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Writer's pictureCadet Kush Rana

Ammonia-Diesel Synergy: Propelling Greener Marine Transport


Disclaimerr: Present-day cadets of DMET are always going to be better than past generations. This is something we all should accept and help them excel in. At Dmet Club, we are opening the blog section for all DMETians, both present-day cadets and alumni, who want to contribute their knowledge and resources to help DMETians rule the ocean and beyond. While this is a small step, it is a step towards a better future for the maritime industry, empowering cadets with access to a plethora of content at their fingertips, free of charge. Thanks to our partners like MarineX, DMECA, and DMET Samvaad, today's blog post is curated by Cadet Kush Rana. Please read and share your feedback at hello@dmetclub.com or hello@dmet.club.

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WE ARE DMETIANS!

MARPOL Annex VI, titled "Regulations for the Prevention of Air Pollution from Ships", enforces stringent regulations to limit direct greenhouse gas emissions into the atmosphere. Additionally, the IMO regulation implemented on January 1, 2020, known as resolution MEPC.280(70), mandates a global-scale reduction in ship emissions. Specifically, it imposes a strict 0.5% cap on sulphur content in marine fuels, a significant reduction from the previous 3.5% limit. Consequently, a pressing need has arisen for an alternative marine fuel that not only complies with these rigorous regulations but is also economically viable.


Our research paper thoroughly explores and advocates for ammonia as the optimal marine fuel alternative, surpassing other available choices. The proposed fuel system utilises gasoline as a pilot fuel. Furthermore, to address nitrogen oxide (NOx) emissions and achieve minimal air pollution, it integrates a Selective Catalytic Reduction (SCR) system, ultimately resulting in substantially reduced or nearly absent emissions. 


 

Dual Fuel Propulsion System using Ammonia

Why Ammonia is a Better Alternative?

Approximately 25% of total carbon emissions are caused by maritime transportation. The main sources of carbon emissions onboard ships originate from two main areas: The main Propulsion and Electricity Production. 


Ammonia has been seen as the best alternative which can replace the existing fuels in the maritime industry, which have been witnessed to have high carbon footprints.


Since the production of ammonia can be done in numerous ways, its manufacture can be done not only on a large scale but is also a cheap alternative. The technical paper focuses more on the mechanism of the proposed Hybrid system, hence the focus is more on the methodology. Keeping in mind making the paper to the point, the methodology has been written in more detail, rather than the characteristics of the fuel.


Although discussions about LNG as an alternative marine fuel have risen, its methane slip, which is unburnt methane, is a factor that needs attention. Methane slip is found to be 25 times more potent Greenhouse Gas emitter than carbon dioxide. Since there are no IMO conventions about methane slip as of now, regulations about the same shall likely come into being in the future.


Here, Ammonia as a marine fuel attracts attention. It has numerous industrial applications, therefore its manufacture, storage and transportation are widely known.


Hydrogen, as a fuel, requires a cryogenic temperature of -253 degrees Celsius and requires a large storage tank as the volume is 4.5 times more than HFO. Contrary to ammonia, Hydrogen burns very fast and has a very high calorific value. Therefore, its combustion control technology in case of any hazard is a factor to be taken into account. Its high NOx emission is also a major problem as it is also an enormous contributor to GHG emissions. Transportation and bunkering of Hydrogen fuel is also a technology that is yet to be developed as stated earlier, due to its highly volatile nature as well as high storage volume.


Ammonia is not only more energy dense (12.5 MJ/l) than Hydrogen but also has a very low flammability range of 4 to 15%. Ammonia also can be stored at room temperature and takes liquid form at -33 degrees Celsius under a pressure of 11 Bar. Its bunkering also does not stand as a factor due to its easy and available technologies in transportation. Structurally, the high octane ring in Ammonia can be used to promote anti-knocking properties in its working. 



 

The Need for a Alternative Fuel: Problems with Ammonia and its solutions:


Ammonia can be used as an environment-friendly and the most pollution-free fuel if some modifications are made to its usage. This is the primary reason why a pilot fuel is proposed.

 

Problem 1: Requirement of High Ignition Temperature

Solution: It is a frequent practice to combine ammonia with conventional fuels used in internal combustion engines, such as petrol, diesel, LPG, ethanol, methanol, hydrogen, etc, in order to overcome the challenging ignition problem of ammonia.


Ammonia-fuel mixtures can minimise the requirement for extra components or engine modifications. Therefore, internal combustion engines can switch to a hydrogen economy at a low cost. Ammonia is frequently introduced into engines together with gaseous air from the air intake manifold. The ammonia, fuel, and air mixture needs to be carefully adjusted in order to produce as much maximum power and as few emissions as feasible. 


A thorough blender design and automatic control system would be necessary for this. To determine the best mixing ratio for ammonia, fuel, and air, an ideal blender should be created for each conventional fuel to be blended with ammonia. Alternatively, ammonia can be ingested by infusing separate liquid phases of fuel and ammonia into the intake manifold. The ammonia and fuel flow rates in this method need to be properly calibrated. To stop the ammonia slide, efficient ammonia injectors should also be created.

