基于响应面和遗传算法的柴油机瞬态过程喷油参数优化

基于台架试验数据,利用响应面法建立了某工程机械用柴油机瞬态过程喷油参数与性能的近似高精度模型,基于此模型采用遗传算法对瞬态过程喷油参数分别进行离线优化研究。结果表明:采用单目标优化确定的燃油消耗率(BSFC)、NO_x比排放量和颗粒质量(PM)比排放量的优化极限分别可达180.23g/(kW·h),8.92g/(kW·h)和0.011 8g/(kW·h),相对原机可降低多达4.5%,34.0%和37.3%。双目标优化的Pareto解集表明,相比于同时优化BSFC和NO_x比排放量,BSFC和PM比排放量更容易同时得到优化。采用权重因子适应度函数的三目标优化结果对应的BSFC,NO_x比排放量及PM比排放量分别为184.70g/(kW·h),12.62g/(kW·h)和0.012 2g/(kW·h),较原机分别降低2.1%,6.6%和35.3%。改进优化模型后,性能优化Pareto解集对应的BSFC和PM比排放量水平都非常接近其优化极限,但NO_x比排放量相对其优化极限仍然较高。     

废气再循环对车用柴油机性能与排放的影响

为了降低车用柴油机的NOx排放，研究了不同工况下EGR率对柴油机性能的影响。试验结果表明，采用EGR可以有效地降低NOx排放。大负荷比小负荷效果显著，但微粒的排放有所增加。小负荷采用EGR时可以改善发动机的燃烧，微粒排放基本没有变化。空燃比是影响微粒排放的关键因素，小负荷宜采用大EGR率，大负荷时宜采用小EGR率，以求在控制NOx排放降低的同时，总的微粒排放不至增加过多。     

柴油机燃烧放热模式分析

研究了NOx和PM的机内净化方法,试验分析了EGR、高压喷射对柴油机排放的影响规律。在此基础上确定低NOx和低PM两种理想燃烧模式对应放热率参数的阈值。结果表明:NOx净化达到欧Ⅳ标准时,所对应的归一化放热率阈值为0.045~0.049°CA-1;PM净化达到欧Ⅳ标准时,对应的归一化放热率阈值为0.045~0.06°CA-1;二者同时达欧Ⅳ的归一化放热率阈值为二者的交集0.045~0.049°CA-1。     

基于一维/三维模型耦合的富氧燃烧天然气发动机数值模拟

以某1.0L3缸汽油机为基础,利用GT-Power与Converge建立了天然气发动机耦合仿真模型,并利用原机试验数据对模型进行了验证,研究了进气富氧与EGR对天然气发动机性能的影响特性,对利用进气富氧与EGR改善天然气发动机的性能进行了探讨。结果表明,随进气氧气体积分数提高,天然气发动机平均有效压力显著提高,最大可提高22.8%(氧体积分数为28%时);同时缸内温度和NOx排放升高,排气与传热的能量损失增加,燃气消耗率略有升高。加入EGR可以降低富氧燃烧下天然气发动机燃气消耗率,随着EGR率增加,燃气消耗率主要呈先减小后增加趋势;且随进气氧浓度提高,各浓度下最低燃气消耗率对应的EGR率逐渐提高;NOx排放随EGR率增加而逐渐降低,在进气氧体积分数为23%,25%,27%,29%时,EGR率分别为10%,15%,20%,25%即可将NOx排放降到原机水平;利用进气富氧与EGR可以有效地改善天然气发动机动力不足与NOx排放高的状况。     

Model based burnt gas fraction controller design of diesel engine with VGT/Dual loop EGR system

-Recently, regulation of NOx and PM emission in diesel engines has become stricter and the EGR system has been expanded into a dual loop EGR system to increase EGR rate as well as to utilize exhaust gas strategically. In terms of engine combustion characteristics, burnt gas fraction is becoming an important factor of solving the NOx and PM emission reduction problem more efficiently but conventional controller focused only pressure and air flow rate targets. Unlike the previous studies, this paper describes a model based burnt gas fraction control structure for a diesel engine with a dual loop EGR and a turbocharger. Feedforward control inputs based on burnt gas fraction states aids in the precise control of diesel engines, especially in transient states by considering coupled behavior within the system. For the controller validation, a control oriented reduced order model of a diesel engine air management system is established to simplify the control input computation and its stability is proved by analysing the internal dynamics stability. Then, a sliding mode controller is designed and controller robustness at certain operating points is validated using an HiLS bench.     

