A team of Australian engineers have successfully converted a diesel engine to run as a hydrogen-diesel hybrid – reducing CO₂ emissions by more than 85% in the process.

The team from UNSW’s School of Mechanical and Manufacturing Engineering spent 18 months developing the Hydrogen-Diesel Direct Injection Dual-Fuel System, which enables existing diesel engines to use 90% hydrogen as fuel.

The researchers say that any diesel engine used in trucks and power equipment in the transportation, agriculture and mining industries could ultimately be retrofitted to the new hybrid system in just a couple of months.

Green hydrogen, which is produced using clean renewable energy sources such as wind and solar, is much more environmentally friendly than diesel.

In a paper published in the International Journal of Hydrogen Energy the team showed their patented hydrogen injection system reduced CO₂ emissions to just 90 g/kWh – almost 86% below the amount produced by the same engine using only diesel.

“This new technology significantly reduces CO₂ emissions from existing diesel engines, so it could play a big part in making our carbon footprint much smaller, especially in Australia with all our mining, agriculture and other heavy industries where diesel engines are widely used,” team leader Professor Shawn Kook said.

“We have shown that we can take those existing diesel engines and convert them into cleaner engines that burn hydrogen fuel.

“Being able to retrofit diesel engines that are already out there is much quicker than waiting for the development of completely new fuel cell systems that might not be commercially available at a larger scale for at least a decade.

“With the problem of carbon emissions and climate change, we need some more immediate solutions to deal with the issue of these many diesel engines currently in use.”

The UNSW team’s solution to the problem maintains the original diesel injection into the engine, but adds hydrogen fuel injection directly into the cylinder.

By specifically timing the hydrogen direct injection, the mixture condition inside the cylinder is controlled, which resolves the problem of harmful nitrogen oxide emissions that have been a major hurdle for commercialisation of hydrogen engines.

“If you just put hydrogen into the engine and let it all mix together you will get a lot of nitrogen oxide (NO_x) emissions, which is a significant cause of air pollution and acid rain,” Prof. Kook said.

“But we have shown in our system if you make it stratified – that is in some areas there is more hydrogen and in others there is less hydrogen – then we can reduce the NO_x emissions below that of a purely diesel engine.”

Importantly, the new Hydrogen-Diesel Direct Injection Dual-Fuel System does not require extremely high-purity hydrogen which must be used in alternative hydrogen fuel cell systems and is more expensive to produce.

And compared with existing diesel engines, an efficiency improvement of more than 26% has been shown in the diesel-hydrogen hybrid.

That improved efficiency is achieved by independent control of hydrogen direct injection timing, as well as diesel injection timing, enabling full control of combustion modes – premixed or mixing-controlled hydrogen combustion.

The research team hope to be able to commercialise the new system in the next 12–24 months and are keen to consult with prospective investors.

They said the most immediate potential use for the new technology was in industrial locations where permanent hydrogen fuel supply lines were already in place.

That includes mining sites, where studies have shown about 30% of greenhouse gas emissions are caused by diesel engines in such items as mining vehicles and power generators.