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The liquid and vapor phases penetrations are important improvement parameters of DI Diesel combustion chamber conception. In this study the effects of the pilot injection timing on the main injection evolution and combustion are investigated using laser based optical diagnostics and 3D modeling. The pilot injection timing is shown to have a strong effect on the main liquid and vapor phases development and these results are more precisely depicted using 3D calculations. The mixing stated derived from laser induced fluorescence and thus the pilot injection combustion process are studied and are also shown to influence the main injection inflammation. These tendencies provide interesting insights in the comprehension of the physical phenomena occurring in a DI Diesel engine of production size.

A optical investigation of injection, and combustion process has been performed in order to understand auto-ignition phenomena into a small 4 cylinder DI Diesel optical engine. Measurements were obtained a representatives partial load condition, corresponding to a motored TDC temperature and density of 800 K and 20 kg/m3. A better comprehension of cyclic fluctuation of auto-ignition sites was provided by a double optical diagnostics set up. Laser induced fluorescence was applied on Diesel fuel liquid phase along with synchronous natural flame imaging. The auto-ignition process has been investigated by a new experimental set up. A spectrally resolved imaging of the first chemical reaction was performed and revealed errors induced by a pressure transducer analysis. A photomultiplier tube, sensible to the OH* radical emission's band was employed to approach the real auto-ignition delay.

A new phenomenological analysis of injection and combustion is established in an 4-cylinders DI Diesel engine of the production size class equipped with an inclined 5 holes injector. Measurements are performed at representative engine conditions for partial load. In a first part, the penetration of the liquid diesel fuel phase is visualized in the whole combustion chamber by simultaneous Laser Induced Fluorescence (LIF) and Mie scattering techniques. The experiments have revealed the influence of the injection timing on the spray penetration and dynamic. The interactions “spray/air motion” and “spray/combustion chamber” are analyzed along with the injection technology influence. In a second part, the auto-ignition and combustion are analyzed by a time resolved direct imaging of the chemiluminescence process.

A new phenomenological model of injection and auto-ignition is established in a 4-cylinder DI diesel engine of the production size class equipped with an inclined 5 holes injector. Measurements are performed at representative engine conditions for partial load. The penetration of the liquid phases is visualized in the whole combustion chamber by simultaneous Laser-Induced Fluorescence (LIF) and Mie scattering techniques. The autoignition and combustion are analyzed by a time-resolved direct imaging of the chemiluminescence process. Experiments based on the correlation of two separated images of the combustion phenomena in a single cycle have allowed a detailed comprehension of spatial and temporal description of the autoignition and reaction zones development. Several autoignition sites are revealed in the vicinity of the injector nozzle. The reaction zone is shown to develop independently and then to merge to a unique one in the whole combustion chamber.

The Lagrangian-Eulerian approach is commonly used to simulate engine sprays. However typical spray computations are strongly mesh dependent. This is explained by an inadequate space resolution of the strong velocity and vapor concentration gradients. In Diesel sprays for instance, the Eulerian field is not properly computed close to the nozzle exit in the vicinity of the liquid phase. This causes an overestimated diffusion that leads to inaccuracies in the modeling of fuel-air mixing. By now it is not possible to enhance grid resolution since it would violate requested assumptions for the Lagrangian liquid phase description. Besides, a full Eulerian approach with an adapted mesh is not practical at the moment mainly because of prohibitive computer requirements. Keeping the Lagrangian-Eulerian approach, a new methodology is introduced: the full Lagrangian-Eulerian Coupling (CLE).

The flow-field of an automotive DI Diesel engine is characterized by experiments in a motored engine using Laser Doppler Velocimetry and by CFD simulations. Only one cylinder is active and a specific swirling intake duct is used. Various bowls with different shapes are investigated: fiat or W-shaped bowls, with or without re-entrant. The influence of engine speed is also studied. The mean velocity and turbulence evolutions are measured with back-scatter LDV experiments using an optical access in an extended piston. The simulations are performed using the KMB code, a modified version of KIVA-II. Along with the detailed flow-field description, integral quantities characterizing the flow are derived. The comparison between LDV data and CFD results is shown to be satisfactory. The effects of geometry and engine speed on spatial profiles and temporal evolution of mean and turbulent velocities are correctly reproduced.