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Despite the known benefits of direct injection spark ignition engines, PFI (port fuel injection) remains a relevant concept for cost-sensitive market segments. PN emissions limits is already expected for future emission legislations also for PFI engines (in China). This paper explains the mechanisms of PN production correlated with: CFD experiments on NA engine (natural aspirated engine) and turbo engine, Visiolution from AVL, Test bench measurements with gas analysis and PN measurement. Previous studies showed impact of the spray layout, injection timing, charge motion, operating points of the engine, temperature and fuel effect. This paper mainly focuses on the spray design of the injector through the pattern, the homogeneity of injector pattern having the main contribution in relationship with PN reduction.

Powerful 1D engine simulation softwares are widely used in the automotive industry to model internal combustion engines. The gas-dynamics exchange process is often well modeled whereas the combustion process is accounted for as a Wiebe function. As the combustion description is a key parameter for engine efficiency evaluation, predictive 0D modeling of heat release seems to be the issue in order to reliably model the cylinder pressure. A 0D phenomenological SI combustion model is proposed in order to predictively describe the heat release rate, this model being developed with Matlab-Simulink and coupled to GT Power. The model is based on eddy burn up approach and takes into account the geometry of the combustion chamber, the turbulent intensity, the RBG effects. As turbulence is a key feature in SI combustion modeling with eddy burn up approach, at this stage of the study turbulent kinetic energy data resulting from 3D CFD computation was employed.

In order to compare potential of VVL and GDI concept on a small displacement engine, tests have been made on a single-cylinder engine. Compared to multi-cylinder, single-cylinder offers good flexibility and accessibility for instrumentation but its gas dynamics non-representativeness has to be taken into account, especially for turbocharged engines. Concepts are tested on same engine basis but combustion system - chamber geometry, injection configuration, internal aerodynamics, valve train - is specifically designed for each version. Results confirm that homogeneous stoichiometric GDI is peculiarly adapted to turbo-charged conditions: GDI engine superior knock resistance allows low-end torque improvement and higher compression ratio. In addition to cooling effect, one of the advantages of direct injection is studied: ability to scavenge residual gases without directly transferring mixture to the exhaust. Some synergies between VVL and turbo-charging are also presented in the paper.

Tumble flow pattern, during the intake and compression strokes, is investigated on a four-valve, four stroke transparent single-cylinder research engine. Two-dimensional in-cylinder velocity distributions are measured with cross-correlation Particle Image Velocimetry (PIV) on planes both parallel and perpendicular to the piston. The velocity fields are obtained at several crank angles. The single-cylinder engine has a transparent quartz liner and an extended piston with a quartz top. PIV investigation in the different planes allows the tumble flow pattern to be deduced from the two-dimensional ensemble-averaged flow pattern. The tumble motion is similar to a 2D roll motion with a rotation axis deformed on the two extremities towards the piston head. With such a pattern, the two-dimensional velocity fields in horizontal sections exhibit two vortices in the upper part of the cylinder.

An experimental investigation is carried out on in-cylinder motion, during the intake and compression strokes of a spark-ignited multi-valve engine. This study is conducted on a single cylinder four valve research engine. The engine is equipped with several optical accesses on cylinder liner and cylinder head. The turbulence and local velocity in combustion chamber were measured by Laser Doppler Velocimetry. Furthermore, effects of different bowl shapes on turbulence, cycle by cycle flow variations, and tumble distortion were studied. Tumble velocity field exhibits a triplet vortices structure composed of one vertical and two horizontal vortices. This structure is induced during the inlet stroke, and remains during compression. In the latest stage of compression, tumble is converted into a pair of horizontal vortices. Velocity measurements in the cylinder show a precession motion of tumble center. Distortion of tumble is very unstable and perturbed with a flat top piston.

An experimental investigation is carried out on the effect of Swirl and Tumble on turbulence and combustion characteristics in four-valve spark ignition engines. This study is conducted on an optically accessed single cylinder research engine. The in-cylinder motion is varied by means of flow-control baffle located between the intake manifold and the cylinder head. Several baffle sizes and shapes have been designed to induce various in-cylinder flow fields. The equivalent angular speed of the tumble and swirl vortices, occurring inside the cylinder, are determined from Laser Doppler Velocimetry. Comparisons with measurements from a conventional steady flow rig which measures air motion speed with a paddle wheel anemometer are presented and show a good correlation between the two measurement techniques.