Investigation on the flow and heat transfer characteristics of diesel engine EGR coolers

An important goal in diesel engine research is the development of a means to reduce the emissions of nitrogen oxides (NOx). The use of a cooled exhaust gas recirculation (EGR) system is one of the most effective techniques currently available for reducing nitrogen oxides. Since PM (Particulate Matter) fouling reduces the efficiency of an EGR cooler, a tradeoff exists between the amount of NOx and PM emissions, especially at high engine loads. In the present study, we performed engine dynamometer experiments and numerical analyses to investigate how the internal shape of an EGR cooler affects the heat exchanger efficiency. Heat exchanger efficiencies were examined for plain and spiral EGR coolers. The temperature and pressure distributions inside these EGR coolers were obtained in three dimensions using the numerical package program FLUENT.     

柴油机多级并联文丘里管进气系统

为了最大限度地降低NOx排放,进行了利用多级并联式文丘里管进气系统提高柴油机EGR率的研究.通过理论计算和模拟试验的方法对各个文丘里管的结构参数和通道开通数的排列组合进行了优化,分析了不同结构参数和排列组合对柴油机工作参数的影响,特别是对EGR率的影响.结果表明,柴油机在采用多级并联式文丘里管进气系统后,有效提升了EG...     

Effect of operating parameters on diesel/propane dual fuel premixed compression ignition in a diesel engine

In this research, the effects of three operating parameters (Diesel injection timing, propane ratio, and exhaust gas recirculation (EGR) rates) in a diesel-propane dual fuel combustion were investigated. The characteristics of dual-fuel combustion were analyzed by engine parameters, such as emission levels (Nitrogen oxides (NO_x) and particulate matter (PM)), gross indicated thermal efficiency (GIE) and gross IMEP Coefficient of Variance (CoV). Based on the results, improving operating strategies of the four main operating points were conducted for dual-fuel PCCI combustion with restrictions on the emissions and the maximum pressure rise rate. The NOx emission was restricted to below 0.21 g/kWh in terms of the indicated specific NO_x (ISNO_x), PM was restricted to under 0.2 FSN, and the maximum pressure rise rate (MPRR) was restricted to 10 bar/deg. Dual-fuel PCI combustion can be available with low NO_x, PM emission and the maximum pressure rise rate in relatively low load condition. However, exceeding of PM and MPRR regulation was occurred in high load condition, therefore, design of optimal piston shape for early diesel injection and modification of hardware optimizing for dual-fuel combustion should be taken into consideration.     

Numerical study of a light-duty diesel engine with a dual-loop EGR system under frequent engine operating conditions using the doe method

Exhaust gas recirculation (EGR) is an emission control technology that allows for a significant reduction in NOx emissions from light- and heavy-duty diesel engines. The primary effects of EGR are a lower flame temperature and a lower oxygen concentration of the working fluid in the combustion chamber. A high pressure loop (HPL) EGR is characterized by a fast response, especially at lower speeds, but is only applicable if the turbine upstream pressure is sufficiently higher than the boost pressure. On the contrary, for the low pressure loop (LPL) EGR, a positive differential pressure between the turbine outlet and the compressor inlet is generally available. However, a LPL EGR is characterized by a slow response, especially at low and moderate speeds. In this study, of the future types of EGR systems, the dual-loop EGR system (which has the combined features of the high-pressure loop EGR and the low-pressure loop EGR) was developed and was optimized under five selected operating conditions using a commercial engine simulation program (GT-POWER) and the DOE method. Finally, significant improvements in the engine exhaust emissions and performance were obtained by controlling several major variables.     

采用低温等离子体同步净化柴油机PM和NO_x(一):物理仿真

为了实现对柴油机尾气中PM和NOx的同步去除,将静电旋风捕集技术与等离子体协同烃类选择性催化还原技术(Plasma/HC-SCR)相结合开发了一套柴油机后处理原理性试验装置。该装置集柴油机PM的静电捕集、PM的氧化燃烧、NOx的选择性催化还原于一体,对在富氧条件下利用烃类选择还原催化和静电旋风捕集同步去除柴油机PM和NOx进行了利用可控标准气体的模拟试验研究,得到了净化效率随相关参数之间的变化规律。在单纯的等离子体环境下,NO浓度降低,NO2浓度增加,但总的NOx基本保持不变;使用催化剂的同时辅助等离子体可以使NO的峰值转化率所对应的温度向低温区偏移50℃左右;催化剂、等离子体、还原HC对于降低炭烟的起燃温度都有影响,同时使用可以使炭烟的起燃温度最低降低到280℃。此装置实现了柴油机PM和NOx的同步去除。     

