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The main objective of the present paper is the application of a detailed kinetic model to study diesel combustion in an optical accessible engine equipped with a common rail injection system. Three different injection schedules made of one to three consecutive injections are considered from both the numerical and the experimental point of view. The numerical model is assessed in such a way to assure its portability with respect to changing injection strategies. The employed detailed kinetic mechanism consists of 305 reactions involving 70 species and is included in the KIVA-3V code. The considered fuel has the liquid phase properties of the diesel oil, the vapor phase properties of C14H28. It is subsequently decomposed into n-heptane and toluene. The chemical solver is based on the use of the reference species technique and on the Partially Stirred Reactor (PaSR) hypothesis. These allow maintaining the computational cost within acceptable limits.

The present paper reports the results of the numerical simulations carried out by means of a modified version of the KIVA-3V code and of the comparison with experimental results obtained by using different optical techniques in a single-cylinder optically accessible diesel engine. The engine is equipped with a commercial four valves cylinder head and a second-generation, Common-Rail injection system. A detailed kinetic model consisting of 283 reactions involving 69 species is applied to simulate the combustion process and the soot and NOx formation. The fuel surrogate model consisting of two constituent components, n-heptane and toluene, approximating the physical and ignition properties of the diesel oil, is considered. The Partially Stirred Reactor (PaSR) assumption is adopted to maintain the computational cost within acceptable limits.

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.