【作者】 王绍明；

【导师】 邓康耀；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2011， 博士

【摘要】 定压增压系统和脉冲增压系统是涡轮增压系统的两种先期基本型式。定压增压系统在高速工况时,泵气损失较小,涡轮效率较高,性能较优;但是在低速工况时,不能充分利用排气脉冲能量。脉冲增压系统既能避免扫气干扰,又能较好地利用排气脉冲能量,低速工况和瞬态工况性能较优;但是在高速工况时,泵气损失较大。可变几何排气管增压系统通过排气管中的可控阀门来实现增压方式的转换,当发动机处于低速工况或加速加载工况时,关闭可控阀门,增压方式转换为脉冲增压;当发动机处于高速工况时,打开可控阀门,增压方式转换为准定压增压。可变几何排气管增压系统同时具有定压增压系统和脉冲增压系统的优点,可以较好的改善发动机高低转速工况的协调性,是一种具有潜在应用价值的增压系统,为此本文对该增压系统开展了计算与试验研究。首先以船用Z8170型柴油机原机仿真计算模型为基础,对船用五缸机、六缸机、七缸机、八缸机、九缸机,分别进行了单阀和双阀可变几何排气管增压系统的方案计算研究。通过各种方案计算结果的对比分析,找到了各机型较优的设计方案,并提出了通用的单阀和双阀可变几何排气管增压系统设计方法。排气管系三通接头计算模型对可变几何排气管增压系统的排气管系设计具有至关重要的影响。为了提高三通接头计算模型总压损失系数的计算精度,对增压系统排气管系常用的两个斜三角“T”型三通接头进行了较高马赫数的冷态吹风试验研究。根据两个三通接头的试验结果,以及已有的三通接头总压损失系数理论计算公式,得到了总压损失系数的修正计算公式。修正计算公式考虑了马赫数的影响,提高了三通接头计算模型总压损失系数的计算精度。为了研究单阀可变几何排气增压系统的综合性能,在利用得到的修正计算公式对排气管系三通接头模型进行修正的基础上,分别对车用六缸机和船用八缸机各自的一种单阀可变几何排气管增压系统进行了详细的计算分析。针对车用六缸机的单阀可变几何排气管增压系统,确定了其外特性阀门开关切换点。结果表明,在额定工况点阀门打开以后,油耗比原机降低3%。针对额定转速分别为1200r/min和1000r/min的船用八缸机单阀可变几何排气管增压系统,确定了它们的推进特性阀门开关切换点。和四脉冲增压系统、PC增压系统、MPC增压系统相比较,新设计的船用八缸机单阀可变几何排气管增压系统性能较优。在推进特性的瞬态工况,可变几何排气管增压系统的阀门关闭以后,能明显改善瞬态性能;其中进气压力上升到90%稳定压力所需要的时间比阀门打开时减少27%,比MIXPC增压系统减少32%。为了进一步验证计算分析的相关结果,对车用六缸机和船用八缸机的单阀可变几何排气管增压系统分别进行了模拟试验研究,得到了这两种机型以燃油经济性为最优原则的阀门开关切换规律。对于车用六缸机的单阀可变几何排气管增压系统,在额定工况点,当阀门处于打开状态时,油耗降低4.7g/kW.h。在突加油门的瞬态工况,当阀门处于关闭状态时,瞬态性能较好,其中增压器转速稳定所需的时间减少30%,进气压力上升到90%稳定压力所需要的时间减少16%,烟度峰值减小15.3%。对于船用八缸机的单阀可变几何排气管增压系统,它能较好地改善发动机的低负荷性能:在推进特性的25%负荷,当阀门处于关闭状态时,油耗比原机降低7.5%,涡轮前平均排温比原机降低32%。试验结果证明了计算分析结果的合理性,也表明可变几何排气管增压系统性能优于其他常规增压系统。更多还原

