Abstract
Keywords: OBD system, vibroacoustics, combustion, compression-ignition engine, engine ecology
A rapid advancement in engines design and technology has continued since the end of the XIX century, when IC (Internal Combustion) engines as propelling units were first introduced. The stimuli for this phenomenon were continuously increasing working parameter requirements and economic considerations as regards vehicles fitted with this type of propulsion. A growing impact of IC engines on the environment substantially influenced the design process and operation of the engine itself. In the whole life cycle of an IC engine all its functional characteristics are modified, leading to a gradual deterioration of the operational characteristics, i.e. wear and tear of the kinematic pairs - deformation or fatigue. A continuous process of engine deterioration, intensified by improper operation, directly leads to a deterioration of the performance quality, imprecision in mixture formation, distortion in the combustion process, drop in engine durability and, consequently, to its ultimate failure. Each of the above factors has impact on the engine exhaust emissions, which is vital for the environment protection and human health. That is why the diagnostics of a unit in its whole period of operation becomes increasingly important. The proper steering of injection and combustion processes in an IC engine at different work conditions is one of the main ways to obtain the best conversion of the fuel energy into the mechanical work and to meet more and more stringent emission regulations. Lack of combustion process makes the energy in fuel lost, causing the excessive emission and, in the result, catalytic converter efficiency is worse.
A little harmfulness for the environment, expressed by the little toxic compounds emission, noise emission and the little fuel consumption (the little CO2 emission) are the requirements which are put forward first during the design process of the contemporary internal combustion engines. The consequence of the concern with the environment is applying by the industrial developed countries more and more stringent emission regulations for the engines vehicles. These actions extract technical progress in the forward of getting less and less emission levels for each toxic compound of combustion gases.
In the aftermath of that, requirements concerning of the on-board diagnostic of engines were applied, at first in SI (Spark-ignition) engines, then in CI (Compression-ignition) engines of passenger cars and in light-duty vehicles. OBD systems give the vehicle owner or a repair technician access to state of health information for various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since the introduction in the early 1980's of on-board vehicle computers, which made OBD possible. Early instances of OBD would simply illuminate a MIL light (Malfunction Indicator Light), if a problem was detected but would not provide any information as to the nature of the problem. Modern OBD implementations use a standardized fast digital communications port to provide realtime data in addition to a standardized series of DTC codes (Diagnostic Trouble Codes), which allow one to rapidly identify and remedy malfunctions within the vehicle.The high level of requirements regarding internal combustion engines and obtained benefits caused, that OBD norms and these systems have been using in wider and wider group of vehicles applications. On the basis of trends of emission norms (in the USA and in Europe), the tendency to bring OBD requirements and systems into non-road vehicles applications is being observed at present [5]. It seems probable that on-board diagnostic will be present in diesel railway traction vehicles in the near future, what confirms usefulness of taking up of OBD system implementation in this group of traction vehicles.
The paper gives the answer for the question about if it is possible to apply vibroacoustic methods for misfire detection in the point of view of realization of the OBD systems which will be using vibration signal parameters to assess the diagnostic engine state and correctness run of processes taking place in the internal combustion engine. The obtained methodology for misfires events diagnoses based on this particular method comprises the detection of the direction of the measuring signal recording, the placement of the vibration transducers, the diagnostic parameter and the conditions for the measurement. It was used then in an exploitation measurements, done for a chosen diesel locomotive engine to check the correctness of the obtained physical rules for this type of the measurement unit and to make bases for the OBD application in these types of sources of a drive.