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The air entrainment of multi-hole diesel injection is investigated by high speed Particle Image Velocimetry (PIV) using a multi-hole common rail injector with an injection pressure of 100 MPa. The sprays are observed in a high pressure, high temperature cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a diesel engine during injection. Typical ambient temperature of 800K and ambient density of 25 kg/m3 are chosen. The air entrainment is studied with the PIV technique, giving access to the velocity fields in the surrounding air and/or in the interior of two neighboring jets. High acquisition rate of 5000 Hz, corresponding to 200 μs between two consecutive image pairs is obtained by a high-speed camera coupled with a high-speed Nd:YLF laser. The effect of neighboring jets interaction is studied by comparing four injectors with different numbers of holes (4, 6, 8 and 12) with similar static mass flow rate per hole.

Quantitative fuel concentration visualizations are carried out to study the mixing process between fuel and air in Direct Injection (DI) Diesel like conditions, and generate high quality data for the validation of mixing models. In order to avoid the particular complication connected with fuel droplets, a gaseous fuel jet is investigated. Measurements are performed in a high-pressure chamber that can provide conditions similar to those in a diesel engine. A gas injection system able to perform injections in a high-pressure chamber with a good control of the boundary conditions is chosen and characterized. Mass flow rates typical of DI Diesel injection are reproduced. A Laser Induced Fluorescence technique requiring the mixing at high pressure of the fluorescent tracer, biacetyl, with the gaseous fuel, methane, is developed. This experimental technique is able to provide quantitative measurement of fuel concentration in high-pressure jets.

A database of information concerning the spray development and pollutant formation in common-rail, direct-injection Diesel engine is constructed using a transparent model Diesel engine. Spray development is investigated using optical diagnostics: Mie scattering and Laser Induced Exciplex Fluorescence (LIEF) make possible qualitative visualization of liquid and vapor phases. The injection pressure/nozzle hole diameter is found to be the most important parameter (in the parameter range used for the study): it reduces the liquid penetration length and improves the mixing of vapor fuel. Direct imaging of combustion development shows the influence of different engine parameters on flame location. Comparison with measured vapor distributions shows the effect of thermal expansion on the vapor plume before any light from combustion is visible. Soot formation is investigated using Laser Induced Incandescence imaging.