How LNG Engines Could Be Converted To Run On Ammonia

Gruber in front of his good friend Betzy. Photo: Helge Stranden, UNINETT / Sigma2

Posted on Jul 2, 2021 2:06 PM by

Gemini News

Andrea Gruber, SINTEF researcher, calculates the numbers – with the help of the Betzy supercomputer. With an endless number of calculations linked together, researchers are now providing answers to what is needed for the well-known chemical ammonia to become a climate solution for large parts of maritime transport.

The chemical has the ability to remain liquid at room temperature at moderate pressure levels, like in regular gas cylinders. In comparison, climate-friendly alternative hydrogen requires a temperature below minus 253 degrees Celsius to stay liquid.

In addition, we already have both production opportunities and a ready distribution network for ammonia. This makes the solution easy to use for large parts of the world. Ammonia can be produced with fully renewable energy sources, or with carbon capture and storage from natural gas.

Because pure ammonia burns poorly and is difficult to ignite in an engine, the researchers’ idea is to use the waste heat from the combustion process to partially break down the ammonia. Ammonia is made up of one nitrogen atom and three hydrogen atoms. After the decomposition, we are left with a fuel composed of ammonia, nitrogen and hydrogen.

The hydrogen content of this fuel helps to start the combustion process well, with the help of large amounts of heated air from the environment. It provides movement and propulsion in the well-known thermal process of the engine.

“The fact that the ‘working medium’ in this combustion is air makes the process simple and inexpensive enough that it can be adapted to larger cargo ships. For battery-powered vessels or vessels that use energy from cell fuel, this is much more difficult, ”says Gruber. “Unlike the electrochemical process in a fuel cell, which is also an attractive alternative in small vessels, the internal combustion engine uses ‘all’ the air and not just the oxygen content (~ 22%),” adds Gruber .

Animation of flame (red) burning through the turbulent mixture of ammonia, hydrogen and air (green). The calculation is carried out in a small proportion (1 cm3) but representative of the entire combustion chamber by solving differential equations of nearly 1 billion points. Animation: Andrea Gruber / SINTEF

Billions of calculations and useful waste heat

The Betzy supercomputer is researchers’ most important tool in the search for the optimal combustion of ammonia. Betzy has five times the existing computing capacity of Norwegian researchers and has a total computing power equivalent to 43,000 “ordinary” laptops. In other words: with a normal laptop, it would take 1,168 years to run the simulations for this project.

The researchers used 80 million hours of computing over roughly three months from December 2020 to February 2021. The mathematical solution shows in detail how ammonia is burned in a ship’s engine compared to natural gas or gas. pure hydrogen.

There are already natural gas (LNG) engines on the market, and once the simulation work is done, researchers have the exact data needed to redesign existing gas engines to run on climate-friendly ammonia. . Thus, these calculations help us on the road to phasing out heavy oil from shipping.

“We’ve done a lot of work with mathematical simulations of internal combustion engines before, but then we had to collaborate with research environments in the United States to be able to use the computing power there. Now we finally have the opportunity. here in Norway, ”says Gruber.

In practice, researchers calculate how 19 chemicals react with each other in 63 different elemental reactions – with different mixing ratios in a turbulent combustion process.

“What we know from before is how a certain mixture of fuel and air is burned without turbulence. But turbulence appears to be an inevitable fact in any practical application of the combustion process. Obtain more and more information. Being more precise about this is absolutely essential for optimizing engines for the best use of fuel and reducing emissions, but it also requires enormous computing power, ”explains Gruber.

The next step is laboratory experiments

The calculations gave the researchers important details about the behavior of ammonia under different combustion conditions and made it possible to simulate virtual flames in a small but representative part of a combustion chamber.

Research shows that under normal operating conditions, pure hydrogen has far too high reactivity as a fuel and a tendency to ignite prematurely, while pure ammonia ignites and burns poorly.

“Neither of the two fuels is therefore favorable for internal combustion engines. However, by using the waste heat from the ship’s engine, the ammonia can be partially broken down on board. The result is an ammonia fuel mixture, d ‘hydrogen and nitrogen “, specifies the SINTEF the researcher explains.

Such a process will be practical for two reasons: First, the waste heat from the engine is recycled to increase the energy content of the fuel, which improves the overall efficiency of the machine. Second, the combustion properties of the new ammonia / hydrogen / nitrogen fuel mixture will be very similar to what can be called standard natural gas.

“This is important, because it means that it will be possible to adapt the engines that are already in the current fleet to burn the fuel mixture,” explains Gruber.

This article is courtesy of Gemini News and is reproduced here in an abridged form. The original (in Norwegian) can be found here.

The views expressed here are those of the author and not necessarily those of The Maritime Executive.


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