车用汽油机EGR率、点火定时和空燃比的优化

通过对安装EGR阀的CA6 10 2试验机进行EGR率、点火提前角、空燃比等因素的匹配试验 ,分析其变化规律 ,找出安装EGR阀后发动机点火和供油的最优匹配。在保持经济性指标的同时 ,最大限度地改善排放     

Experimental study on the effects of HP and LP EGR on thermal efficiency and emissions of a two-stage turbocharged diesel engine

An experimental study was performed to compare the effects of high- and low-pressure exhaust gas recirculation loops (HP and LP EGR loops) on thermal efficiency and emissions of a diesel engine. Tests were conducted on a 12-L six-cylinder turbocharged diesel engine under various operating conditions. We found that at a low speed of 1100 r/min, 1 MPa BMEP, the LP EGR loop could achieve higher brake thermal efficiency and lower emissions than the HP EGR. This is because the lower enthalpy available at the turbine inlet of the HP EGR loop increased the fuel/oxygen equivalence ratio. For the HP EGR, the gross indicated thermal efficiency was reduced by 1%, but pumping losses were only reduced by 0.5%, compared to the LP EGR loop. At a higher speed of 1600 r/min, 1 MPa BMEP, the HP EGR loop attained a higher brake thermal efficiency and lower emissions because of the relatively sufficient flow through the turbocharger. For the HP EGR loop, the gross indicated thermal efficiency was only reduced by 0.5% and pumping losses were reduced by 1.5%, compared to the LP EGR loop. Lower fuel consumption and a longer ignition delay made the distribution of fuel/oxygen equivalence ratio more homogeneous, leading to lower emissions. Our data also showed that at the high speed of 1600 r/min, 0.55 MPa BMEP, the brake thermal efficiency of the HP EGR loop first increased, then decreased as the EGR rate increased. Therefore, under all conditions, a reasonable match of both EGR loops could achieve a good balance between fuel consumption and emissions of NO _x and soot.     

Effect of EGR on the exhaust gas temperature and exhaust opacity in compression ignition engines

In diesel engines, NOx formation is a highly temperature-dependent phenomenon and takes place when the temperature in the combustion chamber exceeds 2000 K. Therefore, in order to reduce NOx emissions in the exhaust, it is necessary to keep peak combustion temperatures under control. One simple way of reducing the NOx emission of a diesel engine is by late injection of fuel into the combustion chamber. This technique is effective but increases fuel consumption by 10–15%, which necessitates the use of more effective NOx reduction techniques like exhaust gas recirculation (EGR). Re-circulating part of the exhaust gas helps in reducing NOx, but appreciable paniculate emissions are observed at high loads, hence there is a trade-off between NOx and smoke emission. To get maximum benefit from this trade-off, a paniculate trap may be used to reduce the amount of unburnt particulates in EGR, which in turn reduce the paniculate emission also. An experimental investigation was conducted to observe the effect of exhaust gas re-circulation on the exhaust gas temperatures and exhaust opacity. The experimental setup for the proposed experiments was developed on a two-cylinder, direct injection, air-cooled, compression ignition engine. A matrix of experiments was conducted for observing the effect of different quantities of EGR on exhaust gas temperatures and opacity     

Various strategies for reducing Nox emissions of biodiesel fuel used in conventional diesel engines: A review

Energy demand, decreasing fossil fuel reserves, and health-related issues about pollutants have led researchers to search for renewable alternative fuels to either partially or fully replace fossil fuels. Among many alternative fuels, biodiesel became one of the most popular choices due to similar properties to that of conventional diesel. Biodiesel produces slightly lower brake thermal efficiency compared to that of conventional biodiesel, but has an advantage of reduced emissions of CO₂, CO, HC, and smoke. However, biodiesel shows higher NOx emission which, when used in increased biodiesel market, may become a serious problem. Various strategies were attempted by different researcher to reduce NOx emissions. In this paper, various strategies, adapted for reducing NOx emissions of biodiesel fuel used in diesel engines for automobile applications, are reviewed and discussed. The strategies are grouped into three major groups, namely combustion treatments, exhaust after-treatments, and fuel treatments. Among various strategies discussed, fuel treatments, such as low temperature combustion, mixing fuel additives and reformulating fuel composition, reduce NOx emission without compromising other emission and performance characteristics and they seem to be promising for future biodiesel fuel.     

