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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.

More emissions are produced when Diesel engines operate in the transient state than in the steady state. This discrepancy is due to mismatching between the air-charging system and the fueling system. Moreover, the difference in the response time between the intake pressure and the exhaust pressure caused by turbo-lag leads to an excess supply of EGR. In this study, a model that can calculate the EGR rate of the intake gas was developed. In the model, temperatures of the air, the EGR gas and the mixture gas were measured with thermocouples which have a fast response. The EGR rate was calculated through the energy balance equation considering heat transfer. Moreover, the estimated EGR rate was applied to a closed-loop control system that receives feedback from 50 % of the mass fraction burned (MFB50) by a 2.2 L Diesel engine. When there is a difference between the target EGR rate and the estimated EGR rate, the target MFB50 can be modified.