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 NO _x , 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 NO _x emissions. CO and UHC emissions are reduced by 24% and 31%, respectively. The NO _x 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.     

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.     

Experimental study of effects of oxygen concentration on combustion and emissions of diesel engine

Effects of oxygen concentration on combustion and emissions of diesel engine are investigated by experiment. The intake oxygen concentration is controlled by adjusting CO₂. The results show that very low levels of both soot and NO _x emissions can be achieved by modulating the injection pressure, timing, and boost pressure at the low levels of oxygen concentration. However, both CO and HC emissions and fuel consumption distinctly increase at the low levels of oxygen concentration. The results also indicate that NO _x emissions strongly depend on oxygen concentration, while soot emissions strongly depend on injection pressure. Decreasing oxygen concentration is the most effective method to control NO _x emissions. High injection pressure is necessary to reduce smoke emissions. High injection pressure can also decrease the CO and HC emissions and improve engine efficiency. With the increase of intake pressure, both NO _x and smoke emissions decrease. However, it is necessary to use the appropriate intake pressure in order to get the low HC and CO emissions with high efficiency. Supported by the National Natural Science Foundation of China (Grant Nos. 50636040, 50676066)     

The effects of EGR and ignition timing on emissions of GDI engine

The effects of EGR and ignition timing on engine emissions and combustion were studied through an experiment carried out on an air-guided GDI engine. The test results showed that the ignition timing significantly affected the GDI engine emissions, that the NO _x emissions significantly reduced when the ignition timing was retarded, and that NO _x emissions decreased with the EGR level increasement. A higher EGR rate could reduce CO emissions while the CO emissions were less affected by the ignition timing. The HC emissions decreased at a lower EGR rate. At 2500 r/min, an appropriate EGR rate could cut down CO emissions. The exhaust gas temperature could significantly decrease with improving the EGR rate, and the exhaust gas temperature at 2500 r/min was clearly higher than that at 1850 r/min. The nucleation mode particles increased clearly, the accumulation mode particle number decreased gradually with the increase of EGR rate, and the typical particle size of nucleation mode particle was in the range of 10–25 nm.     

Effects of mixture inhomogeneity and combustion temperature on soot surface activity and soot formation in diesel engines

The soot surface growth plays significant role on the soot mass accumulation,which starts with H(hydrogen)atom abstraction forming activated soot surface sites,and is followed by the acetylene addition process.In this study,the effect of the mixture inhomogeneity and combustion temperature on the soot surface activity and soot formation was investigated by developing a new multi-step phenomenological(MSP)soot model of diesel engines.A new detailed soot surface growth mechanism was proposed by correlation analysis of combustion parameters with soot formation.The inhomogeneity coefficient of soot surface activityαCH and the specific rate of soot surface growth R CH were derived to highlight the effect of inhomogeneity of mixture and combustion temperature on soot formation.The predicted diesel engine-out soot agreed well with experimental findings in wide ranges of combustion conditions.In the case of lower engine load with single fuel injection and higher EGR(exhaust gas recirculation)rate,it had quiet homogeneous mixtures before ignition when the combustion temperature dominated the soot surface activity.At medium engine load with multi-pulse fuel injections,it got mixture slightly stratified before ignition and revealed that the mixture inhomogeneity became more dominated on soot surface activity than the combustion temperature.An increased soot surface activity led to increased soot emission.Under the full engine loads with single fuel injection but quite high boost pressure over 0.4 MPa,it led to the combustion conditions of higher mixture density and higher mixture heat capacity,which benefits the mixture homogeneity.The decay rate of soot surface activity became lower due to the decreased combustion temperature and the soot surface activity decreased due to improved mixture homogeneity.In addition,the lowered intake oxygen concentration due to usage of EGR played a role to lower the specific rate of soot surface growth R CH,but to increase the soot surface activityαCH.     

