Abstract
Diesel engines technical condition assessment is a very complex process. Most of the malfunctions and troubleshooting in the diesel engine installations are generated by the fuel injection system and valve gear mechanism. Conventional maintenance methods for engine valve gear mechanism depend on valve clearances checks and valve timing diagram checks on crankshaft flying wheel. Fuel injectors have to be checked on the special stands. But how to check fuel injectors and valve’s clearances without stopping the engine and dismantling it, how to observe valve timing diagram on working engine and what is the difference between “static” and “dynamic” valve timing diagram. Answers for these and other questions for truck/bus diesel engines will be given in the presentation. Typical diagnostic methods which base on the analysis of vibration signals amplitude or their frequency are sensitive to engine load and speed changes. Presented diagnostic method is based on the envelope of vibration acceleration signal analysis in crank angle domain. Tests results of this new diagnostic method are presented in the paper. The typical visual analysis of the vibration signal in time/angle domain gives usually limited information. The original method presented in the paper precisely is the angle analysis of the envelope of vibration acceleration. Results of the investigation are the dynamic timing parameters of the engine which could be use by specialists to compare engine internal processes and assess its technical condition. So-called “dynamic” valve gear diagrams are too indispensable to perform an accurate engine tuning. Dynamically estimated values of angles of valves closings and openings are different to the values given in the engine manual. These angles are usually determined in static conditions because of what a special database for prophylactic engine controls has to be created. Dynamically measured the fuel injection valve opens and closing angles and exhaust and inlet valves opens and closing angles are determined by the engine speed and load. Taking into account that maintenance may be taken in different load conditions the database should contain the whole spectrum of measured parameters.
Keywords - diesel engine, diagnostics, tuning, fuel injector, valve gear.