Abstract
KEYWORDS – CFD simulation, mixture formation, spark ignition engine, single cylinder engine, engine testing
ABSTRACT
The flow phenomena during the intake process has a great influence on mixture formation prior ignition. CFD analyses on intake process can offer important data on volumetric efficiency for a spark ignition engine. Thus, the combustion quality can be estimated and moreover it can be verified by experimental research, on a test bench.
The main objective of the paper is to obtain a valid CFD analysis concerning the mixture formation for an experimental spark ignition engine. The engine is a research gasoline single cylinder engine used for thermodynamic tests and is located at the Research Institute of Transilvania University of Brasov.
In order to obtain good simulation results, the complete gas exchange cycle was simulated. In order to compare the results obtained during simulation with the measurements on the running engine, the high accurate 3D model of the real combustion chamber and other supplementary geometry due to the particular shape was used, since the accurate 3D model of the combustion chamber was reconstructed using high end touch probe 3D scanning technology.
The intake process was intended to be simulated step by step using CFD analysis. In order to solve a complex physical problem, simplifications and idealizations were successively made until reaching a simulation model able to follow the real physical processes. The main reason for this was to ensure an accurate simulation model, since the 3D geometry is very detailed and is unstable during simulation, especially when applying moving mesh. These simulation strategies are used to simulate piston travel and poppet valves lift.
Moreover, a properly tuned simulation model may offer possibilities of further customizing it. For example, once the simulation fully runs, supplementary strategies may be added, such as simulating port injection and direct injection with different injection laws which can also be experimented on the tested engine. In order to simulate fuel injection, the two-phase fluid flow physics has to be added to the simulation too.
The CFD analysis method for the intake phenomena and mixture formation can be then resumed to a two-phase fluid flow combined with moving mesh, deformed mesh and automatic mesh refinement.
The results obtained may provide information on the flow phenomena through the intake port, such as pressures, temperatures, fluid velocities and fuel mass fractions. Such parameters can also be measured directly on the running engine, at the testing cell.