Frequently Asked Questions

Jet Fuel - Frequently Asked Questions

What is jet fuel?
Conventional jet fuel is a blend of hydrocarbons (molecules comprised of chains of hydrogen and carbon) that is produced from the distillation and refinement of petroleum. This product stream coming out of the refinery is often referred to as a “middle distillate” fuel (between the streams produced for gasoline and diesel) or more specifically, kerosene-type jet fuel. The hydrocarbon molecules are typically in the C7 to C18 range, and consist of three general molecular forms: paraffins, cyclo-paraffins, and aromatics. Each type of molecule has unique attributes, but when blended together they deliver the characteristics needed and required for safe and efficient use in a turbine engine. Other compounds may also added to jet fuel (usually in very small amounts) to improve its overall suitability for aircraft use, including additives such as antioxidants, metal deactivators, electrical conductivity additives, static inhibitors, icing inhibitor, corrosion inhibitors, biocides, lubricity enhancers, and thermal stability improvers. The jet fuel specifications used by the industry do not prescribe the exact composition or production methodologies to be used to make the fuel, but rather simply define the final physical properties that the fuel must exhibit.

What are the jet fuel types?
Jet fuel carries several common commercial and military names, including Jet A, Jet A-1, Jet B, JP-5, JP-8, TS-1, or ATF (aviation turbine fuel). These fuels differ slightly in a few discrete properties, for instance in minimum freeze point, or maximum flash point. Commercially, Jet A is used primarily in the United States, while Jet A-1 is primarily used outside the United States. Jet B is considered an alternative to Jet A-1 in cases of extremely cold climates but not often supplied because it holds a higher flammability than Jet A-1. However, all of these fuels have detailed specifications that must be met, and these are defined by international bodies, the most common of which are ASTM D1655, DEF STAN 91-91. These specifications define physical properties and performance characteristics that the fuels must exhibit. Physical properties (e.g. D1655 Table 1 Properties) include such things as: acidity, maximum aromatics, volatility, flash point, density, and energy content. Performance characteristics (e.g. D1655 Table X1 Properties) include such things combustion characteristics and atomization. Additives are also controlled (e.g. D1655 Table 2), usually by min or max volume requirements.

How is jet fuel used on an aircraft?
The jet fuel loaded onto an aircraft constitutes a large fraction of the overall takeoff weight of the aircraft, and aircraft are less efficient at heavier weights, so the industry attempts to keep the amount of required fuel or energy onboard to a minimum. Because weight is a key consideration, fuel also serves several functions onboard the aircraft, other than just a chemical source of energy, including as a heat transfer medium, a hydraulic fluid, a lubricant, a ballast medium, a conductivity agent, a swelling agent for seals, etc. Then, the fuel is injected as a continuous, atomized stream into a combustor where it mixes with air while burning to deliver a stream of hot, energetic gas to a turbine. The turbine converts the gas energy to mechanical energy (a rotating fan), producing power for the aircraft. As a result of the above, the aircraft system manufacturers are very concerned over the properties of jet fuel.

How much energy is in jet fuel?
For commercial applications, ASTM D1655 requires jet fuel to produce a minimum amount of energy of 42.8 MJ/kg, with densities between 775-840 kg/m3 (or 18,400 BTU/lbm, with densities of 6.47-7.01 lb/usg).

What are the products of jet fuel combustion?
Similar to any pure hydrocarbon fuel, when pure jet fuel is burned under ideal conditions (with pure oxygen), its combustion by-products are carbon dioxide and water. In real world applications (less than ideal, and in the presence of air, which contains nitrogen) the combustion may also result in the trace release of carbon monoxide, unburned hydrocarbons (in gas and particulate form), oxides of nitrogen, and oxides of sulfur (as a direct function of how much sulfur is in the fuel). Regulations exist that limit the amount of pollutants that can be produced. Jet fuel combustion produces ~3.16 pounds of CO2 per pound of fuel burned.

What makes jet fuel different from automotive fuel?
Automotive fuels for spark and compression ignition engines typically include gasoline (and/or alcohols) and diesel fuel. These fuels contain shorter and longer carbon chain lengths respectively, than jet fuel. The shorter chain lengths typically result in higher volatility, and the longer chain lengths typically result in a higher freeze point, amongst other physical and performance-based property changes, making both types unsuitable for aviation use. Automotive fuels are produced to their own unique specifications. Jet fuel is generally produced to tighter specifications than gasoline or diesel (e.g. to guarantee operability, eliminate contaminants, etc.).

How much jet fuel is consumed in the U.S.?
According to the U.S. Energy Information Administration (EIA), the United States consumed an average of approximately 1.7 million barrels of jet fuel per day in 2017, which equates to approximately 25.8 billion gallons by all users (general aviation, military, U.S. airlines, foreign flag airlines, etc.) per year.

How much jet fuel is consumed in the world?
The International Air Transport Association (IATA) reports 90 billion gallons of jet fuel consumed by airlines in 2017 alone, not including jet fuel consumed for general aviation or military use. This is up from the 85 billion gallons reported in 2016. IATA estimates 2018 jet fuel consumption to be up to 94 billion gallons and forecasts 2019 consumption at 97 billion gallons per year.

