We are in a desperate race to halt our rampant carbon emissions and save the planet from our self-created catastrophe. Some of the most prominent technologies helping us achieve this venture are EVs and hydrogen fuel cells. But due to cost and a slow adoption speed, these technologies have yet to significantly reduce our overall emissions. Fortunately, Australian researchers may have just created a near-perfect bridging technology that can easily convert diesel engines into super-efficient carbon-neutral machines! But how have they done this? And could this cause a carbon-neutral revolution?
Researchers from the University of Sydney have retrofitted a diesel engine to run off 90% hydrogen. This, in turn, has reduced emissions by 85% to only 90g per kWh and has increased engine efficiency by a massive 26%! The oil-derived part of the fuel can easily be swapped out for biofuel with only minor modifications, enabling this engine to run entirely carbon neutrally. Furthermore, this engine doesn’t require high-purity hydrogen and can run off cheaper, easier-to-produce low-purity hydrogen.
But how does this engine work? And why is it better than a pure bio-diesel engine or a pure hydrogen combustion engine? Well, for three reasons: NOx emissions, efficiency, and supply chain reliability.
Firstly, NOx. Diesels operate quite differently to gasoline engines. Rather than a spark triggering combustion, they use compression. When the piston pulls down, it sucks in air and vapourised diesel, which then mix together in the cylinder. When the piston rises, it compresses this gas, which heats it up. The piston compresses it so much that it heats up enough to combust, which pushes the piston back down.
Hydrogen can be used in the same compression ignition style engine, but it has two significant downsides. Firstly, it isn’t very efficient, which means it produces much less power. This is because hydrogen burns far more quickly than diesel fuel, so it has burned up well before the piston has reached the bottom of the cylinder. This, in turn, reduces the force applied to the cylinder and therefore reduces the power of the engine.
Secondly, having a homogeneous mixture of air and hydrogen can create far more NOx emissions than diesel. You see, the high-pressure and high-temperature environment inside a diesel engine causes nitrogen to react with oxygen, producing nitrous oxides (also known as NOx). These emissions are then absorbed by clouds and create acid rain, which can cause massive environmental damage. But because hydrogen burns much more quickly, it ends up burning at a much higher pressure (and therefore much higher temperature) than regular diesel would. This causes a hydrogen-powered diesel engine to produce much higher levels of NOx.
So why not purely bio-diesel? Well, biofuels have a significant problem. They take away from our food supplies and cause rampant habitat loss. I have covered this before in this article. But the long and short of it is that if we are to use biofuels, we need to use them very sparingly to avoid creating an ecological and humanitarian crisis.
This is where the Sydney twin-fuel engine comes in. You see, they installed a second direct-injection system that fires hydrogen straight into the cylinder rather than letting it premix like the diesel. This means that the hydrogen is stratified, or in varying concentrations, in the cylinder. This can slow the flame speed of hydrogen, which means the hydrogen can produce more force on the piston and burn at much lower pressures. Furthermore, it means they can time the injection of the hydrogen to happen at the ideal time, which is later in the cylinder cycle, to produce the largest and cleanest combustion.
In theory, an engine could be made that uses hydrogen in this way as its only fuel. But the researchers wanted to retrofit diesel engines, which are built differently. So to overcome this limitation, they still need to use 10% diesel fuel to keep the cylinders firing correctly. Yet, the overall results are excellent. The engine produces a good amount of power, can be operated carbon neutrally without causing an entirely different ecological disaster, and makes even fewer NOx emissions than a standard diesel engine!
So that’s how this incredible engine works. But why is this useful? And how can it cause a revolution?
Well, this system can be really easily retrofitted to any diesel. So everything from tractors to mining rigs, trucks, and even trains could quickly switch to this system for a very low cost. This technology could be the cheapest way to make these crucial vehicles carbon neutral.
Furthermore, the hydrogen infrastructure should be easy. Hydrogen electrolysis machines are cheap and efficient and can produce loads of low-grade hydrogen for very little money. There are also plenty of biodiesel locations now too, and in the future, they should be even easier to access. So, refusing these machines once converted should be straightforward.
But this hydrogen infrastructure could also be surprisingly efficient. One of the significant problems of hydrogen fuel-cell technology (where you use hydrogen to make electricity and the only byproduct is water) is its overall efficiency. Powering an electrolysis machine and then refining the hydrogen to a high enough purity is very energy-intensive and inefficient. So instead, it makes sense to use this electricity to charge EVs, as they can do far more with far less energy. But this engine needs low-grade hydrogen, which requires much less energy to be produced. Couple that with the increased efficiency of this twin-fuel engine, and it should have a reasonably decent overall efficiency.
With all of this in mind, it is no wonder these researchers are looking to commercialise this engine in the next 12–24 months. In a year or so, people worldwide could be converting their commercial and agricultural diesel machinery into carbon-neutral, ultra-efficient, and clean-burning twin-fuel hydrogen-diesel engines.
The logistics of actually doing these conversions are going to be tough. After all, not all diesel engines are built the same, so they may have to focus their efforts on one model of an engine at a time. But at least in theory, this is a fantastic way to quickly convert diesel-powered vehicles into carbon-neutral ones. Such a bridging technology might be precisely what we need to fend off climate change while we gradually adopt EV technology. So, for the planet’s sake, let’s hope these Aussies have roaring success!