Eco Ship Propulsion Systems for Green Maritime

Combating climate change, which is affirmed to be greatly caused by human behaviour and the use of fossil fuels by all kinds of industries, requires a fundamental rethinking of energy sources. Major international organisations, such as the IMO, strive to set stricter targets for climate protection goals. The IMO also opportunely adapts its regulations to accelerate the reduction of total annual Greenhouse Gas Emissions (GHG) from international shipping to at least 50% by 2050 compared to 2008.

Possible measures could be speed limitations or implementing alternative marine propulsion systems, i.e. green fuels such as biofuels. The IMO also encourages R&D to publish further in-depth studies concerning GHG emissions and logistic chain optimisation, IMO (2018). Hence, Clean Power Generation is also one of the biggest challenges the maritime industry must address in the coming years to reduce carbon dioxide and other harmful emissions from current marine propulsion systems—mostly the notorious ships' diesel engines—and contribute its essential part to global climate protection.

For a long period of time, only emission-free energy sources were used in the ancient marine power supply. The earliest evidence of ships was found in Egypt during the 4th millennium BC (Vance, 2022). These were commonly equipped with sails (wind propulsion) and oars. As the manoeuvring technologies of ships developed, oarsmen were no longer needed, and traditional sea-going ships evolved. Sailing was the only way of shipping until the late 18th century, when the first steamboat with steam propulsion was developed in America, Vance (2022). Because of the poor efficiency of steam turbines which ranges only between 10%-20%, the combustion engine with a better efficiency around 30% was established in the early 1930s, Vance (2022).

This form of power generation also reduced emissions, but still, according to its chemical reaction with oxygen (O2), 1 kg of coal in a steam turbine engine produces 7.348 kg of CO2. A conventional diesel engine burning MGO, which is currently used in shipping, emits approximately 3.3 kg of CO2 per kg of fuel. Heavy fuel oil (HFO) and marine diesel oil (MDO) are also commonly used and more polluted fuels. In 2020, the IMO limited the Sulphur emissions to 0.5%, which means that marine fuels (HFO, MDO, MGO) must meet the sulphur level to be compliant, or the marine vessels with gas turbine propulsion must use a gas turbine exhaust after-treatment system, Senmatic (2022). Therefore, the shipping industry needs to implement clean power for the maritime world as quickly as possible.

As of yet, the shipping industry has been actively looking for feasible technical solutions - some of which have only been applied on a small scale or on land; extrapolating them to the required scale is crucial as the demand increases. Whether it is deploying hydrogen and synthetic fuels into combustion engines, fuel cell systems (Hydrogen Power Generators), or other energy converters, these are considered rising alternatives to transform conventional solutions like diesel engines.

“Alternative fuels” considers all fuels except the recognised traditional petroleum and other fossil fuels, all liquid or gaseous substances that can be converted to energy using a gas turbine as a power generator. And they can be flexibly used for any kind of electrical power generation accordingly. On this path of seeking and innovating, technology pioneers are also fascinated by disclosing promising solutions that were either previously undiscovered or not perceived as promising. All those efforts and initiatives are meant to ensure that shipping remains the most efficient and sustainable carrier for worldwide freight transport.

CO2 emissions of the alternative fuels to Diesel (= 1,00)

Fuels are a form of energy storage converted onboard using a power generator (e.g. combustion engine or fuel cell system) to produce electricity, which then drives the electric motor. Generally, everything that can be ignited can also be burned inside a combustion engine. The available power generators on the market with the best efficiency are fuel cell systems and internal combustion engines (ICEs). However, this is hard to reach in practice, as the combustion engine needs to be adjusted to the respective fuel.

Nowadays, the majority in the maritime world are stuck to such engines i.e. diesel engines, as this energy converter is regarded as the most common and reliable option up to now. Other combustion engines thus far have been developed can burn LNG (Liquefied natural gas), biofuels, methanol, ammonia and hydrogen. As to fuel cell system, is commonly driven by hydrogen, as well as possible by methanol and ammonia. Moreover, methanol and ammonia can be converted to hydrogen, which can then be used to generate power in a fuel cell system or combustion engine. Batteries, another form of alternative power supply, can also be used for energy storage.

Hence, many different raw resources (fuels) can be used for power generation on ships, such as marine engines, as great alternatives or replacements to MGO, i.e., diesel engines. The industries usually evaluate and rank those alternative fuels and respective technologies by taking the aspects into account:

• Sustainability
• Storage possibilities
• Handling on board
• Infrastructure
• Availability
• Propulsion Efficiency
• Well-To-Wake emissions

<-Well-To-Wake (WTW) graphic about fuel pathways. (MeOH: Methanol, CCS: Carbon Capture and Storage, HFO: Heavy Fuel Oil), Law (2021)

Five alternative fuels, hydrogen, ammonia, methanol, LNG and biofuels, have already been introduced and considered in the maritime world. These fuels' availability and existing infrastructure are also already or expected to be soon in place.

Fuel cell systems can be driven by hydrogen, methanol, or ammonia directly on board ships, which have the charming property of having low maintenance requirements compared to gas turbines. They also do not require any lubricating oil.

The efficiency of fuel cell systems usually is between 50% and 55%, much higher than in combustion engines.

Maritime forecast of technology development, DNV (2021)

Hydrogen and ammonia are recognised overall as the best possible alternative fuels to avoid CO2 emissions. And evidently, fuel cell systems driven with hydrogen can achieve locally zero emission.

As to ammonia, although it emits no CO2 and when produced as “green ammonia”, this is a renewable resource from nitrogen, water and oxygen, which can be taken directly from the environment. The drawback of using ammonia is the by-production of the highly effective GHG Nitrous Oxide (N2O) and nitrogen oxides (NOx) during the combustion. Thus, combustion in a conventional engine requires exhaust gas cleaning. The same issue occurs in the fuel cell system, where reformers or crackers retransform the ammonia to hydrogen, but the amount of Nitrous Oxide is much lower, Engel (2021).

Ammonia is also classified as a toxic substance, which might complicate handling this fuel and on-board safety regulations. The use of ammonia on board with a fuel cell system is still subject to research and thus quite expensive, and no reformers have been approved for the maritime market yet.

In recent years, battery technologies have already been well-developed, enabling energy storage and supply on board ships that can be charged from onshore electricity. As electricity could be produced by windmills, solar, coal power, nuclear power, etc., utilising battery systems for storing and supplying electricity has become quite sophisticated.

Learn more about our battery system solutions:
> Battery Energy Storage System – BESS
> Mobile High Power Charger (mHPC)

As one of the few credited technology pioneers and innovators, eCap Marine, on behalf of our like-minded innovators and first-mover clients, has been deploying procurable alternative technologies to serve modern ship propulsion systems and realising their achievable implementations: clean power generation systems for onboard vessels, either inland waterways or seagoing.

With our expertise in shipbuilding, electrification, and engineering, we provide an experienced and competent partner from the initial consultation. This process begins with a feasibility study of the concept, followed by further development, conversion, installation, and after-sales service of emission-free energy generation solutions based on clean fuels such as batteries, hydrogen, or hybrid systems.

Discover more about our expertise:
> Electric or Hybrid Ship Conversion
> Newbuilds