不同增压系统对重型柴油机性能和排放影响的试验研究

Effects of Different Turbocharging Systems on Performance and Emissions of a Heavy-Duty Diesel Engine

在一台电控高压共轨重型柴油机上,基于高压冷却废气再循环(EGR),对比研究了带废气放气阀式单级固定涡轮截面增压器(WGT)、单级可变涡轮截面增压器(VGT)、二级固定涡轮截面增压器(WGT-FGT)和二级可变涡轮截面增压器(VGT-FGT)四种增压方式对柴油机性能与排放的影响。结果表明:可变截面相对固定截面增压系统(VGT相对WGT,VGT-FGT相对WGT-FGT),能显著提高涡前与进气压差,实现更高EGR率和更低的NO_x排放,同时能够提高进气充量,从而改善燃烧过程。随着NO_x比排放的降低,四种增压方式的油耗都呈现上升趋势,并且VGT-FGT、VGT、WGT-FGT和WGT的燃油消耗率依次升高。当NO_x原始排放控制在5.0g/(kW·h)左右,采用WGT-FGT时燃油消耗率相对WGT获得一定改善(与VGT和VGT-FGT相当),碳烟排放与VGT-FGT接近,明显优于WGT。随NO_x排放降低,可变截面增压系统相对固定截面增压系统逐渐表现出优势:当NO_x原始排放控制在3.5g/(kW·h)左右,VGT可以获得与VGT-FGT接近的燃油经济性和碳烟排放;当NO_x原始排放更低(2.8g/(kW·h)以下),VGT-FGT降低油耗和碳烟排放的优势更加明显。

The effects of different turbocharging systems,single-stage turbocharger(WGT),singlestage variable geometry turbocharger(VGT),two-stage turbocharger(WGT-FGT)and two-stage variable geometry turbocharger(VGT-FGT),on the combustion and emissions characteristics were experimentally investigated on a common-rail heavy duty diesel engine.The results show that compared to the WGT and WGT-FGT,the VGT and VGT-FGT can significantly improve the differential pressure between before turbine and air intake manifold,more proportion of EGR can be introduced and lower NO_x emission can be achieved.They can also increase intake air,thus the process of combustion is improved.With the reduction of NO_x emission,these four turbo-charging systems make brake specific fuel consumption(BSFC)increase,the increase sequence of overall fuel consumption is the VGT-FGT,VGT WGT-FGT and WGT.When NO_x emission is controlled around 5.0 g/(kW·h),the WGT-FGT can enable the engine to achieve lower BSFC than the WGT does with soot close to that with the VGT,but apparently superior to that with the WGT.When NO_x emission is controlled about 3.5 g/(kW·h),the VGT can enable the engine to realize almost the same BSFC and soot emission as the VGT-FGT does.At lower NO_x emission,the advantage of the VGTFGT turbocharger becomes more obvious in reducing fuel consumption and soot.