基于汽油/柴油双阶段燃烧模式对低温阶段燃烧及排放性能的影响

在一台高压共轨柴油机进气总管上加装汽油喷射系统,汽油采用进气道喷射形成预混合气,柴油采用缸内大角度预喷并引燃汽油.试验以降低NOx排放和消光烟度为主要目标,探究汽油/柴油双阶段燃烧模式的汽油喷射量、柴油预喷正时、柴油预喷量对低温阶段燃烧及排放特性的影响,并通过对燃烧、排放及经济性综合考量构建喷油参数优化策略.结果表明:引入汽油后的燃烧过程呈现两阶段放热,实现了柴油着火时刻可控;增加汽油喷射量可以有效强化缸内油气混合,使主放热率峰值升高,有助于燃烧完全;该燃烧模式的低温阶段避免了传统柴油机NOx和消光烟度出现的折中关系,消光烟度处于低水平范围,均低于3%,;适度提前柴油预喷正时或减少柴油预喷量能同时降低NOx排放和消光烟度,但CO和HC会出现一定程度恶化.     

不同海拔下VGT对含氧燃料柴油机性能的影响

利用大气压力模拟装置,试验研究了可变几何截面涡轮增压器(VGT)对高压共轨柴油机分别燃用纯柴油和生物柴油-乙醇-柴油(BED)含氧燃料的经济性、排放特性及燃烧特性的影响。结果表明:随着海拔的升高,柴油机经济性恶化,氮氧化物(NO_x)排放降低,而一氧化碳(CO)和碳氢化合物(HC)排放及烟度升高。燃用纯柴油与含氧燃料,随着VGT喷嘴环开度的增大,柴油机的经济性均有不同程度的恶化,而CO、HC排放及排气烟度也都有不同程度的升高。在高海拔地区,燃用纯柴油的经济性优于含氧燃料,但使用含氧燃料有助于改善柴油机的CO、HC排放及烟度。在中等负荷工况下,NO_x排放随着VGT喷嘴环开度的增大呈现先减小后增大的趋势;在高负荷工况下,放热率峰值和最高气缸压力均随着VGT喷嘴环开度的增大而降低,从而降低了NO_x排放。     

共轨柴油机燃用天然气合成油的性能与排放特性

对某共轨柴油机燃用天然气合成油(gas-to-liquids,GTL柴油)和国-Ⅲ柴油进行了动力性、燃油经济性和排放特性研究.结果表明:与国-Ⅲ柴油相比,共轨柴油机燃用GTL柴油时的动力性与国-Ⅲ柴油相当,燃油消耗率降低约4%,GTL 柴油的 HC、CO、Nox、PM 排放分别降低17%、8%、3%、40%,烟度排放降低35%.GTL 柴油明显改善柴油机HC和烟度排放,并能同时降低柴油机Nox和 PM 排放,是一种潜力巨大的低排放柴油清洁代用燃料.     

柴油机掺烧不同比例生物柴油的试验研究

将体积分数为10%2、0%、30%的生物柴油掺混到柴油里组成3种混合燃料,并连同纯柴油共4种燃料,在一台四缸增压中冷柴油机上进行性能、燃烧和排放特性的试验研究.结果表明,柴油机燃用生物柴油与柴油混合燃料的折合油耗率与燃用纯柴油时基本相当;燃用混合燃料的缸内最大爆发压力和压力升高率较低,着火时刻较晚;混合燃料的NOx和碳烟排放与燃用纯柴油时相比均有不同程度的降低,但混合燃料的HC和CO排放只是在1 500r/min时才较纯柴油低,当转速在2 300 r/min时,混合燃料的HC和CO排放更高.     

在直喷式柴油机上燃用低比例生物柴油和柴油的试验研究

在原直喷式柴油机结构和参数不做任何改变情况下,燃用低比例生物柴油和高比例柴油的混合燃料进行试验研究.试验结果表明:发动机燃用20%生物柴油和80%柴油的混合燃料与柴油相比较,在外特性下,B20功率和扭矩均比柴油低,当量油耗率低速时要低,高速时高.在外特性和1800 r/min负荷特性下,混合燃料碳烟、CO和HC排放均降低,NOx排放(除少数工况外)略有增加.该混合燃料对降低柴油机碳烟、C0和HC排放十分有利.     

