各缸废气再循环率不均匀性对柴油机排放影响的试验研究

针对一台由国五升级到国六的重型柴油机原始排放(无后处理系统)超过目标设定值的问题进行研究,提出了一种通过控制各缸废气再循环(exhaust gas recirculation,EGR)率不均匀性来降低柴油机原始排放的方法。建立了柴油机各缸EGR率不均匀性的排放测试试验台架和测试方法,通过分析排放万有特性曲线图确定所研究的进气总管EGR率和柴油机运行工况点,用CO2法在稳态工况下测量各缸EGR率,分析各缸EGR率不均匀对排放性能的影响,确定了达到企业原始排放目标设定值的各缸EGR率不均匀性范围,实现了通过控制各缸EGR率不均匀性来降低柴油机原始排放及降低满足国六排放法规后处理系统匹配难度和成本的目的。     

进气管结构对天然气发动机废气再循环率均匀性的影响

针对某国Ⅵ天然气发动机各缸燃烧一致性差异过大的问题,利用计算流体力学(CFD)软件STAR-CCM+对该发动机的进气管路开展废气再循环(exhaust gas recirculation,EGR)率均匀性分析,发现第1缸～第3缸的EGR率高于第4缸～第6缸,1 200r/min全负荷工况EGR率相对偏差为-29.9%～34.2%。分析表明,EGR的引出方式为第1缸～第3缸单侧取气,导致EGR进气入口存在较大波动,是造成各缸EGR率分配不均的主要原因。从降低管路内EGR废气波动的角度提出了两种进气管路优化方案,使EGR废气在进入稳压腔之前得到了充分混合,各缸EGR率均匀性得到明显提高,EGR率相对偏差在±5%以内。     

柴油机实现高EGR率方法的计算分析

废气再循环是简单有效地减少NOx排放的方法。本文讨论了在柴油机中实现EGR的方法，并以一台4缸柴油机为例计算了不同工况条件下高、低压EGR系统的柴油机性能参数变化情况。结果表明：低压EGR系统在NOx排放上优于高压EGR系统；在高压EGR系统中，背压阀的位置对柴油机性能有一定影响；带有稳压箱的低压EGR系统在相同EGR率下油耗增加和功率损失最小。     

内燃机的废气再循环技术

介绍内燃机废气再循环(EGR)的工作原理、废气再循环量的评价指标EGR率、汽油机的EGR系统控制和柴油机EGR的效果及控制，以及采用EGR对柴油机工作过程和性能的影响。     

废气再循环对柴油机工作过程影响的模拟分析

根据实际柴油机的基本结构,建立了带有废气再循环(EGR)系统的增压直喷(TDI)柴油机的一维工作模型.将柴油机台架试验获得的最佳EGR率MAP图作为一维模型中EGR控制单元的控制MAP图,建立了模拟形式下EGR系统的控制单元,实现了柴油机在使用EGR后,不同工况EGR率条件下,EGR对柴油机工作全过程影响的一维模拟,模拟结果发现柴油机在使用EGR后空燃比、缸压、缸内温度都有所下降,缸内气体质量有所增加,与柴油机台架试验获得的结论吻合.     

汽油机高压EGR均匀性问题研究

近几年汽油机废气再循环系统(EGR)技术迅速发展,外部废气再循环技术可以有效降低缸内爆震倾向,提升汽油机燃油经济性。针对常规布置的高压EGR利用GT-Power进行性能仿真,并提出两缸取废气的非常规取废气方式,可以扩展高压EGR应用区域,同时降低各缸EGR率不均匀程度。     

当量天然气发动机各缸燃烧一致性的试验研究北大核心CSCD

为研究废气再循环气体(exhaust gas recirculation,EGR)和进气方式对当量燃烧的天然气发动机燃烧特征的影响,通过发动机台架测试分别探究了EGR气体和EGR所含水汽以及5、6缸位置进气(右侧进气)与3、4缸位置进气(中间进气)对当量燃烧天然气发动机各缸燃烧一致性的影响规律。试验结果表明:在右侧进气方式下,EGR气体的引入是影响当量天然气发动机各缸燃烧一致性的重要因素,特别是EGR气体中的水汽在各缸的分配。EGR气体除水汽后,各缸最大缸压偏差值由原来的9.5%降低为4.1%,当不引入EGR气体时,各缸最大缸压偏差值降低为2.3%。基于右侧进气方式在引入EGR气体后存在的问题,采用新设计的中间进气方式有效改善了各缸EGR气体的分配,从而显著提高了各缸燃烧一致性,各缸最大缸压偏差值由原右侧进气方式的9.5%降低为2.0%,有效解决了右侧进气在引入EGR时带来的各缸燃烧不一致性问题。     

