Control-oriented PCCI combustion timing model for a diesel engine utilizing flexible intake valve modulation and high EGR levels

This paper describes a simple, analytical, control-oriented and physically-based model for prediction of combustion timing during PCCI combustion. The model includes direct dependence on in-cylinder temperature, in-cylinder pressure, and the total in-cylinder O₂ mass fraction. It is extensively validated with experimental PCCI data from a multi-cylinder engine with almost exclusively stock hardware (stock pistons, injectors/nozzles, turbocharger, etc.) and variable valve actuation. The results show that across a wide range of input conditions the model predicts the start of combustion (SOC) within ±2°CA of the experimental values for all but one of the 119 data points. The experimental SOC ranges from as early as -19.3°CA to as late as +0.6°CA by heavily exercising the control authority over SOC provided by SOI_ecm, IVC/ECR modulation (ECR ranges from 12:1 to 18:1), and the engine´s air-handling system. This PCCI combustion timing model can be coupled with a gas exchange model for control algorithm design.