Control oriented engine model development for Model-based PPC control

In this work, a model-based control approach for Partially Premixed Combustion (PPC) engines is introduced. PPC is a next-generation combustion technology, which has the potential to achieve both ultra-low emissions and high efficiency. As the PPC concept is characterized by a complex chemical-physical process of low-temperature kinetic reactions, it lacks direct trigger of ignition and combustion as well as it is sensitive to varying operating conditions. These complex nature of PPC makes it challenging to control the combustion for optimum efficiency and emissions at broad engine operation with low cyclic variability and without exceeding the maximum allowed in-cylinder pressure rise rate or peak pressure. The nonlinear relationship between the control input and combustion system response makes that conventional lookup table-based control might need too many maps and calibration effort, thus no longer feasible for real operation scenarios. A model-based control approach is proposed to give proper reference for the feed-forward combustion control of PPC engines. The current study presents a simplified first principal model, which has been developed to provide a base estimation of the ignition properties. This model is used to describe the behavior of a single-cylinder heavy-duty diesel engine fueled with a mix of bio-butanol and n-heptane (80vol% bio-butanol and 20 vol% n-heptane). The model has been validated at 8 bar gross Indicated Mean Effective Pressure (gIMEP) in PPC mode. Inlet heating and inlet boosting have been implemented to simulate the variation of operating conditions. The in-cylinder pressure results show that, across the range of input conditions, the physics model is able to capture the auto-ignition characteristics and predicts the start of combustion within a ±2 degree crank angle. As a first step towards model-based control, this model is also been used to examine the effectiveness of combustion phasing control by variable valve timing.