Convegni ATI - Accesso riservato soci CTI

Autore: M. Baratta, A. E. Catania, S. d’Ambrosio, A. Ferrari, R. Finesso, D. Misul, A. Mittica, E. Spessa

Collana: CA - 66 - Rende 2011

Note:
The paper describes multizone modeling approaches for the diagnostics of combustion processes and emission formation in Spark Ignition (SI) as well as Compression Ignition (CI) engines. With reference to SI engines, the diagnostic method is based on a quasi-dimensional multizone combustion model that takes the non-uniform spatial distribution of in-cylinder burned gas thermodynamic and chemical properties into account. The gas
content of the combustion chamber is split in the unburned region and the burned one, which in turn is divided into ‘zones’. Each of these zones is generated at a specified crank angle and no mixing occurs between them, so that temperature gradients
take place across the chamber. As far as temperature calculation is concerned, the energy conservation law is applied to each zone. The multizone thermodynamic approach for mass burning rate analysis is coupled with a CAD procedure for the computation of burned-gas mean expansion speed and burning speed. A new procedure for determining the start of combustion was embedded in the model. The NO calculation is performed on the basis of a six-reaction thermal formation mechanism and includes the contribution from the flame-formed. With reference to CI engines, a new multizone premixed-diffusive combustion model has been developed, assessed and applied to the diagnostics of the burning processes and emission formation in conventional and Premixed Charge Compression Ignition (PCCI) diesel engines. The model is based on the Dec conceptual scheme, which considers combustion as a two-stage quasi steady process: all fuel particles undergo a first rich premixed combustion phase, whose products complete their
oxidation in close-to-stoichiometric conditions at the jet periphery, through a diffusion flame. The combustion chamber contents have been divided into several homogeneous zones, to which the energy and mass conservation principles were applied. The computed thermodynamic and thermochemical properties in the burned gas zones allowed a the post-processing analysis to be made of the nitric oxides (NO), particulate matter (PM) and of the carbon monoxide (CO) formation.