Non-intrusive measurements on Engines – Acoustic radiations
The main advantage to develop non-intrusive measurement procedures rely on the possibility to perfom testing on engines without benching preparations, i.e outside labs. Since this route naturally leads not only on monitoring purposes but also on control duties, it is interesting to look for simple sensing chains which can be utilized on mass productions and can easily integrate with Engine Control Units. Real Time monitoring and control of combustion process in engines is the way to deal with tight pollutant regulations.
On a reciprocating engine the heat released from combustion, compress the charge inside cylinder; with simple thermodynamic models we can relate the progress of combustion to cylinder pressure development. That’s it, cylinder pressure has a key role  to combustion process monitoring, aswell as engine design since it directly couple to engine performance and pollutant emissions.
While piezo-sensors for measuring in-cylinder pressure became cheaper, non-intrusive measuring still have several advantages regardind costs, installation and reliability. Most common strategies to perform non-intrusive measuring on engines is by the measurement of crankshaft angular “istantaneous” speed, block vibrations, and acoustic radiation. Since the beginning acoustic radiations of engines has been used as a valuable diagnostic method. In 1931 sir H. Ricardo, who’s the father of reciprocating engine science, putted his effort to obtain a relation between cylinder pressure and acoustic radiation. By modern Digital Signal Processing of acoustic radiation we may obtain more than cylinder pressure and combustion monitoring, like injection system and mechanical system faulty analysis  ; from another point of view, in depth knowledge of acoustic radiation allows to develop countermeasures and strategies for improving Noise and Vehicle Harshness .
My research effort this year has been devoted to conditioning methods able to extract and/or assign usefull informations from engine acoustic “noise”radiation. These method challenge the task to separate combustion noise from other mechanical sources and to define proper metrics between source emissions and signal ouputs. The purpose here is to define or trace signatures on noise able to return quantitative and qualitative data about thermomechanic processes of the engine. During this first year has been developed a method to estimate a trasfer function between heat release and acoustic radiations. Working on a sets of experimental data with steady state condition of the engine at different speeds and loads it is possible to evaluate the sensitivity to both speed and load for these trasfer functions (on figure ) .
Experimental transfer function between heat release and acoustic radiation, sensivity to speed and load on sub-band analysis.
1 Payri, F., Broatch, A., Tormos, B., & Marant, V. (2005). New methodology for in-cylinder pressure analysis in direct injection diesel engines—application to combustion noise. Measurement Science and Technology, 16(2), 540.
2 Albarbar, A., Gu, F., & Ball, A. D. (2010). Diesel engine fuel injection monitoring using acoustic measurements and independent component analysis.Measurement, 43(10), 1376-1386.
3 Torii, K. (2014). Method Using Multiple Regression Analysis to Separate Engine Radiation Noise into the Contributions of Combustion Noise and Mechanical Noise in the Time Domain. SAE International Journal of Engines, 7(2014-01-1678), 1502-1513.
4 Chiatti, G., Chiavola, O., Conforto, S., & Amalfi, M. (2015). Engine Block Dynamic Response via Combustion Noise Radiation (No. 2015-01-2234). SAE Technical Paper.