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An experimental study was performed to set up a new non intrusive technique to measure the rate of RBG (Residual Burnt Gases) in the cylinder of a firing SI (Spark Ignition) engine. The method is based on time-resolved in-cylinder CO2 concentration measurements; this molecule being used as an RBG tracer. The measurement technique that has been developed is based on the absorption of an IR (infrared) beam (around 4.3μm) that crosses the combustion chamber. The method was first set up in a heated and pressurized constant volume vessel that could be filled with controlled N2/CO2 mixture. Optical filters are used to select the useful part of the IR spectrum (the one which interacts with the CO2 absorption spectrum). It has been pointed out that the CO2 absorption coefficient is temperature and pressure dependent. Moreover, these dependencies vary with the absorption wavelength.

Planar Laser Induced Fluorescence has been set up to study in-cylinder production of NO in a realistic optical GDI engine. The excitation in the A-X (0,1) band of NO around 236 nm has been used for the first time. This was possible by means of an optical parametric oscillator laser system. A very careful choice of the excitation wavelength has been made with the assistance of a spectral simulation code of NO and O2 molecules. The first tests inside the engine running in the early injection mode were performed. Global equivalence ratio was set to 0.9 and NO concentration in the exhaust was about 3200 ppm. Pressure traces were recorded and a combustion analysis was performed. Direct flame and fluorescence images were acquired at numerous crank angle degrees between 320 CAD and 500 CAD (TDC=360CAD). Individual images depicted non-homogeneous NO distribution between 450 CAD and 500 CAD. Interference with oxygen seemed negligible whereas a strong absorption phenomenon was observed.

Combined Catalytic Hot Wires Probe (CHWP) and Fuel Air Ratio Laser Induced Exciplex Fluorescence (FARLIEF) techniques have been applied to a Gasoline Direct Injection Engine to characterize temporal and spatial evolution of the fuel/air ratio in the vicinity of the spark plug. The engine ran below stoichiometric with early injection (homogenous case taken as a reference) or late injection timing with a global equivalence ratio as low as 0.3. Under lean and late injection conditions, the temporal CHWP signal indicates that a rich vapor cloud is carried to the vicinity of the spark plug. CHWP and FARLIEF techniques show that the maximum equivalence ratio in the fuel cloud reaching the spark does not depend on the injection duration. Instead, the duration appeared to affect the size of this rich vapor pocket.

A Catalytic Hot Wire Probe (CHWP) technique has been developed to estimate local fuel concentration near the spark plug of a 4-valves Spark Ignition Engine. Various levels of gasoline concentrations, stratification and tumble levels have been achieved by modifying the injection and intake valve configurations. To validate this CHWP technique, local fuel concentration was also measured by using an optical diagnostic technique: Planar Laser Fluorescence (PLIF). Comparative results show good agreements, capabilities as well as limitations of both techniques. It can be concluded that CHWP is a minimised intrusive, inexpensive and easy technique which allows the evaluation of cylinder mixture preparation near the spark of an SI engine. This is a promising technique which could be used, in the future, to evaluate the mixture stratification in direct injection engines.