NOx emission characteristics of hydrogen internal combustion engine

In order to investigate the NOxemission of hydrogen internal combustion engines.A test system for four-cylinder intake port-fuel-injection hydrogen internal combustion engine(H2ICE)is established to study the effect of fuel-air equivalence ratio,ignition advance angle,engine speed and exhaust gas recirculation on NOx emission.Experimental results show that the fuel-air equivalence ratio is the key factor to NOxemission,NOxemission concentration is always higher than 8 000×10-6 when the fuel-air equivalence ratio is larger than 0.8and lower than 500×10-6 when the fuel-air equivalence ratio is smaller than 0.5.The ignition advance angle and engine speed also play important roles on NOxemission formation.EGR is an useful method to reduce NOx emission concentration at large fuel-air equivalence ratio especially when engine speed is low and EGR ratio is high.     

可变几何截面增压器/废气再循环对重型柴油机性能和排放的影响

将HOLSET400可变几何截面增压器(VGT)应用于CA6DL2-35E3重型柴油机上,并在涡前位置建立了高压回路废气再循环(EGR)系统。在ESC测试循环下分别进行了VGT及VGT/EGR的性能规律试验。试验发现配备此VGT系统的柴油机,试验目标参数均存在特定的VGT开度拐点,而对性能改善最明显的开度均出现在拐点附近。因此采取拐点控制VGT开度可充分发挥VGT的效能,改善除NOx外其余气体排放及燃油经济性。通过VGT驱动废气回流可实现28%高EGR率(转速1330 r/min、25%负荷率)。试验目标参数存在特定EGR率拐点(NOx除外),而在拐点对应EGR率范围内降低NOx排放的同时不会对发动机其他性能参数产生太大影响,具备综合优化发动机气体排放和燃油经济性的潜力。     

Investigation of the combustion deterioration of an automotive diesel engine under transient operation

With increasingly stringent emission regulations and demand for fuel economy by the public,the combustion and emission problems of automotive diesel engines during transient operation have become vital and urgent issues.In this study,combustion deterioration has been experimentally analyzed using a heavy-duty turbocharged diesel engine running under transient conditions(constant speed and increasing torque).Optimization of the transient combustion process was performed by adjusting the fuel injection parameters.The results indicated that the notable combustion deterioration relative to steady state operation while transient was a function of the delay in the air-supply to the turbocharged engine,and took the form of combustion phasing delay,resulting in rapidly increasing smoke emission and fuel consumption.However,the delay in combustion phasing can be controlled by advancing the fuel injection timing,effectively increasing thermal efficiency.Unfortunately,smoke and NO x emissions increased at the same time.The deterioration in combustion phasing can also be improved by increasing injection pressure,resulting in decreased smoke emission while NO x emission increased.It is worth noting that the effective thermal efficiency first increased and then decreased as fuel injection pressure increased during transient operation.     

米勒循环与EGR耦合对增压柴油机性能的影响

以某6缸四冲程两级增压船用柴油机为研究对象,建立两级增压柴油机米勒循环与废气再循环(Exhaust Gas Recirculation, EGR)耦合仿真模型,研究米勒循环和EGR耦合对两级增压柴油机燃油消耗率和NO_x排放的影响.结果表明,当米勒度为-40°CA时,燃油消耗率相对原机降低3.5%, NO_x排放相对原机降低25.5%; EGR率为30%时,燃油消耗率相对原机增加5.0%,NO_x排放降低98.7%;当米勒度为-30°CA与EGR率为20%时,燃油消耗率相对原机仅增加0.1%,NO_x排放降低92.7%.     

废气再循环对柴油机性能影响的试验研究

通过废气再循环（ EGR-Exhausted Gas Recirculation ）可以有效地降低柴油机的氮氧化物（ NOx）排放。但是废气具有一定的热作用和化学作用,因此EGR会对柴油机燃烧过程和排放物的生成造成影响。本文基于4 D20柴油机,重点开展了不同的EGR率对柴油机性能影响的研究。分析试验结果发现,随着EGR率的增大,燃烧滞燃期增长,缸内压力和缸内温度降低,放热率峰值降低,热效率下降;NOx排放随着EGR率的增大而急剧下降;soot排放随着EGR率的增大而增大;CO和HC排放随着EGR率的增大而增大。     

Computation of the Matching Performance of Diesel Engine with Variable Geometry Turbocharger

