Comparative analysis and evaluation of turbocharged Dual and Miller cycles under different operating conditions

Abstract

In this paper, an accurate turbocharged Dual cycle model integrating the pumping process is proposed with all the assumptions of an air-standard cycle are relaxed. Effects of the turbine cross section, turbocharger efficiency, excess air coefficient, load and wastegate on the turbocharged Dual cycle are investigated based on a calibrated diesel engine model in Matlab software. The Miller cycle under different turbocharger matching conditions is compared with the original turbocharged Dual cycle. The results show that there exists an optimum excess air coefficient for the indicated efficiency of the turbocharged Dual cycle when considering the pumping process, and the optimum value increases with the increase of the turbocharger efficiency and the decrease of the engine load. With the wastegate, the amount of intake air can be restricted, and variations of the indicated efficiency depend on the turbocharger matching. The exclusive adoption of the Miller cycle can only increase the engine performance when the original matched turbine has a small cross section. The Miller cycle always needs a high efficiency turbocharger with a small size turbine and a more efficient charge air cooler to realize the low temperature cycle and guarantee the fuel economy at the same time.