Effects Of Fully Hydraulic Variable Valve System On Combustion Process Of Diesel Engine

Traditional diesel engine emits high emissions because of its characteristics of diffusion combustion mode,thus how to reduce the exhaust emissions and improve the thermal efficiency of diesel engine have been focused.Fully variable valve system(FVVS)can realize continuous adjustment in the valve lift,opening duration as well as intake valve closure(IVC),and has great significance in reducing fuel consumption,improving engine performance and reducing emissions pollution.A self-developed fully hydraulic variable valve system was used in this paper.The effects of EIVC on combustion were studied,and the main work is as follows:(1)The structure and working principle of the FVVS are introduced.The system is mainly composed of driving mechanism,controlling mechanism,and seating mechanism.The structure and working principle of the controlling mechanism are also presented.The results of lift measurement show that the FVVS can realize continuous adjustment in the maximum valve lift,opening duration as well as timing,and therefore can be used to firing bench.(2)A test bench was set up.The fully hydraulic variable valve system was installed on the SD2100TA diesel engine.The first cylinder remained unchanged valve timing,and the second cylinder used early intake valve closure.The bottom camshaft of the original machine was transformed to overhead camshaft,and inlet and exhaust cam were integrated on the same camshaft,making the installation of the FVVS easy and compact.To conveniently measure air mass flow and exhaust temperature,the integral intake an exhaust pipes were changed into independent type.(3)The measurement of indicator diagram and data processing were introduced.In order to eliminate the random error in measurement process,the cycles were averaged to eliminate this error.In the process of cylinder pressure curve being used to calculate the pressure rise rate and the heat release rate,it is necessary to filter and smooth pressure data.This paper uses the Butter-Worth filtering and five point three times smoothing methods to calculate pressure rise rate and the heat release rate,and the calculated curves are of clearly identification.(4)The experimental results show that EIVC can effectively reduce the maximum combustion pressure,prolong the ignition delay period,and make the combustion phase delay.At light loads,the peak heat release rate decreases with the advance of IVC,and at high loads,the peak heat release rate increases with the advance of IVC.The peak value of pressure rise rate and heat release rate show the same trend.At light loads,the maximum pressure rise rate decreases with the advance of IVC,and at high loads,the maximum pressure rise rate increases with the advance of IVC.EIVC can effectively reduce the air mass,and improve the exhaust temperature,making the post-processor catalyst work in high efficient area at light loads.EIVC can reduce the maximum combustion pressure under the premise of nearly unchanged indicated thermal efficiency,lowering mechanical load.