Who produces jet fuel, and how?
Most of the large international petroleum producers/refiners produce jet fuel from their standard refinery operations, as do a significant group of regional producers. Crude oil is converted into conventional jet fuel through several processes. First, the oil is heated then distilled to separate raw feedstock into different output streams based on boiling point. While in separate streams, impurities are removed (e.g. acids, sulfur, etc.) after which the streams are blended to ratios to achieve the specific composition of the desired jet fuel type (e.g. Jet A). Finally, certain additives are installed to improve fuel performance and stability to meet the final specifications.

How does jet fuel get transported to the airport?
Typically, large commercial airports have jet fuel delivered by pipeline to a “fuel farm” adjacent to the airport. But jet fuel is also delivered by rail, road (tanker trucks), and water (tankers and barges).

Can commercial aircraft burn fuels other than jet fuel?
Commercial aircraft can only use fuel that is approved for use in the engine and aircraft operating manuals, as only this type fuel is proven to enable the performance and operability guaranteed by the certification of the aircraft. All of the major engine and aircraft manufacturers require usage of fuel which meets the requirements of ASTM D1655 (at a minimum).

What other fuels could work for aviation?
At present, based on today's certifications, no other fuel types, other than jet fuel, satisfy the needs of the jet powered aviation enterprise. It is not an issue of the turbine not physically being able to burn the fuel, but rather that the overall safety and performance of the aviation system cannot be matched by other fuels. Gas turbine engines are regularly used to power ships and provide power for other heavy machinery or power production, and do so using a wide range of fuels, from hydrogen to heavy oils. But use of such fuels cannot today deliver the same level of performance, safety, and cost as jet fuel for aircraft. Going forward, aircraft producers are investigating a wide range of fuel and energy systems to power aircraft, but none of those systems have proven feasible, or appear to be feasible for several more decades. Significant progress is being made on small general-aviation aircraft operating on hybrid or electric propulsion using fuel cells and/or batteries, but such systems still appear to be an order of magnitude off in key performance attributes of delivering sufficient kJ/kg or $/kJ to be reasonable for commercial aircraft. As such, the jet-powered aviation enterprise expects to continue the use of jet fuel through the middle of this century.

⇑ Back to top

Alternative Jet Fuel - Frequently Asked Questions

What do we mean by the term alternative jet fuel?
Generally, the aviation industry means jet fuel derived from a source other than petroleum. Specifically, CAAFI and the Alternative Jet Fuel community means a fuel produced to the requirements of ASTM D7566. It can include drop-in jet fuels produced from a broad range of hydrocarbon sources (feedstocks) using a wide range of conversion processes. We sometimes refer to these fuels as synthetic fuels too—fuel produced from sources other than petroleum via biochemical or thermochemical processes.

What is the difference between an alternative fuel and an alternative jet fuel?
An alternative fuel could be any generic fuel derived from a source other than petroleum. It could include compressed natural gas, liquefied natural gas, hydrogen, alcohols, biodiesel, etc. However, none of these fuels are suitable for jet powered aviation, either current models, or those in development, for various reasons discussed above. The aviation community needs jet fuel for safe and efficient operation, whether that is produced from petroleum, or sources other than petroleum.

How long have commercial aviation entities been pursuing alternative jet fuels?
Alternative aviation fuels activity had been developing slowly since the 1970s, largely through the efforts of the U.S. Air Force and a group of engine companies. When CAAFI formed in 2006, the ASTM committee had begun the process of streamlining their certification processes for alternative jet fuels. A blend of synthetic and conventional jet fuel produced by the South African producer Sasol was approved by ASTM and began being used on flights in and out of Johannesburg in 1999. In 2009, approval of the new ASTM D7566 specification for synthetic aviation fuels, with the ability to add annexes to it for new alternatives, once proven, heralded the true dawn of the era of alternative aviation fuels.

What is a drop-in alternative jet fuel?
Drop-in alternative jet fuels are completely compatible with a conventional (typically petroleum-derived) jet fuel in terms of materials, safety, and composition. A drop-in fuel does not require adaptation of the fuel distribution network or the engine fuel systems, it can be used “as is” in vehicles and engines that have historically operated with only conventional fuel. Some alternative jet fuel blending components may become “drop-in” only after being blended with a conventional fuel to a certain prescribed proportion. Currently, approved drop-in fuels only supplement petroleum-sourced jet fuels in blends. A list of approved fuels and blend levels is available on the Fuel Qualification page. Certain alternative jet fuel concepts do have the potential to be used without blending, but have yet to be approved. Drop-in fuels align with CAAFI’s goal of bringing sustainable alternative jet fuels to market.

What are key challenges relating to alternative jet fuel development and deployment?
General challenges include feedstock availability, required life cycle analysis (LCA) evaluations, understanding the fuel chemistry of alternative fuels, cost competitiveness, commercial production capacity, and competition among other bio-based products, to name a few. The CAAFI R&D Team has developed a series of white papers addressing the key challenges related to alternative jet fuel development.

