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介绍有关涡轮增压汽油机冷却废气再循环(EGR)系统的研究,旨在改善车辆的燃油经济性。近年来,提高压缩比和缩缸强化的策略已被视为是改善涡轮增压汽油机燃油效率的有效途径。在高负荷工况下,尤其在涡轮增压区域,改善燃油经济性特别重要。改善这一区域燃油经济性的关键是抑制爆燃、降低排气温度和增大比热比。冷却EGR系统方案包括低压回路EGR(LP-EGR)、高压回路EGR(HP-EGR),以及其他系统。基于以下理由选用LP-EGR系统:在相对较高的涡轮增压条件下,发动机低转速时可供给足够的再循环废气。为抑制爆燃,清除再循环废气中的氮氧化物非常重要,这意味着要从催化转化器下游抽取再循环废气。另一方面,为了表征LP-EGR系统的较小压差和较长EGR回路,必须应用更加精细的EGR率控制。EGR气流基于EGR阀的压差形成,而压差随空气流率改变,所以,可以用不变的EGR阀开度保持EGR率。虽然这一原理只能用于稳态工况,但已开发一种新的修正控制,通过在排气管取样点上获得的EGR废气压力,并考虑其滞后效应,即使在瞬态工况下也可保持稳定的EGR率。试验结果表明,在涡轮增压状态下,用LP-EGR可使燃油经济性改善达5%,还能降低排气温度。
Describes the research on turbocharged gasoline engine cooling exhaust gas recirculation (EGR) systems designed to improve vehicle fuel economy. In recent years, strategies to improve compression ratio and cylinder shrinkage have been considered as effective ways to improve the fuel efficiency of turbocharged gasoline engines. In high-load conditions, especially in turbocharged areas, improving fuel economy is particularly important. The key to improving fuel economy in this region is to suppress deflagrations, reduce exhaust temperatures and increase specific heat rates. Cooling EGR system solutions include low pressure loop EGR (LP-EGR), high pressure loop EGR (HP-EGR), and other systems. The LP-EGR system is selected for the following reasons: At relatively low turbocharging, enough low-speed engine can supply enough recirculated exhaust gas. To suppress deflagration, it is important to remove nitrogen oxides from the recirculated exhaust gas, which means that recirculated exhaust gas is drawn downstream of the catalytic converter. On the other hand, to characterize the smaller pressure differentials and longer EGR circuits of LP-EGR systems, finer EGR rate controls must be applied. The EGR airflow is formed based on the pressure difference of the EGR valve and the pressure difference changes with the airflow rate, so the EGR rate can be maintained with a constant EGR valve opening degree. Although this principle can only be used in steady-state conditions, a new correction control has been developed that uses the EGR exhaust pressure obtained at the sampling point of the exhaust pipe, taking into account its hysteresis effect, even under transient conditions It is also possible to maintain a stable EGR rate. Test results show that with turbocharging, LP-EGR can improve fuel economy by up to 5% and reduce exhaust gas temperature.