Control of diesel engine dual-loop EGR air-path systems by a singular perturbation method

This paper presents a singular perturbation based method for controlling the dual-loop exhaust gas recirculation (DL-EGR) air-path systems on advanced diesel engines. A DL-EGR air-path system, consisting of a high-pressure loop EGR (HPL-EGR) and a low-pressure loop EGR (LPL-EGR), has significantly different time-scales (fast and slow) due to the inherent difference in the HPL-EGR’s and LPL-EGR’s corresponding control volumes. Such a feature of the DL-EGR systems makes the cooperative control of intake manifold gas conditions challenging. By considering the DL-EGR air-path system as a singularly perturbed system, a composite control law was devised to achieve systematic control of the air-path conditions including gas pressure, temperature, and oxygen fraction in the intake manifold. The effectiveness of the control method is experimentally evaluated on a medium-duty diesel engine.     

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。     

废气再循环在增压中冷柴油机上的试验研究

为了降低车用柴油机的NOx排放,分析了不同工况下EGR率对柴油机性能的影响。通过试验了解到,采用EGR可以有效地降低NOx排放,大负荷比小负荷效果显著。并对控制最佳EGR率的电控脉谱系统提出了初步的探讨。     

柴油机内部EGR的数值模拟分析

应用大型通用CFD软件STAR-CD及网格生成软件ES-ICE,对带有内部EGR的柴油机进气及压缩过程缸内三维瞬态流场进行数值模拟研究,并分析其组分浓度及温度的分布情况,通过研究掌握内部EGR对缸内温度、浓度场的影响,为进一步研究内部EGR对缸内燃烧的影响奠定基础。     

内部EGR对柴油机HCCI高负荷拓展因素的影响

为了研究内部废气再循环(EGR)率对柴油机HCCI高负荷拓展因素的影响,以某型柴油机为例,在不同内部EGR率情况下,采用计算流体力学(CFD)方法对柴油机HCCI燃烧过程进行了仿真计算。结果表明:随着EGR的增大,缸内平均燃烧温度降低;燃空当量比逐渐降低;燃烧持续期先缩短后延长,在EGR率为35%时燃烧持续期最短;缸内最大压力升高率降低;柴油机IMEP(平均指示压力)先增大后降低,在EGR率为35%左右时达到最大,为0.573 MPa。     

文丘里管废气再循环系统对涡轮增压柴油机性能影响的研究

加装文丘里管的高压废气再循环(Exhaust gas re-circulation,EGR)进气系统,在兼顾柴油机经济性、动力性的前提下,研究该进气系统对NO_x排放的影响。根据一款柴油机的基本结构建立柴油机一维仿真计算模型和燃烧室的三维仿真计算模型。在对模型进行标定和对柴油机原机性能仿真计算的基础上,为进气系统引入文丘里管装置并对其结构参数进行优化设计。应用所建立的一维和三维柴油机模型,对文丘里管EGR系统柴油机的经济性、NO_x和Soot排放特性进行仿真计算研究,并对计算结果进行试验验证。研究结果表明,优化设计的文丘里管EGR系统可使柴油机在欧洲稳态循环(European steady state cycle,ESC)各工况下实现较为理想的EGR率,并在不明显影响柴油机燃油经济性的前提下,使NO_x排放量下降了约28.4%。文丘里管进气系统可以实现较为理想的高压EGR循环,在柴油机ESC工况下(怠速除外)能够达到较为理想的EGR率。