Frequently Asked Questions

Improved Efficiencies

Do the engines run only on conventional fuel?

The main engine will become a dual-fuel engine and is able to burn compliant fuel in the conventional way. The engine can also use Propane or Butane or a mix of the two as the main fuel source, with a small amount of compliant pilot fuel. Flexibility is therefore retained by using LPG or compliant fuels to take advantage of optimal fuel market prices.

What is the gas consumption and how is it calculated?

As illustrated in the table below, at 16 knots, the main engines will consume approximately 35.6mt LPG per day and 1.8mt pilot fuel per day with cargo onboard. In addition, the auxiliary engines will consume approximately 4.9mt marine diesel oil (MDO) or compliant fuel per day.

Disclaimer: numbers are for illustration only, and actual consumption could deviate significantly from these numbers. Commercial numbers for specific vessels will be given at request.

Speed (knots)Main engine load (%)Fuel mode (per day)LPG mode (per day)
Main engine (VLSO)Main engine (Propane*)Pilot fuel oil (MGO)Saved fuel in tons

* Running on propane assuming energy content of 46 MJ/kg; running on Butane assuming 43.5 MJ/kg and implying 1.5% higher consumption.

Speed (knots)Main engine load (%)Fuel mode (per day)LPG mode (per day)
Main engine (VLSO)Main engine (Propane*)Pilot fuel oil (MGO)Saved fuel in tons

In addition to the consumption shown above, auxiliary consumption averages 4.9 tons per day at sea (ballast or laden). Total consumption is 5.5 tons per day when the vessel is idle/ anchored, and 10 tons per day whilst loading/ discharging.

The following basic assumptions are made with regards to the above:

  • ISO ambient conditions
  • LPG 46MJ/kg
  • Pilot fuel 42.7 MJ/kg
  • Speed – Power based on new build during sea trial
  • Main engine performance based on shop trial
  • Sea margin 15% included
  • Main engine performance margin 3% included


What is the typical fuel consumption of the 15 VLGCs that are due to be retrofitted for LPG dual-fuel propulsion?

The assumption is made that the vessels will travel approximately 93,000 nautical miles per year, at 14.8 knots on average. The main engines will consume approximately 9,700 tons per vessel while the auxiliary engines will consume approximately 1,800 tons per vessel.

How are emissions calculated?

In Q1 2019, we reported consumption of 81.5k tons of HFO and emissions of 4.5k tons of SOx.

This was calculated as follows:
20*sulphur content, or 70kg of SOx per ton of HFO consumed. The HFO used had lower sulfur content than the 3.5% max limit.

Is the cargo used as fuel for the main engine?

The cargo is not necessarily used as fuel, but cargo can be transferred to the LPG fuel deck tanks for it to be used as fuel. Cargo can be transferred to the fuel gas supply system for the main engine by pumping from the cargo tank to the deck tank.

Is the fuel gas system connected to the cargo system?

Yes, the fuel gas system is part of the cargo system. The deck tanks can be run completely isolated from the cargo tanks or as part of the cargo system.

At what pressure is the LPG fuel delivered to the engine?

The propane or butane is pumped at a pressure of 50 barg to the engine room. The LPG is then further pressurised for the injection to the engine, which is the same process as for conventional fuel.

Does LPG in the deck tanks need conditioning?

Under all normal scenarios, conditioning is not required. The deck tanks applied are semi-refrigerated, but the pressure build is much slower than the rate of consumption with LPG being used as fuel for the main engine. In case the deck tanks are not emptied for consumption, they are connected to the cargo reliquefaction system and can be conditioned independently of the cargo tanks.

Are the deck tanks able to load fully refrigerated cargo?

Yes, the deck tanks can load fully cooled cargo.

Will there be segregation of different cargo grades?

Yes, there is segregation of cargo grades so different fuel can be in the cargo tanks and deck tanks. Both deck tanks will contain the same grade of fuel.

How is the gas consumption measured and monitored?

Both compliant fuel and LPG in the engine is measured using mass flow meters.

Can the engine run on gas during maneuvering?

No, the engine will automatically change over to conventional compliant fuel when the main engine load is below 10%. While the vessel is maneuvering in port, or at any time the engine load is below 10%, the gas burning option cannot be selected.

Is there any possibility of contaminating cargo tanks with the return fuel?