Computation of turbocharged engine match canbe used to predict the engine performance,andtoin-vestigate the influence of various of structural andthermodynamical parameters on engine performanceso that the opti mumparameters can be sought[1,2].Itacts as a guideline on engine design and test.Thevariable geometry turbocharger(VGT)can changethe flow geometry of turbine nozzle when enginespeed decreases,which maintains enough boost pres-sure so that the engine performance can be i mprovedwithinth…     

EGR和VNT的匹配对增压柴油机排放的影响

通过可变喷嘴增压器(VNT)和废气再循环(EGR)系统的匹配试验,考察了VNT对发动机排气和进气的压差以及EGR率的影响规律,研究了降低四缸增压柴油机的排放问题。试验结果表明,EGR系统能在不改变柴油机动力性、经济性和烟度排放的基础上,使柴油机NOx排放量降低20%~47%。VNT通过调节废气涡轮增压器涡前压气后的压差,可将EGR率提高2%~12%。     

Review: Investigation of Partially Pre-mixed Charge Ignitions (PPCI) Engine Mode

This paper embraces the key points of unpolluted internally combusted engine emissions. Core objective is focused on the recent effort to improve compression ignition(CI) and spark ignition(SI) engine to have fuel-efficient and minimized pollutant emissions. There are many advanced internal combustion engines to overcome the challenges of conventional compression ignition engines of the high level of particulate matter(PM) and oxides of nitrogen emission. One of the latest options on which many ...     

Numerical Investigation of the Effects of Rate-Shaped Main Injection on Combustion and Emission in an OPOC Two-Stroke Diesel Engine

The effects of various split injection strategies on the opposed-piston opposed-cylinder (OPOC)diesel engine combustion and emission characteristics have been studied numerically using AVL-Fire CFD tools. The five rate-shaped main injections were used in split injection strategies. The results show that ignition delay from a rectangular injection rate is the shortest. Maximum pressure of the trapezoid injection rate is the largest. And the NO_x emission of the rectangular injection rate is the largest. Meanwhile, the soot emission of the trapezoid injection rate is the least among the five injection rates.     

Effects of H<Subscript>2</Subscript>/CO/CH<Subscript>4</Subscript> syngas composition variation on the NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and CO emission characteristics in a partially-premixed gas turbine combustor

This paper reports the effects of variations in the fuel composition of H₂/CO/CH₄ syngas on the characteristics of NO _x and CO emissions in a partially-premixed gas turbine combustor. Combustion tests were conducted on a full range of fuel compositions by varying each component gas from 0% to 100% at heat inputs of 40 and 50 kW_th. Flame temperature, combustor liner temperature, ignition delay time, and flame structure were investigated computationally and experimentally to judge whether they are significant indicators of NO _x and CO formation. The characteristics of and reasons for NO _x and CO emissions were investigated by analyzing the emission mechanisms and relationships among fuel property, equivalence ratio, flame temperature, liner temperature, flame shape. The flame structures were investigated using the following flame visualization methods: (1) time-averaged OH* chemiluminescence and its Abel-deconvolution; (2) direct photography; and (3) instantaneous OH-PLIF. The flame structures were greatly changed by the fuel composition and heat input, and they were subjected to key affecting parameters of the temperatures of the flames and the liners. NO _x and CO emissions also largely varied according to fuel composition and heat input, showing neither linearly nor exponentially clear proportional trends toward the syngas compositions because of the singular conditions. For example, only the 100% CO flame at low load emitted lots of CO, whereas complete combustion was observed in other cases. However, the qualitative observations showed that the root causes of NO _x emission behaviors were flame temperature and flame structure, which were directly related to the residence time in the flame. Various sets of practical test results were obtained, and these results could contribute to the optimal selection of the fuel-feeding condition when fuel is changed from natural gas to syngas in order to minimize NO _x and CO emissions with stable combustion.     

