jet fuel

Hydrogen-powered aviation

December 16, 2024 By EarthWise Leave a Comment

The transportation sector is responsible for about a quarter of human-generated greenhouse gas emissions. Most of the energy used by transport systems comes from fossil fuels. The transition to electric vehicles – cars, trucks, and buses – is making a real difference. However, the emissions from the aviation industry have continued to grow faster than those of other forms of transportation. There have been increased efforts to develop hydrogen-powered aircraft, but the challenges are substantial.

Hydrogen can be used for aviation both as a directly combusted fuel, or to power electric fuel cells. Its advantages are that its use produces no carbon dioxide, and, in fact, hydrogen produces more energy per pound than jet fuel.

A study by researchers at MIT looked at the prospects for hydrogen use in aircraft and what needs to be done to make it practical. The biggest issue is that the extra bulk of a hydrogen fuel tank and fuel cells in a plane would have to be offset by weight reductions elsewhere, such as reducing payload (cargo or passengers). This would mean there would need to be more flights, thereby reducing the gains made. The researchers argued that improvements in fuel cell power and more weight efficient fuel systems could eliminate the need for additional flights.

The bigger challenge is the infrastructure for generating and distributing hydrogen. There needs to be green hydrogen – hydrogen produced without carbon emissions – and the infrastructure for getting it to planes where it is needed has to also not produce substantial emissions.

The study suggests that the rollout of hydrogen-based aviation should start at locations that have favorable conditions for hydrogen production.

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Fueling greener aviation with hydrogen

Photo, posted December 20, 2016, courtesy of Dylan Agbagni via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Airplanes, corn, and groundwater

January 11, 2024 By EarthWise Leave a Comment

The aviation industry wants to slash its greenhouse gas emissions. One proposed strategy is to replace ordinary jet fuel with ethanol. Ethanol in this country mostly comes from corn. The airlines are enthusiastic about the idea; corn farmers are enthusiastic about the idea. Ethanol suppliers are obviously enthusiastic about it. But is it a good idea?

Today, nearly 40% of America’s corn crop is turned into ethanol. Twenty years ago, the figure was around 10%. The massive growth was the result of mandates for ethanol augmentation of gasoline for environmental reasons.

But the environmental benefits of corn ethanol have always been controversial at best when all the energy factors are considered. But apart from that, a very serious issue is that corn is a water-intensive crop, and it can take hundreds of gallons of water to produce a single gallon of ethanol. As the climate warms and corn crops expand, groundwater in many corn-growing areas is being increasingly depleted and groundwater provides half our drinking water and meets far more than just the needs of corn farmers.

Corn farmers and ethanol producers see the rapid growth of electric vehicles as a threat to their lucrative business of supplying the auto fuel industry. The ambitious goals of the airline industry to reduce its emissions would likely require nearly doubling ethanol production.

The situation is a powerful example of the tradeoffs that can arise as the world tries to make the transition away from fossil fuel. Even green solutions can have their own environmental cost and sometimes that cost may be too steep.

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Airlines Race Toward a Future of Powering Their Jets With Corn

Photo, posted September 2, 2007, courtesy of Rosana Prada via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Sustainable Jet Fuel | Earth Wise

March 29, 2023 By EarthWise Leave a Comment

For several years, a few airlines, notably United here in the US, have been experimenting with the use of sustainable jet fuel. Sustainable aviation fuel is made from such things as used cooking oil and agricultural waste. It produces up to 80% fewer greenhouse gas emissions than conventional jet fuel.

To date, when used it has been blended with fossil fuel jet fuel at a fairly low level. United is the largest consumer of sustainable jet fuel in the US, but it accounts for less than one percent of the airline’s total fuel consumption. Unfortunately, sustainable fuel can be as much as three times more expensive than conventional jet fuel.

Because of increasing governmental policy changes, technological breakthroughs, and climate commitments by airlines, efforts to increase the viability of sustainable jet fuel are ramping up.

Recently, United Airlines, Air Canada, Boeing, Honeywell, and JP Morgan Chase made initial contributions of $100 million to a new venture capital fund that will invest in sustainable fuel technology. United expects the fund to grow to $500 million and make about two dozen investments over the next three years.

Emissions from aviation contribute more than two percent of global greenhouse gas emissions each year. Like many big companies, United Airlines has pledged to stop adding carbon emissions to the environment by 2050. Unlike many, United has also pledged to eliminate emissions without using carbon offsets, which is effectively paying others to do their dirty work without cleaning up their own operations.

Multiple sustainable fuel companies in the US and abroad are working on a variety of ways to make aviation fuel from sustainable sources.

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A Sudden Rush to Make Sustainable Aviation Fuel Mainstream

Photo, posted August 18, 2021, courtesy of Ronen Fefer via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Private Jets and CO2 Emissions | Earth Wise

July 16, 2021 By EarthWise Leave a Comment

During the heart of the Covid-19 pandemic, private jet use saw record levels because chartered aircraft were estimated to have 30 times lower risk for covid than flying commercial. By August 2020, while commercial flights were down 60% year-over-year, private jet traffic was actually up. From an environmental perspective, however, flying on a private jet is about the worst thing one can do for the environment.

Private jets are 10 times more carbon intensive than airlines on average and 50 times more polluting than trains. A four-hour private flight emits as much as the average person does in a year.

In Europe, 7 out of the 10 most polluting routes taken by private aircraft lie in the UK-France-Switzerland-Italy axis, with jets departing the UK and France being the biggest source of pollution. One in 10 flights departing France are private jets, half of which travelled less than 300 miles.