玉米秸秆生物油对直喷式柴油机燃烧与排放的影响

采用超声波乳化法制备了玉米秸秆热解生物油质量分数分别为5%、10%、15%和20%的生物油/柴油乳化油,分别记为CSB5、CSB10、CSB15和CSB20,然后在一台未作改动的直喷式柴油机上研究了其燃烧和排放特性,并与燃用0号柴油进行了比较,旨在为生物油在柴油机中的应用提供依据和理论指导.结果表明,随着生物油质量分数的增加,乳化油的滞燃期逐渐延长,预混燃烧放热量和预混燃烧期增加,燃烧持续期缩短;燃烧放热率峰值和最大压力升高率先增加后降低,最高燃烧压力和燃烧温度逐渐降低.燃用CSB5和CSB10时的燃油经济性与柴油相当,而燃用CSB15和CSB20时的燃油经济性较柴油的略差.与0号柴油相比,随着生物油含量的增加,乳化油的NOx排放逐渐降低,HC和CO排放逐渐增加;碳烟排放先降低后增加,CSB5和CSB10的碳烟排放比柴油的排放值低,而CSB15和CSB20的碳烟排放却比柴油的排放值略高.     

共轨柴油机燃用不同配比生物柴油的性能与排放特性

对某共轨柴油机燃用石化柴油、生物柴油及其混合燃料的动力性、经济性和排放特性进行了研究.在未对原机做任何改动的情况下,分别燃用了0%、5%、10%、20%和100%的5种不同体积配比的餐饮废油制生物柴油与石化柴油的混合燃料,分析比较了不同生物柴油配比对发动机功率、燃油消耗率,以及CO、HC、NO_x和烟度排放的影响.研究表明:共轨柴油机燃用生物柴油与石化柴油混合燃料后,功率略有下降,燃油消耗率有所上升;烟度、CO和HC排放减少,且随着生物柴油掺混比例的升高而降低;NO_x排放上升,且随着生物柴油掺混比例的升高而增加.     

正丁醇对柴油机低温燃烧和排放的影响

在一台改造的单缸柴油机上,研究了柴油中掺入正丁醇燃料在不同EGR率、进气压力下对燃烧、性能和排放的影响.结果表明,柴油中添加正丁醇燃料使着火滞燃期延长,缸内最大爆发压力和燃烧温度下降,低温燃烧"失火"的EGR率降低,指示油耗减少,燃油经济性改善;正丁醇可明显降低碳烟排放,使烟度随EGR率变化趋势更加"平坦",烟度峰值对应的EGR率,变低,正丁醇比例越高,烟度越低;正丁醇对气体排放的影响与进气压力有关,正丁醇可以有效降低NOx排放,进气压力越大,正丁醇降低NOx的效果越明显;进气压力为0.15 MPa时,正丁醇比例越大,CO排放越低,但进气压力为0.24 MPa时,B20燃料CO排放最高;正丁醇对THC排放影响不大,但B20燃料在高EGR率条件下,其THC排放明显增大.因此,柴油燃料添加正丁醇是降低低温燃烧烟度和NOx排放,改善低温燃烧性能的有效途径.     

柴油机实行复合燃烧的试验研究

以柴油机为基础。以LPG或甲醇作为预混合燃料,与喷入的柴油组成部分预混的复合燃烧,大幅度降低了发动排气烟度,同时使氮氧化物排放得到一定改善,发动机的比油耗优于原柴油机,而排气中的未燃烃HC和CO的浓度有所提高,甲醇比LPG具有降低烟度效果更好、氮氧化物降低更多和HC排放相对较低的优越性。     

非直喷式增压柴油机燃用生物柴油的性能与排放特性

研究了非直喷式增压柴油机燃用柴油一生物柴油混合燃料的性能和排放特性。未对原机作任何调整和改动，研究了不同生物柴油掺混比例的混合燃料对功率、油耗、烟度和NOx排放的影响。结果表明：非直喷式柴油机燃用生物柴油后柴油机功率略有下降，油耗有所上升，烟度大幅下降，NOx排放增加明显。油耗、烟度和NOx的变化均与生物柴油掺混比例呈线性关系，合适的生物柴油掺混比例即可以保持柴油机的性能，又可有效地降低碳烟排放，且不引起NOx排放的显著变化。对于该增压柴油机，掺混生物柴油对外特性下的排放影响最大，影响最小的为标定转速下的负荷特性。不论是全负荷还是部分负荷，燃用生物柴油时低速下的烟度降低和NOx上升幅度均比高速时大，而同转速下高负荷时烟度降低和NOx上升更为明显。     

