Application of a methodology for the indirect in-cylinder pressure measurement to a 4-cylinder diesel engine

The increasingly strict European emissions standards are prompting researchers at improving further the combustion process in internal combustion engines, in order to reduce pollutant emissions and fuel consumption. To this end, more effective monitoring and control strategies need to be developed in the near future. In particular, the development of a real-time monitoring technique for the in-cylinder pressure plays a key role. If the use of direct, flush-mounted, in-cylinder pressure sensors is hampered by several disadvantages (harsh environment due to high temperature and pressure, expensive machining to install the sensor inside the combustion chamber), indirect measurement technique could provide relevant benefits. The experimental activity presented in this study was then focused at finding a numerical correlation between the in-cylinder pressure and the mechanical stress of an engine component measured by a strain washer sensor applied to one of the studs of the engine head. The improvement of the working conditions enhances the long-term reliability of the device and it cuts out the installation costs. The activity was performed on a YANMAR four-stroke turbocharged, four-cylinder engine. The main combustion parameters were investigated, such as the peak value, its positioning and the position of the MBF50. Additional experimental tests were carried out for the analysis of transient states in order to assess the capability of the strain washer in detecting phenomena like misfiring and injection variations. The results show the direct comparison between the strain washer and pressure signal, which is considered as benchmark for the assessment of this methodology.