不同海拔高度下自然吸气柴油机经济性及热效率研究  

Effects of Altitude on Fuel Consumption and Thermal Efficiency of Naturally Aspirated Diesel Engines

作　　者：刘胜吉[1] 陈勇[1] 王建[1] 曾瑾瑾 韩维维[1] 

机构地区：[1]江苏大学汽车与交通工程学院,镇江212013

出　　处：《内燃机工程》2016年第6期20-25,30,共7页Chinese Internal Combustion Engine Engineering

基　　金：江苏高校优势学科建设工程项目(苏政办发[2014]37号)

摘　　要：借助内燃机高海拔大气状态模拟试验系统进行了不同海拔高度下自然吸气柴油机的性能试验和缸压采集,试验结果表明:海拔高度增加,柴油机燃油经济性变差,最低比油耗工况负荷略有减小。指示热效率随海拔升高在标定工况时下降最多,中等负荷下降最少。在实测缸内气体压力的基础上采用FIRE软件建立仿真模型探讨高原环境下油气混合过程的变化,模拟结果显示:随海拔高度增加,喷油油束贯穿距变长,油束破碎和蒸发过程减缓,燃烧室近壁面处易形成油气堆积,造成不完全燃烧加剧,使燃烧效率下降。基于实测缸压将实际工作循环简化为理论循环以探讨循环热效率的变化,随海拔升高,一方面燃烧始点滞后,造成压力升高比下降,初始膨胀比增加;另一方面缸内气体温度增加,使得等熵指数减小:两者均使简化后的理论循环热效率下降。此外,缸内燃烧温度和排气温度随海拔升高而增加,使得传热损失、排气损失等不可逆损失增大,实际循环热效率进一步下降。The performance experiments and cylinder pressure measurements of a naturally aspirated diesel engine were conducted under three different altitudes, 10 m, 1 000 m and 1 670 m, with the experimental environments obtained through a plateau simulation system. The results indicate that the fuel consumption of the engine increases and the power at the lowest break specific fuel consumption （BSFC） slightly decreases with the increase in altitude, and that the indicated thermal efficiency reduces most at the rated condition and least at medium load when altitude increases. To explore the air and fuel mixing process at different altitudes, three simulation models were built using the FIRE based on the measured cylinder pressures. The simulation results show that the penetration length becomes longer, as well as the fuel breaking and fuel evaporating process become slower. These make it easy for diesel spray to accumulate near combustion chamber wall, leading to an incomplete combustion, thus contributing to low combustion efficiency. To analyze cycle thermal efficiency at different altitudes, the actual combustion cycle was simplified into a theoretical one based on the measured cylinder pressures. The analysis result indicates that a delayed combustion can cause a decrease in the pressure rise rate and an increase in the initial expansion rate when altitude increases, and the isentropic exponent becomes lower because of higher cylinder temperature. These two can explain the decline of the thermal efficiency of the simplified theoretical cycle. In addition, the combustion and exhaust temperature increase with altitude, causing increases in the heat transfer loss and exhaust loss, which eventually lowers the thermal efficiency of the actual cycle.

关 键 词：内燃机 柴油机 高原 经济性 热效率 

分 类 号：TK421[动力工程及工程热物理—动力机械及工程]