Thermodynamic model and optimization of a miller cycle applied on a turbocharged diesel engine

Abstract

A new thermodynamic model for turbocharged diesel engines is developed for Miller cycle analysis and optimization. The effects of turbocharger efficiency, Miller degree, combustion mode, and air fuel ratio on engine efficiency, power, and NOx emissions are analyzed by the model. Engine performance is optimized by the thermodynamic model under the constraints of maximum cylinder pressure and NOx emissions. Although the Miller cycle is beneficial for NOx emission control, it has adverse effects on engine thermal efficiency and power without parameter redesign. Turbocharger efficiency is a key factor in highly boosted Miller cycle diesel engines. The trade-off relationships among thermal efficiency, break mean effective pressure, and NOx emissions can be improved remarkably by highly efficient turbochargers. Measures with high geometric compression ratio and boost pressure and intensified Miller degree must be applied to reduce NOx emissions and improve thermal efficiency simultaneously. The results provide guidance in designing a Miller cycle system for turbocharged diesel engines.