Predicting NOx emissions in diesel engines via sigmoid NARX models using a new experiment design for combustion identification

•Data-driven modeling of diesel engine NOx emissions using sigmoid NARX model.•A new design of experiments which include both chirp and ramp-hold signals.•Reduction of testing time and improved modeling accuracy in transient cycle.•An easy-to-interpret map as a convenient means for suitable parameter selection.•Higher than 80% and 70% steady-state and transient validation accuracies.