A Look at Sustainable Aviation; Fuel Alternatives For Greener Aviation. - AeroGuard
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A Look at Sustainable Aviation; Fuel Alternatives For Greener Aviation.

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What is Sustainable Aviation?

Flight training, and flying as a whole, uses a large amount of fuel to keep planes safely in the air, however at AeroGuard, we understand the importance of being good corporate citizens, as well as keeping training practices on the forefront of technological advances. In this post, we take a look at the possible advances and fuel alternatives that may reach the mainstream in the coming years, and make flying more ‘green’ and sustainable.

“Sustainability” means interacting with the environment responsibly in order to maintain our natural resources and avoid jeopardizing future generations’ ability to meet their needs. Industry leaders all over the world are trying to figure out how they can carry on their business in a more sustainable manner. When it comes to the aviation industry, concerns have been raised about the environmental impact of greenhouse gas emissions from burning aviation fuel. With approximately 4 billion people worldwide traveling by plane every year, we’re burning a lot of fuel. Despite major improvements in efficiency over the last 60 years, air travel is the fastest-growing source of individual emissions. Furthermore, conventional jet fuel is petroleum-based, and petroleum (i.e. kerosene) is a non-renewable source of energy. It took millions of years to form, and once it has all been extracted and consumed, there’s no way for us to replace it. That’s why researchers are working to develop more sustainable forms of aviation fuel made from renewable materials.

Jet Fuel vs. Avgas

There are two types of conventional fuels in aviation: jet fuel and aviation gasoline (avgas). Jet fuel is used in turbine engine aircraft, and it is made of unleaded kerosene. General aviation piston-engine aircraft use avgas, which is a high-octane version of leaded gasoline. Both types of fuel cause carbon dioxide emissions, but only avgas causes lead emissions as well.

While lead paints and leaded gasoline for automobiles have been banned in the United States, leaded aviation fuel is still being used because there is no easy substitute for the lead. The lead in avgas raises fuel octane, which causes the fuel to burn rather than explode. Ethanol is added to unleaded gasoline to raise its octane, but ethanol’s corrosive properties make it unsafe for aviation fuel. Lead also prevents engine knock, which is when fuel burns unevenly in an engine’s cylinders. Engine knock is a dangerous problem as it can cause sudden engine failure. It is not safe to remove the lead in avgas until we have a reliable substitute.

Improved Aircraft Engine Efficiency

One helpful move the aviation industry has made was to transition from turbojet to turbofan engines in the late 20th century. Both turbojet and turbofan engines are gas turbine engines that use exhaust to create thrust.  While a turbojet engine takes in air and moves all of it through the engine, a turbofan engine has a large fan on the front that pushes most of the airflow around the outside of the engine. A turbofan engine creates more thrust than a turbojet engine with approximately the same amount of fuel because the fan slightly changes the fuel flow rate.

Turbojet engines have been in use since World War II, but they are not very common in aircraft design today. Turbofan engines are the go-to for jet propulsion today because they are quieter, more powerful, cheaper, and more efficient, and they create fewer carbon emissions. Turbofan engine technology continues to improve regarding fuel efficiency. The new GEnx engine for the Boeing 787 Dreamliner and the Boeing 747-8 boasts up to 15% increased fuel efficiency compared to GE’s CF6 engine. With lightweight, carbon-fiber composite fan blades and an advanced low-pressure turbine, the GEnx engine is a huge advancement in propulsion technology.

Alternative Aviation Energy Sources

Weight is a huge factor in aviation as an aircraft can only bear so much weight. An important calculation in the performance of an aircraft is the thrust-to-weight ratio, or the amount of force produced by the engine relative to the weight of the aircraft. Increasing the thrust-to-weight ratio of an aircraft also increased how fast it can accelerate, how much weight it can carry, and how long it can stay in the air. With that in mind, the ideal fuel source for an aircraft would be as light and energy-dense as possible. Energy density is the amount of energy stored in a given amount of space. For aviation, the more energy you can pack into small amount of space, the better. For any alternative energy source to be a viable option, it must energy-dense enough to power the aircraft while maintaining a proper thrust-to-weight ratio.

