CFD analysis of fuel injection on a cold start system CFD analysis of fuel injection on a cold start system Martin Kessler Regis Ataides Victor Arume de Souza Cesareo de La Rosa Siqueira Alessandro F. R. de Miranda 1
Agenda 1. Introduction 2. Goals 3. Computational model Geometry / Computational Mesh Description of the Numerical Model Boundary Conditions 4. Results 5. Comments Introduction A proper and synchronized fuel injection is paramount for a good engine performance, since it provides a homogeneous combustion among the cylinders. In Brazil, around 90% of the vehicles sold today have Flexfuel engines, which accept both gasoline and/or alcohol, in any combination. In practice, most customers fill the tank with alcohol, l due to its lower price. Usually, however, it is more difficult to start the engine with alcohol then with gasoline, specially in cold regions. A cold start system has been developed by VW in Brazil to overcome this difficulty. 4 2
Goals Develop a computational model to study the fluid flow inside the fuel injection system; Study two geometric configurations for the fuel injection system and compare the results between them; Determine the mass flow distribution at outlets, for both geometries. 5 Computational Model First Geometry 1 2 Side injection 3 4 6 3
Computational Model Second Geometry 3 2 1 4 Center injection Computational Model Mesh 1st Model Tetrahedral mesh with ~ 1.4 million of elements Side injection 8 4
Computational Model Mesh 2nd Model Tetrahedral mesh with ~ 1.6 million of elements Center injection Description of the Numerical Model Assumptions: Incompressible Laminar: Re = 92 (based on pipe s diameter at inlet) Fluid properties: Fuel-oil-liquid Density = 960 kg / m^3 Viscosity = 0.048 kg/m s Steady-StateState and Transient simulations 5
Description of the Numerical Model Numerical Data: Solver: ANSYS CFX-11 Convergence Criteria: i < 1e-04 One phase Flow on a Steady state t simulation: Velocity at inlet Two phase Flow (air + fuel) on Unsteady simulation: Velocity at inlet Total time of simulation: 3s Computational Model Boundary Conditions Inlet: Velocity Outlets: Relative Pressure No Slip condition on the Walls 12 6
Streamlines Steady State Side Injection Central Injection Results Unsteady simulation Side injection 7
Results Unsteady simulation Side injection Results Unsteady simulation Side injection 8
Results Unsteady simulation Side injection Results Unsteady simulation Central injection 9
Results Unsteady simulation Central Injection Results Unsteady simulation Central injection 10
Results Unsteady simulation Central injection Results Flow on the Outlets (side injection) Saída a_2 Saída b_1 Flow 4 3 2 1 0 0,5 1 1,5 2 2,5 3 Time [sec] Output1 Output2 Output3 Output4 11
Results Flow on the Outlets (central injection) Saída a_2 Saída b_1 Flow 4 3 2 1 0 0,5 1 1,5 2 2,5 3 Time [sec] Output1 Output2 Output3 Output4 Mass flow distribution at the outlets Side injection State Outlet 1 Outlet 2 Outlet 3 Outlet 4 Steady 26.1% 25.2% 2% 24.5% 24.3% Unsteady 26.2% 25.2% 24.3% 24.3% Central Injection State Outlet 1 Outlet 2 Outlet 3 Outlet 4 Steady 24.8% 25.1% 25.4% 24.7% Unsteady 24.7% 25.1% 25.4% 24.8% The percentage for the transient analyses were obtained integrating over the entire computed time. 12
Comments Both analysis presented similar percentages of mass flow distribution on four outlets; On the model with side injection, the first outlet presented a larger mass flow than the other 3, with about 26.2% of total flow. On the model with central injection, the central outlets (2 and 3) showed larger mass flows than the side outlets (1 and 4). On the model with side injection, the fuel starts to be injected on the first outlet at 0.6 seconds, and on the last outlet (4th) at 0.9 second. On the model with central injection, the fuel starts to be injected on the central outlets at 0.9s second, and on the side outlets at 1.2 seconds. The central injection model took longer to stabilize the injection (about 3 seconds), while the side entrance model stabilized the injection in about 2 seconds. 25 13