【作者】 任立红；

【导师】 舒歌群；

【作者基本信息】 天津大学 ， 动力机械及工程， 2007， 博士

【摘要】 可变进气技术是在发动机的工作过程中,改变传统的单一的进气模式,组织变化的进气方式,使进入缸内的充量大小和运动形式适合变化的发动机运行工况,从而改善发动机中、低速性能。本文对一单缸4气门125ml排量的摩托车发动机,进行了可变进气的改进设计,在不同的运行工况范围,实现不同的可变进气模式,从而达到优化发动机中,小负荷性能的目的。首先,设计一可变进气系统,实现五种进气模式;在气道稳流试验台上对五种进气模式气道进行了试验,进气模式不同时,气道的流通系数随气门升程提高的变化率明显不同,在小节流模式,小气门升程时,节流反而使流量系数增大,而在大气门升程,节流使流量系数降低;在节流增大后,滚流,涡流都加强了,表明缸内气体运动是涡流运动和滚流运动的结合-斜轴涡流。可变进气结构可以有效地调节流量系数和斜轴涡流强度。对发动机不同进气模式在最大气门升程时的进气及缸内流动进行了三维稳态模拟,发现随节流的增加,节流一侧气流变弱,占据范围也变小,同时,非节流一侧的涡旋变大,涡旋的中心逐渐朝气缸中心移。模拟分析了五种可变进气道的流量系数,涡流比和滚流比;进一步,模拟分析了三种可变进气位置,发现右可变位置的涡流比有所增加,但流量系数有一定的下降,从而,发现对可变进气道位置有进一步优化的空间。对可变进气发动机进行进气,压缩,燃烧过程三维瞬态模拟分析,表明进气过程是发动机湍动能的形成过程,压缩终了缸内不同的斜轴涡流比对湍动能有不同影响。发现在一定的工况下提高斜轴涡流比可以显著提高发动机缸内混合气的湍动能,从而增加燃烧放热率,最终提高气缸压力。对可变进气发动机进行了性能及排放试验,从实验结果看出,在25%,35% 50%节气门开度,功率,扭矩有所提高,提高幅度分别为6.37%,5.32%,4.93%。随负荷的增大,改善的幅度减小。表明在中小负荷,适当的节流进气,可以优化发动机的性能。最后对可变进气发动机进行了整机优化分析,表明,进气管长度及直径少量改变对发动机性能有一定影响;而排气管直径和长度对发动机性能有较大影响,在不同的工况下存在一个最优的直径和长度,增大,减小都会使发动机性能降低。进排气正时的优化表明,在不同的工况下存在不同的最优的进排气正时,因此,要根据不同工况采用不同的进排气正时优化发动机性能。更多还原

【Abstract】 Variable inlet technology can improve engine’performance at part load by organizing variable intake flow and changing singular intake charge motion to variety inlet port charge’size and movement suitable for running load of engine. This paper developed a variable intake system on a single cylinder 125 ml engine with four valves. The system made intake charge variety along with the load of engine, and so, it improved part load performance.The developed variable intake system realized five intake mode. A series of experiments were carried out on steady state flow port test-bed for the variable inlet port performance measurement. The flow coefficient of five intake mode’port increase with valve lift by obvious different ratio. For small variable intake mode, variable intake flow coefficient higher than customary intake mode at small valve lift, and variable intake flow coefficient lower than customary intake mode at large valve lift. For large variable intake mode, tumble and swirl ratio higher than customary intake mode. The in-cylinder air motion is the resultant swirl—an inclined-axis swirl instead of single swirl or tumble.The variable intake device can adjust the inclined axis swirl in the cylinder.A three-dimensional steady model of CFD (Computational Fluid Dynamics) was developed to simulate the flow of inlet port and cylinder. The result showed that the swirl intensity weaken and its space become smaller at variable intake side; meanwhile swirl became bigger and swirl center moved to the center of the cylinder at customary intake side with flow area decrease. The model simulated three kind of variable intake position. The result showed that swirl ratio increase but flow coefficient became smaller at rest variable intake position, so three were impossible to optimize variable intake position.A three-dimensional transient model of CFD was developed to simulate the intake compress and combustion in the cylinder. The result showed that tubulence energy form at intake stroke, and variable swirl ratio after compress stroke effected tubulence energy. Tubulence energy increased with swirl ratio in the cylinder, and result that combustion ratio and cylinder pressure increase.The engine performance experiment was carried out. The result showed that the power increased 6.37%,5.32%,4.93% at 25%,35% 50% throttle opening; and improvement became smaller with larger load; so suitable variable intake can improve engine performance at small and middle load.Optimization was carried out for the entire engine, the result showed that the variety of long and diameter of intake manifold had effect to engine performance ; the variety of diameter and long of exhaust manifold had effect to engine performance. There were a most optimized intake-exhaust valves timing along with variable engine load.更多还原