Diagnosing mechanical damages not detected by the OBD system of diesel engines

The paper presents the possibilities of diagnosing with the use of vibracoustic signal of mechanical damages of diesel engines, which are not detected by the OBD system. This system does not recognize such damages, but it masks them delaying information about the damage to the point where the regulatory values of controlling work of the engine will exceed the limit values. This is because the aim of the OBD system is to ensure the minimization of exhaust emissions. There were made measurements of vibroacoustic signal of the head of the car engine with fuel injection system Common Rail, where there were introduced mechanical failures typical and dangerous for the engine. It has been proved that the OBD system does not recognize these damages and the work of the engine is correct. Therefore, there is a need for an additional diagnostic system which supports the OBD system in detection of this type of damages. It seems that the use of vibroacoustic signal as an additional analyzed signal should improve the sensitivity of the on-board diagnostic system to damages of diesel engine. The author tested the sensitivity of vibroacoustic signal to damages introduced to the engine and he presented the proposition of the system based on simple measures of the vibroacoustic signal, which allows for both detecting mechanical damages and their identification.