Effect of exhaust gas recirculation and intake pre-heating on performance and emission characteristics of dual fuel engines at part loads

Achieving simultaneous reduction of NOx,CO and unburned hydrocarbon(UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research.The present work focuses on an experimental investigation conducted on a dual fuel(diesel-natural gas) engine to examine the simultaneous effect of inlet air pre-heating and exhaust gas recirculation(EGR) ratio on performance and emission characteristics at part loads.The use of EGR at high levels seems to be unable to improve the engine performance at part loads.However,it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency,resulting in reduced levels of both unburned hydrocarbon and NOx emissions.CO and UHC emissions are reduced by 24% and 31%,respectively,The NOx emissions decrease by 21% because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.

Collaborative optimization of exhaust gas recirculation and Miller cycle of two-stage turbocharged marine diesel engines based on particle swarm optimization

To meet increasingly stringent emission standards and lower the brake-specific fuel consumption(BSFC)of marine engines,a collaborative optimization study of exhaust gas recirculation(EGR)and a Miller cycle coupled turbocharging system was carried out.In this study,a one-dimensional numerical model of the EGR,Miller cycle,and adjustable two-stage turbocharged engine based on WeiChai 6170 marine diesel engine was established.The particle swarm optimization algorithm was used to achieve multi-input and multi-objective comprehensive optimization,and the effects of EGR-coupled Miller regulation and high-pressure turbine bypass regulation on NO_(x)and BSFC were investigated.The results showed that a medium EGR rate-coupled medium Miller degree was better for the comprehensive optimization of NO_(x)and BSFC.At medium EGR rate and low turbine bypass rates,NO_(x)and BSFC were relatively balanced and acceptable.Finally,an optimal steady-state control strategy under full loads was proposed.With an increase in loads,the optimized turbine bypass rate and Miller degree gradually increased.Compared with the EGRonly system,the optimal system of EGR and Miller cycle coupled turbine bypass reduced NO_(x)by 0.87 g/(kW·h)and BSFC by 17.19 g/(kW·h)at 100%load.Therefore,the EGR and Miller cycle coupled adjustable two-stage turbocharging achieves NO_(x)and BSFC optimization under full loads.

EFFECTS OF COOLED EXTERNAL EXHAUST GAS RECIRCULATION ON DIESEL HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE

The effects of cooled external exhaust gas recirculation （EGR） on the combustion and emission performance of diesel fuel homogeneous charge compression ignition （HCCI） are studied. Homogeneous mixture is formed by injecting fuel in-cylinder in the negative valve overlap （NVO） period. So, the HCCI combustion which has low NOx and smoke emission is achieved. Cooled external EGR can delay the start of combustion effectively, which is very useful for high cetane fuel （diesel） HCCI, because these fuels can easily self-ignition, which makes the start of combustion more early. External EGR can avoid the knock combustion of HCCI at high load which means that the EGR can expand the high load limit. HCCI maintains low smoke emission at various EGR rate and various load compared with conventional diesel engine because there is no fuel-rich area in cylinder.

Combustion and emission characteristics of diesel/n-butanol blends with split-injection and exhaust gas recirculation stratification

Oxygen fuels have broad application prospects and great potential for realizing efficient and clean combustion,and hence this study applies diesel/n-butanol blends to explore the influence of split-injection strategy on combustion and emission characteristics.Simultaneously,changing the way of exhaust gas recirculation(EGR)gas introduction forms uneven in-cylinder components distribution,and utilizing EGR stratification optimizes the combustion process and allows better emission results.The results show that the split-injection strategy can reduce the NO_(x)emissions and keep smoke opacity low compared with the single injection,but the rise in accumulation mode particles is noticeable.NO_(x)emissions show an upward trend as the injection interval expands,while soot emissions are significantly reduced.The increase in pre-injection proportion causes the apparent low-temperature heat release,and the two-stage heat release can be observed during the process of main combustion heat release.More pre-injection mass makes NO_(x)gradually increase,but smoke opacity reaches the lowest point at 15%pre-injection proportion.EGR stratification can optimize the emission results under the split injection strategy,especially the considerable suppression of accumulation mode particulate emissions.Above all,fuel stratification coupled with EGR stratification is beneficial for further realizing the in-cylinder purification of pollutants.

