Experimental Study And Numerical Imulation Of Two-stage Turbo-system On Performance Of Diesel Engine

With the shortage of oil resources and the strictness of emission regulations, it is a major issue to reduce pollutant emissions of diesel engine while still maintaining high thermal efficiency. The two-stage turbocharging technique is an effective measure to improve performance and reduce emissions of diesel engine. The advantage of the two-stage turbo-system over the single-stage system is the increase of the rated power, and at the same time the improved torque at low engine speeds and the transient performance of the diesel engine by rapidly building up boost pressure due to low inertia of the high pressure turbocharger.Based on one-dimensional simulation software GT-Power, this paper presents a matching process between two-stage turbo-system and a six-cylinder HD diesel engine with high-pressure common rail injection system. First, a simulation model is established and calibrated with experiment data to physically describe the HD diesel engine. The two-stage turbo-system is then introduced and analyzed with the model. The results show that two-stage turbo-system can significantly increase intake boost pressure and improve low-speed performance of the engine. However, the BSFC of engine get worse under high-speed conditions, for the reason that smaller flow range of the high pressure turbocharger increases engine pumping losses considerably.According to the BSFC priority, different two-stage turbo-systems are evaluated with GT-Power, and the simulation results agreed well with the data from engine bench test. The high-speed performance of the engine can be improved by increasing the diameter of high pressure turbocharger's waste gate. Then experimental study on the effects of the final matched two-stage turbo-system on the performance and emissions of the engine were conducted. Results showed that the reduction of CO, HC and PM emissions can be achieved by applying this two-stage turbo-system, whereas the NOx emission and BSFC increased slightly compared with the original engine. Finally, further optimization on the structure of two-stage turbo system has been carried out through numerical simulation with GT-Power, with the purpose of providing references for the further optimization of two-stage turbo-system.