 

Problem 2: Low flame velocity

Solution: The decreased flame speed of ammonia compared to other conventional fuels presents additional difficulty when using it in an internal combustion engine. The reduced flame speed reduces power by preventing temperature diffusion in the cylinder throughout the combustion stroke. Both compression engines and spark ignition systems exhibit this issue. As a result, using ammonia in a normal engine is not feasible without experiencing power losses. Ammonia is still a valuable and substantial alternative fuel for internal combustion engines when taking into account that it is a carbon-free fuel and has the potential to lower carbon emissions. All of the aforementioned strategies can assist in resolving poor flame velocity. Higher compression ratios warmed ammonia, and ammonia-fuel blends, specifically, can all increase flame velocity.

 

Problem 3: Slow Chemical Kinetics

Solution: Ammonia's high ignition temperature and low flame velocity make it less efficient as a fuel for internal combustion engines than standard fuels. Because of the slow chemical reaction rate, ammonia is released from the exhaust without being burned. Adding a promoter to an ammonia-air mixture is a typical approach to speed up the chemical reaction rate of ammonia combustion. As mentioned in the preceding section, conventional fuels and hydrogen are frequently employed as a promoter in ammonia-fueled engines. Ammonia-fuel mixtures have the potential to speed up the chemical process of ammonia combustion. Additionally, a catalyst made of NaCl, BaCl2, and NaF is utilised to improve the chemical kinetics of ammonia combustion.

 

Problem 4: NOx Emissions

Solution: It is a post-combustion method wherein the NOx emissions can be controlled by bypassing the NOx gas through a chamber where qualitative and quantitative gas analysis is done by sensors fitted in the chamber. 


The exhaust gas containing NO2 is directed into the SCR chamber, where it passes through a series of layers and channels containing the catalyst. The SCR catalyst typically contains materials like titanium dioxide or vanadium oxide, which act as a chemical catalyst for the reduction reaction. To facilitate the reduction reaction, a reducing agent is injected into the exhaust gas stream. Commonly, an aqueous solution of urea (known as diesel exhaust fluid or AdBlue) is used as the reducing agent. As the exhaust gas flows over the catalyst surface, the nitrogen oxides (NOx), including NO2, react with the reducing agent. The reduction reaction converts the NOx into nitrogen (N2) and water (H2O). The simplified chemical equation for this process is as follows:


2NO₂ + 4NH₃ → 3N₂ + 6H₂O


The treated exhaust gas, now with reduced levels of NO2 and other NOx compounds, exits the SCR chamber and is released into the atmosphere with lower harmful emissions. The SCR chamber is an effective and widely used technology to meet stringent emission regulations and improve air quality by reducing nitrogen dioxide emissions, which are known to contribute to air pollution and respiratory health problems.


Regular maintenance and monitoring are essential to ensure the proper functioning and efficiency of the SCR system.

An SCR chamber designed by SICK sensor intelligence.

 

How the pilot fuel will work: Adopting the Ammonia-Gasoline dual fuel?

By infusing ammonia and gasoline separately into the intake manifold in the liquid phase, ammonia can be employed in spark ignition engines. The crank angle and piston position must be specially adjusted for the spark timing since ammonia burns slower than gasoline. The same quantity of carbon dioxide is reduced when ammonia is used in place of about 70% of Gasoline. If the pressure is not higher than the cylinder compression pressure, ammonia should not be injected into the cylinder. Ammonia is premixed with air and delivered into compression ignition engines through the intake manifold. A small amount of diesel fuel or another promoter is then injected within the cylinder to ignite the ammonia-air mixture. 


How the fuel will be used in an IC engine and demonstration of its working.

Safety

  1. Ammonia is toxic and flammable, posing safety concerns during handling, storage, transportation and bunkering. 

  2. Proper safety protocols and training are essential to mitigate potential risks, Developing safe onboard storage and bunkering procedures at ports are vital aspects of ensuring the feasibility of using ammonia as a marine fuel.

  3.  Crew training in management, storage and usage of Ammonia and operating types of machinery involved in the usage of the dual-fuel must be done thoroughly. 

  4. Double-layered pipelines can be used in the ship to carry the ammonia fuel to prevent leakage in case of any accidental breaking.

Economic Factors

  1. The economic viability of ammonia-gasoline dual fuel depends on factors such as the cost of ammonia production, supply chain logistics, and potential government incentives or carbon pricing mechanisms. 

  2. As demand for sustainable fuels increases and production scales up, the cost of ammonia may become more competitive, improving its feasibility as a marine fuel.

 


The utilisation of ammonia as a marine fuel presents significant promise and challenges that must be addressed to make it a viable option for the shipping industry. The primary limitations of ammonia, such as its low ignition point and flame velocity, can be mitigated through the implementation of a dual fuel approach in combination with high-combustion-rate fuels like gasoline or LNG. 


This strategy enhances engine efficiency and reduces the need for excessively large storage tanks, making the transition more feasible. To ensure success, the development of technology for an auto-controlled ammonia-fuel blend is imperative, including preheating ammonia, increasing compression ratios, and employing ammonia oxidation catalysts for NOx reduction. 


However, a comprehensive approach is required, including adequate crew training and education on the handling and usage of dual fuels and associated machinery to guarantee safety and effectiveness. Ammonia holds great potential as a midterm strategy to meet current carbon and GHG emission standards in shipping.
 

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