高滚流Atkinson循环燃烧系统研究

为进一步提高发动机热效率,提出高滚流Atkinson循环燃烧系统概念。其特征是采用高滚流气道和活塞组合,配合Atkinson循环和废气再循环(EGR)技术,提高缸内的滚流和湍流水平,加快燃烧速度,同时降低汽油机爆震倾向。利用GT-Power和AVL FIRE软件针对某型汽油机进行了一维整机工作过程和三维计算流体动力学(CFD)模拟分析。结果表明:高滚流气道有利于促进缸内滚流运动,滚流比由原机的0.5提高到2.6;配合高滚流活塞后,使进气过程中产生的缸内初始滚流和压缩过程中的滚流维持作用都比原机有所增强,湍动能水平提升6.3%,瞬时放热率与原机相比平均提高15%;在此基础上,采用进气门晚关的方式实现Atkinson循环,并增加EGR系统,降低高压缩比带来的爆震倾向,比油耗在整个万有特性中均呈下降趋势,最低比油耗区明显变大,最低比油耗相比原机下降11.3g/(kW·h)。

Study on Atkinson Cycle with High Tumble Combustion System

For the improvement of engine thermal efficiency, the concept of the Atkinson cycle with high tumble combustion system was proposed, which adopts the combination of high tumble intake port and piston, and coordinates the Atkinson cycle and exhaust gas recirculation(EGR) technology to improve in-cylinder tumble and turbulence level, accelerate combustion speed, and reduce knock tendency. The engine work process model and in-cylinder computational fluid dynamics(CFD) model of a certain engine were set up by the GT-Power and AVL-FIRE software respectively. The simulation results show that a high tumble intake port benefits in-cylinder tumble, which increases from 0.5 of the base engine to 2.6; with high tumble intake ports and pistons, both the initial tumble generated during the intake process and the tumble maintained during the compression process are stronger than the base engine, the average turbulence energy increases by 6.3%, and the average heat release rate increases by 15% compared with the base engine. In order to decrease the knock tendency caused by high compression ratio, the Atkinson cycle, which is realized by late intake valve closing timing, was introduced with EGR based on the foresaid high tumble. The results show that the brake specific fuel consumption(BSFC) in the universal characteristic appears downward trend. The lowest BSFC area becomes larger obviously, and the lowest BSFC decreases by 11.3 g/(kW·h) against the base engine.