Design and optimization of exhaust gas aftertreatment system for a heavy-duty diesel engine

Diesel engines meeting the latest emission regulations must be equipped with exhaust gas aftertreatment system,including diesel oxidation catalysts(DOC),diesel particulate filters(DPF),and selective catalytic reduction(SCR).However,before the final integration of the aftertreatment system(DOC+DPF+SCR)and the diesel engine,a reasonable structural optimization of the catalytic converters and a large number of bench calibration tests must be completed,involving large costs and long development cycles.The design and optimization of the exhaust gas aftertreatment system for a heavy-duty diesel engine was proposed in this paper.Firstly,one-dimensional(1D)and threedimensional(3D)computational models of the exhaust gas aftertreatment system accounting for the structural parameters of the catalytic converters were established.Then based on the calibrated models,the effects of the converter’s structural parameters on their main performance indicators,including the conversion of various exhaust pollutants and the temperatures and pressure drops of the converters,were studied.Finally,the optimal design scheme was obtained.The temperature distribution of the solid substrates and pressure distributions of the catalytic converters were studied based on the 3D model.The method proposed in this paper has guiding significance for the optimization of diesel engine aftertreatment systems.

Analysis of Non-Selective Catalyst Reduction Performance with Dedicated Exhaust Gas Recirculation

Rich burn industrial natural gas engines offer best in class post catalyst emissions by using a non-selective catalyst reduction aftertreatment technology. However, they operate with reduced power density when compared to lean burn engines. Dedicated exhaust gas recirculation (EGR) offers a possible pathway for rich burn engines to use non-selective catalyst reduction aftertreatment technology without sacrificing power density. In order to achieve best in class post catalyst emissions, the precious metals and washcoat of a non-selective catalyst must be designed according to the expected exhaust composition of an engine. In this work, a rich burn industrial natural gas engine operating with dedicated EGR was paired with a commercially available non-selective catalyst. At rated brake mean effective pressure (BMEP) the air-fuel ratio was swept between rich and lean conditions to compare the catalyst reduction efficiency and post catalyst emissions of rich burn and dedicated EGR combustion. It was found that due to low oxides of nitrogen (NOx) emissions across the entire air-fuel ratio range, dedicated EGR offers a much larger range of air-fuel ratios where low regulated emissions can be met. Low engine out NOx also points towards a possibility of using an oxidation catalyst rather than a non-selective catalyst for dedicated EGR applications. The location of the NOx-CO tradeoff was shifted to more rich conditions using dedicated EGR.

Effect of exhaust gas recirculation and ethyl hexyl nitrate additive on biodiesel fuelled diesel engine for the reduction of NOx emissions

Cetane improvers reduce the ignition delay, which in turn reduces the combustion temperatures thereby reduce NOx emissions. Exhaust gas recirculation （EGR） proved to be an effective way to reduce the NOx emissions. In this present experimental work, a combination of exhaust gas recirculation and cetane improver ethyl hexyl nitrate （EHN） is used to investigate the performance and exhaust emissions of a single cylinder four stroke naturally aspirated direct injection and air cooled diesel engine. Test results show that the brake thermal efficiency increases with the increase in the percentage of EGR which is accompanied by a reduction in brake specific fuel consumption and exhaust gas temperatures, and that bio- diesel with cetane improver under 20% EGR reduces NOx emissions by 33% when compared to baseline fuel without EGR. However carbon monoxide （CO）, hydro carbon （HC） and smoke emissions increase with an increase in percentage of EGR.

Experimental Investigation for NO_x Emission Reduction in Hydrogen Fueled Spark Ignition Engine Using Spark Timing Retardation, Exhaust Gas Recirculation and Water Injection Techniques