EGR对DME发动机性能和排放的影响

开展了4100QBZL增压中冷发动机燃用D40二甲醚—柴油混合燃料时采用EGR技术对发动机动力性、经济性、燃烧和排放性能影响的试验研究。试验结果表明:EGR技术可以有效降低D40混合燃料发动机的NOx排放,EGR率越高,NOx排放改善越明显,但会不同程度恶化烟度、HC,CO等排放。     

车用重型高压共轨柴油机EGR性能及优化

在1台CA6DL2—35E3重型高压共轨柴油机上建立原理性低压EGR系统,并进行了EGR性能试验。试验结果表明:在欧Ⅲ高压共轨柴油机平台下,小EGR率即可大幅度降低NOx排放;从性能及排放折中考虑,在中小负荷可适当增大废气回流量以实现低温燃烧;根据优化策略优化EGR率后,仅在13%EGR率范围内气体排放即可达到欧Ⅳ法规水平,而通过对大负荷最佳EGR率的修正,在满足排放要求的同时,可降低EGR散热损失;NOx比排放量随燃烧放热率峰值变化存在拐点(EGR率最优点),可作为改善尾气排放的有效判据。     

EGR在内燃机上的应用

EGR是降低内燃机NOx排放的主要机外净化措施之一。文章介绍了EGR技术对抑制NOx生成的理论基础及EGR率的确定原则：阐述了EGR对发动机排放性、动力性、经济性、气缸磨损的影响以及EGR在其他新型燃料发动机的应用。指出随着EGR的增大,发动机NOx的降低效果非常明显,但是烟度、PM和CO的排放都有增加的趋势,对HC的影响不大;同时,随着EGR的增大,发动机的动力性和经济性都有恶化的趋势,特别是对于发动机的动力性降低较明显。     

EGR回路喷甲醇在柴油机上的应用研究

在YC6A220C柴油机上进行了进气道喷甲醇结合EGR的试验研究,在保持原柴油机动力性基本不变的基础上,研究了在不同负荷下,选用不同的EGR率和不同甲醇消耗率对原机的动力性、经济性、NOx和炭烟排放的影响。研究结果表明:单纯地使用EGR对于降低NOx效果比较明显,但是难以同时降低炭烟的排放,尤其当EGR率超过30%时,随着EGR率或者负荷的增加炭烟也急剧增加。向回路喷入适量甲醇后,不但可以保证NOx排放减少,而且炭烟排放也可以大幅度降低。在1 500r/min(最大扭矩转速)下,在EGR率为20%~35%,甲醇消耗率为50~70g/(kW·h)范围内,可以同时降低NOx和炭烟排放。发动机的动力性和燃油消耗略有降低,排放水平均低于燃用0号柴油。     

废气再循环系统在车用发动机上的应用研究

介绍了EGR系统结构原理、NOx的形成机理以及EGR技术对抑制NOx生成的理论基础;比较了柴油机和汽油机最优EGR率特性场的分布状况;分析了几种常用EGR率的测量方法、测量原理及其应用范围。着重阐述了不同工况下不同EGR率对发动机动力性、经济性及排放性能的影响;最后指出EGR率优化过程中应该考虑的几个重要设计原则。     

Combustion characteristics of hydrotreated vegetable oil – diesel blend under EGR and supercharged conditions

This paper investigates the effects of Hydrotreated vegetable oil-diesel blend to combustion characteristics under various ambient oxygen concentrations and ambient pressure. Combustion characteristics were investigated using heat release rate analysis, two color method, soot concentration measurement and NOx concentration measurement. The experiments were carried out on a rapid compression expansion machine to simulate the ambient condition of a CI engine at TDC. Synthetic gas with oxygen concentrations of 21 %, 15 % and 10 % were used to simulate EGR conditions. A single hole injector was used with five different fuels: commercial diesel, HVO-commercial diesel blends and HVO. The results showed that increasing HVO blending percentages decreased ignition delay, flame temperature, soot concentration and NOx concentration. Heat release at oxygen concentration of 10 % dramatically dropped due to a shortened ignition delay, which resulted in less combustion. A decreased oxygen concentration from applied EGR conditions not only increased ignition delay, heat release, flame temperature and NO_x concentration, but also increased soot concentration. A combination of EGR and supercharged conditions by increasing ambient pressure and decreasing oxygen concentrations resulted in increased heat release, decreased flame temperature, ignition delay and soot concentration, compared to EGR conditions.     

