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Diesel spray mixture formation is investigated at target conditions using multiple diagnostics and laboratories. High-speed Particle Image Velocimetry (PIV) is used to measure the velocity field inside and outside the jet simultaneously with a new frame straddling synchronization scheme. The PIV measurements are carried out in the Engine Combustion Network Spray A target conditions, enabling direct comparisons with mixture fraction measurements previously performed in the same conditions, and forming a unique database at diesel conditions. A 1D spray model, based upon mass and momentum exchange between axial control volumes and near-Gaussian velocity and mixture fraction profiles is evaluated against the data.

The sooting propensity of dual-fuel combustion with n-dodecane pilot injection in a lean-premixed methane-air charge has been investigated using an optically accessible Rapid Compression-Expansion Machine (RCEM) to achieve engine-relevant pressure and temperature conditions at the start of pilot injection. A Diesel injector with a 100 μm single-hole coaxial nozzle, mounted at the cylinder periphery, has been employed to admit the pilot fuel. The aim of this study was to enhance the fundamental understanding of soot formation and oxidation processes of n-dodecane in the presence of methane in the air charge by parametric variation of methane equivalence ratio, charge temperature, and pilot fuel injection duration. The influence of methane on ignition delay and flame extent of the pilot fuel jet has been determined by simultaneous excited-state hydroxyl radical (OH*) chemiluminescence and Schlieren imaging.

A tracer laser-induced fluorescence (LIF) technique for the visualisation of fuel distribution in the presence of oxygen was developed and then used sequentially with high speed chemiluminescence imaging to study the correlation between the mixing and auto-ignition processes of high pressure Diesel jets. A single hole common rail Diesel injector allowing high injection pressures up to 150MPa was used. The reacting fuel spray was 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. Both free jet and flat wall impinging jet configurations were studied. Several tracers were first considered with the objective of developing a tracer-LIF technique in the presence of oxygen. 5-nonanone was selected for its higher fluorescence efficiency.

A low swirl, low compression ratio engine with narrow fuel spray angle injector was used to investigate the cylinder wall wetting process of early direct injection strategies. A methodology was developed in order to detect liquid fuel impingement on the cylinder wall oil film. First, single injection tests were performed in order to investigate the effect of injection pressure and start of injection on the amount of fuel that can be injected in the combustion chamber without liquid fuel cylinder wall impingement. Then double injection strategies were performed to verify the existence of interactions between successive injections for early injection thermodynamic conditions. Finally an optimization of the injection strategy maximizing the fuel quantity without cylinder wall wetting is proposed. Results obtained for single early direct injection show that all conditions of injection timing during the intake stroke lead to cylinder wall wetting above a given injected mass.

Penetration and combustion of fuel sprays is studied in conditions similar to gasoline direct injection engines. A closed pressurized and heated injection cell is used. It is equipped with quartz windows providing large optical accesses. A homogeneous flammable mixture is introduced in the cell and ignited to raise the internal pressure and temperature. Liquid fuel is injected at the time when the desired thermodynamic conditions are reached. Conditions representative of late injection in a direct-injection engine are selected. Gasoline spray ignition and combustion is provided by a spark plug with long electrodes, locating the electrode gap right in the middle of the spray. The combustion does not reach the wall, which makes this experiment interesting for the validation of combustion in CFD codes. Two pressure swirl injectors with spray angles of 60 and 90 degree are used. The fuel is iso-octane with 5% 3-pentanone as tracer.

The fuel film thickness resulting from fuel spray impingement on a flat transparent window was characterized in a high pressure high temperature cell for various thermodynamic conditions, injection pressures, injection durations, fuel types and injector technologies by Refractive Index Matching technique. The ambient conditions at injection timing were similar to that of a direct injection spark ignition engine at Top Dead Center, with the distance between the injector tip and the impinging surface set to 10 mm. The spray axis was set normal to the rough transparent window surface at ambient temperatures of 453 K, 573 K and 673 K, and ambient densities of 5.0 kg/m₃, 6.0 kg/m₃ and 6.5 kg/m₃. Injection pressures of 100 and 200 bar were investigated. Three injector technologies were studied: piezo-electric, multi-holes and swirl types. Two fuels, iso-octane and model gasoline, were tested.

The influence of piston geometry on the in-cylinder mixture distribution and combustion process in an optically-accessible, direct injection HCCI Diesel engine has been investigated. A new, purpose-designed piston which allows optical access directly into the combustion chamber bowl permitted the application of a number of optical diagnostic techniques. Firstly, laser-induced exciplex fluorescence (LIEF) has been applied in order to characterize the fuel spray and vapor development within the piston bowl. Subsequently a detailed study of the auto-ignition and two-stage Diesel HCCI combustion process has been conducted by a combination of direct chemiluminescence imaging, laser-induced fluorescence (LIF) of the intermediate species formaldehyde (CH2O) which is present during the cool flame and LIF of the OH radical later present in the reaction and burned gas zones at higher temperature.