Numerical Simulation Of Air-Fuel Mixture Formation In Gasoline Engine

With intensified of the energy crisis and the increasingly stringent of the laws on emissions, there is a growing high demand on engines. They are expected to be higher-efficiency, more economy and lower-pollution. Various new techniques, such as electronic control and variable valve timing, have been successively applied on the engine. After further studying on these techniques, it can been seen that the core to master these techniques is to understand the mechanical theories of gas flow characteristics in the intake port and cylinder engine, fuel injection characteristics and air-fuel mixing characteristics.Numerical simulation technology is a method that uses the computer to calculate numerical solution and display simulative images, and quantitatively describes flow field numerical solution on certain time and space. With the rapid development of computer technology, computational fluid dynamics, calculating heat transmission and further research on other basic theories, the numerical simulation method has gained more and more attention, and it is widely used to study the working process of the engine.Combining the two aspects mentioned above, three dimensional transient simulation technologies are used to simulate the air intake,fuel injection, air-fuel mixing and combustion process of two four valve port fuel injection gasoline engine(one is a VVT engine). The impact of different injection parameters and valve timing on the air-fuel mixing process is analyzed.This paper expounds the methods which are used to calculate the working process including air intake, oil injection, air-fuel mixing and combustion of the gasoline engine by using numerical simulation. The steady-flow experiment is applied to achieve the steady-flow characteristics of an intake port. Then the steady-flow characteristics of the intake port is calculated and compared with the results of the experiment so as to verify the accuracy of numerical simulation.Three-dimensional dynamic grids model is built for a four valve port fuel injection gasoline engine. The boundary conditions are achieved by AVL-BOOST software. AVL-FIRE is used to do the numerical simulation of the gasoline engine, including air inflow, fuel injection, mixing and burning process. With different injection time (including close valve injection and open valve injection), spray cone angles, the position and direction of the injector in the air-fuel mixing process, the author calculates the mixing process to study the effect of injection parameters on the air-fuel mixing. The combustion process under original conditions is calculated and analyzed.Different sets of dynamic grids are built according different valve timing for another VVT gasoline engine. The boundary conditions are also achieved by AVL-BOOST software. The AVL-FIRE software is used to calculate the air intake process under full load conditions to analyze the influence of intake valve timing on the intake process. The air-fuel mixing process of three different valve timing are calculated under cold start conditions to analyzes influence of intake valve timing on air-fuel mixing process under this condition.