亚/超临界环境下碳氢燃料液滴的蒸发与燃烧特性  

Evaporation and Combustion Characteristics of Hydrocarbon Fuel Droplet at Sub-and Super-Critical Environments

作　　者：马志豪[1] 李智博[1] 朱宇东[1] 陈占耀 贾义[1] 徐胜利[2] Ma Zhihao Li Zhibo Zhu Yudong Chen Zhanyao Jia Yi Xu Shengli(Vehicle and Transportation Engineering Institute, Henan University of Science and Technology, Luoyang 471003, China School ofAerospaceEngineering, TsinghuaUniversity, Beijing 100084, China)

机构地区：[1]河南科技大学车辆与交通工程学院,河南洛阳471003 [2]清华大学航天航空学院,北京100084

出　　处：《内燃机学报》2016年第5期443-448,共6页Transactions of Csice

基　　金：国家自然科学基金资助项目(11372306)

摘　　要：采用挂滴法对正常重力下处于亚/超临界压力环境中的不同碳氢燃料液滴蒸发与燃烧现象做了详细的试验研究.采用嵌入液滴内部的热电偶和高速相机分别记录液滴温度变化和液滴发展图像.结果表明:在亚临界压力环境下,液滴燃烧过程具有平衡蒸发阶段,符合准定常假设,但在超临界压力环境下,液滴燃烧过程不再出现平衡蒸发阶段,准定常假设已不成立;液滴燃烧持续时间在亚临界状态下随着压力的增加而迅速减小,此时相平衡控制液滴燃烧速率的大小,但在超临界状态下,液滴与环境气体之间的界面变得模糊不清,燃烧持续时间随着环境压力的增加不再继续减小,而是趋于一稳定值,此时液滴已不存在相变过程,扩散系数开始影响燃烧速率;燃烧持续时间变化趋势在临界压力处的转变反映出临界压力点是判断液滴是否进入超临界燃烧的重要依据,液滴燃烧过程中液滴完全蒸发所占的时间比重在亚临界压力环境下变化不大,而在超临界压力环境下迅速减小,相对更早地完成液滴蒸发.An experimental study on evaporation and combustion phenomena of single suspended hydrocarbon drop- lets was conducted in sub- and super-critical pressure environments under normal gravity. Droplet temperature and photographs were obtained by utilizing embedded thermocouple and high-speed camera respectively. Experimental results show that equilibrium vaporization stage exists during droplet combustion at sub-critical pressure environments, which accords with quasi-steady assumption. But the equilibrium vaporization stage disappears during droplet combustion at super-critical pressure environments, and quasi-steady assumption is not applicable. Droplet combustion lifetime decreases rapidly with the increase of ambient pressure at sub-critical condition and phase equilib- rium controls the droplet burning rate. Under super-critical condition, the interface between droplet and ambient gas appears ambiguous, and droplet combustion lifetime does not decrease and approaches a stable value. Phase change disappears and diffusion coefficient starts to affect the droplet burning rate under super-critical condition. The change in combustion lifetime variation trend at critical pressure indicates that the critical pressure point of fuel is an important criterion in the super-critical combustion of a fuel droplet. The ratio of droplet evaporation lifetime to droplet combus- tion lifetime has little change in sub-critical pressure environments, but it decreases rapidly in super-critical pressure environments, and this indicates that droplet evaporation process completes earlier in super-critical pressure environments.

关 键 词：碳氢燃料 液滴 亚/超临界环境 蒸发与燃烧 

分 类 号：TK401[动力工程及工程热物理—动力机械及工程]