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Alternative Fuels Online Conference (Oct 2020)

Frequently asked questions

These were some of the most frequently asked questions during DNV’s Alternative Fuels Online Conference on 15 October 2020. They have been compiled from more than 500 questions submitted, considering mainly questions addressed to DNV speakers. 

For any further questions, please contact us.

FAQ - LNG and methane emissions

When calculating greenhouse gas emissions from LNG, there is a debate on whether the 20- or 100-year Global Warming Potential factor should be used. What is the most appropriate factor?


Greenhouse gas (GHG) emissions from using LNG as fuel can be calculated by considering both CO2 and methane emissions associated with the use of LNG. Methane is the main component of LNG, and small amounts of it can escape unburned from engines (also known as methane slip). Methane is a potent GHG and there is often a debate on whether the 20- or 100-year Global Warming Potential (GWP) factor should be used. The 100-year GWP (GWP100) was adopted by the United Nations Framework Convention on Climate Change (UNFCCC) and its Kyoto Protocol and is now used as the default metric. The reason for this is that climate change is a long-term problem, and solutions with the best overall impact in the long term should be considered. DNV is also using this factor, following the UNFCCC approach, to calculate the CO2-equivalent emissions of methane.

What are the overall greenhouse gas emissions from LNG when methane emissions are considered?


Engine emissions with LNG as fuel depend strongly on engine technology. Medium-speed 4-stroke engines tend to have higher methane slip, while large 2-stroke engines have lower methane emissions. Even within these groups, engine technology plays an important role. In the 4-stroke engine family, spark-ignited gas engines typically have lower methane emissions than dual-fuel Otto engines. In 2-stroke engines, high-pressure (diesel) engines virtually eliminate methane emissions due to better combustion, while low-pressure engines have small amounts of methane emissions. Engine makers have been working on reducing methane emissions for more than a decade, and modern designs have significantly reduced emissions compared to five or ten years ago. The new 2-stroke low-pressure engines expected on the market in 2021 are expected to have significantly lower emissions, while the same is true for many modern 4-stroke engines as well.

Finally, the question of methane leaks during LNG production is also often discussed. While emissions from the production of LNG are currently not considered by the IMO, this question should not be ignored. It is important to note that methane leaks often occur during both oil and gas production, therefore this is not a problem associated with LNG only. These leaks vary widely between various oil and gas fields and countries with or without regulations for controlling such emissions.

Based on average values for methane leaks during production, and taking the life cycle of the fuel into account (production and use on board vessels), the following values are currently used by DNV as representative of modern engine designs:

  • 2-stroke engines: 14‒21% reduction in CO2-equivalent, compared to a conventional diesel engine, depending on engine technology. Low-pressure engines are expected to perform even better in future.
  • 4-stroke engines: 6‒15% reduction in CO2-equivalent, compared to conventional diesel engines, depending on engine technology. These engines are also continuously being improved, and the use of methane catalysts is being considered for further reductions.

Are there any solutions for reducing or eliminating methane slip?


Methane slip from internal combustion engines can be reduced in two different ways:

  • Optimization of combustion, to ensure methane is better burned in the combustion chamber and does not escape with exhaust gases. Such measures typically also result in improved engine efficiency, as less fuel is wasted. Both 2-stroke and 4-stroke engines can benefit from such measures.
  • Use of oxidation catalysts for reducing methane from exhaust emissions. Such catalysts are currently being tested, and according to early reports they could reduce methane by up to 70% from 4-stroke engines.

Use of such technology, particularly the oxidation catalysts, will come at a cost. However, this allows for reaching LNG’s potential for reducing GHG emissions by approximately 20%. It should also be noted that proposals for regulating methane emissions from LNG engines have been submitted to the IMO. This topic will be discussed starting in 2021, and it is reasonable to expect that regulations for controlling these emissions will follow in coming years. This will be a positive development, as it will enable use of this technology.

LNG is a fossil fuel. What is its role in a carbon-neutral future?


LNG is criticized as a fossil fuel that can offer only marginal savings in greenhouse gases. It is often argued by critics that instead of investing in LNG infrastructure, other fuels should be developed.

