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Currently, diesel engine-out exhaust NOx emission level prediction is a major challenge for complying with the stricter emission legislation and for control purpose of the after-treatment system. Most of the NOx prediction research is based on the Zeldovich thermal mechanism, which is reasonable from the physical point of view and for its simplicity. Nevertheless, there are some predictable range limitations, such as low temperature with high EGR rate operating conditions or high temperature with low EGR rates. In the present paper, 3 additional considerations, pilot burned gas mixing before the main injection; major NO formation area; concentration correction, were applied to the previously developed real-time NO estimation model based on in-cylinder pressure and data available from ECU. The model improvement was verified on a 1.6 liter EURO5 diesel engine in both steady and transient operation.

Emission regulations and fuel economy regulations are becoming more severe simultaneously, and they give much issue for automotive diesel R&D society. Moreover, emission test cycles are getting more tough transient conditions, like as WLTP. To meet the emission regulations in this trend, in-cylinder combustion requires more precise control. Designing hardware robustly and improving controllable are possible solutions to accomplish the precise combustion control. On the other hand, combustion control based on in-cylinder pressure signal is helpful to control in-cylinder combustion directly. Combustion control using in-cylinder pressure signal is also known to be useful to reducing engine-by-engine exhaust emissions variation due to the manufacturing tolerance, variation of fuel specification and deterioration of engine component during the whole lifetime.