The Numerical Investigation On The Intake Process Of High Efficiency Gasoline Engine For Hybrid Vehicle

The issue of energy saving and emission reduction are difficult to be solved in the development of internal combustion engine.The gasoline direct injection(GDI)engine combines advanced engine technologies such as turbocharging,variable valve timing,exhaust gas recirculation,and high tumble ratio intake system to improve engine performances.In order to improve the thermal efficiency of GDI engine for hybrid vehicle,improving the quality of mixture during the intake process is really important.AVL-FIRE software was selected to simulate the steady-state intake process of a high-efficiency gasoline direct injection engine.The influence of masking,a kind of air flow barrier which locates at the lower outlet of intake port,on the tumble ratio,discharge coefficient and flow field in cylinder of the intake process was studied.Masking models with different structure parameters were established and simulated,which provides the reference for optimization of the high tumble intake system.Firstly,the steady-state intake simulation model of the GDI engine intake port was established to simulate by AVL-FIRE.The discharge coefficient and the tumble ratio at each valve lift were obtained.Compared with the steady-state intake process experimental result,the maximum error at each valve lift is less than 7% and the error of average tumble ratio is less than 4%,which are able to verify the accuracy of the simulation model.In order to analyze the impact of masking on the intake process,according to the structure of the original high tumble intake port,the angle between the intake valve axis and the cylinder center line is changed and obtain three intake ports whose angles are 15°,20° and 25°,respectively.Masking is added on the different angles intake ports to simulate the effect of masking on the tumble motion.Simulation results show that average tumble ratio improves while the angle increases,but average discharge coefficient decreases.In addition,average tumble ratio raises and average discharge coefficient diminish after adding the masking.At the small valve lift,the tumble ratio significantly increases,while the discharge coefficient reduces.At the large valve lift,the tumble ratio decreases slightly and the discharge coefficient increases slightly.It's necessary to study the impact of masking structure on intake process.In order to analyze the influence of masking structure parameters on the intake process,the masking structural parameters such as width,height,fillet radius and circumferential range on the high tumble intake port with the 20° angle were changed.Among these parameters,in a certain degree,reducing the width,fillet radius and increasing height,circumferential range can improve average tumble ratio but decrease average discharge coefficient.Masking height has the most significant impact on the steady-state intake process.When the masking height varies from 1mm to 5mm,the tumble ratio and discharge coefficient curves have the biggest change.The average tumble ratio raise by 6.4% while the average discharge coefficient decrease by 11.4%.As for the masking width changes from 1mm to 0.2 mm,the average tumble ratio add by 1.9% but average discharge coefficient reduce by 5.8%.While fillet radius changes from 3mm to 1mm,the average tumble ratio add by 3.9% but average discharge coefficient reduce by 4.1%.As circumferential range changes from 90° to 180°,the average tumble ratio raise by 2.4% but average discharge coefficient reduce by 3.1%.In addition,the distribution of flow field in cylinder changes,which has impact on the flow separation at the intake port outlet and distribution of turbulent kinetic energy in the cylinder.