An emerging technology - Performance and condition monitoring of diesel engines and gas turbines via acoustic emission measurements

Demand for condition monitoring of diesel engines and gas turbines has advanced at a rapid pace in recent years. Stimulated by the continual drive for improved performance, be it for mechanical, economic, safety or environmental reasons, operational safety margins have diminished and in some cases have been replaced by a delicate balance between optimal operation and damaging conditions. Consequently, the need for monitoring and for better-quality diagnostic information has increased. This has initiated the development of a number of new monitoring techniques. One of the most promising, Acoustic Emission (AE) analysis, is the topic of this paper. This work describes the novel use of AE measurements to provide information pertaining to the running condition of diesel engines and to a lesser extent, gas turbines. For diesel engine applications an AE sensor placed on the external engine surface is shown to reveal detailed information regarding engine events such as fuel injection and valve activity. Most promisingly the ability to offer non-intrusive monitoring of the critical piston ring/cylinder liner interface is described, a process that has traditionally been difficult to inspect in-situ and one which poses significant problems for marine diesels. The findings regar ding the ring/liner interface are established through testing on large, 2-stroke marine diesels and small HSDI engines. For the large engines, AE is shown to be sensitive to the cyclic fluctuation of in-cylinder pressure and to a variation of lubricating condition. Regarding HSDI engines, AE is proposed to arise as a result of boundary friction and/or hydrodynamic lubrication. Encouraging studies have also been conducted on a gas turbine where AE has shown to be responsive to variations in the machine operation, including induced blade damage.