废气再循环(exhaust gas recirculation,EGR)技术是解决柴油机氮氧化物(NO_x)排放的有效措施之一,尤其是经中冷后的EGR在NO_x、颗粒物(particulate matter,PM)的排放以及经济性方面能够实现更好的折衷。在冷却EGR时,排气中所含的干碳烟(...废气再循环(exhaust gas recirculation,EGR)技术是解决柴油机氮氧化物(NO_x)排放的有效措施之一,尤其是经中冷后的EGR在NO_x、颗粒物(particulate matter,PM)的排放以及经济性方面能够实现更好的折衷。在冷却EGR时,排气中所含的干碳烟(soot)和碳氢(carbureted hydrogens,HCs)在热泳力、静电、扩散和凝结等作用下沉积到EGR冷却器的换热元件表面而形成积碳,达到稳定状态的积碳导致EGR中冷换热效率下降达20%~30%,背压达无积碳状态的2倍,由此导致发动机NO_x、PM的排放以及经济性变差。研究表明,温度、soot的粒径分布、HCs的浓度是影响积碳的主要因素,同时EGR冷却器的结构、燃料等也会造成一定的影响。通过对各影响因素的优化可以延缓积碳的形成过程,目前实现EGR冷却器再生的有效手段尚处于研究阶段,可能有效的再生措施有高速气流冲刷表面疏松的soot、蒸发积碳当中的HCs、高温氧化soot以及利用水或酸等弱化积碳的黏附力而自然脱落。展开更多
PM 10 airborne particles and soot deposit collected after a fire incident at a chemical store were analyzed in order to determine the concentrations of polycyclic aromatic hydrocarbons(PAHs). The samples were ext...PM 10 airborne particles and soot deposit collected after a fire incident at a chemical store were analyzed in order to determine the concentrations of polycyclic aromatic hydrocarbons(PAHs). The samples were extracted with 1∶1 hexane-dichloromethane by ultrasonic agitation. The extracts were then subjected to gas chromatography-mass spectrometric(GC-MS) analysis. The total PAHs concentrations in airborne particles and soot deposit were found to be 3.27±1.55 ng/m 3 and 12.81±24.37 μg/g, respectively. Based on the molecular distributions of PAHs and the interpretation of their diagnostic ratios such as PHEN/(PHEN + ANTH), FLT/(FLT + PYR) and BeP/(BeP + BaP), PAHs in both airborne particles and soot deposit may be inferred to be from the same source. The difference in the value of IP/(IP + BgP) for these samples indicated that benzo[g,h,i]perylene and coronene tend to be attached to finer particles and reside in the air for longer periods. Comparison between the molecular distributions of PAHs and their diagnostic ratios observed in the current study with those reported for urban atmospheric and roadside soil particles revealed that they are of different sources.展开更多
文摘废气再循环(exhaust gas recirculation,EGR)技术是解决柴油机氮氧化物(NO_x)排放的有效措施之一,尤其是经中冷后的EGR在NO_x、颗粒物(particulate matter,PM)的排放以及经济性方面能够实现更好的折衷。在冷却EGR时,排气中所含的干碳烟(soot)和碳氢(carbureted hydrogens,HCs)在热泳力、静电、扩散和凝结等作用下沉积到EGR冷却器的换热元件表面而形成积碳,达到稳定状态的积碳导致EGR中冷换热效率下降达20%~30%,背压达无积碳状态的2倍,由此导致发动机NO_x、PM的排放以及经济性变差。研究表明,温度、soot的粒径分布、HCs的浓度是影响积碳的主要因素,同时EGR冷却器的结构、燃料等也会造成一定的影响。通过对各影响因素的优化可以延缓积碳的形成过程,目前实现EGR冷却器再生的有效手段尚处于研究阶段,可能有效的再生措施有高速气流冲刷表面疏松的soot、蒸发积碳当中的HCs、高温氧化soot以及利用水或酸等弱化积碳的黏附力而自然脱落。
文摘PM 10 airborne particles and soot deposit collected after a fire incident at a chemical store were analyzed in order to determine the concentrations of polycyclic aromatic hydrocarbons(PAHs). The samples were extracted with 1∶1 hexane-dichloromethane by ultrasonic agitation. The extracts were then subjected to gas chromatography-mass spectrometric(GC-MS) analysis. The total PAHs concentrations in airborne particles and soot deposit were found to be 3.27±1.55 ng/m 3 and 12.81±24.37 μg/g, respectively. Based on the molecular distributions of PAHs and the interpretation of their diagnostic ratios such as PHEN/(PHEN + ANTH), FLT/(FLT + PYR) and BeP/(BeP + BaP), PAHs in both airborne particles and soot deposit may be inferred to be from the same source. The difference in the value of IP/(IP + BgP) for these samples indicated that benzo[g,h,i]perylene and coronene tend to be attached to finer particles and reside in the air for longer periods. Comparison between the molecular distributions of PAHs and their diagnostic ratios observed in the current study with those reported for urban atmospheric and roadside soil particles revealed that they are of different sources.