DNV’s position can be summarized as follows:

  • LNG in modern engines can provide a GHG reduction of 20%. Combined with efficient vessel designs, in many ship segments this can result in newbuilding designs that can reach the IMO’s ambitions by 2035‒2040.
  • Currently, there are no other obvious solutions for the long term, either due to limited fuel availability (e.g. biofuels, e-fuels) or due to lack of mature technology. Therefore, it is important to explore all possible solutions now.
  • However, waiting until a solution emerges can be a risky bet, as such a solution may not be available before 2030. Therefore, it is important to use fuels that are available today for newbuildings, and these are LNG or LPG (see next question). These fuels can achieve concrete emission reductions today, while they can be a bridge to low-carbon fuels in future.
  • Preparing for fuel flexibility now is also recommended, whether this means retrofitting to ammonia or preparing to use bio-/e-fuels if and when they become available.


Can LPG be part of the solution to decarbonizing shipping?


Using LPG as fuel can help reduce CO2 emissions by approximately 17% over the life cycle of the fuel. It can also contribute to a 15% reduction in the EEDI of newbuildings. Engine technology is commercially available for 2-stroke engines, while 4-stroke engines have been used for power generation on land and can be marinized if there is demand. The fuel is also easier to handle than LNG, as cryogenic materials are not required for the fuel tanks. This also results in lower investment costs for such a system. The first LPG carrier was retrofitted to run on LPG as fuel in October 2020, and several more LPG carriers, both existing ones and newbuildings, are expected to use this fuel in coming years, while there has already been some interest from other ship types. Using LPG as fuel can also be a good first step towards use of ammonia when this technology becomes available, due to the compatibility of materials and expected similarities in engine design.

FAQ - Methanol

How can methanol contribute to decarbonizing shipping? And why is it not used more widely today?


Methanol has been used as a fuel for a number of years, mainly in methanol tankers but also in a passenger vessel. Engine technology is available, both for 2-stroke and 4-stroke engines, while experimentation with methanol for powering fuel cells is taking place. Using methanol from fossil sources (typically produced from natural gas) available today contributes to approximately 10% lower CO2 emissions during combustion. When the life cycle of the fuel is considered, taking into account the production of methanol, the CO2 emission levels are very similar to those with conventional fuel. Methanol can be an interesting fuel when produced as bio-methanol or synthetic/e-methanol, which have the potential to significantly reduce GHG emissions.

So far, methanol has only limited use due to its price, which has become comparable to or higher than MGO in recent years. Low-carbon methanol is expected to be more expensive, therefore regulations providing incentives for using it would be needed to increase the uptake of clean methanol.

FAQ - Biofuels

Are biofuels sustainable? And how can their sustainability be measured?


Biofuels is a very broad term covering a wide range of fuels produced from biomass. Such fuels can be biodiesel, bio-methanol, FAME (Fatty Acid Methyl Esters), HVO (Hydrogenated Vegetable Oil), biogas and many others. Depending on the source of biomass, processing and type of energy used to convert it into a fuel, the carbon reduction or sustainability potential of each fuel will also vary. The supply chain for each fuel can be complex and have an impact on other environmental parameters, such as land use.

Certification is an effective means for proving the sustainability of biofuel and biomass products throughout the supply chain. DNV holds global accreditation for the ISCC (International Sustainability Carbon Certification) scheme. ISCC focuses on GHG reduction through the value chain, sustainable land use, the protection of natural habitats, and social sustainability for the feedstock production. Based on the EU Renewable Energy Director (RED), ISCC requires a minimum GHG emission savings of 60% for installations in which production starts from 2017 onwards. Feedstock production (plantations) also needs to comply with a number of principles.

FAQ - E-fuels

Are biofuels sustainable? And how can their sustainability be measured?


Synthetic fuels, also known as e-fuels or P-t-F (Power-to-Fuel), are fuels that can be produced by combining hydrogen and CO2. The process for producing fuels in this manner is well known and, depending on demand, any type of hydrocarbons can be produced, such as e-LNG, e-methanol, e-LPG or e-MGO. In order for these fuels to be considered “low carbon”, it is important to use hydrogen produced with clean energy (such as electrolysis powered by renewables) and CO2 that is extracted from the atmosphere. In this way, the CO2 that is emitted when using the fuel will be balanced by the CO2 removed from the atmosphere. One important benefit of these fuels is that they can be used in existing infrastructure. However, infrastructure for producing clean hydrogen is needed, and the technology for extracting CO2 from the atmosphere is still expensive and energy intensive. An alternative would be to use CO2 captured from another combustion process, but in this case the overall carbon balance has to be calculated taking into account that CO2 is not completely eliminated.