基于CFD分析的某四缸机进气EGR混合均匀性研究

各缸EGR率的均匀一致性控制,对于发动机NO_x排放达标至关重要。针对某四缸柴油机设计了4种不同EGR结构方案,并采用AVL FIRE软件分别对其进行EGR混合均匀性模拟分析。分析表明:进气接管朝发动机中间,EGR管从进气接管侧方伸入的结构,其EGR均匀一致性最好。为后续的设计奠定了基础。     

船用中速柴油机废气再循环技术研究

废气再循环(EGR)技术是船用中速柴油机应对IMO Tier III排放法规的重要技术措施。本文以船用中速单缸柴油机为研究对象,开展了牺牲某缸的EGR系统中被牺牲气缸的工作过程、性能及排放特性的试验及仿真研究,研究结果可为船用中速柴油机克服进排气压力逆差关键技术的方案选择提供一定的技术依据。     

进气歧管结构差异对发动机各缸EGR率均匀性的影响

针对天然气发动机,废气再循环(EGR)能够有效地有抑制氮氧化物(NO_x)的产生,同时降低发动机缸内的燃烧温度。但各缸EGR率差异会导致各缸燃烧存在差异,从而增加失火和爆燃的风险。基于某国六天然气发动机进行各缸EGR率测试,并对进气歧管进行计算流体动力学(CFD)仿真分析。基于此,通过优化进气歧管结构设计,有效提升了EGR率的均匀性,各缸EGR率均匀性≤2.5%,满足设计要求。研究结果可为后期发动机的进气歧管设计开发提供参考。     

Cycle-by-cycle variations in a spark ignition engine fueled with natural gas–hydrogen blends combined with EGR

Study of cycle-by-cycle variations in a spark ignition engine fueled with natural gas–hydrogen blends combined with exhaust gas recirculation (EGR) was conducted. The effects of EGR ratio and hydrogen fraction on engine cycle-by-cycle variations are analyzed. The results show that the cylinder peak pressure, the maximum rate of pressure rise and the indicated mean effective pressure decrease and cycle-by-cycle variations increase with the increase of EGR ratio. Interdependency between the above parameters and their corresponding crank angles of cylinder peak pressure is decreased with the increase of EGR ratio. For a given EGR ratio, combustion stability is promoted and cycle-by-cycle variations are decreased with the increase of hydrogen fraction in the fuel blends. Non-linear relationship is presented between the indicated mean effective pressure and EGR ratio. Slight influence of EGR ratio on indicated mean effective pressure is observed at low EGR ratios while large influence of EGR ratio on indicated mean effective pressure is demonstrated at high EGR ratios. The high test engine speed has lower cycle-by-cycle variations due to the enhancement of air flow turbulence and swirls in the cylinder. Increasing hydrogen fraction can maintain low cycle-by-cycle variations at high EGR ratios.     

基于多缸运动的气体机进气均匀性计算方法

针对常规废气再循环(exhaust gas recirculation, EGR)率均匀性计算方法不适用于各缸进气量分析的问题,基于CONVERGE软件建立了考虑气门和活塞运动的多缸计算方法,并分析了某国六天然气发动机的进气均匀性。结果表明：采用多缸方法得到的EGR率均匀性计算结果与采用常规方法得到的结果一致,并且多缸方法还能获得各缸的进气量和当量比及各缸的涡流比、滚流比和湍动能等表征缸内流动状态的参数,拓展了计算能力。基于仿真分析和台架试验的结果表明该款发动机的进气均匀性满足设计要求。     

YC某柴油机各缸EGR率均匀分布性研究

以玉柴某带EGR系统的柴油机为研究对象,建立了该发动机性能数值模拟的Boost分析模型;计算得到进气总管入口、EGR管出口和进气歧管出口的气体流量,再用Fire软件对气道内三维流场进行了数值计算;对比分析了不同EGR管引入角、不同EGR位置及结构对各缸EGR分配均匀性的影响。研究结果为EGR管最佳布置方案的确定提供了理论依据。     