A study by the research group Transport & Environment points out that wealthy private jet owners are ideally suited to aid in the decarbonization of the aviation sector. Private jet short hops are prime targets for replacement by clean technologies like electric and hydrogen aircraft. European policy makers could ban the use of fossil-fuel private jets for flights under 600 miles by 2030. Until such a ban, jet fuel and flight taxes could be imposed on private jets to account for their disproportionate climate impact and support technology development. And companies and individuals could commit to substantial reductions in private jet use when alternatives exist that do not unreasonably increase travel time.

The super-rich could be part of the solution instead of part of the problem.

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Private Jet Use Rising, Sending CO2 Emissions Soaring

Photo, posted September 9, 2020, courtesy of Mackenzie Cole via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Plants Paying For Biofuels | Earth Wise

May 7, 2020 By EarthWise Leave a Comment

Biofuels are an important element in broader strategies to replace petroleum in transportation fuels like gasoline, diesel, and jet fuel. The idea is that biofuels recycle carbon by getting it from growing plants rather than from fossil sources. The biggest problem with biofuels is that they cost more than conventional petroleum fuels, so there is economic incentive to keep burning the fossil fuels.

One strategy to make biofuels cost competitive is to have the plants provide additional economic benefits beyond being a feedstock for fuel. This in principle can be done by engineering plants to produce valuable chemical compounds, or bioproducts, as they grow. Bioproducts include such things as flavoring agents and fragrances as well as biodegradable plastic. These bioproducts can be extracted from the plants and then the remaining plant material can be converted to fuel.

Researchers at Lawrence Berkeley National Laboratory recently published a study to determine what quantities of bioproducts plants need to produce to result in cost-effective biofuel production.

The study looked at a compound called limonene, which is used for flavoring and fragrance. They calculated that if this compound was accumulated at 0.6% of the biomass dry weight, it would offer net economic benefits to biorefineries. This corresponds to recovering 130 pounds of limonene from 10 tons of sorghum on an acre of land.

Such quantities are completely practical but, on the other hand, none of these substances are needed in huge quantities. Just six refineries could supply the world with limonene. So, fuel crops would need to be engineered to produce a broad range of bioproducts to enable a viable cost-effective biofuel industry.

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Making Biofuels Cheaper by Putting Plants to Work

Photo, posted September 28, 2019, courtesy of Michele Dorsey Walfred via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Jet Fuel From Acetone | Earth Wise

February 25, 2020 By EarthWise Leave a Comment

Acetone is a common organic solvent. It is used to make plastic, fibers, drugs, and other chemicals. It is commonly used by consumers as nail polish remover. Acetone is a manufactured chemical, but it is also found naturally in the environment in plants, among other places. There are now companies that produce acetone entirely by fermentation of plant feedstocks, such as corn.

Researchers at Los Alamos National Laboratory have now developed a process by which acetone can be converted into a fuel additive that can improve the performance of petroleum-based jet fuel, providing both environmental and economic benefits.

The process takes biomass-derived acetone and converts it to isophorone, which they produce by a process called photochemical cycloaddition that creates more complex hydrocarbons. They then use ultraviolet light to convert the isophorone into cyclobutane, which is a type of hydrocarbon with high energy density that is suitable for aviation fuel applications.

Acetone itself is quite volatile and is unsuitable for fuel applications. It also cannot be added directly to any fuel supply since it can dissolve engine parts and o-rings. Cyclobutane, on the other hand, is a safer and more energy-dense fuel that can be a replacement for additives that require high-pressure hydrogen treatment in their synthesis. Currently, most hydrogen is produced by a process that generates carbon dioxide. The new conversion process does not result in carbon emissions.

According to the Los Alamos researchers, their process can result in a domestically generated product that will provide environmental benefits, create domestic jobs, improve U.S. energy security, and further U.S. global leadership in bioenergy technologies.

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Acetone plus light creates a green jet fuel additive

Photo, posted December 18, 2007, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Plant-Based Jet Fuels

May 9, 2019 By EarthWise Leave a Comment

The global aviation industry uses a whole lot of fuel: more than 5 million barrels a day. It is an incredibly energy-intensive industry and almost all of its energy comes from petroleum-based fuels.

While other large energy sectors such as electric power, ground transportation and commercial buildings have well-defined pathways to adopting renewable energy sources, the aviation industry does not have such a straightforward way to make a transition to sustainability. Electrifying planes using batteries or fuel cells is very challenging for a number of reasons, notably the weight restrictions on aircraft. So liquid biofuels as replacements for petroleum-based fuels remain the most promising approach.

A new study at the Lawrence Berkeley National Laboratory concludes that sustainable plant-based biofuels could provide a competitive alternative to conventional petroleum fuels if current development and scale-up initiatives are successful.

Multidisciplinary teams based at the Department of Energy’s Joint BioEnergy Institute are focused on optimizing each stage of the bio-jet fuel production process. This includes bioengineering ideal source plants and developing methods for efficiently isolating the carbohydrates in non-food biomass that bacteria can digest and bioconvert into fuel molecules.

The critical issue is cost. The theoretical cost of bio-jet fuel has come down dramatically in recent years but is still around $16 a gallon. The cost of standard jet fuel is about $2.50 a gallon. So, the real challenge is bridging that gap.

Reducing the cost of the fuel could come both from the material and process improvements that are underway as well as by finding ways to turn the leftover lignin residuals from the bioconversion process into valuable chemicals.

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