The minimisation of tail-pipe emissions and fuel consumption during cold-start can be viewed as a constrained optimisation problem involving many parameters. Examining this problem mathematically first requires an accurate and computationally practical model of the engine and exhaust system. This paper proposes such a model for use during the cold-start of a conventional spark ignition engine. This model uses as much physics-based modelling as is computationally practical for optimisation and control studies. It takes a given set of engine control inputs to simulate tailpipe CO, HC and NO emissions, and is both calibrated and validated using detailed measurements obtained on a transient engine dynamometer following the New European Drive Cycle (NEDC).

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The cold start emissions from gasoline fuelled vehicles are a major challenge when meeting vehicle emissions regulation. Vehicle manufacturers therefore undertake extensive design and testing of the entire exhaust and engine control systems, which is both time consuming and costly. This is particularly an issue with the growing number of control parameters in modern powertrains. This paper presents a methodology that integrates appropriate physics-based models of the engine and aftertreatment into a numerical optimisation scheme, and is proposed as a possible means of reducing this calibration effort. The methodology is demonstrated over a prescribed drive cycle by identifying the optimal spark timing trajectory that maximises fuel economy while meeting emissions constraints. The trends in the resulting control policy are explained and the results are validated where possible.