How do alternative aviation fuels perform with respect to life cycle greenhouse gas (GHG) emissions?
Depending on the feedstock and production pathway used, alternative aviation fuels may offer reductions in GHG emissions when compared to conventional fuels. For example, research suggests that hydroprocessed esters and fatty acids (HEFA) from palm or soy oil can have as little as half the emissions of conventional Jet A, assuming no land-use change (see Stratton et al. PARTNER report). However, land-use change can be critical with any biomass, as converting tropical or peatland rainforest to biomass production can increase the life cycle emissions by several orders of magnitude over that of traditional Jet A. More about land use change can be found on the EPA webpage on Sources of Greenhouse Gas Emissions. CAAFI and the aviation community are committed to carbon neutral growth starting in 2020 and therefore are interested in alternative jet fuels that have GHG reductions compared to standard petroleum-based jet fuels.

How do alternative jet fuels perform with respect to local air quality pollutant emissions?
Synthetic fuels afford the opportunity to lower local air pollutant emissions through the reduction of sulfur and aromatic compounds. Thus, when blended with traditional fuel, overall sulfur and aromatic content is reduced. Research also suggests that some alternative fuels may produce less particulate matter (a growing concern for local air quality).

Do alternative jet fuels affect aircraft performance?
Effects can be slightly positive and negative, but overall operability and safety are maintained. For example, lower density fuels can improve fuel burn, but adversely affect an aircraft's maximum payload-range. CAAFI and the airlines are exploring all performance impacts.

How will alternative fuels affect airports?
Benefits to airports are possible with alternative fuels. To the extent that airlines have access to environmentally beneficial alternative jet fuels for aircraft, the emissions associated with airline flights may be reduced on a life cycle basis. Airports that own and operate ground service equipment can also see environmental improvements in the operation of their own equipment, as alternatives for such equipment can reduce greenhouse gas and local emissions as well. A handbook to evaluate costs and benefits at airports has been completed via Project 02-07 of the Airport Cooperative Research Program (ACRP).

How are feedstocks converted into alternative jet fuel?
The industry has determined that there are several ways to convert the carbon or hydrocarbon content of various sources into the chemical components of jet fuel. These can include biological process (fermentation or microbial conversion), or thermochemical processes (gasification, torrefaction, pyrolysis, catalytic conversion, hydroprocessing, etc.).

Before aircraft can use any alternative jet fuels, those fuels must meet rigorous criteria spelled out in aviation fuel specifications, both physical properties and fit-for-purpose properties. The specifications for alternative jet fuels are defined in ASTM Standard D7566, and specific annexes to the Standard apply to individual processes for producing alternative jet fuel.

What alternative jet fuels can be used today?
A list of approved drop-in alternative fuels is available on the Fuel Qualification page.

What is the process for jet fuel development and approval?
CAAFI has developed guidance on getting an alternative jet fuel approved by ASTM, and participated in the creation of ASTM D4054 which outlines the process for producers. Before the process of jet fuel approval begins, it is first important to evaluate whether the fuel encompasses three major factors: appropriate composition, material compatibility, and fungibility. The first suggested step is familiarizing your company with the aviation community. The next step is to perform a technical and environmental evaluation of the fuel in several critical areas to determine the environmental benefit and viability as a fuel for aviation. The third step in the process is receiving fuel approval. Finally, once approval is reached, networking to initialize collaboration with appropriate stakeholders (e.g. feedstock producers) and purchasers (e.g. airlines) for commercial production must be undertaken. For an extensive overview on jet fuel development and approval as well as links to helpful resources, see the CAAFI Path to Alternative Jet Fuel Readiness. An overview of the D4054 Qualification Process is outlined on the Fuel Qualification page.

What drop-in alternative jet fuels are on the way to evaluation and approval?
A process has been established to regulate the sequence in which the current roster of alternative fuels and additives will be reviewed by the OEMs. Progression through the process is based on the technical substantiation and test work accomplished by the producer and the task force that has been assisting with the development and review of the product. Several alternative fuel pathways have task force activity in process, and several additional pathways are in development at various stages of fuel readiness level (FRL). CAAFI continues to work with the ASTM community to improve the fuel qualification process, while other industry participants continue to focus resources on timely qualification. A table of pathways actively pursuing certification is available on the Fuel Qualification page.

Are alternative fuels economically viable?
The two chief barriers to deployment (in many cases) include the availability of capital to construct the required initial infrastructure, as well as the availability of reasonably priced feedstocks and supply chains. CAAFI, through its members, partners, and work programs are attempting to drive down these barriers to implementation. In the long run, all of the parties involved in CAAFI understand that being the first transportation mode to move forward with drop-in, sustainable, alternative fuels will help ensure aviation's economic viability and environmental acceptability.

Additional studies, including “Near-Term Feasibility of Alternative Jet Fuels” (PARTNER COE and The RAND Corporation) and “Market Cost of Renewable Jet Fuel Adoption in the United States” (PARTNER COE) also discuss the potential economics of alternative aviation fuels.

⇑ Back to top