Recently, it is predicted that the fossil fuels will be sufficient for a few decades at the present extraction rates. So, the performance studies of the internal combustion engines play an important role to achieve th...Recently, it is predicted that the fossil fuels will be sufficient for a few decades at the present extraction rates. So, the performance studies of the internal combustion engines play an important role to achieve the best operating point at different weather temperatures. In the present study, the effects of the inlet air temperatures on the engine performance characteristics were studied at different cooling loads. Several experiments were carried out on a single cylinder diesel engine （SCDI）. The performance characteristics of SCDI included： brake power, specific fuel consumption, brake thermal efficiency and exhaust emissions （carbon dioxide, CO2, carbon monoxide CO, and hydrocarbon HC）. The findings show that the inlet air temperature and cooling conditions have appreciable effect on the performance characteristics of the SCDI especially at low cooling rate. It can be concluded that the high cooling rate leads to the enhancement in the brake thermal efficiency, the b.s.f.c, and the emitted COz, CO, and HC. On the other hand the high cooling rate leads to the decrease in the volumetric efficiency. So, a compromising between the inlet air temperature and the cooling rate should be recommended for the engine best performance.展开更多
To study the influence of an elbow inlet on the rotating stall characteristics of a waterjet propulsion pump(WJPP),a three-dimensional internal flow field in a WJPP under a straight-pipe inlet and elbow inlet is numer...To study the influence of an elbow inlet on the rotating stall characteristics of a waterjet propulsion pump(WJPP),a three-dimensional internal flow field in a WJPP under a straight-pipe inlet and elbow inlet is numerically simulated.By comparing the hydraulic performance of WJPP under the two inlet conditions,the internal relationship between the inlet mode and the flow pattern in the pump is clarified.Based on unsteady pressure fluctuation characteristics and wavelet analysis,the influence of the inlet mode on the rotating stall is revealed,and the stall transient propagation characteristics under critical stall conditions are analyzed.The disturbance effects of the inlet channel geometry disappear under low flow rate conditions,the main disturbance is induced by the highspeed countercurrent,and the flow pattern under the elbow inlet is better than that under the straight-pipe inlet.Under the straight-pipe inlet,the single-stall nucleus in the WJPP temporarily experiences a low-frequency and high-amplitude disturbance,which subsequently transforms into a mode of multi-stall nuclei with high-frequency circumferential disturbance.Under the elbow inlet,the rotating stall always maintains a mode of high-amplitude and low-frequency disturbance,which represents the transient characteristics of a single stall core propagating in the circumferential direction inside the channel.The results of this study have a reference value for structural design optimization in a WJPP.展开更多
文摘Recently, it is predicted that the fossil fuels will be sufficient for a few decades at the present extraction rates. So, the performance studies of the internal combustion engines play an important role to achieve the best operating point at different weather temperatures. In the present study, the effects of the inlet air temperatures on the engine performance characteristics were studied at different cooling loads. Several experiments were carried out on a single cylinder diesel engine （SCDI）. The performance characteristics of SCDI included： brake power, specific fuel consumption, brake thermal efficiency and exhaust emissions （carbon dioxide, CO2, carbon monoxide CO, and hydrocarbon HC）. The findings show that the inlet air temperature and cooling conditions have appreciable effect on the performance characteristics of the SCDI especially at low cooling rate. It can be concluded that the high cooling rate leads to the enhancement in the brake thermal efficiency, the b.s.f.c, and the emitted COz, CO, and HC. On the other hand the high cooling rate leads to the decrease in the volumetric efficiency. So, a compromising between the inlet air temperature and the cooling rate should be recommended for the engine best performance.
基金the Key International Cooperative research of National Natural Science Foundation of China(52120105010)National Natural Science Foundation of China(52179085)+1 种基金the National Key R&D Program Project(2020YFC1512405)the Fifth“333 High-Level Talented Person Cultivating Project”of Jiangsu Province,and Funded projects of“Blue Project”in Jiangsu Colleges and Universities.
文摘To study the influence of an elbow inlet on the rotating stall characteristics of a waterjet propulsion pump(WJPP),a three-dimensional internal flow field in a WJPP under a straight-pipe inlet and elbow inlet is numerically simulated.By comparing the hydraulic performance of WJPP under the two inlet conditions,the internal relationship between the inlet mode and the flow pattern in the pump is clarified.Based on unsteady pressure fluctuation characteristics and wavelet analysis,the influence of the inlet mode on the rotating stall is revealed,and the stall transient propagation characteristics under critical stall conditions are analyzed.The disturbance effects of the inlet channel geometry disappear under low flow rate conditions,the main disturbance is induced by the highspeed countercurrent,and the flow pattern under the elbow inlet is better than that under the straight-pipe inlet.Under the straight-pipe inlet,the single-stall nucleus in the WJPP temporarily experiences a low-frequency and high-amplitude disturbance,which subsequently transforms into a mode of multi-stall nuclei with high-frequency circumferential disturbance.Under the elbow inlet,the rotating stall always maintains a mode of high-amplitude and low-frequency disturbance,which represents the transient characteristics of a single stall core propagating in the circumferential direction inside the channel.The results of this study have a reference value for structural design optimization in a WJPP.
