塔克拉玛干沙漠热力浮尘天气特征初步研究

浮尘天气对区域气候、生态环境及社会生产具有重要影响。热力浮尘(沙尘气溶胶来源于热力起沙)作为浮尘天气的重要组成部分,未受到广泛关注。基于塔克拉玛干沙漠塔中气象站常规地面观测资料和PM10浓度资料,初步分析研究区热力浮尘天气的基本特征。结果表明:(1)典型热力浮尘天气过程中,气温呈显著的上升趋势,最高温差达5.0℃以上;气压呈显著的下降趋势,最高气压差达5.0 hPa以上;(2)热力浮尘天气仅出现在5—9月,其中6月发生频次最高,占总发生频次的47.1%;92.9%的热力浮尘天气发生在夜间(20:00—08:00),最大值出现在03:00—04:00,占日发生总频次的21.4%;(3)热力浮尘天气平均持续时长为598.5 min,最长达1120.0 min。

江苏秋冬季重度霾的分型研究

利用常规观测资料、探空资料和NCEP再分析资料对江苏秋冬季重度霾的环流背景、边界层特征、热力条件、动力条件及气流轨迹进行了分析,探讨重度霾的形成机制。结果表明,2014年秋冬季纬向环流较常年显著增强,500 hPa转西北气流对重度霾缓解有6—12 h的提前指示意义。重度霾发生时的地面形势可分为3类:均压区型、冷锋前部型和低压倒槽型。东路冷空气驱霾效果优于西路冷空气。重度霾发生时主要是贴地逆温,风速在4 m/s以下,霾消散前一致转北风,日变化明显,下午霾常有所减轻。逆温强度方面,低压倒槽型强于西路冷锋前部型,强于均压区型;逆温持续时间方面,低压倒槽型长于西路冷锋前部型,长于均压区型;逆温厚度方面,3种类型基本相当;东路冷空气影响时逆温消失。不同类型逆温强度不同可能与925 hPa和近地面的风向风速、锋前升温及气团源地有关。逆温层多在300 m以下,逆温强度为1—5℃/(100 m),近地层有浅薄湿区,相对湿度为40%—90%。动力条件方面,低层辐合下沉区域霾常加重,并伴有明显气流停滞区,区域过程累积风矢量和很小,在100—500 m/s范围内,不利于污染物的水平扩散。冷锋前部型气流输送的气溶胶主要来源于西北—华北地区,低压倒槽型则主要来自华南,均压区型主要来源于本地。通过研究江苏秋冬季重度霾的天气特征得到了一些有意义的结果,可为今后预报提供更多参考依据。

Matching between mechanics and thermodynamics among 4 individual strokes in a 4-stroke engine by non-circular gear mechanism

The relationship between engine mechanics and thermo-dynamics has been investigated by means of numerical simulation.The inherent mismatching between the mechanical behaviors and the thermodynamic process in internal combustion engine is identified,which is believed to be one of the important limiting factors of energy efficiency for conventional engines available in the current market.An approach for engine efficiency improvement through optimal matching between mechanics and thermodynamics(OMBMT)is proposed.An ideal matching model is defined and the conflicts due to the constraints among the mapping strokes in a 4-stroke engine are analyzed.A novel mechanical model is built for approaching optimal matching among all 4 individual strokes in a 4-stroke spark-ignition engine,which is composed of non-circular gears(NCG)and integrated with conventional slider crank engine mechanism.By means of digital mechanical model and numerical simulation,the matching gains among all 4 strokes are defined and calculated for quantifying the NCG engine efficiency improvement by comparing with a baseline engine.The potentials with the OMBMT implemented and the enhancements made by NCG mechanism for engines in terms of overall engine efficiency are reported.Based on the results achieved,it is recommended that the feasibility studies and the experimental validations should be conducted to verify the engine matching concept and effectiveness of the NCG mechanism engine model proposed,and the engine performance and NCG design parameters should be further optimized.