米勒循环及低压废气再循环技术对汽油机性能的影响研究

在某2.0L涡轮增压商用车缸内直喷汽油机概念设计阶段,运用GT-Power软件进行了一维热力学计算分析,并着重研究了米勒循环技术与低压废气再循环(exhaust gas recirculation,EGR)技术对燃油经济性的影响。仿真结果显示,长米勒循环和短米勒循环都存在使燃油经济性达到最佳的可变气门正时角度。在中高转速范围内,因为质量流量和流速过高导致长米勒循环的缸内空气无法顺利回流,米勒效应减弱,所以短米勒循环的燃油经济性更好;另外长米勒循环具有两次泵气过程,致使其泵气损失也大于短米勒循环。在低转速范围内,短米勒循环的增压压力需求更大,导致其泵气损失大于长米勒循环,所以长米勒循环的燃油经济性更好。对于试验用汽油机来说,短米勒循环具有明显的优势。低压EGR技术能够使缸内最高温度降低,减轻爆震倾向,因此燃烧重心可以适当提前,从而改善燃油经济性。另外,EGR和新鲜空气总量的增加也使最高燃烧压力增大,有利于燃油经济性的提高。不同工况下,缸内最高温度均随EGR率的增加而降低,因此在一定范围内EGR率越高燃油经济性越好,涡前排温越低,但EGR冷却器需要的散热功率也增大。在发动机燃烧开发阶段,推荐采用短米勒循环技术并结合8%的EGR率。为了验证仿真结果的准确性,开展了性能试验,试验结果与仿真结果在趋势上有很好的一致性。     

电控喷油五气门汽油机排气再循环性能的实验研究

以稀薄燃烧的汽油机电控喷油系统及排气再循环系统为实验平台，对可变进气五气门汽油机采用化学计量比时的排气再循环燃油经济性和排放性能进行了实验研究，结果表明，燃油消耗率明显改善(2．8％-5．5％)，NO，显著降低(90％-95％)，HC改善不明显．为了进一步挖掘稀燃发动机的低油耗和低排放性能，用稀燃运行时加入适量排气的方法，结果显示，NO，显著降低．     

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 investigation of the Exhaust Gas Recirculation effects on irreversibility and Brake Specific Fuel Consumption of indirect injection diesel engines

An experimental study was carried out to investigate the effect of using Exhaust Gas Recirculation (EGR) on various exergy terms of an IDI diesel engine cylinder. In this paper also the effectiveness of total in-cylinder irreversibility on Brake Specific Fuel Consumption (BSFC) in a diesel engine is investigated. To serve this aim an exergy analysis is conducted on the engine cylinder which provides all the availability terms by which the evaluation of in-cylinder irreversibilities is possible. The availability terms including heat transfer, inlet and exhaust gases and work output are presented during the engine operation at different load and speeds. To clarify the effect of using EGR in each case, EGR is introduced to the cylinder at various ratios during the tests. Finally, the dependence of total in-cylinder irreversibility and engine BSFC at particular engine operating conditions is introduced and the variations are compared. The results show that using EGR mostly increases the total in-cylinder irreversibility mainly due to extension of the flame region which reduces maximum combustion temperature. Also, the results revealed that the variations of the total in-cylinder irreversibility and engine BSFC follow the same trend especially at high load conditions.     

高/低压EGR对汽油机和增压器影响的试验研究

在一款涡轮增压汽油缸内直喷(gasoline direct injection,GDI)汽油机上进行了高压(HP)废气再循环(exhaust gas recirculation,EGR)和低压(LP)EGR对发动机和增压器性能影响的试验研究。分别对比了HP EGR和LP EGR系统在外特性和部分负荷工况对发动机燃烧、油耗、进排气的影响及增压器相应的工况变化,并分析了出现这些变化的原因。结果表明,汽油机EGR系统能够优化缸内燃烧,减少泵气损失,从而降低油耗。低压EGR系统在部分负荷工况热效率比高压EGR更高,主要原因为低压EGR系统的涡轮增压器可利用的尾气能量更多,且进入发动机的废气温度较低,能进一步优化缸内燃烧。