Development Of Control System Of Variable Valve Mechanism And Experimental Study On Optical Engine

Diesel engine is facing heavy pressure from increasing global environmental pollution,increasing shortage of oil resources and increasingly stringent emission regulations and fierce competition from the new energy vehicles,improving its economy,power and emissions is imminent.EGR is a general technology to reduce NOx emissions of diesel engine,which can reduce the combustion temperature and control the combustion rate,but excessive EGR will lead to the increase of soot emission.In recent years,domestic and foreign researchers,according that NOx and soot of the diesel engine generates from different conditions in the cylinder,control combustion process,apply EGR technology,base on EGR stratification technology,distribute EGR to NOx production area and fresh air to soot production area,in order to solve the trade-off of NOx and soot in the combustion process.The engine intake system affects the distribution of EGR in the cylinder.The variable valve timing system can not only realize the internal EGR,but also affect the distribution of the external EGR in the cylinder through the flexible control of the valve timing,which can realize the different forms of EGR distribution.Optical testing method has the advantages of non intrusive,visual and visualization,and it has been widely used in the research of the distribution of working fluid,the pollutants formation and the development of flame in the cylinder.In this study,hydraulic-driven vertical four valve single-cylinder diesel engine with fully variable valve mechanism as the research object,developed the variable valve control system,the engine valve is flexible and controllable and the rational design of single-cylinder diesel engine,set up a PLIF optical test platform,explores the influence of tangential port introducing EGR and valve phase on the distribution of EGR in cylinder.The control system of variable valve mechanism is developed,and completed the hardware design,software design and on line monitoring and calibration function.Due to the delay of the hydraulic-driven valve movement,in order to control the accuracy of the phase control in the software design,the relationship between the engine speed and valve delay is studied based on the variable valve mechanism.The results show that when the speed is lower than 360r/min,there is no delay in the valve opening process.When the speed is higher than 360r/min,the valve opening delay angle is proportional to the engine speed.The valve closing delay always exists when the speed is higher than 240r/min,and has a linear relationship with the speed.Valve opening and closing time fluctuates in ± 2 degrees,which meets the test requirementsBased on the optical engine equipped with variable valve mechanism,the PLIF optical test platform is built,and the PLIF calibration test is carried out.By means of optical test,the influence of Tangential intake introducing EGR and valve timing on the distribution of EGR in cylinder was studied experimentally,The results show that the tangential port introducing EGR,keeps the intake advance angle is 14 degrees,40 degrees BTDC unchanged in compression stroke,the distribution of EGR in the cylinder was that EGR was thick at the top of cylinder and was thin at the bottom of combustion charmber,which tangential port can guide the gas to form the distribution that gas was thick at the top,thin at the bottom.The study on the influence of different valve timing on EGR distribution shows that the valve timing has a great influence on the distribution of EGR in the cylinder,which will directly affect the formation of NOx and soot.For the tangential port introducing EGR,intake advance angle of helical port is fixed at 14 degrees,change intake advance angle of tangential port,The gas that firstly enters the cylinder distributes at the bottom,and the gas that back enters the cylinder distributes at the top.Under the combined action of the valve timing and tangential port,When EGR is introduced into tangential port,the intake advance angle is less than 49 degrees,The EGR concentration at the top was greater than EGR concentration at the bottom.However,the EGR concentration in the top of the cylinder decreases with the increase of intake advance angle,the EGR concentration in the bottom of the cylinder increases,the difference of EGR concentration between the top and the bottom gradually decreased.When the intake advance angle is 49 degrees,the EGR concentration at the top is lower than EGR concentration at the bottom.