Scientists retrofit diesel engines to use hydrogen as fuel, increasing efficiency 26%

Engineers at the University of New South Wales (UNSW) have successfully retrofitted a diesel engine to use hydrogen as a fuel to reduce carbon emissions, TechXplore reported. The team spent 18 months developing the dual-fuel injection system that uses 90 percent hydrogen as fuel but is confident that future retrofits could be completed in a matter of months.

Electrified transport has been getting a greater push in recent months, with states and countries banning the sales of internal combustion engine-powered vehicles in the next decade. While this is a step in the right direction, there is also a need to rapidly advance technologies that could replace the larger and long-haul vehicles that do the heavy lifting across industries.

Last week, Interesting Engineering reported that Tesla Semi Trucks would roll off the production line before the end of the year, and other electric truck makers could also follow suit. However, a complete overhaul of heavy vehicles to zero emissions could take years, perhaps even decades.

Retrofitting existing vehicles

This is why the effort of the UNSW engineers is commendable. Retrofitting existing diesel engines would be a much faster way to transition to a cleaner fuel-burning system to get the job done.

Hydrogen can be much more environmentally friendly when produced using renewable energy than burning fossil fuels like diesel. The research effort led by Shawn Kook, a professor at the School of Mechanical and Manufacturing Engineering, has demonstrated to have reduced carbon dioxide emissions to 90 g/ kWh, which is about 86 percent lower than that produced by a diesel-powered engine.

How does the dual fuel system work?

The team has retained the original diesel injection into the engine and directly added a hydrogen fuel injection to the cylinder. Interestingly, the team's efforts also found a way out of the high nitrogen oxide (NOx) emissions associated with hydrogen engines.

Instead of putting hydrogen into the engine and letting it mix well, the researchers found that its stratified addition significantly reduces NOx emissions. This means that the hydrogen presence is more in certain parts of the engine while being lesser in other parts. Overall, the nitrogen oxide emissions, causative of acid rain and air pollution, were reduced in the dual-fuel engine.

More importantly, unlike hydrogen fuel cell systems, the dual fuel system developed by the UNSW researchers does not require high-purity hydrogen to be used as fuel. Since producing high-purity hydrogen is expensive, the new system could be deployed at lower costs for the end users.

An added benefit is the increase in energy efficiency over existing diesel engines, which the researchers reported to have improved by as much as 26 percent. This was achieved by independently controlling the timings of injection of both fuels.

The research team is confident of commercializing the technology within the next two years and plans to first deploy it in industrial locations such as mining sites where piped hydrogen lines already exist. Following this, the team will look to make its technology more mobile, where a hydrogen storage system will also be required.

The research findings were published in the journal International Journal of Hydrogen Energy.

Abstract

Up to 90% hydrogen energy fraction was achieved in a hydrogen diesel dual-fuel direct injection (H2DDI) light-duty single-cylinder compression ignition engine. An automotive-size inline single-cylinder diesel engine was modified to install an additional hydrogen direct injector. The engine was operated at a constant speed of 2000 revolutions per minute and fixed combustion phasing of −10 crank angle degrees before top dead centre (°CA bTDC) while evaluating the power output, efficiency, combustion and engine-out emissions. A parametric study was conducted at an intermediate load with 20–90% hydrogen energy fraction and 180-0 °CA bTDC injection timing. High indicated mean effective pressure (IMEP) of up to 943 kPa and 57.2% indicated efficiency was achieved at 90% hydrogen energy fraction, at the expense of NOx emissions. The hydrogen injection timing directly controls the mixture condition and combustion mode. Early hydrogen injection timings exhibited premixed combustion behaviour while late injection timings produced mixing-controlled combustion, with an intermediate point reached at 40 °CA bTDC hydrogen injection timing. At 90% hydrogen energy fraction, the earlier injection timing leads to higher IMEP/efficiency but the NOx increase is inevitable due to enhanced premixed combustion. To keep the NOx increase minimal and achieve the same combustion phasing of a diesel baseline, the 40 °CA bTDC hydrogen injection timing shows the best performance at which 85.9% CO2 reduction and 13.3% IMEP/efficiency increase are achieved.