【Abstract】 Constant-pressure turbocharging system and pulse turbocharging system are the two basic styles of turbocharging system. The turbine efficiency of the constant-pressure turbocharging system is higher and the negative pumping work of it is less than that of the pulse turbocharging system during the high speed operation. The constant-pressure turbocharging system works better during the high speed operation, while it works worse during the low speed operation because the pulse energy can’t be used sufficiently. The pulse turbocharging system has a relatively small exhaust manifold volume, which can avoid scavenging interference and get the pulse energy better utilized. It works better during the low speed and the transient response operation. But the negative pumping work of the pulse turbocharging system is bigger than that of the constant-pressure turbocharging system during the high speed operation. Variable geometry exhaust manifold (VGEM) turbocharging system can realize the switch between two charging modes by the switch valve. The VGEM turbocharging system works as a pulse turbocharging system when the switch valve is closed at the low speed or the transient response operation, and it works as a semi-constant pressure turbocharging system when the switch valve is opened at the high speed operation. The VGEM turbocharging system has the advantages of the constant pressure and the pulse turbocharging system, it can improve the coordination of the high speed operation and the low speed operation, and it has the potential application value. So, computational and experimental study on the VGEM turbocharging system has been performed in this paper.In this paper, firstly, the program simulation of the VGEM turbocharging systems for five-cylinder, six-cylinder, seven-cylinder, eight-cylinder, nine-cylinder marine diesel engines has been done respectively. The fundamental simulation model is built on the Z8170 marine diesel engine. The excellent design programs of the five engines have been found by comparing the program simulation results. The general design method of the VGEM turbocharging system has been put forward. The exhaust manifold junction model is very important for the design of the exhaust manifold in the VGEM turbocharging system. The cold wind tunnel experiments with higher Mach number for two oblique triangle“T”junctions have been carried out in order to improve the simulation accuracy of the total pressure loss coefficient. The corrected formula of the total pressure loss coefficient has been put forward by using of the experimental results and the existing theoretical formula. The corrected formula related with the Mach number. The simulation accuracy of the total pressure loss coefficient can be improved by the corrected formula.In order to study on the overall performance of the VGEM turbocharging system with one switch valve installed on the exhaust manifold, detailed simulation of the VGEM turbocharging system for the six-cylinder vehicle diesel engine and the eight-cylinder marine diesel engine has been done respectively after the junction model is corrected. For the VGEM turbocharging system of the six-cylinder vehicle diesel engine, the switch point at full load characteristic has been defined, and the simulation results indicate that the BSFC can be reduced by 3% on the rated operation condition. For the VGEM turbocharging systems of the 1200 r/min and the 1000 r/min eight-cylinder marine diesel engine, the switch points of the propeller law have been defined. The performance of the new designed VGEM turbocharging system is excellent compared with four pulse, PC,and MPC turbocharging systems. The transient simulation results of the propeller law indicate that the transient performance can be improved obviously when the switch valve of the VGEM turbocharging system is closed; the time for the intake pressure increased to the 90% stable pressure can be reduced by 27% compared with the state that the switch valve is opened, and it can be reduced by 32% compared with the MIXPC turbocharging system.Simulated experiments for the VGEM turbocharging systems of the six-cylinder vehicle diesel engine and the eight-cylinder marine diesel engine have been performed respectively in order to certify the simulation results. Based on the principle of optimum fuel economy, the switch rules of the switch valve are found by comparing the steady experimental results. For the VGEM turbocharging system of the six-cylinder vehicle diesel engine, the BSFC can be reduced by 4.7g/kW.h on the rated operation condition when the switch valve under the opened-state. The transient experimental results indicate that the time for the turbocharger speed became stable can be reduced by 30%, the time for the intake pressure increased to the 90% stable pressure can be reduced by 16%, and the peak value of the smoke opacity can be reduced by 15.3% when the switch valve under the closed-state. For the VGEM turbocharging system of the eight-cylinder marine diesel engine, the lower load performance can be improved. The BSFC can be reduced by 7.5% and the exhaust temperature before turbine can be reduced by 32% at 25% load when the switch valve under the closed-state. The experimental results have proved that the simulation results are reasonable, and the VGEM turbocharging system is excellent compared with other conventional turbocharging systems.更多还原