Kaul, B., Lawler, B., and Zahdeh, A., "Engine Diagnostics Using Acoustic Emissions Sensors," SAE Int. J. Engines 9(2):684-692, 2016, doi:10.4271/2016-01-0639.
Engine acoustics measured by microphones near the engine have been used in controlled laboratory settings for combustion feedback and even combustion phasing control, but the use of these techniques in a vehicle where many other noise sources exist is problematic. In this study, surface-mounted acoustic emissions sensors are embedded in the block of a 2.0L turbocharged GDI engine, and the signal is analyzed to identify useful feedback features. The use of acoustic emissions sensors, which have a very high frequency response and are commonly used for detecting material failures for health monitoring, including detecting gear pitting and ring scuffing on test stands, enables detection of acoustics both within the range of human hearing and in the ultrasonic spectrum. The high-speed acoustic time-domain data are synchronized with the crank-angle-domain combustion data to investigate the acoustic emissions response caused by various engine events.Combustion can clearly be identified as a high energy event in the acoustic emissions data with the frequency of the response corresponding to a resonant mode of the combustion chamber. Additionally, both the start and end of fuel injection result in short-duration, high energy, frequency-independent acoustic bands. Some valve closing events can be identified as well. Hardware configuration changes to the piston ring pack resulted in different acoustic emissions signatures indicating the ability of acoustic emissions sensors to detect ring-liner interactions. A change of 25° C to the coolant (and thus liner) temperatures displayed distinct changes in the observed acoustic emissions. Finally, these sensors and this technique were highly sensitive to end-gas knock with a significant response to even very light end-gas knock.