Effects Of Different Turbocharging Systems On Performance And Emissions Of A Heavy-Duty Diesel Engine

The core objective of combustion optimization in diesel engine is to significantly reduce NO_x and PM emissions,while improving fuel economy and reducing CO₂emission.In January 2013,the Euro VI emission regulation has been implemented in European Union,and the China VI emission regulation will also be implemented all over the country in January 1,2020.Stringent emission regulations put forward severely challenges to the technology for heavy duty diesel engine.In order to meet more strict emission regulations,in addition to SCR and DPF aftertreatment technologies,it is important to optimize the combustion process.The combustion optimization can not only improve the fuel economy and reduce NO_x,PM and CO₂emissions,but also relieve the high requirements and reduce the complexity of the aftertreatment system,which could also improve the feasibility of engineering implementation.In the current study the effects of different turbocharger systems coupled with EGR on combustion,performance and emissions of diesel engine will be explored,based on which the turbocharger system and combustion control optimization approaches to meet emission requirement based on different original NO_x emission can then be proposed.The effects of different turbocharging systems,including a single-stage fixed geometry turbocharger?WGT?,single-stage variable geometry turbocharger?VGT?,two-stage fixed geometry turbocharger?WGT-FGT?and two-stage variable geometry turbocharger?VGT-FGT?,on the combustion and emission characteristics were experimental investigated in a common-rail heavy duty diesel engine.The results show that compared to WGT and WGT-FGT,VGT and VGT-FGT can significantly improve the pressure difference between the vortex and the air intake,thus,more EGR can be introduced and lower NO_x emission can be achieved.The intake air flow mass can also be increased to improve the combustion process.With the decrease of NO_x emission,the brake specific fuel consumption?BSFC?increased.For 28.9 kW/L specific power,when NO_x emission is maintained at around 5.0 g/kW-h,the WGT-FGT can achieve lower BSFC than WGT,the soot is close to VGT,but still better than WGT.When NO_x emission is kept at about 3.5 g/kW-h,VGT can achieve almost the same BSFC and soot emission compared to that of VGT-FGT.,the advantage of VGT-FGT turbocharger to reduce fuel consumption and soot become more obvious as NO_x emission is further reduced.For 24.5 kW/L and 21.0 kW/L specific power,when NO_x emission is higher than 3.5 g/kW-h,WGT-FGT is a better choice;when the NO_x emission is higher than 8 g/kW-h,WGT shows advantages in both cost and installation space.For each specific power condition,the exhaust temperature at 25%load of all four turbocharger systems is lower than the SCR optimal catalytic temperature,While at 100%load,the exhaust temperature of WGT exceeds the optimal catalytic efficiency temperature range,and the reliability of turbocharger is compromised.Therefore,it is critical to apply effective exhaust thermal management strategy for the aftertreatment to meet the strict emission regulations.