Electric Aircraft

If we have electric cars, why can’t we have electric planes? The problem goes back to energy density: most batteries are too heavy and have an energy density too low compared to conventional aviation fuel. Right now, a tank of conventional aviation fuel provides approximately 43 times more energy than a battery of the same weight. For batteries to be useful in even small-scale aviation, they will need to increase their energy density at least five times.

That’s not to say that electric aircraft aren’t in the works. Over a dozen companies are working on battery-electric or hybrid prototypes. Airbus, for instance, has been working since 2010 to create an all-electric, four-engine aircraft, CriCri. In 2015, their all-electric, twin-propeller aircraft, E-Fan, managed to cross the English Channel. They continue to work on building and testing more powerful electric aircraft. Meanwhile, the Slovenian company Pipistrel is already selling the first all-electric aircraft certified as airworthy by the FAA, the Alpha Electro. With a battery that holds about one-fifth of the power of Tesla Model S battery, it can keep a pilot and one passenger aloft for about 90 minutes. While no one is ready to sell electric aircraft to commercial airlines yet, those plans are certainly in the works: Wright Electric aims to have built a fleet of 186-seat electric aircraft for easyJet by 2030. However, given our current rate of development, analysts estimate that we could be 20 or 30 years away from electric flight.

Sustainable Aviation Fuel

Since electric aircraft are not a viable option yet, the aviation industry is dependent on fuel for now. One sustainable option that already exists is sustainable aviation fuel (SAF). SAF is not derived from fossil fuels (e.g. petroleum, coal, or natural gas), and it gives up to an 80% reduction in carbon emissions compared to conventional aviation fuel over the life cycle of the fuel. Potential energy sourced for SAF include cooking oil and non-palm waste oils from plants and animals, solid waste from homes and businesses, and forestry waste. SAF derived from only living matter is called “biofuel.” Studies have shown that SAF can match conventional jet fuel in terms of energy density and thrust-to-weight ratio, and manufacturers say that SAF can be dropped straight into existing infrastructure without any need for retrofitting. Currently, however, the cost of SAF is too high for it to be an attractive option for airlines.

Replacing conventional aviation fuel with SAF seems to be an airline’s best option for moving toward sustainable aviation at the moment. Carbon dioxide makes up the vast majority of the “greenhouse gas” emissions that contribute to climate change, and burning conventional aviation fuel jet fuel emits a great deal of carbon dioxide. Some major airlines have made news by announcing their efforts to go “carbon-neutral,” or ensure that the amount of carbon dioxide released into the atmosphere by their activities is equal to the amount being removed. Airlines for America, a group that represents major U.S. airlines including American, Delta, and United, have committed to working with the U.S. government and the aviation industry to achieve carbon neutrality by 2050. In order to go carbon-neutral, these airlines will likely have to begin introducing SAF in their aircraft soon.

What Does Sustainable Aviation Mean for Future Pilots?

United Airlines made history in October of 2021 by launching a test flight of a commercial jet containing 100% SAF. The Boeing 737 Max 8 circled IAH airport for 90 minutes, and there were no operational issues with the test fuel. Delta Air Lines has announced plans to spend $30 million in order to offset 13 million metric tons of carbon emissions, and they also intend to replace 10% of their aviation fuel with SAF by 2030. The Biden administration is pressuring all U.S. airlines to do more to reduce greenhouse gas emissions. The push for more sustainable practices in the aviation industry is likely not going anywhere any time soon.

It is important for the next generation of pilots to pay attention to trends in sustainable aviation as these trends will certainly impact their careers in both the short- and long-term as airlines implement them. Fuel is the main operating cost for commercial airlines. An airline’s operating costs determine just about everything from the number of employees they can hire to the price they charge customers for tickets. With airlines working toward more sustainable practices, including gradually switching to fuel made from renewable resources and attempting to go carbon-neutral, future fuel costs for airlines are uncertain. Airlines may have to allocate more of their budgets to fuel costs than ever before in order to adapt.

Here at AeroGuard, we continue to evaluate the available options in the marketplace and hope to be early adopters of new fuel technology for general-aviation aircraft once commercially available. Additionally, as we train future commercial airline pilots (LINK) for long, and successful careers that will likely take see many of these, or similar advances, we will update and include any new procedures that come with adopting SAF or electric powered planes, and keep our curriculum updated to always be ahead of the status quo.

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