喷射参数对二甲醚PPCCI发动机燃烧与排放特性的影响

在一台6缸增压电控共轨二甲醚发动机上进行试验,研究了预喷时刻、预喷燃料量、喷射压力、主喷时刻等喷射参数对二甲醚部分预混合充量压缩燃烧(PPCCI)发动机燃烧与排放特性的影响。试验结果表明:随预喷时刻提前,缸内压力峰值降低,二甲醚发动机缸内燃烧由两阶段放热转变为PPCCI三阶段放热,氮氧化物(NOx)排放显著降低,HC和CO排放升高;随预喷射燃料量增加,缸内压力峰值及预混合燃烧的冷焰反应和热焰反应速率明显增大,NOx排放逐渐降低,HC和CO排放显著升高;随喷射压力降低,预混合燃烧热焰反应速率增加,主喷扩散燃烧始点推迟,扩散燃烧放热率峰值和NOx排放明显降低,HC和CO排放升高;随主喷时刻推迟,预喷预混合燃烧几乎没有变化,主喷扩散燃烧延后,缸内压力峰值和放热率峰值降低,NOx排放显著降低,HC和CO排放升高。     

倒装式自封阀设计

该自封阀是根据某游艇机配套倒装式机油滤清器的功能要求设计的产品,安装于倒装式机油滤清器旋装滤内腔,与滤芯进口止回阀相结合,在维护机油滤清器需拆下旋装滤时可快速将滤芯进、出口封断,防止油液从滤芯进出口流出,减少维护时对环境的污染。     

无电晕式高温高压静电除尘器的数值模拟

基于实验研究结果，对无电晕式高温高压静电除尘器的阴极电子发射、粉尘荷电、浓度扩散、烟气流动、尘粒捕集等过程进行了数值模拟，从理论上分析讨论了温度、压力、电压、流速、含尘浓度、比电阻以及粒径等因素对除尘效率的影响，计算结果与实验结果基本吻合。研究发现，与传统的电晕式静电除尘器不同，无电晕式静电除尘器可以在较高含尘浓度和较低电压下正常工作，且特别适用于高温(高压)烟气的除尘。图11参6     

保安过滤器滤芯堵塞分析及对策

某热电厂8~#和9~#发电机组使用多介质→活性碳→保安过滤器→反渗透的预脱盐系统。一般纯化水处理设备前都要安装5μm滤芯的精密过滤器即保安过滤器,其作用之一是保证反渗透膜不被大颗粒的悬浮物划伤;作用之二是通过滤芯使还原剂充分混合反应以中和氧化剂。本文通过调查统计找到了滤芯更换频繁的主要原因,并制定了相应的措施,使保安过滤器滤芯更换次数降到预期的目标值。     

多段喷射对低速二冲程船舶柴油机燃烧与排放的影响

使用CONVERGE2.3对一台EX340EF-UA二冲程船机建立了三维模型,通过数值模拟研究了75%负荷工况时多段喷射对船机燃烧与排放的影响.模拟结果与实验数据有较好的吻合.模拟结果显示,顺序喷射使NO_x排放减少,燃油消耗率略有增加,碳烟排放随着顺序喷射间隔的增大而增大.小主预喷间隔匹配合适的预喷率易获得较低的NO_x排放,大主预喷间隔匹配合适的预喷率易获得较低的燃油消耗率.采取合适的主预喷间隔和预喷量可以实现NO_x排放和燃油消耗率的同时降低.     

柴油机分段喷射下混合气形成及其对燃烧排放的影响

基于数值模拟计算,研究了不同预喷策略下某非道路直喷柴油机混合气形成和燃烧过程,分析了挤流和涡流对主、预喷燃油当量比分布和燃烧的影响。结果表明:适当的主预喷间隔(20°)能够使预喷燃油在挤流带动下进入燃烧室凹坑;适当强度的进气涡流比(1.5～2.0)能使预喷油束偏转并在相邻两束主喷油束之间燃烧。二者都可以改善主喷和预喷油束的重叠,并且可以充分利用预喷燃油的放热量促进主喷燃油的混合和提升燃烧速率。优化喷油策略结合适度的进气涡流可以提高发动机功率,降低碳烟排放,但会使NOx排放增加。     

温度对无电晕式静电除尘器除尘性能的影响

基于实验研究 ,分析讨论了含尘气流温度对无电晕式静电除尘器除尘性能的影响。结果表明 ,提高温度可明显改善其荷电性能 ,提高除尘效率。与高温情况相比 ,在低温区 ,温度对除尘效率的影响更加显著。     

