Research On The Diesel Engine Spiral Airway-In-cylinder Flow Field Analysis And Intake Charge Control

The close cooperation between the air movement in the cylinder of the diesel engine and the fuel injection determines the combustion quality in the cylinder.The form of airflow organized by the intake port of the diesel engine directly affects the mixing of air-fuel,and will also have a greater impact on the flame propagation rate.By analyzing the intake port-cylinder flow fields of diesel engine,this paper grasps the corresponding relationship and change law of the two,and based on it,reasonably organizes the form of air movement in the cylinder,realizes stratified combustion,and then studies EGR stratified combustion on the engine.Combustion and emission characteristics impact studies.Research on intake port-cylinder steady/transient flow fields analysis shows,the distribution of particle density corresponds with velocity vector on the near wall surface of cylinder,and that streamlines near the cylinder wall also correspond with gradient boundary lines of the tracer concentration consistently.the intake air from the upper right section of the helical intake port is mostly distributed in the central area of the cylinder;the intake air from the upper left section rotates along the cylinder axis;the intake air from the lower left section moves close to the cylinder wall and makes a rotary motion to the lower part of the combustion chamber;and the intake air from thelower right section collides with the valve guide and the airflow is divided into two groups and runs in the opposite direction.By analyzing the transient flow fields in the cylinder,it is known that the swirl intensity of each radial section in cylinder and the?combustion chamber during the intake stroke is dominated by intake airflow,while the swirl intensity during the compression stroke is dominated by the piston movement.The swirl squeezed into the?combustion chamber is strengthened because of the shortening radius of rotation,whereas the swirl of air at the bottom of the combustion chamber is weakened by friction with the wall.According to the study of zoned air intake,in the four intake sections of the YN33 helical intake port,the intake air volume of the intake section on the lower right side of the intake passage is the most,accounting for 27.3%of the total intake air.The intake air volume of the upper left intake section is the least,accounting for 22.4%of the total intake air.The time-separated intake air indicates that the difference in the contribution of the four regional intakes to the total intake of the cylinder is determined by the intake of the front section and the intake of the latter section,and the influence of the intake of the latter section is greater.On the whole,the intake air in the front part of the cylinder will form the distribution characteristics of thin upper and thick lower;In the middle intake,The intake air in the upper left and lower left area of the inlet is more obviously distributed in the cylinder,The concentration gradient difference between the upper right zone and the lower right zone of the inlet is small in the cylinder;The rear section of the intake air will form a thick upper and thin lower distribution in the cylinder.The research on the swirl intensity in the cylinder by the key structural parameters of the intake port is carried out.The results show that when the YN33 intake port is rotated counterclockwise around the central axis of the valve,the swirl intensity in the cylinder increases.When the intake port is rotated clockwise,the swirl intensity in the cylinder is greatly reduced.The height of the YN33 inlet spiral chamber is increased or decreased,and the swirl intensity in the cylinder is reduced.As the distance between the YN33 intake port and the cylinder center axis increases,the swirl intensity in the cylinder decreases gradually.When the intake port is close to the cylinder center axis,the swirl intensity in the cylinder decreases first and then increases,and the increased swirl intensity is slightly higher than the original swirl intensity.The intake port structure parameters are studied for the annular stratification of the in-cylinder charge.The results show that under different intake port deflection angles,for the intake section the A and B zones,as the counterclockwise rotation angle of the intake port increases,the internal swirl intensity increases in the cylinder,and the swirl rotating motion enhances the guiding effect of the intake of the zone,so that the A and B zone intakes gradually form a more regular annular distribution in the combustion chamber.Under different screw chamber heights,as the height of the intake port spiral chamber increases or decreases,the B zone will be annular distribution in the combustion chamber tends to be regular,but due to the rotation angle of the B zone intake valve around the valve guide change,the distribution of high concentration CO₂ in the combustion chamber is also different.Under different intake port eccentric distances,the intake of Zone B,as the intake port is close to the cylinder wall,the annular distribution in the combustion chamber is more regular,and due to the decrease of the distance between the intake port and the cylinder wall,the high concentration CO₂ region that it is also closer to the cylinder wall,and as the intake port is away from the cylinder wall,the high concentration CO₂ area is also gradually approaching the cylinder center.In the D zone,when the eccentricity of the intake port increases,the inlet of the zone initially forms a circular distribution but is not obvious,and the concentration gradient in the combustion chamber is small at this time.The research on the combustion and emission characteristics of EGR axial and radial stratification in the cylinder shows that the cylinder pressure,cylinder temperature and cumulative heat release are significantly larger than AShom _EGR under Max-AS_EGR conditions.Compared with AShom _EGR,NO_X in the Max-AS_EGR cylinder increased by 4.9%,Soot decreased by 12.9%,and CO decreased by 11.6%.Compared with RShom _EGR,the Max-RS_EGR flame propagation rate is slowed down,which leads to a decrease in cylinder pressure and temperature.The pressure in the cylinder and the temperature peak drop by 0.3 MPa and 48K,respectively.The deterioration of combustion caused the fuel under Max-RS_EGR to be insufficiently burned,and the cumulative heat release was also reduced by 41J.Under Max-RS_EGR conditions,the NO_X in the cylinder decreased by 22.6%,the Soot increased by 19.9%,and the CO increased by10.7%.With the increase of the axial concentration gradient stratification,the amount of NOx production increased,but the increase was small,and the Soot and CO production decreased significantly.As the stratification of the radial concentration gradient increases,the NOx emissions are greatly reduced,but the Soot and CO emissions are greatly increased,and the in-cylinder combustion is rapidly deteriorated.