P. Belardini

Application of a reduced kinetic model for soot formation and burnout in three-dimensional diesel combustion computations

Using a modified version of the Kiva-2 code, three-dimensional computations of combustion and soot formation were performed, burning tetradecane and n -heptane in a direct injection, naturally aspirated diesel engine. A coupled soot formation and combustion model is proposed. Assuming acetylene as the crucial pyrolitic species, the model takes into acount the fuel-to-acetylene pyrolysis, acetylene oxidation, soot nucleation, and surface growth and soot oxidation. The numerical predictions are compared with the expermental data of heat-release patterns and with the in-cylinder measurements of acetylene concentration and soot volume fraction. C 2 H 2 data were collected using a fast-acting valve, while soot loading was measured with the two-color technique. The improved code is able to predict correctly the combustion and heat-release patterns of the two fuels without any retuning of the model constants. The computational results demonstrate that the reduced kinetic soot model is capable of predicting, with satisfactory accuracy, the local amount of soot and pyrolytic products in the combustion chamber, keeping the main features of the diesel combustion.

Combustion Patterns in Common Rail D.I. Engines Inferred by Experiments and CRD. Computations

Some particular features of combustion evolution and emission performance of new direct injection diesel engines for passenger cars are discussed. Two engines were employed for the experiments: a single-cylinder optical research engine and a real four-cylinder engine. The optical engine combustion system design was similar to the four-cylinder engine one. Both engines were equipped with a common rail injection system. Single-cylinder findings were verified with the four-cylinder tests and reproduced with the CFD simulation by KIVA3V code. High-speed visualization of spray and combustion processes indicated a strong sensitivityto the combustion system design and the chosen injection strategy. The analysis showed that the mechanism involved in the increase of the net soot mass emitted at the tailpipe, when pilot injection is active, is very complex, accounting for both chemical and physical effects of pilot products on main combustion evolution.

Combustion and pollutant emissions from light duty diesel engines: the influence of mixing process and transient operating conditions

Abstract The influences of transient operating conditions and mixing process on exhaust emissions of the direct injection (DI) diesel combustion system are pointed out. With the use of a transient dynamic facility the combustion process was characterized and the combustion parameters when employed in order to explain the emission behaviou of the engine. With the joint use of three dimensional modeling and field experiments two different combustion system were compared and the emission behaviou was fully explained. Finally a mixing parameter was defined allowing a more useful use of 3-D calculations to the design of the combustion system.