RANS simulations on combustion and emission characteristics of a premixed NH3/H2 swirling flame with reduced chemical kinetic model

Ammonia (NH₃) is considered as a potential alternative carbon free fuel to reduce greenhouse gas emission to meet the increasingly stringent emission requirements. Co-burning NH₃ and H₂ is an effective way to overcome ammonia’s relative low burning velocity. In this work, 3D Reynolds Averaged Navier-Stokes (RANS) numerical simulations are conducted on a premixed NH₃/H₂ swirling flame with reduced chemical kinetic mechanism. The effects of (A) overall equivalence ratio Φ and (B) hydrogen blended molar fraction X_H2 on combustion and emission characteristics are examined. The present results show that when 100%NH₃-0%H₂-air are burnt, the NO emission and unburned NH₃ of at the swirling combustor outlet has the opposite varying trends. With the increase of Φ, NO emission is found to be decreased, while the unburnt ammonia emission is increased. NH₂ → HNO, NH → HNO and HNO → NO sub-paths are found to play a critical role in NO formation. Normalized reaction rate of all these three sub-paths is shown to be decreased with increased Φ. Hydrogen addition is shown to significantly increase the laminar burning velocity of the mixed fuel. However, adding H₂ does not affect the critical equivalence ratio corresponding to the maximum burning velocity. The emission trend of NO and unburnt NH₃ with increased Φ is unchanged by blending H₂. NO emission with increased X_H2 is increased slightly less at a larger Φ than that at a smaller Φ. In addition, reaction rates of NH₂ → HNO and HNO → NO sub-paths are decreased with increased X_H2, when Φ is larger. Under all tested cases, blending H₂ with NH₃ reduces the unburned NH₃ emission, especially for rich combustion conditions. In summary, the present work provides research finding on supporting applying ammonia with hydrogen blended in low-emission gas turbine engines.     

AIT环境对卫星热控白漆性能影响的试验

热控白漆喷涂之后至卫星发射之前需要经过数个月的部件组装和测试（AIT）阶段,AIT环境是否影响热控白漆的性能是一个疑问。将与卫星天线相同热控ACR-1白漆的试验膜放置在AIT环境中,对其吸收率和发射率进行了六次测量。通过测量数据,对比分析了AIT过程中温度、湿度、洁净度等环境因素对热控白漆性能的影响程度。结果表明,在试验周期内,ACR-1白漆的吸收率和发射率变化量不大,对白漆性能可靠性的影响度不明显;洁净度对ACR-1白漆的吸收率影响较大。因此,在AIT阶段卫星环境应保持较高的洁净度。     

影响气冷式个体热防护装备致冷力的因素分析

个体气冷系统是一种致冷有效、穿着舒适的热防护装备,在设计和使用中 提高其致冷效率是至关重要的。从工程和生理上分析了影响个体气冷系统致冷力的多种 因素,包括供气温度、湿度、流量以及它们之间的相互关系、致冷面积、流量分配、隔热性 能等。得出了提高蒸发性和对流性两类通风服致冷力和舒适性的方法。为不同工况下合理设 计和选用气冷式个体热防护装备,使之具有更高的人机工效和更好的舒适性提供了参考和借 鉴作用。〖JP〗     

FOX-7的热分解机理

采用热原位红外、热裂解色谱-质谱、热重分析(TG)、差示扫描量热法(DSC)研究了FOX-7的热分解过程,通过测定程序升温过程中凝聚相的化学结构变化和生成的气相产物,研究了FOX-7的热分解机理。研究结果表明,FOX-7在转晶后可能发生了缩合反应,使其处于缩合产物的平衡状态,随着温度的升高该平衡被打破,FOX-7开始分解成一些小官能团产物和小分子产物;气相产物中首先检测到NO,说明热分解的"脱硝"过程存在硝基与亚硝基互变反应过程。     

宇航用元器件锡晶须生长研究

通过分析锡晶须的研究历史,将锡晶须的研究归结为三个阶段:早期对锡晶须现象的研究、锡晶须生长机理的研究和减缓锡晶须生长方法的研究。比较了锡晶须长度及密度的测量方法。总结了目前抑制锡晶须生长的方法:在不同基底材料上采用不同厚度镀锡层;使用Ni、In等阻挡层;对镀层表面进行热处理和回流处理;避免使用纯锡镀层,镀层合金化;在镀层表面覆盖保形涂层。     

