The optimization of the combustion process in diesel engines is one of the challenges to improve performance, emissions, fuel consumption and NVH characteristics. This work constitutes one of the last steps of a comprehensive research program in which vibration sensors are used with the purpose of developing and setting up a methodology that is able to monitor and optimize the combustion process by means of non-intrusive measurements.
Previously published results have demonstrated the direct relationship that exists between in-cylinder pressure and engine block vibration signals, as well as the sensitivity of the engine surface vibration to variation of injection parameters when the accelerometer is placed in a sensitive location of the engine block. The accelerometer trace has revealed the ability to locate, in the crank-angle domain, important phenomena characterizing the combustion process (the start of pre-mixed combustion, the crank angle value corresponding to the beginning of diffusive combustion and the in-cylinder pressure maximum value). Moreover, the accelerometer signal has been used to quantify the in-cylinder pressure development by evaluating the pressure peak value and the pressure rise rate caused by the combustion process.
The aim of this paper is to address the applicability of the technique on the signals obtained when a wide variation of the injection parameters settings is imposed on the engine, with the final objective of setting up a reliable, innovative methodology that retains great potential in the field of engine diagnostic and/or optimization procedures in which only non-intrusive measurements are employed.
For this purpose, tests have been carried out in which the injection strategy (single or multiple injection), the injection timing and duration have been varied in a wide range of values; results are presented and discussed.