FAQ - Ammonia

What are the emissions from an ammonia engine? Can N2O emissions be a risk for ammonia as fuel?


Ammonia engines are currently under development and are expected to be commercially available in around 2023‒2024. While it is not possible to know exactly the emission levels from these engines, some general comments on what can be expected can be made:

  • NOx emissions: it is expected that these engines may have high NOx emissions. However, a Selective Catalytic Reduction (SCR) catalyst can be used to reduce them to levels compliant with IMO requirements.
  • N2O emissions: there is a risk of forming N2O (nitrous oxide), which is a very potent greenhouse gas, 265 times stronger than CO2. Engine makers are considering their options for eliminating such emissions, by optimizing the combustion process and/or by using a catalyst in the exhaust gas system.
  • NH3 slip: it is also possible to have small amounts of unburned ammonia escape through the exhaust gases. While this is not a greenhouse gas, ammonia is very toxic even at very low concentrations and has a very distinct unpleasant odour. Therefore, engine makers are also considering their options for eliminating such emissions.

Finally, it is expected that a pilot fuel injection will be required for igniting ammonia and maintaining a smooth combustion process. Therefore, a certain amount of CO2 will be emitted, and such an engine will not be 100% carbon-free unless a carbon-neutral fuel is used as pilot (such as e-MGO).

FAQ - Nuclear propulsion – atomic batteries

Can nuclear propulsion / atomic batteries be a feasible solution for decarbonizing shipping?


DNV believes that all fuel options for decarbonizing shipping should be explored, as there is no single solution that appears to be a clear winner. We have been monitoring technology developments in this field over the years.

The Molten Salt Reactor proposed by Core Power is a technology that has the potential to resolve many of the challenges with conventional designs and which is being actively promoted. It is our understanding that if everything goes according to plan, a demonstrator reactor will be ready in 2024, while a marinized reactor of 10‒20 MW will be available in 2028. This is a sign that there are still several technical challenges to be resolved, and we cannot still safely know when this technology will be commercially available for newbuildings. The question of public perception of such technology should also not be underestimated, even though it is radically different from conventional nuclear reactors.

Assuming that the technology’s development goes according to plan, we will not be able to conclude before the mid-2030s whether it’s a commercially feasible option, and even then it is reasonable to assume that this technology could be used in newbuildings only. Based on the above, we believe that penetration of such technology on a large scale can only start around 2035‒2040.

In brief, it is important to support exploration of such technologies, but we cannot take for granted today that they will be the solution to decarbonizing shipping. In the meantime, it is important to use fuels that are currently available for reducing GHG emissions.

FAQ - Carbon capture on board vessels

Can carbon capture on board vessels be used to reduce the carbon footprint of shipping?


There are several carbon capture technologies that have been explored in the past or are under development now. While the technology is working in principle, it requires a significant increase in fuel consumption and the installation of complex equipment on board, which may have implications for vessel design and stability. An additional complication is related to storing the captured CO2 on board until reaching appropriate facilities where it can be safely disposed of. Such facilities are still not available, and it is not clear if or when such infrastructure could become available.

Capturing CO2 from land-based power plants producing marine fuels may also be an option for reducing the carbon footprint of shipping. More generally, if carbon capture technology starts being adopted by land-based industries in future, the infrastructure for handling and storing CO2 will also be developed and could potentially be used by ships with such systems. It is, however, difficult to make an estimate on whether or when such infrastructure will become available.

FAQ - Use of electricity

What is the expected contribution of electricity in decarbonizing shipping?


According to DNV’s Maritime Forecast 2050, the share of electricity as part of the fuel mix will be quite low towards 2050. While electricity can be used to power ships in port (shore power), with current battery technology it is only feasible to use electricity for the propulsion of very small vessels operating in areas with charging infrastructure, such as small ferries. New battery chemistries are in the R&D phase, which could result in batteries with much higher energy density in future. If such technologies become commercially available, it is conceivable that they will be used to power larger vessels in future, assuming that the appropriate charging infrastructure is developed.

A more relevant application of batteries is in the form of hybrid propulsion designs, which can help increase energy efficiency and reduce local pollution from such ships.

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