High exhaust temperature on one unit during a loaded voyage
The container ship Kition Bay is 26 hours out of Piraeus for Suez, loaded, in moderate weather. The main engine is a six-cylinder low-speed two-stroke, MCR 9,600 kW at 105 rpm, driving a fixed-pitch propeller. It is running at 78% MCR, 92 rpm, on VLSFO with injection viscosity 13 cSt; no fuel change has been made in the last 24 hours. The alarm log shows No.4 unit exhaust gas outlet temperature 438°C, while the other units are 392–401°C. No.4 fuel rack index is about 4% higher than the average. Scavenge air pressure is 2.65 bar, turbocharger speed is normal, and No.4 cylinder liner temperature is normal. The exhaust valve has not been overhauled for 11,000 running hours; the injector was changed 900 hours ago. The next port is about 30 hours away. The chief engineer must decide whether to continue, reduce load, or stop for inspection, and what to monitor meanwhile.
1. What immediate actions and monitoring would you take during the first 30 minutes, and why?
Read the worked answer
Priority: protect the cylinder and keep propulsion available.
- Inform the bridge and chief engineer; log the deviation and start a timed trend every 15 minutes.
- Reduce load gradually to about 65–70% MCR, not by suddenly tripping the fuel pump. Lower cylinder pressure and exhaust temperature reduce the risk of exhaust-valve burning and scavenge-space ignition while preserving manoeuvrability.
- Compare No.4 exhaust temperature with load, scavenge air pressure, turbocharger speed and rack index. A high exhaust temperature with normal scavenge pressure and normal liner temperature points away from a simple air shortage and toward late/poor combustion, an injector fault, a fuel-pump timing/quantity fault, or an exhaust-valve leak.
- Check scavenge-space drains and mist detectors; if oil or sparks appear, treat as a scavenge fire and follow the emergency procedure. Do not open crankcase or scavenge covers while running.
- Keep the fuel rack under observation; if it reaches the stop or No.4 temperature continues rising after load reduction, prepare to stop. The judgement is to create margin first, then diagnose; cutting out a unit at 78% load could overload the remaining units and lose manoeuvring capability.
2. Set out a structured diagnostic sequence to distinguish an injector/fuel-pump fault, an exhaust-valve leak and a turbocharger/scavenge-air problem.
Read the worked answer
At reduced load, use a stepwise isolation:
- Swap the No.4 injector with a spare or with another cylinder and repeat the load test. If the high temperature moves with the injector, the injector is at fault; if it stays on No.4, continue.
- Check fuel-pump rack calibration and timing; compare pump suction and leak-off. A worn plunger/barrel or delivery valve can raise rack index and distort injection timing.
- Take indicator diagrams/compression pressure if equipment permits. A leaking exhaust valve usually lowers compression and may show a higher or erratic exhaust temperature; an injector fault often raises exhaust temperature with normal compression.
- Inspect the exhaust valve spindle and seat by borescope at the first safe stop; 11,000 hours without overhaul makes valve leakage credible.
- Check turbocharger air filter, charge-air cooler and scavenge air pressure; normal turbo speed and scavenge pressure make a major air-side fault less likely, but a partially blocked cooler can still affect one cylinder unevenly. Do not rely on one symptom. The rack index plus exhaust-temperature deviation is the strongest clue, but the injector swap is the quickest discriminator.
3. Recommend whether to continue at reduced load or stop for repairs, stating the criteria for aborting the passage.
Read the worked answer
Recommendation: reduce to 65–70% MCR and continue only under defined limits. With 30 hours to port and moderate weather, continuing is defensible if No.4 exhaust temperature stabilises within the manufacturer’s limit, rack index returns near normal, liner temperature remains normal, and there is no scavenge mist, smoke, vibration or turbocharger surge. Keep the engine ready for immediate load reduction and have the bridge informed so a stop can be planned in safe water. Abort and stop if any of the following occurs: exhaust temperature exceeds the alarm or continues rising at reduced load; rack reaches the maximum; scavenge drain shows oil; turbocharger surges; or the engine cannot maintain steering/propulsion safely. An overdue exhaust valve at 11,000 hours means the risk of a burnt valve is real, so the threshold for stopping should be lower than for a recently overhauled unit. Record trends, notify the technical manager, and arrange injector and exhaust-valve inspection at the next port. The decision is not ‘continue or stop’ in the abstract; it is ‘continue with a tested abort criterion’.