Engineers have retrofitted a diesel engine to burn clean hydrogen
Vehicles fueled by hydrogen are much more energy-efficient than those powered by fossil fuels, and they only emit water vapor and warm air. But these vehicles need special battery-like devices called fuel cells to drive their motors.
Not anymore. Researchers in Australia have retrofitted diesel engines to run on 90 percent hydrogen as fuel, emitting 86 percent less carbon.
Trucks, trains, ships, and farm and construction equipment all use diesel today. Existing diesel engines be retrofitted to the new hybrid system in a few months, the researchers say. This switch could speed up the transition to clean hydrogen transportation.
The hydrogen economy, after decades-worth of hype and anticipation, has picked up speed in recent years. Hydrogen is a clean and energy-dense fuel, but it is only truly sustainable when produced by splitting water with the help of renewable electricity. Governments and industries around the world have set goals recently to speed up the production of green hydrogen.
Green hydrogen could play a big role in cutting carbon emissions from transportation and heavy industry. A handful of companies are now testing hydrogen fuel cell trucks and battery-powered trucks. But a move to such zero-emission trucks and machines could take many years, if not decades.
Retrofitting existing diesel engines should be faster and easier. So mechanical and manufacturing engineering professor Sanghoon Kook and colleagues at The University of New South Wales in Sydney modified a car-sized diesel engine by adding a hydrogen injector to it along with its original diesel injector.
Past attempts to run engines on hydrogen have resulted in high emission of toxic nitrogen oxides, which cause respiratory diseases and acid rain. The researchers got around this by precisely timing the injection of hydrogen into the engine to coincide with a certain position of the engine’s crankshaft in relation to its piston. This controls the diesel-hydrogen mixture in the engine and how it burns, reducing nitrogen oxide emissions.
At its best performance the converted hybrid engine not only had less carbon dioxide emissions, it was also 13 percent more efficient. The results appear in International Journal of Hydrogen Energy.
The research team hopes to commercialize the technology within the next two years. They plan to deploy it initially at mining sites and other industrial locations where piped hydrogen lines already exist.
Source: Xinyu Liu et al. Direct injection of hydrogen main fuel and diesel pilot fuel in a retrofitted single-cylinder compression ignition engine, International Journal of Hydrogen Energy, 2022.
Direct injection of hydrogen main fuel and diesel pilot fuel in a retrofitted single-cylinder compression ignition engine
- •90% hydrogen substitution by energy in a hydrogen-diesel dual direct-injection engine.
- •Combustion mode switch by injection timing control to influence charge stratification, IMEP and NOx.
- •At 90% hydrogen, optimised IMEP and NOx emissions at 40 °CA bTDC injection.
- •Up to 85.9% reduction of CO2 with 13.3% higher efficiency than conventional diesel combustion.
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 angledegrees 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% CO2reduction and 13.3% IMEP/efficiency increase are achieved.
Green trucking offers a bigger climate justice bump than green buildings
Prioritizing the rollout of electric and hydrogen fuel cell trucks for moving goods around California would benefit disadvantaged communities even more than decarbonizing building operations with clean energy, according to a new analysis.
Disadvantaged communities are disproportionately impacted by air pollution. Decarbonization means cleaner air, less air pollution, and better health for all. But there are lots of different technologies that could contribute to decarbonization, and few studies have evaluated how different decarbonization strategies will specifically affect disadvantaged communities.
That leaves untapped a major opportunity for environmental justice. “The substantial effort that California is taking to reduce the emission of greenhouse gasses (GHG) can and should also achieve environmental justice benefits by providing cleaner air within socially and economically disadvantaged communities,” says study team member Scott Samuelsen, a clean energy researcher at the University of California in Irvine.
The new study suggests that by tweaking the technologies and fuels that are used in different sectors of the economy, policymakers can design climate change mitigation strategies to maximize improvements in public health in disadvantaged areas.
Samuelsen and his collaborators modeled the greenhouse gas, air quality, and corresponding public health benefits of two scenarios designed to reduce California’s 2050 greenhouse gas emissions by 80% compared to 1990 levels. One scenario emphasized decarbonizing buildings with renewable electricity, and the other focused on decarbonizing trucking with electric and fuel cell vehicles.
Overall, decarbonizing buildings saves somewhat more carbon emissions and has about 15% greater health benefits for California’s population compared to decarbonizing trucking, the researchers report in the journal Nature Communications.
That’s because the renewable electricity that would power buildings in the green building scenario has lower carbon emissions than the renewable natural gas that would power buildings in the green trucking scenario.
But that’s not the whole story. “While building electrification achieves greater total health benefits in the region as a whole than zero-emission trucks, the deployment of clean trucks disproportionally attains air quality health benefits in disadvantaged communities,” Samuelsen says.
In fact, both scenarios deliver a disproportionate benefit to disadvantaged communities. But the disproportionality is even more pronounced in the green trucking scenario. Green trucking benefits low-income residents more effectively because they tend to live and work closer to ports, industrial facilities, and highways.
Both scenarios especially reduce air pollution in the San Joaquin Valley in Central California and the South Coast Air Basin around Los Angeles.
The health co-benefits are greater than the cost of implementing either decarbonization scenario.
Both building electrification and decarbonization of trucking are necessary to meet California’s greenhouse gas targets and maximize public health benefits for the population as a whole and for disadvantaged communities, adds Samuelsen.
A major unanswered question is how to time the rollout of clean energy technologies while balancing economics and climate and public health impacts, he says. The researchers are now analyzing additional decarbonization scenarios to address this question, and explore how to meet California’s new greenhouse gas reduction target of reaching carbon neutrality by 2045.
Source: Zhu S. et al. “Decarbonization will lead to more equitable air quality in California.” Nature Communications 2022.
Image: National Renewable Energy Lab via Flickr.