不同喷射策略低温预混合燃烧模式排放试验

基于一台4缸增压柴油机,研究了不同喷射参数分别在单次喷射预混合燃烧(PPC)和预喷模式PPC下对发动机排放生成的影响,其中重点关注了颗粒物的排放特性.结果表明:单次喷射形成早期喷射PPC后可以显著降低颗粒物的数量、质量以及几何平均直径(GMD),但是当喷射正时过于提前,颗粒物数量又会上升到与常规模式相当.总体上,预喷可以显著地降低碳烟排放,但是当预喷正时提前到某一特定值时,如果继续提前预喷角,颗粒物质量、数量以及GMD将基本不变.提高预喷燃油比例,形成更高比例的预混合燃烧,颗粒物数量和质量可以同时下降,颗粒物GMD先增加后降低.单次喷射早喷PPC模式下NOx排放较高,相比之下采用预喷的方式却可以在降低碳烟排放的同时很好地控制NOx排放.早喷PPC模式下由于压缩阶段负功增加导致燃油消耗率急剧升高,而预喷模式下燃油消耗率随预喷正时的提前以及预喷燃油比的增加略有升高.     

低温预混合燃烧模式的燃烧与排放特性试验研究

在一台电控高压共轨涡轮增压柴油机上研究了低温预混合燃烧模式对柴油机燃烧及排放的影响。采用早喷或晚喷预混方式,结合高废气再循环(EGR)率实现低温预混合燃烧,并研究了喷油正时、EGR、喷油压力和负荷率变化对预混燃烧模式的放热规律、排放特性和经济性的影响。研究结果表明:长的燃空预混合期是实现缸内预混燃烧的一个关键因素,中低负荷时,无论是早喷或晚喷预混模式,均具有长预混合期,短的扩散燃烧过程,兼具预混燃烧和低温燃烧的特征,高负荷下扩散燃烧比例增大;晚喷预混燃烧模式下,碳烟和氮氧化物(NO_x)排放同时获得降低,但低温燃烧和稀薄的混合气易导致燃烧不完全,喷油推迟较晚时引起HC和CO排放显著增加,并导致燃油消耗率增大;增加喷油压力可以同时改善碳烟、CO和HC排放,但是NOx排放增加,单纯提高喷射压力并不能获得性能的全面提高。     

两次喷射策略对汽油/聚甲氧基二甲醚高预混燃烧及排放的影响

在一台改造的单缸柴油机上进行了预主喷两次喷射策略对汽油/聚甲氧基二甲醚(PODE)高预混合燃烧(HPCC)影响的试验研究。研究结果表明:预主喷两次喷射策略能缩短主喷滞燃期,提前着火时刻;预主喷间隔较小或较大时,汽油/PODE HPCC燃烧放热率峰值较低;预主喷间隔为35°时燃烧放热率峰值最高,放热更加集中。预喷比例越大,预主喷间隔和主喷时刻对最大压升率和指示热效率的影响越大。通过预主喷两次喷射策略优化,可以显著提高汽油/PODE HPCC燃烧的指示热效率,减少碳氢和碳烟排放,但最大压升率有所增加。高负荷时,汽油/柴油HPCC因为碳烟排放的限制,适合采用两次喷射策略;汽油/PODE HPCC受限于最大压力升高率,更适合采用单次喷射策略。     

一种纤维颗粒过滤器的参数模型

应用柴油机颗粒过滤器来控制柴油机废气中排放的颗粒含量是十分重要的。纤维过滤器结构简单，所用材料低廉，是一种十分有效的柴油机颗粒过滤器。但迄今为止，讨论与时间相关的纤维过滤器模型的文献很少。本文提出了一种简单纤维过滤器的机理模型，其中过滤器的压力降、颗粒收集量及收集效率是运行时间和过滤器设计参数、运行参数的函数，这些参数包括纤维填充密度、过滤器长度、废气的流速和废气中颗粒浓度。根据此模型可以进行过滤器的优化设计，得到合理的设计参数和运行参数。     

Thermal management of electronic components with thermal adaptation composite material

Thermal adaptation composite material is a kind of composite material with required thermal conductivity or coefficient of thermal expansion through the selection and design of its components. A kind of thermal adaptation composite material that has excellent thermal conductivity and heat storage capacity is prepared by absorbing paraffin into expanded graphite. An electronic cooling experimental system based on the thermal adaptation composite material is built. The temperature variations of the simulative chip are respectively measured in this system and the traditional cooling system to investigate the effect of the thermal adaptation composite material on electronic cooling. At the same time, the impacts of composite material dosage and combining active cooling manner on the performance of electronic cooling are also studied. The experimental results show that the apparent heat transfer coefficients of the electronic cooling experimental system are 1.25–1.30 times higher than those of the traditional cooling system. It also can be found that the dosage of composite material has positive impact on the performance of electronic cooling. By combining active cooling manner, it can compensate the deficiency of cooling capacity in phase change thermal control.     

