Analysis of Combustion and Emissions in a EURO V Diesel Engine by Means of a Refined Quasi-Dimensional Multizone Diagnostic Model 2012-01-1066

A quasi-dimensional multizone combustion model, that was previously developed by the authors, has been refined and applied for the analysis of combustion and emission formation in a EURO V diesel engine equipped with a piezo indirect-acting injection system.

The model is based on the integration of the predictive non-stationary variable-profile 1D spray model recently presented by Musculus and Kattke, with a diagnostic multizone thermodynamic model specifically developed by the authors.

The multizone approach has been developed starting from the Dec conceptual scheme, and is based on the identification of several homogeneous zones in the combustion chamber, to which mass and energy conservation laws have been applied: an unburned gas zone, made up of air, EGR (Exhaust Gas Recirculation) and residual gas, several fuel/unburned gas mixture zones, premixed combustion burned gas zones and diffusive combustion burned gas zones. The fuel parcels first undergo a premixed combustion phase; if the latter occurs in rich conditions, the incomplete combustion products are oxidized by a stoichiometric diffusive flame at the periphery of the jet.

The 1D spray model is capable of calculating the mixing process dynamics of the fuel parcels with the unburned gas, starting from the experimentally derived injection rate, and of evaluating the equivalence of the mixture zones as a function of time. The oxidation rate of the mixture zones is derived from the experimental pressure trace, which is used as an input quantity for the model, since the approach is of the diagnostic type.

The main model outcomes are the in-chamber mass and temperature evolutions of the different zones, which are used for the subsequent implementation of the submodels that are capable of evaluating the formation of NO_x (Nitrogen Oxides), CO (Carbon Monoxide), soot and THC (Total Unburned Hydrocarbons).

In the present paper, the quasi-dimensional model has been refined by means of the implementation and assessment of a specific submodel which is used to evaluate the post-combustion mixing dynamics of the burned gases with the surrounding unburned gas. A detailed comparison between the results obtained with the original and the refined approaches has been carried out, and the main effects on the pollutant formation submodels have been analyzed in great detail. The complete model, including the post-combustion dilution of the burned gas, was then applied to investigate the effects of different injection calibration parameters, such as rail pressure, number of injection shots, and DT (dwell-time) between the pilot and main injections, on combustion and emissions, with particular reference to the interaction between the spray dynamics and the soot formation process.