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This paper reports on the analysis of flame kinematics and cycle variation in port fuel injection (PFI) spark ignition (SI) engine. The engine was equipped with a four-valve head and with an external boost device. Different operating conditions were considered. Cycle-resolved digital imaging was used to investigate flame motion and the effects of an abnormal combustion due to the firing of fuel deposition near the intake valves and on the piston surface. Various algorithms are applied to the acquired images. Coefficients of Proper Orthogonal Decomposition (POD) were computed and used for a statistical analysis of cycle variability. The advantage is that the analysis can be run on a small number of scalar coefficients rather than on the full data set of pixel valued luminosity.

Nowadays HCCI combustion process is revealing the most useful technique for reducing pollutant emission from internal combustion engines. In the present paper, HCCI combustion was realized by means of single late injection at high pressure and heavy EGR, up to 50%. A transparent Direct Injection (DI) diesel engine equipped with high pressure Common Rail (CR) injection system was used. The engine was fed with commercial diesel fuel and ran in continuous mode. Digital imaging and spectroscopic techniques, with high temporal and spatial resolution, were applied to study the low temperature combustion process. Injection and combustion phases were analysed by digital imaging. Mixing process, autoignition and pollutants formation were investigated by Broadband Ultraviolet - Visible Extinction Spectroscopy (BUVES) and flame emission measurements. Radicals and species such as OH, CH and CO were detected in the combustion chamber.

Use of EGR (Exhaust Gas Recirculation) and after-treatment devices allows diesel engines to comply with actual emission regulations. In order to satisfy future emission standards it will be necessary a careful analysis of peculiarities and limits of the current systems for pollution control and of their possible influence on production of other harmful substances. Engine control maps determine optimal EGR considering a trade-off between NOx and smoke emissions. However, actual control strategies do not consider, in the definition of optimal EGR, its effect on particle number density, which has a great importance for the optimal functioning of after-treatment systems. In this paper a soft computing model that gives real time information on the characteristic of exhaust particles, is proposed. The model, by using a neural network approach, is able to provide information on the effect of EGR on particulate mass concentration and particle size distribution.

Flame images are collected and Proper Orthogonal Decomposition (POD) coupled with interpolation is applied to reconstruct information in between consecutive measurements. The POD basis is determined from samples (“snapshots”) taken during experiments conducted on an optically accessible Spark Ignition Engine. Reconstructed luminosity fields are then compared with the available (but not used in the computations) experimental data. In a second application, dynamic in-cylinder pressure data collected together with images are compared to those of a “base” cycle and the differences are used to weight the “snapshots” collected over different cycles. By this means, pseudo-cycle-resolved image sequences can be obtained.

Homogeneous Charge Compression Ignition (HCCI) combustion was applied to a transparent diesel engine equipped with high pressure Common Rail (CR) injection system. By means of CR system the quantity of fuel was split into five injections per cycle. Combined measurements, based on digital imaging and spectroscopic techniques, were applied to follow the evolution of HCCI combustion process with high temporal and spatial resolution. Digital imaging allowed to analyse injection and combustion phases. Broadband ultraviolet - visible extinction spectroscopy (BUVES) and flame emission measurements were carried out to evaluate the presence of radicals and species such as HCO, OH, CH, and CO. In particular, BUVES measurements were performed to follow fuel oxidation, and pollutant formation and oxidation. During injection and cool combustion, bands of aromatic compounds and alkyl peroxides, indicating fuel decomposition, and hydrogen peroxides were detected.

Broadband ultraviolet-visible extinction and scattering spectroscopy (BUVESS) and Laser Induced Incandescence (LII) were used at the undiluted exhaust of a Common Rail diesel engine for detection, sizing and counting nanoparticles. BUVESS and LII are powerful in situ and non intrusive techniques. BUVESS is based on multiwavelength extinction and scattering spectroscopy. It overcomes the intrinsic limitations of single wavelength techniques because it takes advantage of data at several wavelengths to retrieve primary particle size distribution with better accuracy. LII measures volume concentration and mean size of primary particles with a large measurement range, not limited by aggregate size. The optical results were compared with those obtained by conventional methods like opacimeter for mass concentration and Electrical Low Pressure Impactor (ELPI) for sizing.

Non-intrusive diagnostic techniques based on broadband (190-550 nm) extinction and scattering spectroscopy were applied to undiluted exhaust Common Rail (CR) diesel engine. The influence of engine speed and load on soot mass concentration, size distribution of emitted particles and NOx concentration was analysed. NOx concentration was evaluated by “in situ” ultraviolet-visible absorption measurements and compared with those obtained by conventional analyser. The extinction and scattering spectra were compared with those evaluated by the Lorenz-Mie model for spherical particles in order to retrieve the size, the number concentration of the emitted particles and particulate mass.

Spectroscopic measurement and high speed visualization were used in single cylinder, four-stroke DI diesel engine, optically accessible. It was equipped with a four valves head and fully flexible electronic controlled ‘Common Rail’ injection system. The effect of pilot and main injection on combustion process was evaluated. Mixing formation, autoignition and soot formation process were analyzed by broadband ultraviolet-visible flame emission spectroscopy and high-speed digital imaging. The autoignition phase occurred near the tip of the jet and was characterized by strong presence of OH radicals for both investigated conditions The presence of C2 and OH radicals strongly characterized CR diesel combustion process during soot formation and evolution. In particular, high presence of OH concentration for the whole process from the autoignition to the soot formation and successive phases contributes to lower soot levels.

Diesel combustion process was studied and characterized by digital imaging and ultraviolet-visible flame emission, extinction and scattering spectroscopy. Optical measurements were applied to a transparent diesel engine, realized by modifying a single cylinder, air-cooled, 4-stroke diesel engine by means of an external combustion chamber on the top of the engine, connected to the main chamber by a tangential passage. Diesel engine was equipped with a fully flexible electronic controlled ‘Common Rail’ injection system. Measurements were performed at 1000 rpm engine speed for two typical injection strategies. The first one consisted of a main injection in order to compare the results with those ones obtained by conventional injection system operating at low pressure. The other one was based on a pilot and main injection that is typical of current direct injection diesel engines.