No, any fuel that is returned from the fuel gas system will not be returned to the cargo system. All the LPG flows from the deck tanks into the fuel gas system which then supplies the engine. The engine cannot supply fuel gas directly from the cargo tanks. Once pumped from the deck tanks, it will be contained within the closed loop system fuel gas system. This includes a small tank called a catch tank. Any fuel gas returned will be stored in the catch tank.

How much pilot fuel is used?

Pilot oil consumption will be 5% of the gas consumption, down to a load of approximately 75%. At lower loads, the pilot oil will increase gradually to about 15% of the gas consumption at an engine load of 25%. Fully loaded with cargo at 16 knots, pilot fuel consumption is approximately 1.8mt per day and at 14 knots, it is approximately 2.2mt per day

What happens if there is a gas leak in the engine room?

In the event of a gas leak, the gas master valves will close and the double wall piping to the engine room and the main engine will be purged with nitrogen.

What kind of cylinder lubrication oil (CLO) will the engine use?

The engine will use the same cylinder lubricating oil (CLO) as currently in use for 2020 compliant fuel. The cylinder lubrication will need to be adjusted accordingly to the cylinder condition, which is also currently the case with vessels burning 2020 compliant fuel and LNG burning engines.

Future Proof

Can using LPG as a fuel help achieve IMO targets?

LPG is a zero-sulfur fuel, which achieves full compliance with IMO 2020 SOx regulations. In addition, the carbon content per energy is lower in LPG than conventional fuel, which means that LPG as a fuel also helps meet 2050 IMO GHG targets. LPG also gives credit towards IMO EEDI compliance requirements for the same reason. Compared to 2020 compliant fuel, the following reductions are seen when using LPG as a fuel:

  • SOx down by 99%
  • CO2 down by 15%
  • NOx down by 10%
  • Particular matter down by 90%


How are the quantities in the deck tanks measured?

The deck tanks are fitted with level radars, the same as the cargo tanks. There is no flow meter fitted to the filling line of deck tanks. Quantity calculations will be completed the same way as cargo tank calculations.

Are there extra gas detectors in the engine room?

Yes, two extra gas detectors will be added: one in the bottom of the engine room and one at the LPG line connection to the engine.

What type of pilot fuel can be used when running on gas mode?

The engine can use any fuel oil as pilot fuel. To be compliant with IMO 2020 regulations under the current flag approvals, only compliant fuels can be used.

Is the gas injection system the same as on LNG vessels?

The engine philosophy and safety systems are greatly based on the ME-GI engine, but the injection is different. Whereas LNG or methane is injected as a gas, the LGIP engine will inject LPG as a liquid. Consequently, LPG only needs about 50 barg supply pressure to the engine and is boosted in pressure in the engine for injection, in the same manner as conventional fuel.

Cost Savings

Is it cheaper to run on LPG?

LPG is traditionally a cheaper fuel than marine gas oil (MGO). Using our dual-fuel engine technology, you can also take advantage of fluctuating fuel prices in the future. Importantly, the ability to use LPG cargo as a supplement fuel source provides significant cost savings for VLGC owners or charterers, including reduced time and fees for fuel bunkering.

Does running on gas affect speed and performance of the vessel?

No, running on gas will not affect the speed of the vessel. The performance and efficiency will remain the same. The higher energy content (calorific content) of LPG vs compliant fuel means consumption of LPG will be reduced by about 10%.

Will the vessel’s range be affected? What is the deck tank range?

At deck tank volumes, the endurance at 16kts will be about 27 days. With the use of the cargo remaining onboard after delivering 46,200mt of LPG, the endurance is increased to more than the vessel’s current endurance on compliant fuel. In combination, this will allow enough LPG for the delivery of a full cargo and to complete a full return voyage from the US gulf to Japan via the Panama Canal.

Readily Available Supply

Is there any quality criteria for the gas that will be used as fuel?

See attached minimum requirements for the gas to be used as fuel.

Where are the bunkers loaded at the discharge port?

There is no need to load bunkers at the discharge port if enough fuel is kept for the ballast voyage. If not, then compliant fuel would be used.

How are bunkers loaded?

Bunkers are loaded through the cargo system directly into the deck tanks. This is done in parallel or in sequence with the loading of the cargo tanks.

Can LPG be bunkered directly into the deck tanks?

Yes, bunkering is done directly into the deck tanks from the cargo manifold. However, the cargo systems and fuel gas system are connected so bunkering directly from the cargo tanks is also an option.