Marine System Simulation for LNG Carriers: Improving Fuel Efficiency and Reducing Emissions

The maritime industry is navigating one of the most significant transitions in its history. As global trade continues to grow, vessel operators face increasing pressure to reduce fuel consumption, lower greenhouse gas emissions, and comply with evolving environmental regulations.

The International Maritime Organization (IMO) has established ambitious decarbonization targets, pushing ship owners and operators to explore new ways of improving efficiency across their fleets. While alternative fuels and new propulsion technologies receive significant attention, substantial opportunities also exist within existing vessel architectures through improved operational strategies and energy management. For many operators, retrofitting existing vessels has emerged as a practical pathway to improve efficiency, reduce emissions, and extend asset value without the cost and complexity of building new ships.

Achieving these gains requires a comprehensive understanding of how complex onboard systems interact under real operating conditions. This is where system-level simulation becomes a valuable engineering tool. Using GT-SUITE, engineers can model propulsion, electrical, thermal, and cargo management systems within a unified simulation environment to support better design and operational decisions.

The Challenge of Optimizing LNG Carrier Operations

Modern LNG carriers are among the most complex vessels operating at sea. Unlike conventional ships, LNG carriers must manage not only propulsion and electrical power generation but also the cargo itself.

As liquefied natural gas is transported, a portion naturally evaporates and becomes boil-off gas (BOG). This gas can be:

• Used as fuel for propulsion systems
• Consumed in auxiliary boilers
• Re-liquefied and returned to storage
• Safely disposed of through gas combustion systems

Each option impacts fuel consumption, cargo retention, emissions, and overall vessel efficiency. At the same time, propulsion systems, electrical generators, steam production systems, and cargo handling equipment continuously interact throughout the voyage.

Because of these interdependencies, optimizing individual components often fails to deliver the best vessel-level efficiency.

Why System-Level Marine Simulation Matters

Marine vessels operate as integrated energy systems rather than collections of independent components.

A change in engine loading can influence fuel consumption, waste heat availability, steam generation, electrical demand, and cargo management strategies. Understanding these relationships requires a simulation approach capable of representing the entire vessel and its operating environment.

Using GT-SUITE, engineers can create integrated models that combine:

• Main propulsion system
• Dual-fuel engines
• Auxiliary generators
• Boilers and steam networks
• Waste heat recovery systems
• Reliquefaction and gasification plants
• Power distribution strategies
• Hull performance characteristics

This integrated approach enables engineers to evaluate how operational decisions affect overall vessel performance, fuel consumption, and emissions.

Modeling LNG Carrier Energy Systems with GT-SUITE

A system-level model of an LNG carrier captures the flow of energy throughout the vessel.

Key subsystems include:

Propulsion and Power Generation

Dual-fuel engines provide propulsion while auxiliary generators supply electrical power for onboard systems. Their operating efficiency varies significantly with load conditions, making power distribution an important optimization variable.

Steam Generation Systems

Boilers and economizers support thermal requirements across the vessel. Waste heat recovery systems can improve overall efficiency by converting otherwise lost energy into useful steam production.

Boil-Off Gas Management

Managing boil-off gas is a critical operational challenge. Simulation of the flow and heat exchange allows engineers to evaluate how different system designs of gasification and reliquefaction plants and BOG handling strategies are impacting the energy household, the cargo retention, fuel consumption, and emissions throughout a voyage.

Gasification and Reliquefaction Systems

A gasification plant on an LNG carrier vaporizes liquid natural gas into gas form so it can be used as fuel for the vessel’s propulsion or delivered in gaseous form when required. A reliquefaction plant on an LNG carrier captures and recondenses boil-off gas back into liquid form, reducing cargo loss and maintaining tank pressure. Understanding when to utilize these systems requires balancing energy consumption against cargo preservation and operational requirements.

Capturing Real-World Vessel Operations

Marine operations rarely occur at a single steady-state condition.

Vessels encounter varying:

• Speed
• Cargo conditions
• Metocean Weather conditions
• Hotel load demands
• Operational modes

To accurately represent these conditions, voyage profiles can be combined from operating scenarios, each representing a specific combination of propulsion, electrical, and thermal loads.

The voyage profiles can be simulated as transient or steady state scenarios. In latter case the steady state scenarios can be recombined by weighting factors according to their occurrence during a voyage, which allows engineers to quickly generate predictions of fuel consumption and system-level performance.

This approach transforms simulation from a design tool into a decision-support platform capable of evaluating actual vessel operations.

Identifying Hidden Efficiency Opportunities

One optimization study focused on the operation of auxiliary generator engines aboard an LNG carrier.

Simulation revealed that multiple generators were frequently operating at relatively low loads. While this operating strategy met power requirements, it reduced overall engine efficiency.

Using optimization techniques, alternative generator loading strategies were evaluated across the voyage profile. The objective was straightforward:

• Meet all operational requirements
• Maintain vessel reliability
• Minimize fuel consumption and emissions

The optimized solution consolidated loads onto fewer engines operating at higher utilization levels, where engine efficiency was significantly improved.

Results: Small Changes, Significant Impact

The optimized operating strategy delivered measurable benefits without requiring hardware modifications. The optimization results presented in this article are based on a detailed LNG carrier study conducted by CLEOS using GT-SUITE. The full presentation provides additional information on model architecture, voyage profiles, optimization methodology, and detailed performance results.

The study demonstrated:

While these percentages may appear modest, their impact becomes substantial when applied across long voyages and entire fleets. Even small efficiency improvements can translate into considerable fuel savings, lower operating costs, and meaningful emissions reductions.

Perhaps most importantly, these benefits were achieved through operational optimization rather than capital-intensive equipment upgrades.

Building Marine Digital Twins for Vessel Optimization

As marine operators continue pursuing efficiency and decarbonization goals, simulation models are increasingly evolving beyond traditional engineering studies.

Once validated against operational data, system-level vessel models can serve as digital twins that support:

• Voyage planning
• Fuel management strategies
• Operational optimization
• Retrofit evaluations
• Future fuel assessments
• Predictive maintenance initiatives

These capabilities allow operators to evaluate decisions virtually before implementing them onboard, reducing risk while improving confidence in operational strategies.

Conclusion

The path toward maritime decarbonization extends beyond new fuels and hardware technologies. Significant opportunities remain within existing vessel architectures through smarter operation and improved energy management.

For LNG carriers, where propulsion, electrical systems, thermal networks, and cargo management are tightly interconnected, system-level simulation provides the visibility needed to identify and evaluate these opportunities.

By leveraging GT-SUITE to model and optimize vessel-wide energy flows, engineers can uncover practical strategies that improve operational efficiency and hence reduce fuel consumption and emissions, and, helping operators meet both business objectives and environmental targets.

As marine systems become increasingly complex, simulation-driven engineering is becoming a critical capability for shipbuilders, vessel operators, and marine technology providers. System-level marine simulation enables faster design decisions, improved operational efficiency, and better pathways toward maritime decarbonization.

 

 

FAQ
What is marine system simulation?

Marine system simulation models the interactions between propulsion, electrical, thermal, and cargo systems to predict vessel performance.

How is GT-SUITE used in marine applications?

GT-SUITE enables engineers to model vessel energy systems, optimize operations, evaluate alternative fuels, and develop marine digital twins.

What are the benefits of LNG carrier simulation?

Simulation helps optimize fuel consumption, emissions, boil-off gas management, and overall vessel efficiency before implementing operational changes.