Simply put, commercial and fighter planes tend to use kerosene-based fuel, but certain products are usually added to the fuel. This includes antifreeze, hydrocarbons, metal deactivators, and antioxidants , all of which prevent corrosion and freezing at higher altitudes, to name a few. Although there are blends and mixtures of airplane fuel, it all begins with three basic types, and they are described below. Kerosene-based fuel for airplanes is usually broken down into various types, according to physical qualities and certain specifications.
These types include:. This is a very popular type of airplane fuel that is often used by small piston-powered aircraft. It is specifically used for tasks such as crop-dusting and for private flying, flying clubs, and even flight training.
AvGas fuel works on these planes because their pistons work much like those in car engines, and the fuel itself works much like gasoline does on these systems, although the two fuels themselves are different. As a consequence, aircraft may either have to carry fewer passengers to make space for the storage tanks, or become significantly larger.
The first option, which applies to Airbus's first two concept planes, would mean a reduction in ticket revenue, other things being equal. The second option, embodied in Airbus's third concept, requires a bigger airframe, which is subject to more drag. Further, an entire new infrastructure would need to be put in place to transport and store hydrogen at airports.
In addition, there is the question of whether hydrogen can be produced at scale and at a competitive price without itself having a large carbon footprint. The great majority of hydrogen used in industry today is created using fossil fuel methane, releasing carbon dioxide as a waste product. Hydrogen can be produced from water through a process called electrolysis, driven by renewable power , but this process is currently expensive and requires large amounts of energy.
Aviation passenger numbers are projected to double by , meaning many more greenhouse gas emissions unless sustainable alternatives are found Credit: Getty Images. As things stand, liquid hydrogen is more than four times as expensive as conventional jet fuel. Over the coming decades the price is expected to drop as infrastructure is scaled up and becomes more efficient. But according to Britain's Royal Society and the management consulting group McKinsey , it is likely to remain at least twice as expensive as fossil fuels for the next few decades.
These factors, and others, give pause for some major players in aviation. Sean Newsum, director of environmental strategy at Boeing Commercial, Airbus's main rival, recently told the Financial Times : "Our belief is that it will take a while for all the technology and elements of hydrogen propulsion to be worked out before we can get to… commercial use.
So what are the alternatives? In September , t he Air Transport Action Group, a Geneva-based body that speaks on behalf the global aviation industry, published a set of scenarios which suggest that, even as the volume of air traffic increases, it will be possible for global aviation to reach zero emissions of carbon dioxide — but only a decade or so later than According to these scenarios, the direct use of hydrogen will play only a marginal role, but the game-changer will be what are termed "sustainable aviation fuels", or SAFs.
This catch-all term covers a range of products, such as biofuels, that result in low net emissions of carbon dioxide and other pollutants associated with conventional jet fuel. The advocates of SAFs argue they have a number of clear advantages over pure hydrogen. Because they are chemically identical to existing jet fuel, they can in principle be "dropped in" to existing systems with little or no redesign, without delay, and without the substantial ancillary investments required for hydrogen-powered airframes and their supporting infrastructure.
Paul Stein, chief technology officer at the engine makers Rolls Royce, argues they are the key to a more sustainable future. Biofuels are one alternative to fossil fuels for aviation, but they require large tracts of land to grow Credit: Getty Images.
SAFs can be divided into two categories. The first are biofuels made through the chemical or thermal treatment of biomass such as agricultural residues and other wastes. A second category is electro fuels, or "E fuels". Through these fuels, which are also known as "power to liquid", hydrogen could end up playing a key role in aviation after all.
E fuels are made by reacting hydrogen with carbon dioxide to make "syngas". This is then converted through what is known as Fischer-Tropsch process into "e-crude" — a crude oil substitute that can be refined to jet fuel and other fuels. If the large amount of energy required at each stage of manufacture is sourced from zero carbon sources, then the whole process can be carbon neutral, with no more carbon dioxide in the atmosphere after the flight than before the fuel was made.
The next step in would be a plant capable of million litres a year. And one of the biggest could be flying over your head right now. You can still buy additives for classic cars without hardened valve seats, and even at some fuel pumps for off-road vehicles, marine engines, and some farming machinery.
These exemptions are classified as "off-road" by the Environmental Protection Agency and have been since the Clean Air Act banned the sale of leaded fuel for passenger cars in That being said, there's one rather thirsty user of lead-based fuels that's more representative than the examples above: airplanes.
And piston-based aircraft running on leaded gas are the largest contributors to airborne lead in the nation. Tetraethyllead TEL , as awful as it is for public health and the environment, is really good at keeping engine knock at bay.
That single property helped automakers develop higher compression engines by helping to reduce improper ignition of fuel during the combustion process, and thus, squeeze more power from an engine. Its specifications call for a maximum lead content of 0. According to the EPA , leaded road-use gasoline Mogas contained as much as 3 grams of lead per gallon in or around 0. By , this was cut to 0.
Similar to the gasoline that you use to fill up your car, Avgas is given an octane rating. This number is a performance measurement of fuel stability, not a physical property. More specifically, it measures how resistant fuel is to detonating outside of the optimal combustion process, something which the addition of TEL helps bolster. According to Shell , Avgas is able to surpass the rating of Mogas by as much as 15 octane thanks to the addition of this lead additive.
The result is a more stable engine less prone to spontaneous and catastrophic failure.
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