During a planned inspection on our customer’s Auxiliary Engine; MAKER: DAIHATSU, TYPE: 6DK20, OUTPUT: 900 kW, RPM: 900.
We identified several issues. One of these issues involved significant wear on the injector nozzle tip, which was discovered through vibration and combustion pressure measurements.
Our Service Engineer performer vibration and combustion pressure measurements on the Auxiliary Engine cylinder head (Fig.1) at approx 80% load.
Analysis and Inspection
After transferring all the measured data it was quickly recognized that there was an issue (Fig. 2).
It is clearly seen that the High-frequency vibration trace (Red line) near the TDC (0°) corresponds to the working of the fuel injector. In a normal working injector, these vibrations are much higher and have a specific pattern. Additionally, we observed that the pressure curve after TDC is tilted. Further data such as indicated power, and peak pressure angle, also pointed toward a problem with the fuel injector. It is worth to mentioning that Pmax and exhaust gas temperature from this unit were within limits and balanced.
A recommendation was made to check and clean the nozzle tip and to verify the fuel injector opening pressure.
Feedback and evidence of Fuel injector condition.
The crew sent us positive feedback and photos of the injector (Fig. 3).
n Fig. 3 we can see that the injector nozzle has some carbon deposits on it, which could explain the weak vibrations and low indicated power. Additionally, the crew reported that the injector opening pressure was below normal. After cleaning, overhauling and readjusting the injector was reinstalled.
Conclusion
Marine Diesel Engine Diagnostic: The Role of Advanced Measurement Techniques
Marine Diesel Engine Diagnostic techniques, such as Advanced Combustion Engine (ACE) measurement, have proven essential for assessing the condition of Auxiliary Engines. Vibration analysis and combustion pressure monitoring provide a more comprehensive understanding of engine performance and potential issues.
Relying solely on Pmax and exhaust gas temperature can be insufficient for accurate diagnostics. By incorporating ACE measurement, marine engineers can detect problems early, prevent failures, and extend the lifespan of critical engine components.
A key advantage of Marine Diesel Engine Diagnostic tools like ACE is efficiency—engine crews can avoid unnecessary disassembly. In one case, ACE measurement helped the crew save time by eliminating the need to extract and inspect all injectors.