The experimental tests were carried out on a single cylinder hydrogen fueled spark ignition(SI)generator set with different spark timings(4-20℃A bTDC),exhaust gas recirculation(EGR)up to 28% by volume and water injection up to 1.95 kg/h(maximum water to fuel mass ratio of 8:1).The engine speed was kept constant of 3000 r/min.The NOx emission and thermal efficiency of engine with gasoline and hydrogen fuel operation at 1.4 kW power output are 5 g/kWh and 12.1 g/kWh,and 15% and 20.9% respectively.In order to reduce the NOx emission at source level,retarding spark timing,exhaust gas recirculation(EGR),and water injection techniques were studied.Nox emission decreased with spark timing retardation,EGR,and water injection.NOx emission with hydrogen at 1.4 kW power output decreased from 12.1 g/kWh with maximum brake torque(MBT)spark timing(10℃A bTDC)to 8.1 g/kWh with retarded spark timing(4℃A bTDC)due to decrease in the in-cylinder peak pressure and temperature.The Nox emission decreased to 6.1 g/kWh with 20% EGR due to thermal and chemical dilution effect.However,thermal efficiency decreased about 33% and 17% with spark timing retardation and 20EGR respectively as compared to that of MBT spark timing.But,in the case of water injection,the NOx emission decreased significantly without affecting the thermal efficiency of the engine and it is 5.6 g/kWh with water-hydrogen ratio of 4:1(water flow rate of 0.92 kg/h).Water injection is the best suitable method to reduce the NOx emission in a hydrogen fueled engine compared with the spark timing retardation and EGR technique.

Influence of Exhaust Gas Recirculation on Low-Load Diesel Engine Performance

In the condition of constant speed and light load, an experimental study of a turbocharged and intercooled diesel engine with exhaust gas recirculation （EGR） system focuses on the influence of different EGR rates on combustion process, dynamic performance, economic performance and emission performance of a diesel engine. With the increase of EGR rate, the oxygen concentration of the intake-side decreases, the fuel air equivalence ratio increases, and the maximum explosion pressure in the cylinder decreases. Meanwhile, the average temperature in the cylinder drops, the ignition delay is prolonged, the ignition timing delays, and the maximum heat release rate decreases. The increase of EGR rate makes NOx emissions decrease obviously and continue to decline. When EGR is low, the smoke rate enlarges slowly with the increase of EGR rate, and enlarges greatly at the rate higher than 43% and reaches the maximum at the rate of 57%. When EGR rate is higher than 61%, the smoke rate drops rapidly, and the content of CO and hydrocarbon （HC） increases rapidly with high EGR rate.

Combustion analysis of a hydrogen-diesel fuel operated DI diesel engine with exhaust gas recirculation

The rapid depletion of fossil fuel and growing demand necessitates researchers to find alternative fuels which are clean and sustainable. The need for finding renewable, low cost and environmentally friendly fuel resources can never be understated. An efficient method of generation and storage of hydrogen will enable automotive manufacturers to introduce hydrogen fuelled engine in the market. In this paper, a conventional DI diesel engine was modified to operate as gas engine. The intake manifold of the engine was supplied with hydrogen along with recirculated exhaust gas and air. The injection rates of hydrogen were maintained at three levels with 2 L/min, 4 L/min, 6 L/min and 8 L/min and 10 L/min with an injection pressure of 2 bar. Many of the combustion parameters like heat release rate （HRR）, ignition delay, combustion duration, rate of pressure rise （ROPR）, cumulative heat release rate （CHR）, and cyclic pressure fluctuations were measured. The HRR peak pressure decreased with the increase in EGR rate, while combustion duration increased with the EGR rate. The cyclic pressure variation also increased with the increase in EGR rate.

船用柴油机涡轮辅助EGR系统多参数优化匹配研究

为获得柴油机、排气再循环(EGR)系统和涡轮增压系统的耦合优化匹配运行规律,以SC7H两级增压柴油机为研究对象,在GT-Power软件中搭建并校核原机一维模型,并进一步建立了涡轮辅助EGR两级增压柴油机一维模型。针对涡轮辅助EGR与两级增压耦合系统的匹配问题,提出了基于过量空气系数λ和EGR率需求的三步骤匹配计算流程。匹配规律显示:高/EGR涡轮匹配流量比和高/低压级压比比基本呈线性关系,涡轮辅助EGR进排气压差随压比比增大先增加后减小,在压比比为1附近取最优,比高压EGR高35.35 kPa,涡轮辅助EGR具有更优的泵气过程。建立全连接神经网络优化代理模型并采用NSGAⅡ算法开展耦合系统多参数多目标优化研究。结果显示:涡轮辅助EGR具有更优的BSFC和NOx排放效果,在TierⅢ的加权NOx排放限值条件下,涡轮辅助EGR可调两级增压系统的全负荷加权油耗比传统高压EGR可调两级增压系统低5.20 g/(kW·h)。

