Exhaust Heat Management Based On DI Engine’s Fully Hydraulic Variable Valve System

Under the current emission regulations,stricter requirements are imposed on engine NOx emissions.Currently,selective catalytic reduction technology(SCR)is a mainstream treatment method for NOx in diesel engines to treat exhaust emissions.There is a minimum requirement for exhaust gas temperature,but under urban road conditions,because diesel engines are frequently in low-load operating conditions when starting and stopping,it is difficult for the engine exhaust temperature to reach the minimum temperature limit for SCR after-treatment.In this paper,by modifying a two-cylinder naturally aspirated diesel engine SD2100TA,a fully hydraulic variable valve system(FHVVS)based on the independent research and development of the research group was added.The effect of the fully variable hydraulic valve on the intake,combustion and exhaust temperature of the diesel engine.The specific research content is as follows:(1)Measured the parameters of engine intake and combustion under different load,fuel advance angle,and intake valve closing angle under the SD2100TA diesel engine at 1200r/min and 1650r/min.The GT-Power simulation was established.The model determines the combustion model based on the main technical parameters of the experimental model and the heat release rate obtained from the experimental data processing.The comparison between the experimental data and the simulation data shows that the error is within the allowable range and meets the model calibration requirements.(2)EIVC can realize continuous adjustment of the engine’s excess air coefficient;closing the engine’s intake valve in advance can effectively reduce the maximum pressure in the cylinder when the engine is operating,improve the engine’s working condition,and help extend the life of the engine.(3)The effeect of the fully variable hydraulic valve on the combustion in the cylinder is studied.The early closing of the intake valve can reduce the total heat capacity of the working fluid in the cylinder and increase the combustion temperature.At the same time,EIVC will reduce the engine’s indicated thermal efficiency.This can be improved by delaying the fuel advance angle(4)The exhaust heat management of SD2100TA diesel engine is researched.The research shows that the EIVC and the early opening of the exhaust valve can significantly improve the exhaust temperature of the diesel engine at low and medium loads.However,opening the exhaust valve too early will cause the pressure in the cylinder to drop too fast,which will reduce the torque and reduce the engine’s power performance.Increasing the fuel supply advance angle will decrease the engine exhaust temperature and increase the combustion temperature in the cylinder,resulting in an increase in NOx;however,if the fuel supply advance angle is too small,the combustion center of gravity will be shifted backward,and the heat released by fuel combustion cannot be effectively used for piston work,thereby reducing the fuel economy of the engine;The back pressure can raise the exhaust temperature of the engine to a certain extent,but the excessive exhaust back pressure at the middle and high speed will cause the deterioration of fuel economy.