Experimental evaluation of SOF effects on EGR cooler fouling under various flow conditions

An experiment was conducted to characterize the effects of SOF on EGR cooler fouling. A removable singletube test rig combined with a soot generator was developed to represent an EGR cooler and diesel exhaust gas. The use of a soot generator, which controlled the size and concentration of soot particles, enabled independent variables to be completely controlled. Either n-dodecane or diesel lube oil as substitute SOFs were vaporized and injected into the test rig to evaluate their effects on the growth of PM deposits and the degradation performance of the EGR cooler. Coolant temperature, which seemed to be associated with SOF content, was chosen as an independent variable, and PM deposit mass per unit area and the effectiveness drop versus time increased as the coolant temperature decreased. The PM deposit mass per unit area and effectiveness drop had maximum values at a coolant temperature of 40°C for every n-dodecane injection rate. For substitute SOFs tested in this experiment, the deposit mass increased when either n-dodecane or diesel lube oil was injected, but the effect of lube oil was more significant. Diesel lube oil seemed to have a stronger effect on the reduction of thermal conductivity by filling pores in the deposits. When diesel lube oil was injected, the deposit mass per unit area increased 127% compared to dry soot without injection. The effectiveness drop after 10 hours increased only 12.5%.     

Enhancement of NOx-PM trade-off in a diesel engine adopting bio-ethanol and EGR

For realizing a premixed charge compression ignition (PCCI) engine, the effects of bio-ethanol blend oil and exhaust gas recirculation (EGR) on PM-NOx trade-off have been investigated in a single cylinder direct injection diesel engine with the compression ratio of 17.8. In the present experiment, the ethanol blend ratio and the EGR ratio were varied focusing on ignition delay, premixed combustion, diffusive combustion, smoke, NOx and the thermal efficiency. Very low levels of 1.5 [g/kWh] NOx and 0.02 [g/kWh] PM, which is close to the 2009 emission standards imposed on heavy duty diesel engines in Japan, were achieved without deterioration of the thermal efficiency in the PCCI engine operated with the 50% ethanol blend fuel and the EGR ratio of 0.2. It is found that this improvement can be achieved by formation of the premixed charge condition resulting from a longer ignition delay. A marked increase in ignition delay is due to blending ethanol with low cetane number and large latent heat, and due to lowering in-cylinder gas temperature on compression stroke based on the EGR. It is noticed that smoke can be reduced even by increasing the EGR ratio under a highly premixed condition.     

基于Ascet平台的高压共轨柴油机电控EGR控制策略研究

针对电控EGR控制策略,结合电控系统模块化的设计思路,设计了基于Ascet平台的电控发动机EGR控制系统。通过对转速、油量等参数进行标定,运用Ascet软件实现了EGR控制模型的模拟仿真,保证了系统稳定性及可靠性,加快了EGR系统的响应速度,实现了对排气再循环系统的闭环控制。将调试好的EGR电控系统安装在高压共轨柴油机上,在标定转速3 600 r/min下进行试验,试验结果表明,EGR控制系统能够按照控制策略实现对EGR的精确控制,与原机相比,NOx排放下降明显。     

Improvement of combustion efficiency and emission characteristics of IC diesel engine operating on ESC cycle applying Variable Geometry Turbocharger (VGT) with vaneless turbine volute

Based on experimental data, the present study investigates the influence of turbine adjustment in a turbocharger with vaneless turbine volute on diesel combustion efficiency indices and emission characteristics. Experimental investigations were conducted on engine modes as set out by the European Stationary Cycle (ESC). The adjustment algorithms selected for the experiment under ESC modes included adjustment to achieve minimal values of specific fuel consumption (SFC), NOx, CO and particulate matter (PM). In present research only VGT adjustment was investigated, the factors like fuel injection timing and EGR were not investigated. As a result we were able to make a comparison of the engine combustion efficiency and emission indices for VGT and a common turbocharger running on ESC cycle modes.