Control-Oriented Statistical Model of In-Cylinder Pressure, Combustion Phasing, and Torque for Compression-Ignition Engines Operating with Low Cetane Fuels

Sustainable alternative fuels can reduce the carbon footprint of compression-ignition (CI) internal combustion engine powered vehicles. However, the diversity of ignition behavior in these fuels poses a challenge to achieving robust and efficient engine operation. Specifically, low cetane fuels with poor ignitability exhibit highly variable combustion phasing and torque production unless fuel is injected earlier during compression. The tradeoff is that earlier fuel injection may cause dangerously high in-cylinder pressure rise rates. Novel models that can simulate these competing behaviors are needed so that appropriate strategies may be developed for controlling combustion at low cetane fueling conditions. This work builds upon a previously developed model that simulates asymmetrical combustion phasing distributions as a function of fuel cetane, fuel injection timing, and electrical power supplied to an in-cylinder thermal ignition assist device. An extension of the model is presented in which the cycle-to-cycle phasing output is used to reconstruct in-cylinder pressure traces as a function of crank angle, by which indicated mean effective pressure (IMEP) can then be quantified. Additionally, a functional form is parametrized for modeling maximum pressure rise rate (MPRR) in-cylinder. The model’s parameters are regressed using a total 60,000 engine cycles of experimental data from a commercial CI engine operating with four fuel blends with cetane number ranging from 25 to 48. This work marks the first time a low-order, control-oriented model simulates statistical distributions of phasing, IMEP, and MPRR. The model will facilitate the design and validation of closed-loop combustion control strategies that can enable CI engines to adapt to fuels with a wide range of ignition behaviors in adverse ambient conditions.