Scientific Article for Students

Introduction Burning fossil fuels is one of the main causes of global warming. This is because fossil fuels produce carbon dioxide when burned. Carbon dioxide is a greenhouse gas. It traps outgoing energy from the Earth’s surface. Extra carbon dioxide in the atmosphere causes the Earth to warm. A main contributor to carbon emissions is airplane travel. That’s because airplanes use jet fuel that comes from oil. This jet fuel has a high energy density – a large amount of energy stored in a small amount of fuel. Airplanes need to keep the weight of their fuel down so that they can travel long distances and carry more people and luggage. Air travel currently produces 2% of all greenhouse gas emissions. This will increase as more people travel by airplane. So, how can the aviation industry lower their carbon emissions? Airplanes will need to use alternative fuels known as sustainable aviation fuels. We wanted to know more about the availability and use of alternative fuels for airplanes. That is why we reviewed and summarized information about alternative jet fuels. Methods We reviewed information about different sources of fuel for airplanes. These sources are not made from fossil fuels. Then we summarized our findings. We organized what we learned into three categories: Biomass Hydrogen Electricity Results There are many alternative fuels for airplanes (Fig.1). Biomass Alternatives Biomass is organic matter that can be used for fuel. Biomass includes: agricultural crops forest residues such as leaves, branches, or bark waste oils and fats sewage manure garbage Making fuel from biomass requires different processes. That’s because the structure of each type of biomass is different. Examples of biomass conversion processes are: Hydrogenation: Scientists add the element hydrogen to vegetable oils and animal fats. This process changes their structure, making them usable as fuel. This is the only commercial biofuel alternative used currently by airlines. Fermentation: Plant sugars and starch change to alcohol, such as ethanol. After the sugar transforms to alcohol, scientists change it into jet fuel. Hydrothermal liquefaction: Water and biomass experience high temperatures and pressure. The heat and pressure cause the biomass to change into bio-crude oil. This crude oil is then refined into jet fuel. Scientists are still researching this process. Hydrogen Scientists make hydrogen by splitting water (H₂O) into hydrogen gas (H2) and oxygen gas (O2) using electricity. To make the hydrogen more usable, scientists cool it down into a liquid. It is then stored in tanks. Using hydrogen requires a redesign of airplanes. They will need space to hold the hydrogen tanks. These tanks can be heavy, so the airplane design will need to include this extra weight. New airplanes also need to include a way to transform the hydrogen into electricity, such as a hydrogen turbine or fuel cell. There are several companies working on hydrogen airplane designs. We can also combine hydrogen with carbon dioxide extracted from the atmosphere. This produces a hydrocarbon fuel similar to current jet fuel that we can use in existing planes. We call these e-fuels. Electricity Electric airplanes use batteries to store energy. Then the airplane’s systems use this stored energy during flight. Currently there are many hybrid designs. These airplanes use jet fuel during the high energy parts of the flight, such as takeoff. They then switch to the batteries when the airplane is cruising. Many companies are also working on fully electric airplanes. Scientists need to design new battery systems that can store enough energy for long flights. They will also need to redesign the airplane to run only on electricity. Discussion Our review showed that there are many alternatives to conventional jet fuel. But we are still exploring many of these options. They are also more expensive. These fuels can be two to five times more expensive than regular kerosene jet fuel. But they do reduce emissions! We estimate that fuels developed using sustainable biomass can reduce emissions by 65% or more. Hydrogen and electricity emissions could decrease by 95%. We found that biomass fuels and e-fuels are a good alternative fuel. That’s because they can provide the same fuel energy density as regular kerosene jet fuel. Their use also requires the least amount of airplane redesign. Hydrogen and electricity are also good options. But these options need large changes in airplane design. We need to do more research and development to make them usable for long flights. Some alternative fuels need electricity for their production or use. So, can we still reduce carbon emissions? Yes, if the source of the electricity used to make these fuels is renewable. If the electricity comes from a fossil fuel power plant, the reduction of carbon emissions is much less, or even worse. Conclusion You can help reduce the carbon emissions produced by airplanes. Try to take as few airplane trips as possible. Instead, travel closer to home and use public transportation whenever possible. You can also plan a staycation! Take time to enjoy relaxing activities at home or explore interesting sights in your area. And if you do travel by airplane, try to choose companies that are using sustainable aviation fuels.