Evaluation of electrically heated catalyst control strategies against a variation of cold engine start driver behaviour
Paper in proceeding, 2022
An electrically heated catalyst (EHC) in the three-way catalyst (TWC) aftertreatment system of a gasoline internal combustion engine (ICE) provides cold engine start exhaust pollutant emission reduction potential. The EHC can be started before switching on the ICE, thereby offering the possibility to pre-heat (PRH) the TWC, in the absence of exhaust flow. The EHC can also provide post engine start heat (PSH) when the heat is accompanied by exhaust mass flow over the TWC. A mixed heating strategy (MXH) comprises both PRH and PSH. All three strategies are evaluated under a range of engine start variations using an ICE-exhaust aftertreatment (EATS) simulation framework. It is driven by an engine speed-torque requested trace, with an engine-out emissions model focused on cold-start, engine heating and catalyst heating engine measures and a physics- based EATS with EHC model. Engine-start idle, strategic air-fuel ratio control and retarded ignition timing are the main engine control measures used to control cold-start emissions. These control measures are hindered by variation in vehicle idle and high engine power demand. In this paper, the sections of vehicle idle are varied in duration and position within the drive cycle. Drive cycles are constructed with different speed-torque segment combinations to reflect a distribution of emission intensive cycles. To evaluate the performance of cold-start control strategies, an equivalent exhaust emission for the electrical energy consumed by the EHC is proposed. A simple controller based on such a metric is presented. EHC PRH is found to result in the best pollutant conversion with some minor exceptions in comparison to the other strategies, though it might be difficult to enforce in practice. The presented evaluation framework including the construction of drive cycles along with the evaluation metric, could help develop novel cold engine start control strategies.