In order to meet the stricter and stricter emission regulations, cleaner combustion concepts for Diesel engines are being progressively introduced. These new combustion approaches often requires closed loop control systems with real time information about combustion quality. The most important parameter for the evaluation of combustion quality in internal combustion engines is the in-cylinder pressure, but its direct measurement is very expensive and involves an intrusive approach to the cylinder. Previous researches demonstrated the direct relationship existing between in-cylinder pressure and engine block vibration signal and several authors tried to reconstruct the pressure cycle on the basis of information coming from accelerometers mounted on engine block.
This paper proposes a method, based on the analysis of the engine vibration signal, for the diagnosis of combustion process in a Diesel engine. To this aim, the vibration signal was firstly pass-band filtered and then, using this signal, some global variables which characterize the combustion quality were estimated. Finally, a possible control system using the estimated combustion indicators was described.
All the experimental tests were carried out on a four-cylinder Diesel engine running with operating conditions which ensured low temperature and premixed combustions.