Reaction mechanism of H2 generation for H2O/Zn/Fe3O4 system

Several ideas on the reaction mechanism of H₂O/Zn/Fe₃O₄ water splitting system were considered from the aspect of Zn mobility. The vapor deposition of Zn onto the Fe₃O₄ surface was confirmed by H₂ generation reaction with Zn and Fe₃O₄ set separately. XPS measurements suggested that the surface of Fe₃O₄ is covered by Zn before the reaction with steam. The rapid reaction process has been supported by this Zn deposition, which greatly enlarges the number of sites of Zn/Fe₃O₄ pair that is ready to react with steam. In order to keep the Zn from vaporizing off the system, the Zn/Fe₃O₄ mixture was covered with additional Fe₃O₄ to capture the Zn vapor. This resulted in improved H₂ yield of 99.5%.     

Numerical study of the O2/CO2, O2/CO2/N2, and O2/N2-syngas MILD combustion: Effects of oxidant temperature,O2 mole fraction,and fuel blends

Moderate or Intense Low-oxygen Dilution (MILD) combustion of a syngas fuel under air-fuel, oxygen-enhanced, and oxy-fuel condition are numerically studied with using counterflow diffusion flame. Fuel composition, temperature of oxidant (T_ox), and oxygen mole fraction (X_O2) are selected as the main parameters. Fake species (FCO₂) with the same CO₂ physical properties is used for separation the physical and chemical effects of replacing CO₂ with N₂. According to the results, under the high preheating temperatures, the chemical effect of changing the oxidant composition from N₂ to CO₂ is the main reason of the changes in flame structure, ignition delay time (IDT) and heat release rate (HRR) while physical differences play a more prominent role in the low preheating temperature MILD combustion. In all X_O2, the physical and chemical effects of replacing CO₂ with N₂ have almost the same role on the maximum flame temperature. The results of IDT expressed that chemical discrepancies of CO₂ and N₂ play a key role on IDT enhancement by increasing CO₂ in the oxidant composition. The sensitivity analysis of CH₂O for variations of T_ox and X_O2 shows that reactions R54, R56, R58, and R101 are the main responsible of lower HRR and higher IDT by moving from air-syngas to oxy-fuel MILD combustion.     

Experimental investigation of ignition and combustion characteristics of single coal and biomass particles in O2/N2 and O2/H2O

Oxy-steam combustion is a potential new-generation option for CO₂ capture and storage. The ignition and combustion characteristics of single coal and biomass particles were investigated in a flow tube reactor in O₂/N₂ and O₂/H₂O at various oxygen concentrations. The ignition and combustion processes were recorded using a CCD camera, and the two-color pyrometry was used to estimate the volatile flame temperature and char combustion temperature. In O₂/N₂ and O₂/H₂O, coal ignites heterogeneously at <O₂> = 21–50%. In O₂/N₂, biomass ignites homogeneously at <O₂> = 21–30%, while it ignites heterogeneously at <O₂> = 40–50%. In O₂/H₂O, biomass ignites homogeneously at <O₂> = 21–50%. With increasing oxygen concentration, the ignition delay time, volatile burnout time and char burnout time are decreased, and the volatile flame temperature and char combustion temperature are increased. At a certain oxygen concentration in both atmospheres, the ignition delay time, volatile burnout time and char burnout time of biomass are shorter than those of coal. Moreover, biomass has a higher volatile flame temperature but a lower char combustion temperature than coal. The ignition delay time, volatile burnout time and char burnout time in O₂/H₂O are lower than those in O₂/N₂ for coal and biomass. The presence of H₂O can improve the combustion rates of coal and biomass. The volatile flame shows a lower temperature in O₂/H₂O than in O₂/N₂ at <O₂> = 21–50%. The char combustion shows a lower temperature in O₂/H₂O than in O₂/N₂ at <O₂> = 21–30%, while this behavior is switched at <O₂> = 40–50%. The results contribute to the understanding of the ignition and combustion characteristics of coal and biomass in oxy-steam combustion.     

