Ravaglioli, V., Ponti, F., De Cesare, M., Stola, F. et al., "Combustion Indexes for Innovative Combustion Control," SAE Int. J. Engines 10(5):2371-2381, 2017.
The continuous development of modern Internal Combustion Engine (ICE) management systems is mainly aimed at combustion control improvement. Nowadays, performing an efficient combustion control is crucial for drivability improvement, efficiency increase and pollutant emissions reduction. These aspects are even more crucial when innovative combustions (such as LTC or RCCI) are performed, due to the high instability and the high sensitivity with respect to the injection parameters that are associated to this kind of combustion. Aging of all the components involved in the mixture preparation and combustion processes is another aspect particularly challenging, since not all the calibrations developed in the setup phase of a combustion control system may still be valid during engine life.The most important 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 evaluated starting from in-cylinder pressure measurement; however, the use of in-cylinder pressure sensors would significantly increase the cost of the whole engine management system. Due to these reasons, over the past years, many methodologies have been developed by the authors of this paper in order to evaluate combustion characteristics using low-cost sensors or sensors that are already present on-board. The approaches considered in this paper are based on engine speed fluctuations and engine block vibration. These measurements are performed through the magnetic pick-up facing the toothed wheel already present on-board and a low-cost accelerometer mounted on engine block. Each of these measurements allows estimating a combustion characteristic that can be used for combustion control, such as IMEP, pressure peak position, CA50. The paper presents how the combination of the information that can be extracted from the low or zero cost sensors employed enables the control of innovative combustions, as for example dual-fuel RCCI combustion.