Research On The Calibration Between Turbochargers And High Pressure Common Rail Diesel Engine

Diesel engines'sharing larger market is a non-stopping trend. The main automobile manufactures share the same point of view that, diesel engines would be the mainstream for 21st century's vehicles. Diesel engines are of higher heat efficiency, higher reliability, while consuming less fuel and outputting more torque. Comparing with gasoline, diesel has much better energy density and lower price. As basically all diesel engines have taken different techs to improve output power, reduce fuel consumption and cut emissions, turbocharging needs further study and development as an important measure to improve diesel engines performance.Since the fifths in 20th century, turbocharing has been the most prevalent tech to increase inlet air, and the study and manufacturing about turbochargers has been highly developed. In Europe, VGT is rather a mature tech, and many kinds of products have been put into market; two-stage turbocharging and other techs are also sharing part of the market. But VGT still has disadvantage in some areas, such as the complex control systems, high cost and poor reliability. Though the wastegate(WG) turbocharging system is less fuel-efficient in high speed area, it still has potential to get further developed as it is low-cost and high reliable.WG turbocharging system's A/R is fixed while VGT's is variable. When engine gets a certain speed(outlet exhaust flow is certain), reducing A/R increases exhaust flow's moment of momentum, then the rotational speed of the turbocharger increases, which gets better pressure ratio; otherwise, increasing A/R causes reduction of the moment of momentum, then the turbocharger slows down, pressure ratio falls. So, it is important to properly choose A/R ratio for calibration with diesel engines.A/R ratio has great influence on the engines'velocity characteristic. Properly reducing A/R would improve low speed performance, but it is disadvantageous for high speed performance, which means certain A/R is only suitable to a certain engine speed and not suitable to others. This paper studied the calibration between a diesel engine and turbochargers with different A/R ratio. Firstly I built a model of the GW2.5TC diesel engine as well as two different turbochargers with simulation software GT-POWER, and then did simulations about calibration.Firstly, this paper studied the influence of A/R ratio to the calibration between diesel engine and turbochargers, then analyzed engine's power output, fuel efficiency and emissions. It is proved that smaller A/R turbine effectively increases mass of inlet air at low engine speed, which greatly improves power output and fuel efficiency, as well as cutting soot emissions. However, smaller A/R turbine does bad to the performance at high engine speed. Considering all engine speed areas, there should be a most proper A/R turbine to fit the engine well.Secondly, exhaust-driving wastegate is only used to limit the pressure ratio at high engine speed, so it is not able to match different operation situations of the engine. This paper studied the new wastegate which self-adjusts opening area relied on engine's operation situations, simulated the calibration between engine and wastegate and studied the influence from opening area of wastegate to the engine performance. The inlet pressure to engine and the inlet pressure to turbine are a pair of factors which affects each other, and they both affect engine performance greatly and complexly. By flexibly controlling opening area of the wastegate, the two pressures could get best balance, and then engine reaches best performance.This paper analyzed the effect of calibration between diesel engine and different A/R turbochargers by simulation, and got some guiding conclusions, which will support following parameter designing and calibration.