Supervisory control of complex propulsion subsystems

Doctoral thesis, 2022

Modern gasoline and diesel combustion engines are equipped with several subsystems with the goal to reduce fuel consumption and pollutant exhaust emissions. Subsystem synergies could be harnessed using the supervisory control approach. Look-ahead information can be used to potentially optimise power-train control for real time implementation. This thesis delves upon modelling the exhaust emissions from a combustion engine and developing a combined equivalent objective metric to propose a supervisory controller that uses look-ahead information with the objective to reduce fuel consumed and exhaust emissions.

In the first part of the thesis, the focus is on diesel engine application control for emissions and fuel consumption reduction. Model of exhaust emissions in a diesel engine obtained from a combination of nominal engine operation and deviations are evaluated for transient drive cycles. The look ahead information as a trajectory of vehicle speed and load over time is considered. The supervisory controller considers a discrete control action set over the first segment of the trip ahead. The cost to optimise is defined and pre-computed off-line for a discrete set of operating conditions. A full factorial optimisation carried out off-line is stored on board the vehicle and applied in real-time. In a first proposal, the subsystem control of the after-treatment system comprising the lean NOx trap and the selective reduction catalyst is considered. As a next iteration, the combustion engine is added to the control problem. Simulation comparison of the controllers with the baseline controller offers a 1 % total fuel equivalent cost improvement while offering the flexibility to tailor the controller for different cost objective.

In the second part of the thesis, the focus is on cold-start emissions control for modern gasoline engines. Emissions occurring when the engine is started until the catalyst is sufficiently warm, contribute to a significant proportion of tailpipe pollutant emissions. Electrically heated catalyst (EHC) in the three way catalyst (TWC) is a promising technology to reduce cold-start emissions where the catalyst can be warmed up prior to engine start and continued after start. A simulation framework for the engine, TWC with EHC with focus on modeling the thermal and chemical interactions during cold-start was developed. An evaluation framework with a proposed equivalent emissions approach was developed considering the challenges associated with cold-start emission control. An equivalent emission optimal post-heating time for the EHC is proposed that adapts to information which is available in a real-time on-line implementation. The proposed controller falls short of just 1 % equivalent emissions compared to the optimal case.