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Analysis of Combustion and Emissions in a EURO V Diesel Engine by Means of a Refined Quasi-Dimensional Multizone Diagnostic Model
Abstract:
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 NOx (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.