The present work has the aim of developing a semi-empirical
correlation to estimate the NO₂/NOx ratio as a function
of significant engine operating variables in a modern EURO VI
diesel engine.
The experimental data used in the present study were acquired at
the dynamic test bench of ICEAL-PT (Internal Combustion Engine
Advanced Laboratory at the Politecnico di Torino), in the frame of
a research activity on the optimization of a General Motors Euro VI
prototype 1.6-liter diesel engine equipped with a single-stage
variable geometry turbine and a solenoid Common Rail system. The
experimental tests were conducted over the whole engine map.
A preliminary analysis was carried out to evaluate the
uncertainty of the experimental acquired data and the
NO₂/NOx ratio. The main engine variables which were
expected to be related to the NO₂ formation were then identified,
and a second-order polynomial model was introduced to model the
NO₂/NOx ratio as a function of the abovementioned
related engine variables. All the input variable combinations were
considered in the investigation, in order to identify the most
important for the evaluation of the NO₂/NOx ratio.
Finally, a simplified exponential correlation was established to
estimate the NO₂/NOx ratio, that could be used in
several applications, including feed-forward model-based combustion
control. The model was tested and validated on a NEDC cycle (New
European Driving Cycle).