Ammonia as a Fuel: A Closer Look at its Potential

Chinese manufacturer GAC, in collaboration with Toyota, has recently made headlines by successfully running a car engine on carbon-free ammonia. While the idea of using ammonia as a fuel may seem unconventional, further examination reveals that it is not as far-fetched as it sounds. Research into the use of ammonia as a substitute for fossil fuels has been ongoing for many years, with applications in both petrol and diesel engines.

Ammonia has a chemical formula of NH3, consisting of one atom of nitrogen and three atoms of hydrogen. This composition makes it a dense “hydrogen carrier.” When ammonia is combusted, the engine essentially runs on hydrogen. However, there are challenges associated with using ammonia as a fuel. It contains less energy than petrol or diesel and has a slower combustion rate. Previous research has explored two approaches: splitting ammonia into hydrogen and nitrogen for combustion or using a small amount of fossil fuel to ignite the ammonia.

GAC has not provided specific details about their approach, but it is possible to ignite ammonia directly. Mahle Powertrain, a leading automotive technology company, has conducted extensive research on ammonia combustion as a replacement for diesel in heavy-duty engines. They have tested two methods, including a dual-fuel approach and the use of their innovative Mahle Jet Ignition (MJI) system.

The dual-fuel approach involves retrofitting heavy-duty turbo diesels with a second set of injectors to introduce gaseous ammonia as the primary energy source. On the other hand, Mahle Powertrain has successfully run their single-cylinder research engine on pure gaseous ammonia using the MJI system. This system eliminates the need for fossil fuel as an ignition source and produces ultra-clean combustion with minimal harmful pollutants.

The MJI system incorporates a small pre-chamber in the top of each combustion chamber, equipped with holes at the bottom. A spark plug and a fuel injector are inserted into the pre-chamber. A small charge is injected into the pre-chamber while the main charge enters the cylinder through the inlet ports. When the charge in the pre-chamber ignites, hot gas is expelled through the holes into the cylinder, effectively igniting the main charge.

One advantage of using ammonia as a road fuel is its ability to liquefy under relatively low pressure, around 7.5 bar. This allows for easier transportation in tankers compared to hydrogen, which typically requires storage at 750 bar. Additionally, ammonia’s clean combustion properties make it an attractive option for reducing harmful emissions such as NOx.

While ammonia may not possess the same energy density as traditional fossil fuels, its potential as a clean and sustainable fuel cannot be overlooked. As the automotive industry continues to explore alternative fuel sources to reduce carbon emissions, ammonia presents a viable option. Its convenient chemistry as a hydrogen carrier and the advancements in combustion technology, such as Mahle Powertrain’s MJI system, make it a promising candidate for future applications.

However, further research and development are necessary to address the challenges associated with ammonia as a fuel. Improving its energy density and combustion rate will be crucial to ensure its viability as a mainstream fuel option. Additionally, infrastructure for ammonia production, storage, and distribution will need to be established to support widespread adoption.

In conclusion, ammonia’s clean combustion properties and convenient chemistry make it an intriguing option as a fuel substitute. Ongoing research and collaborations, such as GAC and Toyota’s recent achievement, are driving innovation in this field. While there are challenges to overcome, ammonia holds promise as a sustainable fuel for the future of transportation. As the automotive industry continues to prioritize environmental sustainability, ammonia may play a significant role in reducing carbon emissions and achieving a greener future.