Diesel Auxiliary Engine no. 1 / Engine Unbalance, Inlet and Exhaust Valves & Injectors Concern

This document consists of the analysis and detection of engine power imbalance, valve clearance incorrectness and injector problems on Diesel generator no.1 of a MAN B&W 7L28/32H. Combustion pressure, high, raw and ultra signals were checked with vibration equipment.

1. INTRODUCTION

The main engine condition is based on the real load calculated by our measuring equipment and vibration an ultrasonic measurements collected. The fuel system overflow valve condition is based on the pressure readings taken during the engine operation. The data obtained from the engine analysis was processed, analyzed and compiled by a qualified professional analyst, resulting in the following recommendations:

2. THEORETICAL REFERENCES

Early or late valve closure may indicate a problem with clearance, issues with valve drive mechanism, wear on camshaft cam.

Too low or to high indicated power may indicate a problem with injector opening pressure, injector nozzle, injector timing, fuel pump fuel rack wrong setting or fuel pump timing. Low indicated power may be a result of low compression pressure or an issue with inlet valve closing time. Too high or too low exhaust gas temperature can also be a result of too low or too high indicated power, or an issue with exhaust valve closing time.

3. ANALYSIS ROUTE

 

3.1 Vibrations

High freq. vibrations are checked to verify valve timing is correct. Between -200 and -100 is the signal for inlet valve closure and after -300 is the signal for exhaust valve closure.

Unit 1, 2, 3 and 7 – Inlet and Exhaust valve timing looks correct.

Unit 4 and 5 – The Exhaust valve closing signal is delayed (Unit 5), small and stretched (Unit 4), therefore a recommendation to check the valve clearance and condition of valve spring was issued.

Unit 6 – The Inlet signal is delayed, the Exhaust valve signal is small and stretched therefore a recommendation to check the valve clearance and condition of valve spring was issued.

The vibration signal on the Fuel pumps didn’t indicate or show any problems, no actions are needed to be recommended there.

3.2 Engine Balance

A balanced engine is an engine in which the indicated load per unit is equal, typically +/- 5%. Even load ensures the safe operation of the engine, minimizes stress on mechanical components of the crankshaft, reduces engine vibration, and lowers emissions and fuel consumption. When analyzing, load balance, thermal balance, compression pressure and other parameters are taken into account.

There is a problem with indicated power balance, unit 1 and 5 generate less power. Possible causes are:

  • Improper injector opening pressure,
  • The injector nozzle is partially clogged,
  • Fuel pump timing,
  • Low compression pressure,
  • The issue with inlet and exhaust valve timing

From the above diagrams, we can see that this engine exhaust gas temperature and compression pressure is balanced. Unit 5 exhaust valve closure signal is delayed, but this does not effect the exhaust gas temperature significantly.

Fuel pump from units 1 and 5 vibrations do not indicate any issues. This leaves with only 2 possibilities for low indicated power on unit 1 and 5:

  • Improper injector opening pressure,
  • The injector nozzle partially clogged

Therefore a recommendation to check injector opening pressure and nozzle condition was issued for both units.

4. FEEDBACK FROM THE SHIP

After the analysis was finished and reports sent to the ship we received feedback from the crew:

5. SUMMARY:

The recommendations issued for this engine were correct. Valve clearance needed to be readjusted, the opening pressure of the injectors was too low and the injector nozzle was found leaking and needed to be replaced. Our recommendations should significantly improve the engine’s operation, the improvement will be visible after the next measurement.