气口喷射DMM/柴油混合燃料实现HCCI燃烧

为了促进缸内均匀混合气的形成,将不同比例的DMM/柴油混合燃料通过气口喷射,在单缸发动机上实现了具有超低排放特征的HCCI燃烧方式,考察了混合燃料中DMM的比例、冷却EGR率对HCCI燃烧的转速和负荷范围的影响,以及负荷、冷却EGR率和进气温度对HCCI燃烧的影响.研究表明,由于DMM/柴油混合燃料显著改善了燃料的雾化特性,因此混合燃料能够在较宽的转速和负荷范围内实现HCCI燃烧.此外,由于混合燃料含有很高比例的氧份,因此容许采用较大比例的废气再循环,并且因为冷却的废气再循环推迟了HCCI的着火时刻.通过燃料改性结合外部废气再循环在较大范围内实现了HCCI燃烧.     

Experimental Study on the Performance and Emission of Chinese Small Agricultural Diesel Engine Fuelled with Methanol/Biodiesel/DTBP

中国小型农用柴油机燃用甲醇/生物柴油/DTBP的性能与排放试验研究

李瑞娜^1,2,3,张亮¹,朱佳隆¹,华琰¹,王忠¹

（1、江苏大学汽车与交通工程学院,江苏 镇江212013;

2. 汽车测控与安全四川省重点实验室,成都 610039;

3. 四川省新能源汽车智能控制与仿真测试技术工程研究中心,成都 610039）

摘 要：

为了研究甲醇和生物柴油对小型农用柴油机性能、经济性和排放的影响,分析了甲醇和生物柴油的物理化学性质（十六烷值、低热值、粘度等）。甲醇和生物柴油的性质在一定程度上表现出良好的互补性。当在生物柴油中加入大量甲醇时,甲醇/生物柴油混合物的十六烷值将大幅度降低。由于混合燃料的十六烷值对柴油机的燃烧过程有很大影响,在对甲醇/生物柴油的混合比进行试验后,分别用5%（BM5）、10%（BM10）、15%（BM15）的甲醇添加到生物柴油中制备了混合燃料。选择过氧化二叔丁基（DTBP）作为十六烷值改进剂添加到甲醇/生物柴油混合物中。在BM15中分别加入0.25%、0.50%、0.75%的DTBP。在186FA柴油机上进行台架试验,研究了甲醇和DTBP对发动机性能和排放的影响。结果表明,在额定工况下,与生物柴油相比,BM5、BM10和BM15的NOx浓度分别降低了5.02%、33.85%和21.24%,烟度分别降低了5.56%、22.22%和55.56%,发动机功率降低了5.77%、14.23%和25.41%,比能耗提高了3.31%,7.78%和6.37%。在甲醇/生物柴油中添加DTBP可以将发动机功率恢复到柴油的水平。DTBP对降低比能耗、降低NOx、CO、HC浓度有较好的效果,但排气烟度略有增加。

关键词：甲醇、生物柴油、农用柴油机、燃烧、性能、排放

     

低压EGR系统对缸内直喷发动机性能影响的研究

为研究低压废气再循环系统（Exhaust Gas Recirculation,EGR）对缸内直喷发动机油耗、排放和泵气损失的影响,基于某2.0T缸内直喷发动机,提出了一套低压EGR系统控制策略。试验结果表明,在各个工况下,随着EGR率的升高,比油耗出现降低的情况,泵气损失得到良好改善,排气端的一氧化碳（CO）和氮氧化物（NO_x）含量降低,总碳氢化合物（Total Hydrocarbons,THC）含量略有升高。     

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     

Effect of heat transfer space non-uniformity of combustion chamber components on in-cylinder soot emission formation in diesel engine

Combustion chamber components (cylinder head, cylinder liner, piston assembly and oil film) are treated as a coupled body. Based on the three-dimensional numerical simulation of heat transfer of the coupled body, a coupled three-dimensional calculation model for the in-cylinder working process and the combustion chamber components was built with domain decomposition and boundary coupling method, in which the coupled three-dimensional simulation of in-cylinder working process and the combustion chamber components was adopted. The simulation was applied in the influence investigation of the space non-uniformity in heat transfer among combustion chamber components on the generation of in-cylinder emissions. The results show that the space non-uniformity in heat transfer among the combustion chamber components has great influence on the generation of in-cylinder NO _x emissions. The heat transfer space non-uniformity of combustion chamber components has little effect on soot formation, and far less effect on soot formation than on NO _x . Under two situations of different wall temperature distributions, the soot in cylinder is different by 1.3% when exhaust valves are open.