基于充分搅拌反应器模型简化详细反应机理

基于充分搅拌反应器(perfectly stirred reactor)模型,改进了相关性分析方法和主成分分析方法的应用方式,对航空煤油(替代燃油)的详细反应机理进行了简化.该详细反应机理由航空煤油替代燃油(80%的正癸烷,20%的1,2,4-三甲基苯组成,以质量计)的反应机理和的NO_X反应机理综合得到,总共包含131种组分,1020个不可逆基元反应.简化工况选为:充分搅拌反应器进口温度800 K、压力101325 Pa、停留时间3 ms、体积为常数、忽略热损失;目标是使得简化机理在绝热的充分搅拌反应器中计算得到的温度和重要组分(CO,CO₂,NO)的摩尔分数与详细机理的计算结果在5%的误差范围内.结果表明,在简化工况宽广的当量比范围内(0.5～2.0)简化机理均能满足设定的目标.      

纳米颗粒在储层微流道中的减阻机理实验研究

用SNP1-1、SNP2-2和SNP2-4三种疏水纳米材料分别与柴油配制成3种油基纳米液,用SNP2-2分别与ND3和ND4配制成2种水基纳米液,通过岩心流动实验测试了这5种纳米液的减阻效果。实验结果显示,3种油基纳米液使岩心水相渗透率提高了42%、49%和24%,2种水基纳米液分别使岩心水相渗透率提高了17.5%和75%,5种纳米液都具有减阻效果,但不同纳米液的效果差异明显,这说明增注液不具有唯一性,但纳米粒径、修饰剂和分散剂对减阻效果有明显的影响。测试了SNP2-2油基纳米液处理岩心的耐冲刷能力,岩心经180倍孔隙体积（PV）水的驱替,仍具有一定的效果,说明纳米边界层流道壁面有较强的吸附能力。现场采用SNP2-2和ND4配制的纳米液进行了三口井的增注试验,注水压力最大降幅12.5MPa。研究结果与实验前的设想相符,较好地说明了纳米减阻机理。     

空间碎片防护研究现状与国内发展建议

文章回顾了近期国外空间碎片防护领域的研究现状和热点问题;介绍了“十一五”期间国内空间碎片防护研究的若干进展;立足我国研究现状,通过对国内航天器防护工程需求分析,提出了未来我国空间碎片防护领域研究发展建议。     

发汗式主动冷却金属热防护系统主动冷却效率研究

发汗式主动冷却金属热防护系统是一种新型概念,将发汗冷却方法应用于金属热防护系统中,用于提高金属热防护系统的热载荷承载能力,是解决临近空间高超声速飞行器防热问题的有效方法。设计并建立了发汗式主动冷却金属热防护系统的实验模型,分析了发汗式主动冷却金属热防护系统的基本冷却原理,测量了同一实验模型分别在有无发汗冷却作用下,沿厚度方向不同位置测量点的温度响应。结果表明：在相同的加热条件,采用发汗冷却方法,可以使受热蒙皮材料达到相同温度的时间明显滞后;在发汗冷却作用的过程中,内部隔热层的温度不会超过水的沸点温度;采用发汗冷却方法,可以使同一结构热载荷承载能力至少提高70%;通过合理的结构设计,可以减少受热蒙皮由于热膨胀而引起的结构变形。
     

Mars Sample Return: Do Australians trust NASA?

Mars Sample Return (MSR) represents an important scientific goal in space exploration. Any sample return mission will be extremely challenging from a scientific, economic and technical standpoint. But equally testing, will be communicating with a public that may have a very different perception of the mission. A MSR mission will generate international publicity and it is vital that NASA acknowledge the nature and extent of public concern about the mission risks and, perhaps equally importantly, the public’s confidence in NASA’s ability to prepare for and manage these risks. This study investigated the level of trust in NASA in an Australian population sample, and whether this trust was dependent on demographic variables. Participants completed an online survey that explored their attitudes towards NASA and a MSR mission. The results suggested that people believe NASA will complete the mission successfully but have doubts as to whether NASA will be honest when communicating with the public. The most significant finding to emerge from this study was that confidence in NASA was significantly (p < 0.05) related to the respondent’s level of knowledge regarding the risks and benefits of MSR. These results have important implications for risk management and communication.