Remote Sensing Methodology for the Closed-Loop Control of RCCI Dual Fuel Combustion

The continuous development of modern Internal Combustion Engine (ICE) management systems is mainly aimed at complying with upcoming increasingly stringent regulations throughout the world. Performing an efficient combustion control is crucial for efficiency increase and pollutant emissions reduction. These aspects are even more crucial for innovative Low Temperature Combustions (such as RCCI), mainly due to the high instability and the high sensitivity to slight variations of the injection parameters that characterize this kind of combustion. Optimal combustion control can be achieved through a proper closed-loop control of the injection parameters. The most important feedback quantities used for combustion control are engine load (Indicated Mean Effective Pressure or Torque delivered by the engine) and center of combustion (CA50), i.e. the angular position in which 50% of fuel burned within the engine cycle is reached. All these quantities can be directly calculated through a proper processing of in-cylinder pressure trace. However, the on-board installation of in-cylinder pressure sensors would significantly increase the cost of the whole engine management system. Consequently, over the last years, the increasing request for combustion control optimization spawned a great amount of research in the development of remote combustion sensing methodologies, i.e. algorithms that allow extracting useful information about combustion via low cost sensors that are already present on-board. The approach presented in this paper is based on the real-time analysis of engine block vibration. This measurement is used to real-time estimate the center of combustion (CA50), that needs to be kept around a proper target value to guarantee high efficiency and combustion stability. In addition, engine acceleration is used to determine knock intensity and detect misfires and poor combustions. The paper describes how the combination of the mentioned quantities (extracted from the accelerometer employed) can be used to set-up a closed-loop combustion control strategy suitable for the control of innovative combustions, as for example dual fuel RCCI combustion. Such methodology keeps CA50 to its optimal value and guarantees combustion stability while controlling the occurrence of knock events.