Improvement of the Control-Oriented Model for the Engine-Out NO _X Estimation Based on In-Cylinder Pressure Measurement

Nowadays, In-Cylinder Pressure Sensors (ICPS) have become a mainstream technology that promises to change the way the engine control is performed. Among all the possible applications, the prediction of raw (engine-out) NO_X emissions would allow to eliminate the NO_X sensor currently used to manage the after-treatment systems. In the current study, a semi-physical model already existing in literature for the prediction of engine-out nitric oxide emissions based on in-cylinder pressure measurement has been improved; in particular, the main focus has been to improve nitric oxide prediction accuracy when injection timing is varied. The main modification introduced in the model lies in taking into account the turbulence induced by fuel spray and enhanced by in-cylinder bulk motion. The effectiveness of the new model has been tested with data acquired during an extensive experimental campaign during which a 2.0l 4 cylinders Diesel engine, whose after-treatment system allows to fulfil the EU6 legislation limits, has been operated on the overall engine map. It is shown that, comparing measured and estimated NO_X on a wide range of engine settings, the improved model is quite effective in capturing the effect of injection timing on engine-out NO_X emissions: the average error between measured and estimated NO_X is reduced of about 10% while the correlation coefficient is increased from 0.86 to 0.97.