CFD Modeling of Gas-Fuel Interaction and Mixture Formation in a Gasoline Direct-Injection Engine Coupled with the ECN Spray G Injector

The thorough understanding of the effects due to the fuel direct injection process in modern gasoline direct injection engines has become a mandatory task to meet the most demanding regulations in terms of pollutant emissions. Within this context, computational fluid dynamics proves to be a powerful tool to investigate how the in-cylinder spray evolution influences the mixture distribution, the soot formation and the wall impingement. In this work, the authors proposed a comprehensive methodology to simulate the air-fuel mixture formation into a gasoline direct injection engine under multiple operating conditions. At first, a suitable set of spray sub-models, implemented into an open-source code, was tested on the Engine Combustion Network Spray G injector operating into a static vessel chamber. Such configuration was chosen as it represents a typical gasoline multi-hole injector, extensively used in modern gasoline direct injection engines. Afterwards, the Spray G injector was coupled with the Darmstadt optical engine and full-cycle simulations were carried out for three operating points, combining two engine speeds, respectively equal to 800 rpm and 1500 rpm, and two different engine loads, with pressures of 0.95 bar and 0.4 bar in the intake manifold. The case at 800 rpm and 0.95 bar represented the reference condition. By switching to 1500 rpm and 0.95 bar the effect of the piston speed on the in-cylinder flow and spray evolution was analysed, while the reduction of the intake pressure down to 0.4 bar, coupled with the engine speed of 800 rpm, allowed to study the effects of the engine load on spray evolution and mixture fraction formation. Furthermore, comparisons between the engine cases at 0.95 bar and the simulations in vessel allowed to understand the effects exerted by the turbulence generation on the spray morphology. A detailed post-processing was proposed for each condition. For the vessel, axial vapor and liquid penetrations were assessed, along with spray morphology and liquid mass distribution inside the jet. In the engine, quantities such as in-cylinder gas velocities, mixture fraction distribution and charge homogeneity were investigated. The achieved results demonstrated the potential of the computational fluid dynamics as an effective tool for direct-injection, spark ignition engines optimization towards the goals of emissions reduction and increased efficiency.