Experimental analysis of the absorption and desorption rates of HCOOK/H2O and LiBr/H2O

This paper evaluates the absorption and desorption rates of a potassium/water binary mixture and compares them to those of lithium bromide/water. The experimental procedure involved small-scale absorption chiller test rig. Extensive instrumentation was used so that identical operating conditions could be obtained for all tests to ensure a good comparison. Analysis of results has shown that the absorption rates for potassium formate/water is approximately 5% lower than lithium bromide/water. The desorption rates of potassium formate/water was found to be higher than that of lithium bromide/water. Heats of absorption and condensation were also recorded. © 1998 John Wiley & Sons, Ltd.     

Cu/La2O3/Al2O3催化剂上甲醇水蒸气重整制氢反应

研究以并流共沉淀法制备Cu/La2 O3 /Al2 O3 系列催化剂催化甲醇水蒸气重整制氢反应过程 ,考察了La2 O3含量、反应温度、水醇比、液体空速 (WHSV)等因素对催化剂活性的影响。结果表明 :催化剂表现出较好的低温活性、高氢气选择性和稳定性。La2 O3 质量分数为 15 % ,在 2 5 0℃反应时 ,催化剂活性表现最佳 ,甲醇摩尔转化率为94 .5 % ,氢气选择性为 10 0 % ,CO摩尔分数为 1.0 5× 10 -7。     

The intrinsic reactivity of coal char conversion compared under different conditions of O2/CO2, O2/H2O and air atmospheres

The reasons for the intrinsic reactivity differences in coal char conversion under an O₂/H₂O atmosphere compared with that under an O₂/CO₂ or O₂/N₂ atmosphere have been investigated in a thermogravimetric analyzer by a simple variable activation energy (SVAE) method combined with an adsorption/desorption reaction mechanism. The results show that only CO₂ or H₂O chemisorption occurred in the non-isothermal experiments, not gasification; however, the intrinsic reaction rate (IRR) of coal char conversion at the same O₂ concentration still increases in an orderly manner under O₂/CO₂, O₂/N₂ and O₂/H₂O atmospheres. This result is due to the different chemisorption mechanisms of CO₂ and H₂O, namely, the production of C(CO), C(OH) and C(H) from CO₂ and H₂O chemisorption. At the same O₂ concentration, the trends and magnitudes of variable activation energies for coal char combustion under O₂/CO₂ and O₂/N₂ atmospheres are similar, while they are very different from those under O₂/H₂O conditions. Therefore, CO₂ has little influence on the reactivity, while H₂O changes the reactivity. In addition, according to the developed reaction mechanism, it is concluded that the SVAE method contributes to the characteristic intrinsic reactivity of coal char conversion under different atmospheres.     

Cu/ZnO/Al2O3催化剂涂层工艺参数的优化

针对甲醇水蒸汽重整制氢反应，研制了一种新型的适用于微槽道反应器的Cu/ZnO/Al2O3催化剂涂层。通过对其关键制备参数的优化，筛选出COAT-14-6（CuO 14wt．％，ZnO6wt．％）为性能最佳的催化剂涂层。研究发现Cu，ZnO／Al2O3涂层催化剂的活性与活性铜的表面积和催化剂的还原性密切相关。100h的连续性实验结果表明，涂覆了COAT-14-6的微槽道反应器可以与10W的燃料电池配套。     

Effects of H2/O2 and H2/O3 gases on PtMo/C cathode PEMFCs performance operating at different temperatures

This study reported the activity of catalysts synthesized from platinum and molybdenum alloys in different atomic ratios and used as cathode electrocatalysts in the PEMFC. The structural properties of PtMo/C and Pt/C catalysts were analyzed by XRD analysis. The composition and distribution of these alloys in Vulcan XC-72R Carbon were determined by SEM and EDX techniques. CV studies assessed electrochemical properties such as ORR and ECSA activity. The performance of PEMFC cathodes that supplied pure hydrogen and oxygen was examined using polarization curves at different temperatures. Another way to improve the cathodic reaction is to use ozone as a potent oxidizing agent. It was measured that the OCV of the H₂/O₃ PEM fuel cell was 1.60 V, much greater than the open circuit voltage of the traditional H₂/O₂ PEM fuel cell. The PtMo/C catalyst achieved its highest power density of 137 mWcm⁻² at 70 °C, 128 mWcm⁻² at 60 °C, 101 mWcm⁻² at 50 °C, and 85 mWcm⁻² at 40 °C when exposed to H₂/O₂. As the temperature of the cell was raised, it was seen that the catalyst's catalytic activity increased.The maximum power density was detected to be inversely related to the rise in temperature when ozone was used. At low current densities, however, ozone was observed to greatly boost activation polarization.