Dual Fuel Engines

Engineering Marine Engineering
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Wärtsilä also released a new engine model in both diesel and dual-fuel flavors, and promises ammonia in the future:

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I”m surprised to see fuel lines made of copper. . Copper is a poor material for fuel because it will become brittle and crack with vibration. Aluminum or steel is much safer.

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Any Engineer here that care to answer this question?:

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Opportunity? usually when trying to make “everything” work something else suffers.

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Below is a practical based on experience Issues.

1. Methane Slip (especially Otto-cycle X-DF engines)

One of the most discussed issues.

  • Unburned methane escapes with exhaust gas, particularly at low loads

  • More pronounced in low-pressure, Otto-cycle DF engines

  • Reduces real GHG benefit of LNG due to methane’s high global warming potential

  • Hard to eliminate without after-treatment or design compromises

:backhand_index_pointing_right: Seen as an environmental and regulatory risk as methane rules tighten.

2. Combustion Instability & Knocking

Dual-fuel engines must handle very different combustion characteristics.

  • Risk of knocking / misfiring, especially during:

    • Rapid load changes

    • Fuel mode switching

    • Low-load operation

  • Poor gas quality (methane number variations) increases instability

  • Requires constant tuning of control parameters

:backhand_index_pointing_right: Crews often report “engine feels sensitive” compared to diesel-only units.

3. Pilot Fuel System Problems

Even in gas mode, pilot diesel injection is critical.

  • Injector fouling and wear

  • Pilot fuel pump failures

  • Incorrect pilot quantity leads to:

    • Misfire

    • Increased methane slip

    • Higher cylinder pressure fluctuations

:backhand_index_pointing_right: Small pilot system issues can cause large operational consequences.

4. Fuel Gas Supply System (FGSS) Reliability

The engine is only as reliable as the gas system feeding it.

Common issues include:

  • Valve sticking or freezing

  • Gas compressor or pump failures

  • Pressure control instability

  • Sensor and actuator faults

Gas mode trips often originate outside the engine, forcing fallback to diesel.

5. Mode Switching & Load Limitations

  • Gas mode usually restricted below certain load levels (often <10–20%)

  • Automatic or manual switching can:

    • Cause transient instability

    • Trigger alarms and slowdowns

  • Crew confidence varies—many prefer staying in one mode when possible

:backhand_index_pointing_right: Frequent switching increases wear and human error risk.

6. Cylinder Lubrication & Wear Issues

Dual-fuel operation affects combustion chemistry.

  • Different acid formation compared to HFO/MGO

  • Risk of:

    • Liner polishing

    • Ring wear

    • Incorrect BN lubrication strategy

  • Engines may require fuel-mode-dependent lube oil adjustment

Improper management leads to long-term mechanical damage.

7. Control System Complexity & Sensor Dependence

Modern DF engines are software-driven machines.

  • Heavy reliance on:

    • Pressure sensors

    • Temperature sensors

    • Gas quality measurements

  • Sensor drift or failure can:

    • Force diesel fallback

    • Reduce engine availability

  • Troubleshooting often requires OEM support

:backhand_index_pointing_right: Engineers report increased dependence on laptops, not spanners.

8. Safety System Trips & Gas Detection Issues

Gas operation introduces stricter safety logic.

  • False gas detection alarms

  • Ventilation interlock trips

  • Emergency shutdowns (ESD) triggered by minor faults

  • Tight safety margins can reduce operational flexibility

While safety improves, availability can suffer.

9. Maintenance Skill Gap & Training Burden

  • Traditional marine engineers may lack:

    • Gas handling experience

    • Control logic understanding

  • OEM training is essential but time-consuming

  • Mistakes during maintenance can have safety implications

This is more a human factor issue than a mechanical one.

10. Long-Term Unknowns & Degradation

Many DF engines are still relatively young in service.

Open questions include:

  • Long-term valve seat wear in gas mode

  • Control system obsolescence

  • Spare part availability for electronics

  • Lifetime methane slip performance

Owners are learning in real time.

Summary Table (Quick View)

Issue Area Typical Problem
Emissions Methane slip
Combustion Knocking, misfire
Fuel System FGSS reliability
Operation Mode switching instability
Wear Liner & ring issues
Controls Sensor & software dependence
Safety Gas trips, false alarms
Human Factors Training & skill gaps

Bottom line

Two-stroke dual-fuel engines on cargo ships are technically impressive but operationally demanding. They are not “plug-and-play replacements” for conventional diesel engines. Their success depends on:

  • High-quality gas supply

  • Well-trained crews

  • Strong OEM support

  • Conservative operational practices

In short, they offer real opportunity, but only if operators are prepared to manage dual complexity, not just dual fuel.

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