Estimation of the Engine-Out NO2/NOx Ratio in a EURO VI Diesel Engine

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.