废气入射管道参数对缸内EGR分层的影响

为了在某款摩托车汽油机缸内实现废气再循环(exhaust gas recirculation,EGR)分层以减少泵气损失,降低NOx排放,将原有的进气旁通系统改造为EGR系统,使用GT-POWER模型求解出3000 r/min、60 mg进气量工况下废气入射管道以及进排气道的边界条件和初始条件,并将这些条件导入发动机的CONVERGE模型中进行计算,通过对比不同废气入射管径、不同安装角度、不同安装距离条件下的缸内流动特性、缸内速度场以及缸内废气质量分数分布,确定了最佳废气入射管道参数。结果表明:在3000 r/min、60 mg进气量工况下,当废气入射管径为5 mm,入射角度为17.5°,安装距离为22 mm时,气缸内能实现EGR分层。

预喷与外部EGR对车用柴油机燃烧和排放的影响

以某四缸水冷车用柴油机为样机,应用GT-Power软件搭建车用柴油机仿真模型,通过改变预主喷间隔、预喷油量和废气再循环(EGR)开度,研究中等负荷及转速工况下,不同的预喷策略以及引入外部EGR后两者共同作用对车用柴油机燃烧和排放性能的影响。试验结果表明:随着预喷正时从-17°CA提前到-37°CA,预喷油量从3.3 mg增加到9.9 mg,燃烧特性、碳氢化合物(HC)和一氧化碳(CO)排放均得到有效改善,但燃油消耗率和NOx排放总体呈上升趋势。在预喷策略的基础上引入外部EGR后,随着EGR率从5%增加到25%,NOx排放保持在较低水平,但缸内燃烧变差,HC和CO排放增多。在1 800 r/min、50%负荷的试验工况下,较小的预喷油量、中等的预喷间隔以及中等的EGR开度更有利于车用柴油机的燃烧和排放。

EGR对柴油发动机燃烧与排放特性仿真与试验研究

在废气再循环(EGR)条件下,以一台柴油发动机为试验对象,搭建柴油机整机及EGR系统模型。研究EGR系统对柴油发动机性能、燃烧及排放特性的影响。试验结果表明,随着EGR开度的增大,废气的引入降低氧气(O_(2))浓度,使着火延长期增大,燃烧速度减慢,导致最高爆发压力下降且降低明显;EGR降低了空燃比,使燃烧过程滞燃期增长向膨胀阶段延长,部分燃油无法在上止点附近充分燃烧,导致功率小幅度下降和油耗小幅度上升。但EGR的使用减少了缸内燃烧时氮氧化物(NOx)的形成,中高负荷时随着EGR阀开度的增大,氮氧化物(NOx)降低幅度极为显著,最大降低幅度为52.4%。结论表明合理应用EGR系统可以在维持发动机燃油经济性以及动力性的条件下,能够明显抑制氮氧化物(NOx)排放。

EGR的热效应和稀释效应对柴油机燃烧和排放的影响

以改进的KIVA-3V程序为计算平台,在转速为1,600,r/min,每循环喷油量为52.8,mg工况下,分别进行了EGR的热效应和稀释效应对柴油机燃烧和排放影响的数值模拟.结果表明,EGR的热效应对滞燃期影响较大,而稀释效应成为制约最高爆发压力和缸内温度的主要因素,且随着氧气体积分数的降低,热效应对最高爆发压力的影响增强;EGR导致碳烟排放增加是由于EGR的稀释效应,低温燃烧时碳烟排放的降低是EGR的稀释效应和热效应相互作用的结果;相比稀释效应,EGR的热效应是实现低温燃烧的主要因素,高进气热容更易改善NOx和碳烟排放的折衷关系.

