Alternative fuels and green aviation - Biomass as Energy Source: Resources, Systems and Applications - page 178

to the final biodiesel cost, although the numbers vary from about 60-95% (Balat, 2011a; Razon,
2009). Embedded within that issue are considerations of the economics and logistics of manu-
facturing, economies of scale (Knothe, 2010a), sustainable land development, lack of refining
infrastructure, and market considerations, particularly with regard to the fluctuating price of oil.
In section 11.2, the international standards for jet fuel are outlined, along with a description
of the most important physical characteristics for aviation fuel. Fuel composition and its corre-
sponding effects on fuel properties are the subject of section 11.3. The following sections discuss
alternative fuel feedstocks (section 11.4), biorefining techniques (section 11.5), and an introduc-
tion to Life Cycle Analysis for aviation fuel (section 11.6). For those without a solid background
in chemistry and petroleum engineering, see Appendix A for a review of definitions and basic
hydrocarbon chemistry.

11.2 AVIATION FUEL REQUIREMENTS

11.2.1 Jet fuel specifications
Aviation fuel must operate in extreme conditions, and so must live up to carefully developed
standards, which have evolved over time (Edwards, 2007). If the temperature and pressure on the
ground are 15 degrees Centigrade ( ◦ C) and 101.3 kiloPascals (kPa), then at a cruise altitude of
11,000 meters (m), the external temperature is about 56.5 ◦ C and the pressure is 22.6 kPa.

All aviation fuels are blends of various hydrocarbons. There are two basic types of jet fuel,
which differ by the proportions of hydrocarbons present in the fuel. The carbon number is a
measure used to indicate the number of carbon atoms present in a hydrocarbon molecule. For
example, methane (CH 3 ) is assigned a carbon number of C1, and octane (C 8 H 18 ) is C8. The most
common type of jet fuel is a kerosene blend with carbon numbers from C8-C12, while the less
typical naphtha/kerosene blend is a “wide-cut” fuel with a broader range of about C5-C12. By
including the lighter hydrocarbons, the fuel's vapor pressure is reduced and it has better cold
temperature properties. For civilian aircraft, the most common aviation fuels for powering jet and
turboprop engines are:
•

− ∼

Jet A : a kerosene-grade fuel used throughout the US, designed to operate under the demanding
conditions of flight. Its freeze temperature must be 40 ◦ C

≤−

• Jet A-1 : a kerosene-grade fuel widely available outside the US. It has a lower freeze point of

≤− 47 ◦ C, and there are other minor differences relative to Jet A.

• Jet B : a naptha/kerosene blend, used primarily in cold climates such as northern Canada.

Although it operates more effectively at lower temperatures, it is also more volatile, so it
exhibits greater evaporation loss at high altitude. In addition, it is a greater fire hazard on the
ground, and it makes a plane crash less survivable.
The most common military fuels are:

• JP-4 : the military equivalent of Jet B with the addition of corrosion inhibitors and anti-icing
additives. It used to be the primary fuel of the USAir Force, but it was phased out in the 1990s
due to safety concerns. Although still in use by other air forces around the world, it is in limited
production.
• JP-5 : a high flash-point, wide-cut kerosene fuel used by the US Navy, primarily for aircraft
carriers.

• JP-8 : the military equivalent of Jet A-1 with the addition of corrosion inhibitor and anti-icing

additives.

Other common additives include antioxidants to prevent gumming; antistatic agents to dissipate
static electricity; metal deactivators to remediate the effects of trace materials in the fuel that affect
thermal stability; and biocides to reduce the likelihood of microbial growth within the system,
which could plug filters and produce corrosive metabolites (Raikos et al. , 2011). Many countries