Bizhan Befrui

Fuel System Pressure Increase for Enhanced Performance of GDi Multi-Hole Injection Systems

The progressive trend towards the GDi engine downsizing, the focus on better fuel efficiency and performance, and the regulatory requirements with respect to the combustion emissions have brought the focus of attention on strategies for improvement of in-cylinder mixture preparation and identification and elimination of the sources of combustion emissions, in particular the in-cylinder particulate formation. This paper discusses the fuel system components, injector dynamics, spray characteristics and the single cylinder engine combustion investigation of a 40 [MPa] capable conventional GDi inwardly-opening multi-hole fuel injection system. It provides results of a study of the influence of fuel system pressure increase between 5 [MPa] to 40 [MPa], in conjunction with the injector static flow and spray pattern, on the combustion characteristics, specifically the particulate and gaseous emissions and the fuel economy. The combustion data shows the marked effect of fuel pressure increase on reduction of the combustion emissions and improvement of fuel consumption. It also illustrates an influence of the injector specifications that is evident at all system pressures.

GDI Multi-Hole Injector Internal Flow and Spray Analysis

The spray plume geometry and fuel atomization characteristics of the gasoline direct-injection (GDI) multi-hole injectors are of paramount importance with respect to the GDI engine homogenous-charge combustion and emission characteristics. A major component of the GDI combustion system development is the optimization of the spray-targeting and mixture preparation. Significant R&D efforts are directed towards optimization of the nozzle design and the manufacturing process in order to achieve optimum multi-plume spray characteristics. The Volume-of-Fluid Large-Eddy Simulation (VOF-LES) of the injector internal flow and near-field primary atomization has been receiving attention as a tool to enable analysis of the influence of nozzle design on the key spray parameters and reduce reliance on hardware trial-and-tests for multi-objective spray optimizations. In combination with current state-of the-art computational fluid dynamic (CFD) methods for simulation of spray atomization and transport processes, they afford a notable capability to expedite the injector valve-group and spray targeting optimization in order to reduce the time and costly hardware iterations. The present publication reports studies of a GDI multi-hole injector valve-group and the corresponding spray plumes, with the aid of the current state-of-the-art CFD methods. The LES method is applied to study the structure and primary breakup of a single plume from a GDI multi-hole injector. A complementary study comprising the injector internal flow with the conventional Reynolds-averaged CFD method, coupled to the simulation of the spray atomization and transport processes using the stochastic Discrete Droplet method, has been performed. The correlation of simulated spray geometry with experimental data is encouraging.

Primary Atomization of a GDi Multi-Hole Plume Using VOF-LES Method

This study is concerned with quantitative analysis of the primary atomization, regarding the droplet size-velocity distribution function, of a multi-hole GDi plume through application of the Volume-of-Fluid Large Eddy Simulation (VOF-LES) method. The distinguishing feature of this study is the inclusion of an accurate seat /nozzle flow domain into the simulation. A VOF-LES study of the seat-nozzle flow and the near-field primary atomization of a single plume of a GDi multi-hole seat is performed. The geometry pertains to a purpose-built 3-hole GDi seat with three identical flow hole and counter-bore nozzles, arranged with 120° circumferential spacing. The VOF-LES prediction of the jet primary breakup structure and near-field macroscale is compared with spray imaging data. The droplet size and velocity distributions within a 4mm vicinity of the nozzle are analyzed. The results show production of a wide droplet size distribution through the jet primary atomization. Analysis of the droplet-size probability function, through comparison with the jet turbulence and KelvinHelmholtz parameters, indicates the dominant role of jet turbulence in the primary breakup process. The simulation results, in the form of the droplet size probability function and the joint droplet size-velocity distribution function, enable a complete description of the plume initial conditions for Lagranagian spray simulation.

A Comparative Study of the Fuel Pressure and Temperature Effects on the GDi Multi-Hole Spray

The gasoline direct injection (GDi) engine cold-start emissions of unburned hydrocarbons (UHC) and particulate emissions, prior to the full catalyst warm-up, are a substantial source of engine emissions and the primary challenge to meet the Euro6D and US Tier5 emission regulations. Figure 1 presents typical accumulated particulate emissions from a GDi engine, with homogeneous combustion operation, under the new European drive cycle (NEDC). It illustrates the large proportion of particulate emissions during the engine cold-start phase.