不同增压方式下EGR对高压共轨柴油机燃烧和排放的影响

在一台电控高压共轨柴油机上,采用单级增压、两级增压和可变几何截面增压3种增压方式,进行了高压冷却废气再循环(EGR)的燃烧与排放试验研究.结果表明,柴油机采用可变几何截面增压时,涡前与进气压差较低,泵气损失小,具有良好的燃油经济性;大负荷、等EGR率情况下,单级增压、两级增压和可变几何截面增压的缸内最大爆发压力和主燃烧期的瞬时放热率依次增加,燃烧持续期缩短.随着EGR率的增加,可变几何截面增压器的进气压力增加,导致缸内爆发压力保持较高值,两级增压和可变几何截面增压的烟度和CO排放较单级增压大幅度降低,并能明显改善NOx排放和烟度之间的trade-off关系;中小负荷时,单级增压的HC排放最高,两级增压的缸内最大爆发压力最大,但CO排放最低,可变几何截面增压的燃烧相位较单级增压和两级增压有所推迟,预混燃烧比例增加,烟度下降.

EGR率对ZS195柴油机性能和排放的影响

为了降低ZS195柴油机的NOX排放,文章研究了不同EGR率对ZS195柴油机性能和排放的影响。试验结果表明,EGR技术可以有效降低NOX排放,负荷较大时更为明显,但CO、HC和烟度排放有所增加;EGR技术可以降低缸内峰值压力和峰值压力升高率,改善柴油机的工作粗暴性;EGR技术对ZS195柴油机的动力性有一定的不良影响,对经济性的影响较小,小负荷时经济性还略有改善;高负荷时,EGR技术会降低ZS195柴油机的经济性,HC、CO和烟度排放也会增加,必须对大负荷时的EGR率进行限制。

EGR率对柴油机排放特性影响的试验

研究了增压直喷柴油机在不同工况下不同EGR率对性能和排放的影响规律,确定了各个工况下EGR率的优化原则,并获取了柴油机最佳EGR率的M AP图,设计出一套EGR电子控制系统,可以对EGR系统中的进气节流阀和EGR阀进行控制,确保不同工况的最佳EGR率。发动机台架试验证实,设计的EGR电控系统按所获取的最佳EGR率运行,可以使NOx排放量降低19.9%,CO和HC排放量略有增加,动力性和经济性与原机相当,对EGR回路冷却可以抑制柴油机因使用EGR技术而导致的PM排放的增加。

EGR对GDI汽油机燃烧和排放特性的影响

通过改变EGR率,在一台GDI汽油机上进行了EGR对燃烧和排放特性影响的试验.结果表明:加入EGR后,燃烧持续期增大;且随EGR率增加,着火时刻先提前后延迟;放热率曲线峰值逐渐降低且后移,放热过程迟缓,缸内压力和缸内温度逐渐降低,压力峰值前移.此外,EGR率增加导致NOx排放逐渐降低,最高降低比例达80%以上,THC和CO排放逐渐增加,最大增加比例分别约为25%和7%.GDI汽油机排气颗粒物呈核态和积聚态的双峰分布;积聚态颗粒物峰值数密度随EGR率升高逐渐降低,核态颗粒物峰值数密度和颗粒物总数量浓度在加入EGR后均明显增加,核态和积聚态颗粒物峰值粒径受EGR的影响较小.

基于EGR技术的低排放重型柴油机燃烧系统开发

针对一台共轨重型柴油机,围绕进气增压系统、燃烧室与喷油器结构参数和EGR参数等因素对重型柴油机燃烧过程、性能和排放特性的影响机理展开深入研究.结果表明,随转速降低和负荷增加,两级增压相比单级增压能明显提高EGR循环能力和空燃比,有效改善NOx与燃油消耗率(BSFC)以及NOx与碳烟之间的trade-off关系.通过合理降低燃烧室压缩比、优化设计燃烧室结构参数(缩口直径、凹坑深度)并采用带倒锥度喷孔喷油器,能同时有效改善碳烟和BSFC并降低缸内最大燃烧压力至合理水平.国4的欧洲稳态测试循环结果表明,随升功率增加,两级增压相比单级增压在性能和排放方面逐渐表现出明显优势.对于29.8,kW/L的功率段,两级增压耦合EGR在无后处理下使各项排放指标均满足国4限值要求,十三工况加权BSFC相对基于选择催化还原(SCR)技术的国4柴油机仅增加3%左右.因此,两级增压是基于EGR技术的高升功率柴油机实现无后处理国4排放的一项有效燃烧优化技术.