Electrospun imidazolium functionalized multiwalled carbon nanotube/ polysulfone inorganic-organic nanofibers for reinforced anion exchange membranes

Novel electrospun inorganic-organic nanofiber reinforced anion exchange membranes were developed by incorporating imidazolium functionalized multiwalled carbon nanotubes (FMWCNTs) into imidazolium functionalized polysulfone nanofibers via co-electrospinning. Under a high-voltage electrostatic field, FMWCNT inorganic nanofibers were able to align along the axis of the electrospun nanofibers, thereby solving the problem of easy agglomeration of FMWCNTs in cast-composite anion exchange membrane, synergistic with the polymer nanofibers to reinforce the membranes. Small angle x-ray suggests that ion clusters are more likely to aggregate in a co-electrospun composite membrane, indicating continuous and lower-energy-barrier pathways for hydroxide transport. As a result, composite electrospun membranes exhibit higher OH^? conductivity and better single fuel cell performance. With an additive amount of 0.4 wt.%, hydroxide conductivity reaches a maximum value of 67.5 mS cm^?1 (30 °C). However, the maximum power density (102.5 mWcm^?2) is much higher than that of the electrospun (2.1 times) and cast (3.3 times) membranes without FMWCNTs. Fibration of polymer and alignment of multiwalled carbon nanotube nanofibers also greatly enhance the membrane strength. For fully hydrated membranes, tensile stress dramatically increases from 5.6 MPa for a cast membrane without FMWCNTs to 24.4 MPa for an electrospun membrane with 0.4 wt.% FMWCNTs addition. The strategy for co-electrospinning of imidazolium functionalized multiwalled carbon nanotubes/polysulfone presented in this work provides a way to enhance the organic-inorganic interface compatibility, and improve ionic conductivity and mechanical strength of anion exchange membrane simultaneously.     

移动颗粒层过滤除尘的数值模拟及实验对比

采用离散颗粒运动数学模型，对移动颗粒层过滤除尘器中粉尘颗粒与过滤介质颗粒碰撞以及对除尘效率的影响进行了初步研究，模拟计算了碰撞次数与系统风速之间的变化关系，与实验结果对比发现，随系统风速的变化，颗粒碰撞频次与除尘效率之间存在定性的一致。研究结果表明颗粒间碰撞作用对移动颗粒层除尘性能起着重要作用。     

Bursting problem of filament wound composite pressure vessels

Using the nonlinear finite element method, we have calculated the stresses and the bursting pressure of filament wound solid-rocket motor cases which are a kind of composite pressure vessel. Maximum stress failure criteria and a stiffness-degradation model were introduced to the failure analysis. The effects of material performance and geometrical nonlinearity on the relative loading capacity of the dome were studied. For the model I case with skirts, relative loading capacity of the dome increased when geometrical nonlinearity was considered and composite material of higher strength was used. But for the model II case without skirts, the conclusion obtained was contrary to that for the model I case.     

用直接数值模拟对移动颗粒层除尘的研究

利用气固两相流数值模拟计算模型 ,分别采用了不同粒径的移动颗粒层过滤除尘器 ,对不同粒径粉尘颗粒的碰撞次数进行统计 ,对移动床除尘中过滤介质尺寸与粉尘粒径尺寸之间的相互选择性进行了初步研究。模拟计算了在同一风速下碰撞次数与粉尘粒径以及移动层颗粒粒径之间的关系。计算统计的结果与实验结果对比发现 ,二者存在定性上的一致。研究结果表明在移动床过滤除尘器中不同粒径的过滤层对不同粒径尘粒具有明显的选择性。     

Thermal properties and characterization of palmitic acid/nano silicon dioxide/graphene nanoplatelet for thermal energy storage

