Alcohol as fuel, what are the challenges and opportunities?
Alcohol fuels are interesting and important in the context of the energy transition because their combustion does not release sulfur oxides and particulate matter, unlike the combustion of diesel oil. The alcohol fuel methanol is even considered one of the most feasible 'clean' options that can be widely applied within the international shipping industry. In this article, we list the alcohol fuels that can be used in engines and discuss the challenges and (future) opportunities.
The difference between alcohol fuels and renewable diesels
Unlike renewable diesels HVO and BTL, alcohol fuels have little to no lubricating properties. This is a challenge for high-pressure fuel injection systems and other systems that require lubrication. For example, fuel injection pumps and fuel injectors – all moving parts need lubrication. However, this does not mean that combustion engines cannot run well on alcohol fuels, as they emit no sulfur oxides (SOx) and particulate matter (PM).
Catalyst for filtering out nitrogen oxides
Due to the high combustion temperatures, the use of alcohol fuels does produce nitrogen oxides (NOx). These are compounds that consist of nitrogen (N) and oxygen (O). It is expected that the nitrogen oxide content will be lower, but this also depends on the engine settings. Additionally, incomplete combustion can form formaldehyde (CH2O), a gas with a strong, unpleasant odor. The solution for this is a catalyst, which cleans the exhaust gases of these harmful substances.
Alcohol fuels that can be used in engines
Production
Methanol is a type of alcohol that is not suitable for consumption. It is one of the most commonly used raw materials in the chemical industry. Nearly half of all methanol is used to make formaldehyde, which is a raw material for, among other things, adhesives, paint products, and plastics.
However, methanol is also suitable as a fuel and can be used in engines and fuel cells, as well as in the production process of biodiesel (vegetable diesel oil). To date, most methanol is derived from natural gas and coal (black methanol), but green methanol is on the rise. More on that later.
Emissions and application
The great advantage of an alcohol fuel like methanol is that it contains no sulfur. Therefore, its combustion does not release sulfur oxides or particulate matter. The small amount of particulate emissions that do exist comes from the engine's lubricating oil consumption and the pilot injection. It does not come from the methanol itself, which burns cleanly, meaning that the exhaust gas after-treatment can be less complex and smaller than in diesel engines.
Methanol is a relatively safe fuel, which is liquid at ambient temperature and can therefore be stored well. Since the temperature at which methanol starts to evaporate is lower than that of diesel oil, additional safety regulations apply. These should be taken into account, but they do not obstruct large-scale storage and use.
Because methanol is liquid, just as diesel oil is, it is a strong candidate to replace diesel oil. However, the properties of methanol differ significantly from diesel oil. Therefore, engines, fuel systems, and fuel storage must be adapted before it can be used. Converting existing ships can be costly and is not always possible.
What is green methanol?
A small but growing percentage of methanol is produced from renewable raw materials, such as biomass. This methanol is called green methanol because its production involves a carbon cycle (the natural carbon cycle between the Earth's surface and the atmosphere). Green methanol has the same composition as methanol produced from fossil fuels and is therefore well suited for use in combustion engines.
Bio-ethanol
Production
Bio-ethanol is the alcohol found in alcoholic beverages. Synthetic ethanol is used in solvents, plastics, medicines, perfumes, antibacterial gels, and cosmetics because it easily dissolves in water and other organic compounds.
Synthetic ethanol is made from petroleum. Bio-ethanol is produced by fermenting the sugars naturally found in grains and other sources, which is also the limitation. It is not sustainable to use even more fertile land to produce the raw materials for bio-ethanol (rapeseed, sugar beet, sugar cane, and grains such as corn and wheat) instead of for food. But this would be necessary if you want to use it on a large scale as fuel for the shipping industry.
Emissions and application
Like methanol, pure ethanol is highly flammable, with relatively clean combustion products (the substances produced from the combustion of a fuel). In Brazil, many cars run on bio-ethanol, and in the Netherlands, among other places, it is blended into Euro 95 gasoline (E10). For pure use in diesel engines, the same modifications are required as for methanol.
DME (Dimethyl Ether)
Production
Dimethyl Ether is a gaseous ether. For the production of DME, several steps are needed. It starts with biomass, which is dried and compacted, then converted into a gas mixture of carbon dioxide, carbon monoxide, and hydrogen using steam.
After that, it is converted into methanol using a catalyst and then dehydrated into DME. DME is used in household chemicals, aerosol sprays, spray paints, varnishes, mounting foam, and polystyrene foam, and it is also suitable as a fuel.
Emissions and application
The combustion of DME releases CO2, but this falls within the carbon cycle if you produce it from biomass and sustainable hydrogen. Additionally, DME has a low auto-ignition temperature, which means that when used in a regular diesel engine, no pilot fuel is needed for ignition (the liquid that helps the engine ignite the fuel).
The use of DME in combustion engines is being researched worldwide by car and truck manufacturers. However, a significant drawback is that it needs to be kept under pressure to remain liquid at ambient temperature, making it more challenging to use and making the storage systems much more expensive. Additionally, the availability and distribution network of DME are much less developed than, for example, those of methanol.
Which alcohol fuel has the future?
We believe that methanol will be the alcohol fuel of the future for maritime applications. This will become clear when you list the main disadvantages and advantages of the different types of alcohol fuels.
We are not yet at the point where methanol can be produced and used as cost-efficiently and on as large a scale as fossil fuels, but the differences are becoming increasingly smaller due to the sharp rise in fossil fuel prices.
The disadvantages and advantages of 3 alcohol fuels at a glance
1. Bio-methanol and e-methanol
| Disadvantages | Advantages |
| Toxic, requiring stricter safety regulations | Multiple methods of production |
| Because the energy density is slightly lower than that of the other two alcohol fuels, a ship needs to carry more of it | Scalable |
| Contains no sulfur | |
| Well-preserved | |
| Liquid at ambient temperature, allowing it to be bunkered like diesel oil | |
| Relatively clean combustion products |
2. Bio-ethanol
| Disadvantages | Advantages |
| Not scalable due to being mostly produced by sugar fermentation | Contains no sulfur |
| The production process depends on a single type of feedstock, which requires land you would rather use for food production | Non-toxic |
| The amount of bio-ethanol needed for the shipping industry cannot be produced due to this limitation | Well-preserved |
| During the production process, 45% of the feedstock is converted into CO2 | Liquid at ambient temperature, allowing it to be bunkered like diesel oil |
| Relatively clean combustion products |
3. DME (gaseous ether)
| Disadvantages | Advantages |
| During the production process, methanol is dehydrated into DME, which is inefficient: it converts a useful fuel into another fuel | Scalable |
| Because it is a gas, it needs to be kept under pressure to remain liquid at ambient temperature, making it more difficult to use and the storage systems much more expensive | Contains no sulfur |
| Non-toxic | |
| Relatively clean combustion products |
Proof of concept and dual-fuel methanol/diesel powered tugboats
As a proof of concept, we at Pon Power ran a Cat engine on methanol in 2020. It was a great success. The concept was not intended for market launch, but it helped us better understand how it works and what challenges remain.
Furthermore, in November 2022, Damen Shipyards, Caterpillar Inc, and Pon Power signed a Memorandum of Understanding for the joint development of a series of dual-fuel methanol/diesel powered tugboats. The aim of the collaboration is to jointly learn how (green) methanol can be optimally used as a fuel on ships, including all aspects related to bunkering, storage, management, and power.
MORE INFORMATION
Would you like to know more about methanol and the use of alternative fuels in Caterpillar engines? Please feel free to contact us.