Power generation on board a ship is not just important – it’s essential. Whether you’re navigating narrow channels, operating pumps for cargo, or simply keeping the bridge equipment alive, a reliable generator is non-negotiable. Even a few minutes of blackout can lead to a cascade of emergencies – from collision risks to cargo damage.
To avoid such scenarios, ships are equipped with multiple auxiliary engines (generators), maintained diligently by marine engineers. These engines ensure continuous power for critical operations, but like all machines, their performance can dip over time.
Let’s explore the most common causes of reduced auxiliary engine performance, so you know exactly where to look before reaching for that standby generator.
Why Does a Generator Need to Perform at Its Best?
A ship engineer strives to run only the required number of generators, ideally one at optimal load. Why?
- It improves fuel efficiency
- Reduces wear and tear
- Minimizes emissions
- Extends service intervals
But when one generator underperforms, you’re forced to run another in parallel – which means higher fuel consumption and unnecessary strain on equipment.
Symptoms of Reduced Performance
- High exhaust gas temperature
- Low peak firing pressure
- Unbalanced load sharing
- Frequent need to start standby generator
Let’s dive into the root causes.
Causes of Reduced Auxiliary Engine Performance
1. Low Fuel Oil Pressure
Low fuel pressure = poor combustion. This can be caused by a worn-out fuel oil pump or fuel that’s too thin (low viscosity), especially when cold MGO is used.
2. Change in Fuel Type
Switching from HFO to MDO or LSFO? These lighter fuels reduce fuel injection pressure due to their lower viscosity, leading to poor atomization and reduced power.
3. Fuel Pump Leakage
Worn-out plungers or barrels in the fuel pump lead to internal leakage, dropping pressure at the injector. This causes weak combustion and reduced cylinder performance.
4. Fuel Temperature Too High
When fuel temp exceeds 60°C, viscosity drops too low, weakening the injection pressure and combustion quality.
5. Firing Pressure Imbalance
If one cylinder’s peak pressure differs significantly from the others, it creates uneven firing and a noticeable drop in total engine output.
6. Blocked Fuel Filter
Choked fuel filters restrict flow to the engine, starving it of fuel and reducing output. Regular checks and replacements are crucial.
7. Incorrect Valve Clearance
Too much clearance means valves may not open fully, or close too late. This leads to leakage of fresh air or combustion gases, disturbing power output.
8. Damaged Exhaust Valve or Seat
A worn or leaking exhaust valve allows combustion gases to escape during the power stroke, leading to power loss and increased exhaust temperature.
9. High Exhaust Back Pressure
Fouled silencers or poorly routed exhaust piping cause high backpressure. The engine struggles to expel exhaust gases, reducing efficiency.
10. Contaminated Exhaust Manifold
Soot or carbon buildup in exhaust passages slows gas flow, elevates exhaust temperature, and reduces engine breathing.
11. Insufficient Fresh Air Supply
Air is fuel’s best friend in combustion. If your scavenge blower is dirty, filters are clogged, or intake paths are obstructed, expect poor combustion and power loss.
12. High Turbocharger Suction Air Temperature
Hot regions = hot ambient air. If the turbocharger sucks in hot air and your intercooler isn’t working efficiently, engine performance drops sharply.
13. Low Scavenge (Charge) Air Pressure
Low charge air pressure means less air entering the cylinders. Less air = less oxygen for combustion = less power. Watch for low T/C RPM or dirty filters.
14. Incorrect Charge Air Temperature
Charge air that’s too hot (or too cold) throws off combustion efficiency. Cooler control valves must be set correctly for optimal air temperature.
15. Contaminated Charge Air Cooler
A dirty air cooler (seawater or air side) won’t cool intake air effectively. Warm charge air = poor combustion = high exhaust temp.
16. High Seawater Temperature
Hot seawater has less capacity to absorb heat. If the ship is in warm regions, cooling air or jacket water becomes less efficient, impacting engine performance.
17. Air Cooler Seawater Bypass Valve Left Open
This valve controls how much seawater flows through the cooler. If it’s left open too much, water bypasses the cooler core, resulting in poor air cooling.
18. Turbocharger Damage
Damaged nozzle rings, worn turbines, or fouled compressor blades reduce air supply. Turbochargers must be cleaned and overhauled as per PMS.
19. Scavenge Air Leakage
Leaks in scavenge air manifolds or flanges reduce delivery pressure, leading to oxygen-deficient combustion.
20. Incorrect Tappet (Cam Follower) Clearance
Wrong tappet clearance causes poor valve timing, impacting both intake and exhaust functions. Even minor deviations affect overall engine rhythm.
What Fuel Do Auxiliary Engines Use?
Auxiliary engines commonly use:
- Heavy Fuel Oil (HFO) – cost-effective but needs preheating
- Marine Diesel Oil (MDO) or Marine Gas Oil (MGO) – cleaner but more expensive
- LSFO or ULSFO – to comply with emission regulations
Fuel type affects combustion characteristics, injector settings, and maintenance requirements.