Palmitic acid (PA), nano silicon dioxide (nano SiO₂), and graphene nanoplatelets (GNPs) were fabricated to composite phase change materials (PCMs) for thermal energy storage. PA acted as PCM, nano SiO₂ was used as supporting material. GNP as thermal conductivity promoter was added to modify composite PCM. Nano SiO₂ has good adsorption property and can adsorb liquid PCM to prevent leakage. Leakage measurement indicated that PA maximum content in composite PCM is 70 wt%. Chemical and crystal structures, and microstructure of composite PCM were tested by Fourier transformation infrared spectroscope, X-ray diffractometer and scanning electronic microscope, which showed that the raw materials are well mixed by physical action. Differential scanning calorimeter result presented that composite PCM possess phase change temperature at about 60°C and latent heat of 128.42 kJ/kg. Thermogravimetric analyzer and thermal cycle experiment showed that composite PCM have outstanding thermal stability and durability. Thermal conductivity apparatus measurement results indicated that thermal conductivity of composite PCM with 5 wt% GNP is 1.65 times that of composite PCM without GNP. Therefore, this composite PCM are potential materials for thermal energy storage.     

Preparation of capric acid/halloysite nanotube composite as form-stable phase change material for thermal energy storage

A novel form-stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing capric acid (CA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT-IR and DSC analysis techniques. The composite can contain capric acid as high as 60 wt% and maintain its original shape perfectly without any CA leakage after subjected to 50 melt-freeze cycles. The melting temperature and latent heat of composite (CA/HNT: 60/40 wt%) were determined as 29.34 °C and 75.52 J/g by DSC. Graphite (G) was added into the composite to improve thermal storage performance and the thermal storage and release rates were increased by 1.8 times and 1.7 times compared with the composite without graphite, respectively. Due to its high adsorption capacity of CA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost-effective latent heat storage material for practical applications such as solar energy storage, building energy conservation and agricultural greenhouse in the near future.     

Influences of expanded graphite on structural morphology and thermal performance of composite phase change materials consisting of fatty acid eutectics and electrospun PA6 nanofibrous mats

In the present work, three fatty acid eutectics of capric acid (CA)–lauric acid (LA), capric acid–palmitic acid (PA), and capric acid–stearic acid (SA) were prepared through melt-blending followed by ultrasonication and were investigated as model phase change materials (PCMs); for comparison, the individual fatty acid of CA was also studied. The DSC measurements indicated that the phase transition temperatures of fatty acid eutectics were lower than those of individual fatty acid of CA. Thereafter, the polyamide 6 (PA6) nanofibers and PA6/EG composite nanofibers with 10 wt.% expanded graphite (EG) were prepared by electrospinning; and then composite PCMs with fatty acid eutectics absorbed in and/or supported by the overlaid mats of electrospun nanofibers (e.g., PA6 and PA6/EG) were explored for storage and retrieval of thermal energy. Influences of the EG on structural morphologies, thermal energy storage properties and thermal energy storage/retrieval rates of composite PCMs were respectively characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and measurement of melting/freezing times. The results indicated that the additions of EG caused the interfaces between fatty acid eutectics and PA6 nanofibrous mats to become more illegible; increased the absorption capacity of fatty acid eutectics within nanofibrous mats. The enthalpies of melting and crystallization of composite PCMs with EG were higher than those of the corresponding composite PCMs without EG, whereas there were no appreciable changes on the phase transition temperatures. The EG improved thermal energy storage/retrieval rates of composite PCMs were also confirmed by comparing the melting/freezing times of CA/PA6/EG and CA–SA/PA6/EG with those of CA/PA6 and CA–SA/PA6, respectively. The results from the SEM observation showed that composite PCMs had no or little variations in shape and surface morphology after heating/cooling processes.     

Experimental research on heat transfer mechanism of heat sink with composite phase change materials

A rapid thermal response composite phase change material (PCM) is prepared by absorbing paraffin into expanded graphite, which is of excellent absorbability. The highest thermal conductivity of the composite samples can reach 4.676 W m⁻¹ K⁻¹. The prepared composite PCM has excellent thermal storage performance and its heat storage period and heat release period are shortened 65.3% and 26.2%, respectively, compared with that of the paraffin. Applying the composite PCM to an electronic device’s heat sink can effectively improve the performance of resisting the shock of high heat flux and ensure the reliability and operating stability of electronic and electrical equipment. The experimental results show that the apparent heat transfer coefficients of the experimental heat sink with the PCM are 1.36–2.98 times higher than those of the heat sink without the PCM. Based upon the quadratic equation, the total relative uncertainty of the experimental system is estimated that .