the cylinder. Nonetheless, despite the excellent properties of hydrogen for internal combustion, unburned hydrogen emissions and poor combustion efficiency have been previously observed at low-load conditions of compression ignition engines.The focus of the present study is to assess the effects of different engine operation and diesel injection parameters on the combustion efficiency of a heavy-duty dual-fuel engine while observing their interactions with the brake thermal efficiency (BTE) and emissions formation of the engine. In an attempt to reduce the unburned hydrogen rates at the exhaust of the engine, exhaust gas recirculation (EGR) and different diesel injection strategies were implemented. Statistical methods were applied in this study to reduce the experimental time.The results show a strong connection between unburned hydrogen rates, combustion and brake thermal efficiencies with the EGR rate. Higher EGR rates increase the intake charge temperature and provide improved hydrogen combustion and fuel economy. Operation of the dual-fuel engine at low-load with high EGR rate and slightly advanced main diesel injection can deliver simultaneous benefits to most of the harmful emissions and the BTE of the engine. Despite the efforts to achieve optimal engine operation at low loads, the combustion efficiency for most of the tested cases was in the range of 90%. Thus, increased hydrogen rates should be avoided as the benefits of the dual-fuel operation are weak at low-load conditions.     

车用稀燃天然气(CNG)发动机的开发研究

采用稀薄燃烧方式，是降低发动机排放和改善经济性的有效手段。在以柴油机为原型机开发的单燃料天然气发动机中，对进气系统和燃烧系统等进行了优化设计，采用了增压中冷、多点顺序喷射、高能直接点火以及综合电控技术，使之达到空燃比的精确控制和高能点火，以实现天然气的稀薄燃烧。同时对研制的样机在稀薄燃烧状态下的性能进行了试验研究，获得了良好的经济性和排放性能。     

Effect of exhaust gas recirculation on diesel engine nitrogen oxide reduction operating with jojoba methyl ester

Jojoba methyl ester (JME) has been used as a renewable fuel in numerous studies evaluating its potential use in diesel engines. These studies showed that this fuel is good gas oil substitute but an increase in the nitrogenous oxides emissions was observed at all operating conditions. The aim of this study mainly was to quantify the efficiency of exhaust gas recirculation (EGR) when using JME fuel in a fully instrumented, two-cylinder, naturally aspirated, four-stroke direct injection diesel engine. The tests were carried out in three sections. Firstly, the measured performance and exhaust emissions of the diesel engine operating with diesel fuel and JME at various speeds under full load are determined and compared. Secondly, tests were performed at constant speed with two loads to investigate the EGR effect on engine performance and exhaust emissions including nitrogenous oxides (NO_x), carbon monoxide (CO), unburned hydrocarbons (HC) and exhaust gas temperatures. Thirdly, the effect of cooled EGR with high ratio at full load on engine performance and emissions was examined. The results showed that EGR is an effective technique for reducing NO_x emissions with JME fuel especially in light-duty diesel engines. With the application of the EGR method, the CO and HC concentration in the engine-out emissions increased. For all operating conditions, a better trade-off between HC, CO and NO_x emissions can be attained within a limited EGR rate of 5–15% with very little economy penalty.     

基于轻型柴油车的柴油机氧化催化器入口温度升温特性及策略研究

选取了高、中、低负荷的3个典型工况,研究了进气节流及喷油策略对柴油机缸内燃烧过程、排放性、经济性及柴油机催化氧化器(diesel oxidation catalyst,DOC)入口温度的影响,得到全工况区域的DOC入口温度的升温策略。试验结果表明:随进气节流阀开度减小,进气流量降低,压缩压力下降,燃烧始点滞后,最高燃烧压力下降,循环指示功降低;HC排放得到抑制,其他排放恶化;DOC入口温度得到有效提升,负荷越小,温升效果越显著。喷油规律耦合进气节流发现,主喷提前角的推迟使得滞燃期缩短、后燃加重,DOC入口温度小幅度提升;近后喷油量增加可提高DOC入口温度,推迟近后喷,DOC入口温度先增大后降低,存在最佳的近后喷时刻。依据样机全工况排温分布特征,提出了不同工况区域DOC入口温度升温控制策略。