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Global environmental and safety concerns may require use of alternative fuels and the elimination of leaded fuels to address emissions and volatility concerns. Blends of biofuel such as Jet-A have led to as much as 50% emissions reductions during operations, both on the ground and in the air. Even blends of as little as 10% have been shown to produce a substantial effect on emissions.
There are a number of potential routes available, including synthetic kerosene or Fischer-Tropsch fuels from coal or biomass. There is also the possibility to use bio-fuels such as Fatty Acid Methyl Esters (FAMEs) in aviation, and plans to test these are in hand. One potential issue in developing these biofuels, however, is determining what feedstocks they should use. For instance, the proliferation of palm oil-based fuels could lead to an increase in demand for palm plantations, which could drive deforestation. Companies have used materials ranging from non-edible animal waste to sustainable corn to develop their biofuels.
Alcohol-to-Jet (ATJ) fuels may be the next big advance in terms of reducing the aviation industry’s reliance on petroleum and improving its carbon footprint. Gevo, a Finnish company, has developed a method of converting bio-gased isobutanol to an ATJ paraffinic synthetic kerosene, which is currently in use by Alaska Airlines and other providers. According to analysis, if Alaska Airlines replaced just 20% of its fuel supply at Sea-Tac Airport with ATJ, it could reduce carbon emissions by 142,000 metric tons.
While emissions concerns and the rising price of jet fuel are driving sustainable fuel innovation, issues of feedstocks and startup costs remain prominent. Many biofuel companies, including Cool Planet, have stalled out or shifted the focus of their operations, due to the costs of operating a full-time facility reaching hundreds of millions of dollars.

Potential hazard

Engine failure/degradation due to:

– fuel specifications with differing properties such as lubricity, lower aromatic content, etc.

– cross contamination with incompatible fuels in pipelines

Contamination levels from particular refineries may exceed allowable limits. Sources of contamination can include water, particulates or biodegradation (which forms a gummy residue in the fuel), bacterial growth or overuse of biocide used to control bacterial growth.

The migration of fuel specifications in response to environmental and economic pressures needs to be controlled to assure the performance, reliability and safety of aircraft fuel systems and engine hardware.

Corroborating sources and comments

2014 – A biofuel is a fuel that uses energy from a carbon fixation

These fuels are produced from living organisms. Examples of this carbon fixation are plants and microalgae. These fuels are made from a biomass conversion. Biomass refers to recently living organisms, most often referring to plants or plant-derived materials. This biomass can be converted to energy in three different ways: thermal conversion, chemical conversion, and biochemical conversion. This biomass conversion’s can be in solid, liquid, or gas form. This new biomass can be used for biofuels. Biofuels have increased in popularity because of the raising oil prices and need for energy security. However, according to the European Environment Agency, biofuels do not necessarily mitigate global warming.

Examples are Bio ethanol, bio diesel

From Skybrary:

Prior to in-flight use, HEFA fuels were exhaustively tested under both laboratory and ground engine run conditions. Blends containing conventional jet fuel and up to 50% biofuel were compared against unblended petroleum based fuel with no significant performance variances observed. Inflight testing milestones include:

February 2008 – Virgin Atlantic 747-400 flight with one engine burning a 20% biodiesel blend

December 2008 – Air New Zealand 747-400 flight with a 50/50 blend of Jatropha based biofuel and convential fuel

January 2009 – Continental Airlines operates the first flight with an algae derived biofuel

January 2009 – Japan Airlines 747-300 flight with a 50/50 blend of jet fuel and Camelina/Jatropha/Algae based HEFA fuel June 2011 – Boeing Company 747-800 freighter transAtlantic flight with all engines burning a 15% HEFA fuel blend

August 2011 – Aeromexico 777-200 transAtlantic flight with revenue passengers using a 30% Jatropha based blend

Since 2011, the use of blended biofuel in commercial operations has become increasingly more common although price and availability have, thus far, limited its widespread utilization. One of the main candidates for GA is butanol, a close chemical relative of the fuel in butane cigarette lighters. It’s more suitable for aviation than ethanol, which offers only modest energy outputs, isn’t fully compatible with existing internal combustion engines, and corrodes the pipelines it travels through.

Croft, John Fuel Supply Suspect In CFM56 Thrust Instabilities, Source: Aviation Week & Space Technology;

Boeing and CFM International are scrutinizing fuel supplies and the Honeywell-built fuel-control system in the CFM56-7B following a series of thrust-instability events on Boeing 737NG aircraft.

Their findings could have broader implications for the Jet A supply chain and fuel-testing regimen if contamination is behind the incidents. “We’re doing a root-cause analysis, looking at the fuel-control unit and the entire fuel supply chain,” says Boeing. “The problem might be fuel-based.”

The instabilities, described as a fluctuation in N1 (low-pressure spool) and N2 (high-pressure spool) speeds, are occurring at high power settings, for example in climbing to cruise altitude, after which “engine operation typically returns to normal,” says Boeing.

There have been 32 thrust-instability events since the first was reported in January 2008, with 17 of the events in the Alaska Airlines fleet, according to Boeing. (Besides new design and configurations, this post, by an affiliate of the Royal Aeronautics Association, discusses miniaturization and alternative fuel sources.) (NASA revealed the results of its ACCESS II initiative. Emissions were reduced by 50%, on the ground and in the air, when Jet-A, a 50-50 hybrid of traditional fuel and biofuel, was used. NASA’s DC-8 engine alternated between burning Jet-A and biofuel, leading to overall reduction of emissions.) (In 2016, Alaska Airlines sent two aircraft powered by alcohol-to-jet biofuel from Seattle to San Francisco International Airport and Ronald Reagan Washington National Airport. The combined flights used 1,500 gallons of biofuel; if it replaced just 20% of its fuel supply, it could reduce carbon emissions by 142,000 metric tons. The company developing the fuel, Gevo, converts bio-based isobutanol to an alcohol-to-jet paraffinic synthetic kerosene. Alaska Airlines’ goal is to have all flights from at least one of its major airports use aviation biofuel by 2020.) (In June 2017, Airbus delivered an A350-900 aircraft to Hong Kong, flying to the territory from Toulouse on a 10% blend of sustainable jet fuel. The plan is to deliver bio-fueled aircraft from Germany and the U.S. by next year.) (In response to emissions regulations under the Obama administration, Boeing started the SAFUG, or Sustainable Aviation Fuel Users Group, to develop alternative fuels. Food sources and trees were ruled out due to public interest concerns. Neste, a Finnish company which initially used palm oil and other FAMES, switched to non-edible animal waste products to create hydrogenated vegetable oil, a kerosene substitute; they also pioneered a drop-in fuel that can be used in multiple aircraft. Other companies, i.e. Cool Planet, have struggled to raise initial investment costs to build their plants.) (Would be a useful overview of the state of play for biofuel and other compositions… if it weren’t locked behind a paywall.) (Biofuel has steadily become more viable over the past decade, to the point where some kinds are being used in 50% blends with traditional jet fuel; however, it hasn’t gone commercial. Rising jet fuel prices and fuel insecurity are driving innovation, but the costs of production, limited availability of feedstocks, and lack of legislative support are hurting the market. Dated 2014.)

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