Study On Reducing NOx Emissions Of Diesel Engine Achieved By Miller Cycle And Variable Valve Actuation

Although diesel engines remain the fuel economy leaders, the drive for improvements in fuel efficiency remains strong. In particular, as emission regulations on diesels increase, it is a challenge to maintain, let alone reduce fuel consumption. Therefore, many technologies are being examined to improve the emissions and fuel consumption tradeoff. One of the technologies being examined for diesels is variable valve actuation (VVA) which is proved preponderant in actual application.The paper sorts most of variable valve timing actuation researched by domestic and overseas institutions according to the principle of structure and analyzes the characteristic and shortage of systems. Elaborating the design of fully variable valve system working principle, design concept and structure arrangement. To obtain appropriate valve lift curve based on valve lift profile of TBD314diesel engine, adjusting the opening and closing time of solenoid valve according to the need for numerical simulation of miller cycle. Establishing mechanical hydraulic model of the experiment system by AVL Hydsim to guide the optimization experiment set of controllable parameters in order to save cost and time simultaneously.Then paper simulates working process of the object engine applying Boost software for one dimension numerical in which the valve lift curve is obtained through the experiment to implement the miller cycle. Impacts of performance on engine achieved by miller cycle and valve overlap period are analyzed. Simulation results show that the valve timing moment influence on the charging process significantly. The miller cycle achieved by early intake valve closing (EIVC) can reduce the temperature in cylinder effectively, thus reducing NOx emission, and with the increase of advanced angle the decreasing amount increased obviously. This is one of the best measures to drop the NOx emission. While late intake valve closing (LIVC) is adopted to realize the miller cycle, the decreasing amplitude of temperature in cylinder and NOx is less than that in EIVC. In conclusion, according to the different performance requirements can adopt different ways to realize miller cycle has produced important influences on performance of the engine.